NRRPT Prep Detection and Measurement

Question Number: 567 Detection and Measurement The average energy expended to produce an ion pair is called: A) W value. B) dosimetry constant. C) ion pair energy. D) kinetic energy. E) rest mass.

The correct answer is: A "W value" is expressed in units of electron volts per ion pair. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26

Question Number: 664 Detection and Measurement A ZnS detector must be within at least inches of a surface to properly detect alpha contamination? A) 1/4 B) 3/4 C) 1 D) 2 E) It cannot detect alpha, only beta gamma.

The correct answer is: A .Alpha particles only travel approximately 1-2 inches in air, and the probe must be close enough for the alpha particle to travel through both the air and the detector window.

Question Number: 415 Detection and Measurement You determine the background of a proportional counter by measuring 35 counts in a period of 45 minutes and conclude the background count rate to be 0.78 cpm. What is the estimated standard deviation of this background count rate? A) 0.13 cpm B) 0.27 cpm C) 0.3 cpm D) 1.0 cpm E) 6 cpm

The correct answer is: A 1 sigma = (count rate/count time)1/2 = (.78 cpm/45 m)1/2 = +/- 0.13 cpm

Question Number: 665 Detection and Measurement A ZnS detector suddenly starts registering a very high count rate while surveying outdoors near some barbed wire, at a distance of approximately 6 inches from the ground. This is most likely due to: A) a puncture in the mylar window with the barbed wire, and light entering the detector. B) a dead battery that caused the instrument to fail high. C) a cable that was cut by the barbed wire. D) a very large area of alpha contamination, that causes alpha particles to travel further in air due to extensive ionization. E) a large gamma source being brought into the area.

The correct answer is: A A hole in the mylar window would let light into the detector and cause a high count rate.

Question Number: 685 Detection and Measurement The simplest device to locate fixed S-35 contamination in a medical laboratory would be: A) Portable GM detector B) Fixed (laboratory based shielded) GM Detector C) ZnS based detector D) Liquid Scintillation Detector (LSC) E) Thin window NaI detector (0.125" thick)

The correct answer is: A A portable GM detector may have low efficiency for the S-35 beta particles, but would be simple and would work.

Question Number: 534 Detection and Measurement The provisions of ANSI N13.11-1983 "American Dosimetry Performance Criteria for Testing" apply: A) to neither pocket dosimeters nor extremity dosimeters. B) to pocket dosimeters but not to extremity dosimeter. C) only to beta and gamma radiation. D) to extremity dosimeters but not to pocket dosimeters. E) to film badges but not to TLD.

The correct answer is: A ANSI N13.11 represents NVLAP requirements for external dosimetry programs, which neither apply to pocket or extremity dosimeters.

Question Number: 402 Detection and Measurement If the DAC for Rn-222 is 3.0 x 10 -8 µCi /ml, the working level is: A) 9.0 x 10-8 µCi /ml B) 9.0 x 10-9 µCi /ml C) 3.0 x 10-9 µCi /ml D) 6.0 x 10-7 µCi /ml E) 6.0 x 10-8 µCi /ml

The correct answer is: A According to 10 CFR Part 20 Appendix B, the DAC for Rn-222 is 1/3 of the working level.

Question Number: 573 Detection and Measurement "Doping" a semi-conductor material involves adding an impurity that has: A) a loosely bound electron. B) a lack of electrons in the outer shell. C) same number of electrons as an insulator. D) same W value as the semi-conductor. E) a different decay mode than the semi-conductor.

The correct answer is: A An impurity with a loosely bound electron is called a "donor" substance. This donor decreases the band-gap width to some small value. Adding phosphorus to silicon reduces the band gap to only 0.045 eV. Since conduction in this case involves negative charges (electrons) the substance is called an n-type semi-conductor. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26.

Question Number: 523 Detection and Measurement A worker has an inhalation intake of 1000 Bq of Class Y Co-60 and 6000 Bq of Class D I-131. The ICRP 30 stochastic based annual intake limits are 1 x 10 6 Bq and 6 x 10 6 Bq respectively for Co-60 and I-131. Lacking any other specific information, the worker's committed effective dose equivalent is properly estimated as: A) 10 mrem B) 8 mrem C) 6 mrem D) 4 mrem E) 2 mrem

The correct answer is: A CEDE = (intake/sALI) * 5 rem = [(1000/1 x 106) + (6000/6 x 106)] * 5 rem = 10 mrem

Question Number: 556 Detection and Measurement Quenching effects in a liquid scintillation counter are the result of which two processes? A) Chemical and color quenching B) Color and temperature quenching C) Precipitation and chemical quenching D) Stratification and color quenching E) Electrical and chemical quenching

The correct answer is: A Chemical quenching is caused by de-excitation of electronically excited molecules which would otherwise emit photons. Color quenching is caused by adsorption of emitted photons by materials in a sample. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 479 Detection and Measurement A researcher is working with a 0.5 millicurie Cs-137 source for 7 hours at a distance from his hand of 7 cm. The specific gamma constant is 3.33 R cm2 mCi-1 hr-1. What is his extremity dose? A) 0.23 rem B) 0.476 rem C) 3.33 rem D) 11.65 rem E) 23.32 rem

The correct answer is: A D = GA/r2 Where: D = absorbed dose rate (rad/hr) G = specific gamma constant A = activity (mCi) r = distance So: D = (3.33 R cm2 mCi-1 hr-1)(0.5 mCi)/(7cm)2 = .034 rad/hr And: .034 rad/hr * 7 hrs = 0.238 rad And, for gamma: = 0.238 rem

Question Number: 497 Detection and Measurement A chemical which has shown some success as an internal chelating agent for plutonium is: A) diethylenetriaminepentaacetic acid (DTPA). B) thenolytrifluoracetone (TTA). C) versene. D) potassium permanganate (KMnO4). E) nitrile triacetic acid (NTA).

The correct answer is: A DTPA is typically used as a chelating agent for Pu and Am. For Cs-137, Prussian blue is somewhat effective. KMnO 4 is used as a topical decontamination agent when soap and lukewarm water are ineffective.

Question Number: 533 Detection and Measurement Tissue dose from fast neutrons (0.1 to 14 MeV) is due primarily to: A) elastic scattering. B) resonance scattering with nuclei. C) inelastic scattering with nuclei. D) Coulomb scattering with nuclei. E) nuclear capture and spallation.

The correct answer is: A Elastic scattering with hydrogen produces high LET recoil protons, significant in fast neutron dose production in tissue.

Question Number: 672 Detection and Measurement An ion chamber that reads out in R/hr also has a beta window. When using the beta window, you must be careful in reporting the exposure rates because: A) exposure is not defined for beta particles. B) exposures can be higher due to the higher quality factor for beta particles. C) exposure is generally given as energy deposited per unit mass, and beta particles do not interact well enough to deposit energy. D) exposure due to neutrinos can impact the readings when the window is open. E) positrons can interfere with beta particle exposure readings.

The correct answer is: A Exposure is defined as the charge produced in air by gamma or x-rays only.

Question Number: 437 Detection and Measurement Which of the following combinations of instruments would be MOST effective to establish dose equivalent rates in a mixed neutron and gamma radiation field? A) Air ionization chamber survey meter and tissue equivalent boron trifluoride counter B) Extendable Geiger-Mueller survey meter and tissue equivalent boron trifluoride counter C) Air ionization chamber survey meter and gas flow proportional counter D) Extendable Geiger-Mueller survey meter and gas flow proportional counter E) Air ionization chamber survey and zinc sulfide scintillation detector

The correct answer is: A For gamma, since "air dose" is nearly equal to deep dose equivalent (1 roentgen = .98 rem), an air ionization chamber would be best for gamma. Obviously, a tissue equivalent neutron detector (the BF3) is the best instrument given for neutron dose equivalent measurement.

Question Number: 644 Detection and Measurement A reactor accident involving the release of large quantities of I -131 has occurred. Milk contamination is suspected. What is a simple rapid technique that could be used to screen large numbers of milk samples to qualitatively determine which samples contain I -131. The BEST method would be counting with a: A) thin window GM counter. B) BF3 proportional counter. C) windowless gas flow proportional counter. D) liquid scintillation counter. E) NaI(Tl) scintillation counter.

The correct answer is: A Gas flow is impractical. NaI may be useful, but is not the BEST answer for a RAPID technique. The LSC would not work due to color ( milk), and BF 3 is insensitive to gamma. Knoll, Radiation Detection and Measurement.

Question Number: 657 Detection and Measurement Kerma is a commonly misunderstood radiation dosimetry term. Kerma is actually an acronym for which of the following? A) Kinetic energy of radiation produced per unit mass in matter B) Kinetic energy radiated in materials C) Kinetic energy deposited in mass D) Kinetic energy that is mass absorbed E) Kinetic energy released in mass and absorbed

The correct answer is: A KERMA includes all energy released, whereas absorbed dose only includes energy released by particle collision. Cember, H. Introduction to Health Physics.

Question Number: 622 Detection and Measurement For a typical NaI scintillation detector, the energy resolution for a 662 keV Cs-137 gamma photon is approximately: A) 7% B) 15% C) 25% D) 40% E) 50%

The correct answer is: A Memorize this or remember that the FWHM for the Cs-137 photopeak on a NaI system is roughly 50 keV. Since percent resolution = (FWHM/Photopeak energy) * 100%, a 50 keV FWHM yields an energy resolution of 7.5%. Gollnick, D. Basic Radiation Protection Technology

Question Number: 535 Detection and Measurement ANSI N13.11-1983, "American National Standard for Dosimetry: Personnel Dosimetry Performance Criteria for Testing": A) forms the basis for the NVLAP for dosimetry processors. B) provides guidance for individual variability from reference man. C) provides guidance for summing the external and internal dose. D) is applicable to the entire range of gamma energies. E) is not required to be implemented by 10 CFR Part 20.

The correct answer is: A NVLAP represents the National Voluntary Laboratory Accreditation Program, which is not voluntary at all for "dosimetry processors" under 10 CFR Part 20 .

Question Number: 422 Detection and Measurement An individual breathes a concentration of 2.0 x 10 -8 µCi / ml of Cesium-137 for two and one-half hours. If the DAC for Cesium-137 is 6.0 x 10 -8 µCi / ml, his approximate committed effective dose equivalent will be: A) 2 millirem B) 12.5 millirem C) 17.5 millirem D) 25 millirem E) 27.5 millirem

The correct answer is: A One DAC-hour based upon sALI = 2.5 mrem And: DAC fraction x hours = DAC-hours Therefore: (2.0 x 10-8/6.0 x 10-8 x 2.5 hrs) x 2.5 mrem/DAC-hr = 2.08 mrem

Question Number: 582 Detection and Measurement A long counter is encased in a cadmium jacket to: A) remove thermal neutrons. B) provide detector integrity. C) compensate for tissue-equivalency. D) provide electrical continuity with detector circuits. E) shield against photon radiation.

The correct answer is: A Outside wall of the tub is enclosed in a cadmium jacket. This jacket absorbs all neutrons with energies < 0.5 eV to remove all unwanted thermal neutrons. A brass jacket that provides mechanical strength is used to cover the cadmium jacket. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg. 12-35.

Question Number: 599 Detection and Measurement On a mass basis, which of the following gives the correct descending order of the elements found in soft tissue? A) Oxygen, Carbon, Hydrogen, and Nitrogen B) Hydrogen, Oxygen, Nitrogen, and Carbon C) Nitrogen, Carbon, Oxygen, and Hydrogen D) Oxygen, Nitrogen, Carbon, and Hydrogen E) Nitrogen, Oxygen, Carbon, and Hydrogen

The correct answer is: A Oxygen, Carbon, Hydrogen, and Nitrogen is the correct descending order of elements found in soft tissue, on a mass basis.

Question Number: 560 Detection and Measurement You are analyzing a sample containing Na-24 which emits two gamma photons at 2.76 MeV and 1.37 MeV with 100% abundance. On the gamma spectrometer spectrum, two additional peaks are seen at 2.25 MeV and 1.74 Mev. These two additional peaks are due to: A) escape of one or more pair production gammas from the detector. B) another radionuclide contaminant in the sample. C) backscatter from interaction with lead shielding. D) activation gammas from detector walls. E) relaxation gammas from sample.

The correct answer is: A Pair production occurs to photons with energy in excess of 1.022 MeV. The e+ e- pair created in the detector cause the production of the two peaks. In this case, either all the original photon energy will be detected as charge particles loose their kinetic energy and annihilate with both photons being detected OR one or both of the two 0.511 MeV photons will escape from the crystal without being detected. 2.76 - 0.511 = 2.25 2.25 - 0.511 = 1.74 Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 602 Detection and Measurement The process of transferring photon energy to matter is commonly called: A) ionization. B) interactions. C) excitations. D) stopping power. E) LET.

The correct answer is: B The photon interactions of importance in matter are photoelectric effect, Compton scatter, and pair production.

Question Number: 590 Detection and Measurement The efficiency for collecting ion pairs produced in an ionization chamber is greater using which of the following? A) Parallel plate electrodes B) Negative feedback C) Cylindrical shaped collecting electrodes D) A guard ring E) Spherical shaped collecting electrodes

The correct answer is: A Parallel plate electrodes yields the greatest efficiency for collecting ion pairs in an ionization chamber for the methods listed above.

Question Number: 416 Detection and Measurement Quality factor is a function of the: A) collision stopping power of the radiation in water. B) collision stopping power of the radiation in any absorber. C) attenuation of the radiation in the air. D) absorption of the radiation by any absorber. E) attenuation of the radiation in any absorber.

The correct answer is: A Quality factor is represented in ICRP Publication 26 (1977) as a function of the collision stopping power of the radiation in water. It has been replaced with the concept of radiation weighting factor in ICRP Publication 60 (1990).

Question Number: 511 Detection and Measurement Glass is frequently selected as a material for liquid scintillation vials in the analysis of tritium, primarily to: A) prevent diffusion of the tritium from the sample. B) enhance the light output from the sample. C) minimize optical quenching in the system. D) minimize chemical quenching in the system. E) avoid undue natural background radiation from the components of plastic liquid scintillation vials.

The correct answer is: A Since plastic is a hydrogenous material, H-3 will readily diffuse from a sample into the plastic vial. Glass does have the disadvantages of natural radioactivity and optical quenching.

Question Number: 529 Detection and Measurement Which of the following instruments would have good sensitivity to neutrons while providing the best discrimination against gammas? A) BF-3 proportional counter in polyethylene moderator B) GM tube at greater than 2 atmospheres in polyethylene moderator C) Silverwrapped GM tube inserted in polyethylene moderator D) LiI(Eu) scintillator inserted in polyethylene moderator E) Cadmium wrapped LiI(Eu) scintillator

The correct answer is: A Since the BF-3 detector operates in the proportional region, and is set at an alpha voltage to detect the B-10(n,alpha)Li-7 reaction, discrimination against gammas is excellent.

Question Number: 530 Detection and Measurement In a field of mixed neutron and gamma radiation, the gamma dose measured on a phantom is: A) greater than the gamma dose measured in air due to the H (n,gamma) D reaction in the phantom. B) less than the dose measured in air due to the moderation of neutrons in the phantom. C) the same as the measured dose in air because phantoms do not influence gamma irradiation. D) less than the dose measured in air because some incident gamma rays are absorbed in the phantom. E) not a quantity of interest in a dosimetry program.

The correct answer is: A Since the H concentration in tissue (represented by a phantom in this case) is much higher than that in air, it could be expected that the (n,gamma) reaction would produce a greater gamma contribution in the phantom than in air.

Question Number: 519 Detection and Measurement At medium gamma energies (100-300 keV), the BEST explanation for the decrease in Ge(Li) detector counting efficiency is which of the following? A) Photoelectric absorption decreases linearly when graphed on a log-log scale. B) Compton scattering decreases linearly when graphed on a log-log scale. C) Pair production does not become a significant interaction in Ge(Li) until gamma energies are above 5 MeV. D) Energy absorbed from Compton scattering decreases with increasing energy. E) The K-edge for Ge(Li) occurs at 4 MeV.

The correct answer is: A Since the efficiency of a gamma spectroscopy is largely dependent on the full transfer of energy from the incident photon to electrons in the detector (photoelectric effect), higher energies where Compton interactions predominate result in a reduced efficiency. Compton interactions begin to predominate at 200 keV.

Question Number: 666 Detection and Measurement Dose for water soluble nuclides that are inhaled is normally determined by which of the following? A) Urinalysis B) Whole body counting C) Mixed method activation counting combined with HPGe measurements D) NaI(Tl) direct placement E) TLD or OSL

The correct answer is: A Soluble nuclides are normally eliminated via this pathway.

Question Number: 494 Detection and Measurement A NaI counting system would be appropriate for measurement of the radioactivity concentration in water of all of the radionuclides listed EXCEPT: A) Sr-90 B) Cs-137 C) Co-60 D) I-131 E) Cs-134

The correct answer is: A Sr-90 is the only "pure beta-emitter" listed. All other nuclides listed include significant gamma emissions in their beta-minus decays.

Question Number: 510 Detection and Measurement A worker stands 12 feet from a gamma point source which reads 3 R/hr at 3 feet. If the worker remains there for three hours and breathes 10 DAC air the entire time, what is his approximate total effective dose equivalent? A) 640 millirem B) 610 millirem C) 590 millirem D) 570 millirem E) 560 millirem

The correct answer is: A TEDE = DDE + CEDE and,using the inverse square law: DDE = [(3 R/hr)(3)2]/(12)2 * 3hrs = .1875 rem/hr * 3 hrs = .5625 rem = 562.5 mrem And: CEDE = (10 DAC * 3 hrs) * 2.5 mrem/DAC-hr = 75 mrem So: TEDE = 562.5 mrem + 75 mrem = 637.5 mrem

Question Number: 667 Detection and Measurement The dose to a person who has inhaled a large quantity of Co-60 may be determined best by: A) Whole body counting B) Urinalysis C) Mixed method activation counting combined with HPGe measurements D) Gas Flow proportional counter direct placement E) TLD or OSL

The correct answer is: A The 1.17 and 1.33 MeV photons will penetrate the chest wall to a detector and could be counted. Urinalysis would not be as accurate, and TLD/OSL would not measure the dose to the lungs.

Question Number: 471 Detection and Measurement A sample is measured using a proportional counter. 100 counts are observed in seven minutes. What is the counting rate and its associated standard deviation? A) 14.3 cpm ± 1.4 cpm B) 14.3 cpm ± 7.4 cpm C) 14.3 cpm ± 3.9 cpm D) 100 cpm ± 7 cpm E) 100 cpm ± 10 cpm

The correct answer is: A The counting rate and the standard deviation (1 sigma) are calculated as follows: counts/count time ± (count rate/count time)½ 100 c/7 min ± [(100c/7min/7min)]½ 14.28 ± 1.43 cpm

Question Number: 625 Detection and Measurement What is the approximate efficiency for the detection of Xe-133 on activated charcoal? A) 1% B) 10% C) 50% D) 95% E) 99%

The correct answer is: A The efficiency is usually less than 1%. This radioisotope of Xenon is a byproduct of the fission process in a nuclear reactor and is used in nuclear medicine as a lung scanning agent.

Question Number: 552 Detection and Measurement One of the components of the liquid scintillation cocktail is the solvent. Its purpose is to: A) keep the scintillator in solution and absorb the decay energy of the radioisotope. B) keep the scintillator in the center of the cocktail and adsorb the light generated during decay of the radionuclide. C) convert radionuclide excitation energy to light photons. D) keep the scintillator in solution and shift the wave length of light emitted from the blue to red spectrum. E) keep the scintillator in solution and at the correct temperature for light production.

The correct answer is: A The energy from the excited solvent molecule then excites the solute (fluor) molecule, which in turn de-excites and emits light. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 645 Detection and Measurement An evaluation is being made of various shielding materials for use in an experiment. The experiments are using photon emitters. Tracer amounts of the photon emitter are being used. The attenuation coefficient, µ, is one of the important considerations for shielding in the shielding equation: I = I o e - µt, since if µ is large, it means that the shielding: A) is an effective shield at that energy. B) is an ineffective shield at that energy. C) should not be used for shielding at that energy. D) has a buildup factor attenuation function. E) can shield less effectively at other energies.

The correct answer is: A The larger µ is, the better the shield for the given parameters.

Question Number: 698 Detection and Measurement When operating a portable NaI detector near energized accelerator magnets: A) false readings are possible due to the magnetic fields. B) the magnets can be influenced by the NaI photomultiplier tube, causing overheating of the magnets. C) magnetic fields have no influence on NaI detectors, and are specifically suited for this type of work. D) the NaI crystal needs to be cooled to liquid nitrogen temperatures to work properly. E) the battery in the NaI detector may "self charge" and can be operated for extended periods by using the parasitic energy of the magnet.

The correct answer is: A The magnet may influence the movement of electrons in the photomultiplier tube if the probe is not shielded from the magnetic field.

Question Number: 430 Detection and Measurement The major internal pathway for radionuclides is which of the following? A) Inhalation B) Ingestion C) Activation D) Absorption E) Injection

The correct answer is: A The most common pathway for internally deposited radionuclides, whether the exposures are occupational or environmental (non-occupational) is by inhalation.

Question Number: 570 Detection and Measurement A gas-filled detector in which the current is independent of the voltage but proportional to the amount of radiation to which the instrument is exposed is working in the region. A) ionization B) recombination C) proportional D) Geiger-Mueller E) limited proportional

The correct answer is: A The output is flat across the voltage in the ionization region, thus independent of the voltage. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26., pg 10-5.

Question Number: 439 Detection and Measurement A positron emitter is counted in a deep well detector. What would be the predominant peak(s)? A) 0.511 MeV B) 1.022 MeV C) 0.511 and 1.022 MeV D) 1.533 MeV E) A positron emitter will not yield a peak in this configuration.

The correct answer is: A The positrons will annihilate with electrons, creating two .511 MeV gammas. Although the simultaneous interaction of these gammas would produce a sum peak at 1.022 MeV, such interaction is improbable.

Question Number: 594 Detection and Measurement Which of the following reactions is most commonly used for TLD monitoring of thermal neutrons? A) Li-6 (n, alpha) H-3 B) Li-6 (n, gamma) Li-7 C) F-19 (n, proton) 0-19 D) Ca-40 (n, alpha) Ar-37 E) Tm-169 (n, gamma) Tm-170

The correct answer is: A The reaction is Li-6 + n = H-3 + alpha + 4.8 MeV

Question Number: 671 Detection and Measurement An ion chamber is used to find a crack in some shielding. The 3" diameter ion chamber is held up next to the 0.25" wide crack, and reads 10 mR/hr. This reading is probably: A) lower than the actual exposure rate, since the crack is smaller than the ion chamber. B) higher than the actual exposure rate, since the crack is smaller than the ion chamber. C) correct. D) not useful, as ion chambers do not typically measure gamma rays well. E) not correct, due to the over-response caused by buildup in shielding around the crack.

The correct answer is: A The reading is probably lower than the actual exposure rate, since only a portion of the ion chamber is being ionized by the streaming radiation.

Question Number: 580 Detection and Measurement For protons and neutrons, most of the interactions occur in the of the ion chamber. A) wall B) center C) proximity of the needle D) gas E) discriminator

The correct answer is: A The secondary radiation produced results in ionization in the gas. The problem is then to relate the ions collected in the gas to the energy imparted to a unit mass of the wall material. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg. 12-2.

Question Number: 689 Detection and Measurement When using a portable instrument to measure larger quantities of high energy beta emitters, which of the following would be the best choice? A) GM Detector with short time constant, so that resolving time is minimized B) GM Detector with long time constant, so that resolving time is minimized C) HPGe with MCA and long time constant for determining the energy of the beta particles D) HPGe with MCA and short time constant for determining the energy of the beta particles E) BF3 detector with short time constant

The correct answer is: A The shorter time constant will minimize resolving time, minimizing the loss of counts. The HPGe detector is not portable and the BF3 is a neutron detector.

Question Number: 548 Detection and Measurement To obtain count rates that will fall in the mid-range of the mid-high range Noble gas effluent detectors when subjected to high gas concentrations the detectors are designed with a: A) lower sensitivity and smaller viewing volume of gas. B) higher sensitivity and smaller viewing volume of gas. C) higher sensitivity and larger viewing volume of gas. D) lower sensitivity and larger viewing volume of gas. E) extreme sensitivity and smaller viewing volume of gas.

The correct answer is: A These detectors must have low sensitivity so that high gas concentrations will produce moderate count rates (< 1.0 x 106 cpm) for the appropriate range. Maletskos, C.J., Radiation Protection at Nuclear Power Plants.

Question Number: 462 Detection and Measurement The detection of radioactive tritium in an air sample is best accomplished with: A) a liquid scintillation counter. B) a thin 7 mg/cm2 end window proportional counter. C) a GM detector. D) an internal ionization chamber. E) a gas flow detector having a window sufficiently thin to detect alpha radiation.

The correct answer is: A Tritium (H-3) is a "pure beta-emitter" with an endpoint energy (Emax) of 18.6 keV. This energy is so low that the sample must actually be immersed in the detector material, which is the principle behind liquid scintillation counting.

Question Number: 614 Detection and Measurement A GM detector with a resolving time of 100 microseconds indicates a net sample count rate of 55,540 cpm. The true sample count rate is approximately: A) 61,200 cpm B) 50,830 cpm C) 364,000 cpm D) 56,060 cpm E) 101,660 cpm

The correct answer is: A True Count Rate = Observed Count Rate/1-(Observed Count Rate)(resolving time) = 55,540 cpm/1-(55,540 cpm)(100 µsec)(1 sec/1 x 106 µsec)(1 min/60 sec) = 61,206 cpm

Question Number: 592 Detection and Measurement Which planchet material would yield the highest sample count rate in a gas filled proportional counter? A) Tungsten B) Copper C) Steel D) Aluminum E) Plastic

The correct answer is: A Tungsten is the densest material listed. This material will result in the most beta and gamma backscatter into the detector.

Question Number: 504 Detection and Measurement The exposure rate at two feet from a point source is 20 R/hr. What is the expected exposure rate at four feet from the source? A) 5 R/hr B) 10 R/hr C) 1.25 R/hr D) 0.1 R/hr E) 0.5 R/hr

The correct answer is: A Use the inverse square law: R1 (D1)2 = R2 (D2)2 20 R/hr (2) 2 = R2 (4)2 5 R/hr = R2

Question Number: 444 Detection and Measurement A stack is 5 feet in diameter, the flow rate in the stack is 43,000 cubic feet per minute, and the sample line is 0.325 inches in diameter. What is the proper sample flow rate for isokinetic conditions to exist? A) 1.26 cubic feet per minute B) 3.88 cubic feet per minute C) 7.57 cubic feet per minute D) 75.69 cubic feet per minute E) 232.9 cubic feet per minute

The correct answer is: A V1(D2)2 = V2(D1)2 43,000 cfm * (0.325 in) 2 = V2 * (5 ft x 12 in/ft) 2 [43,000 * (0.325 in) 2]/(60 in)2 = V2 1.26 cfm = V2

Question Number: 475 Detection and Measurement The dose in rads due to energy deposition from Po-210 alpha particles which would cause the same dose equivalent as 10 rem of fast neutrons is: A) 0.5 B) 1 C) 5 D) 10 E) 20

The correct answer is: A We know that: rads * QF = rems rads * 20 = 10 rems rads = 0.5

Question Number: 650 Detection and Measurement Cobalt-57 emits a single 127 keV photon per decay. Spectral analysis in a high quality NaI detector of Co-57 has a peak at 127 keV and a small peak at 100 keV. The peak at 127 keV is the full photo peak and the small 100 keV peak is due to: A) the escape of the characteristic x-ray from iodine. B) the presence of a contaminant in the sample. C) the backscatter peak. D) the Compton effect. E) the bremsstrahlung in the sample.

The correct answer is: A When the 127 keV photon is absorbed in the NaI(Tl), the resulting characteristic x-ray energy is not absorbed in the crystal and not counted.

Question Number: 638 Detection and Measurement If an isotope has a DAC of 1 x 10 -8 µCi/ml and it will be released through a stack with a flow rate of 1 x 10 how many µCi of the isotope can be released at a constant rate in one day without exceeding the DAC? A) 240 µCi B) 120 µCi C) 24 µCi D) 1.0 µCi E) 0.4 µCi

The correct answer is: A 6 liters/hr, In this problem, it is helpful to examine what units are given and what units the answer will be expressed in. The answer is in units of µCi. We are given µCi/ml and L/hr. If we know how many µCi are acceptable in one ml (the DAC), we can calculate how many µCi are acceptable in any amount of ml. Therefore: 1 x 10 -8 µCi/1 ml = X µCi/[(1 x 106 L/hr)(1 x 10 3ml/L)(24 hr)] X = (1 x 10 -8 µCi/1 ml)(1 x 106 L/hr)(1 x 10 3 ml/L)(24 hr) X = 240 µCi

Question Number: 648 Detection and Measurement A "summation peak" in the photon spectrum of a positron emitting radionuclide is attributed to the: A) annihilation radiation. B) beta gamma coincidence interaction. C) summation of characteristic x-rays. D) bremsstrahlung in the shielding. E) Compton effect in the surrounding shielding.

The correct answer is: A Summing the two 0.511 MeV photons yields a summation 1.02 MeV peak.

Question Number: 661 Detection and Measurement A "pancake" GM tube has a window that is typically made of: A) Mica B) Mylar C) Beryllium D) Carbon Fiber E) Aluminum

The correct answer is: A 2 Most are approximately 4 to 7 mg/cm in thickness.

Question Number: 619 Detection and Measurement A sample with mixed alpha and beta emitting nuclides is counted with a gas flow proportional counter at the alpha voltage (A) and at the beta voltage (B). The alpha and beta count rates, respectively, may be estimated from these count rates as: A) B-A and B B) A and B-A C) B-A and A D) A and A-B E) A-B and A

The correct answer is: B "A" represents the detector voltage at which only counts due to alpha radiation will be detected. "B" represents a higher detector voltage at which both alpha and beta radiation will be detected. The count rate at voltage "A" is simply the alpha count rate. Subtracting the count rate at voltage "A" from the higher count rate at voltage "B" will yield the count rate due to beta radiation only.

Question Number: 404 Detection and Measurement The full width at half maximum peak energy for a Cesium-137 photopeak using a GeLi detector is 3 keV. The photopeak energy is 0.662 MeV. The percent resolution of the detection system for this energy is: A) 0.22% B) 0.45% C) 4.53% D) 22.0% E) 45.3%

The correct answer is: B % resolution = (FWHM/peak energy) * 100% = (3 keV/662 keV) * 100% = .453 %

Question Number: 597 Detection and Measurement One coulomb per kilogram in air equals how many roentgens? A) 8,700 B) 3,880 C) 3,440 D) 2,580 E) 1,000

The correct answer is: B (1R/2.58 x 10-4 C/kg)(1 C/kg) = 3,880 R

Question Number: 463 Detection and Measurement A counting rate of 40 cpm is measured in 2 minutes. What is the standard deviation of this counting rate? A) ± 6.3 cpm B) ± 4.5 cpm C) ± 5.0 cpm D) ± 6.0 cpm E) ± 4.7 cpm

The correct answer is: B 1 sigma = (count rate/count time)½ = (40 cpm/2 m)½ = ± 4.47 cpm

Question Number: 693 Detection and Measurement If a gamma ray produces the photoelectric effect in a HPGe detector, it will result in: A) a sum peak. B) a full photopeak. C) the Compton edge. D) a backscatter peak. E) a peak at 0.511 MeV.

The correct answer is: B The photoelectric effect will result in all of the photon energy being absorbed in the detector.

Question Number: 634 Detection and Measurement Indoor unattached radon decay products are commonly measured using all of the following EXCEPT: A) Diffusion battery B) Cyclone precollectors C) Electrostatic collectors D) Diffusion tubes E) Screen samples

The correct answer is: B A cyclone precollector is designed to remove larger non respirable particles from a sample stream and is not used for measuring radon decay products which have a much smaller particle size.

Question Number: 557 Detection and Measurement A gamma spectrometer spectrum of a quantity of Cs-137 reveals two peaks, one at 0.662 Mev and one at 32 keV. The 32 keV peak is due to: A) electron interactions with lead shielding. B) internal conversion x-rays. C) Compton edge. D) annihilation x-rays. E) backscatter.

The correct answer is: B A radionuclide undergoes decay emitting a gamma photon which interacts with an internal orbital electron. The electron absorbs the photon and is ejected from the atom. Another electron moves from a higher orbital shell to the vacated spot in the lower orbital. An x-ray is emitted in the process. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 500 Detection and Measurement For NaI and HPGe detectors, as gamma energies increase above 200 keV, the efficiency of the detector is: A) linear. B) decreased. C) increased exponentially. D) increased proportionally. E) supralinear.

The correct answer is: B Above 200 keV, Compton effect begins to predominate for gamma interactions in a material. For a given incident photon energy whose accurate measurement is dependent on photoelectric effect, efficiency is reduced. Higher energy photons are also less likely to interact with the detector material at all, further decreasing the efficiency as photon energy increases.

Question Number: 584 Detection and Measurement Choose the BEST answer that describes the difference between stopping power and LET. A) Stopping power is a function of the absorbing medium and LET is a function of the charged particle. B) Stopping power includes both radiative and collision losses and LET considers only collision losses. C) LET is a function of the absorbing medium and stopping power is a function of the charged particle. D) LET is a function of the specification ionization of the charged particle and stopping power is a function of specific ionization of the absorbing medium. E) LET and stopping power are the same.

The correct answer is: B According to the ICRU, stopping power includes losses due to collisions (ionizations, excitations) and radiative losses (bremsstrahlung). LET includes losses due to collisions which in turn is energy that will be locally deposited.

Question Number: 438 Detection and Measurement If 100 counts are recorded with a detector in one minute, and the efficiency of detection is 0.35 counts/disintegration, then the activity of the source is: A) 4.50 x 10-5 µCi B) 1.29 x 10-4 µCi C) 7.72 x 10-2 µCi D) 2.86 x 10-2 µCi E) 5.36 x 10-2 µCi

The correct answer is: B Activity (dpm) = count rate (cpm)/efficiency = 100/.35 = (286 dpm)(1 µCi /2.22 x 106 dpm) = 1.29 x 10-4 µCi

Question Number: 546 Detection and Measurement Gas and aerosol detectors (smoke detectors) use radiation to cause ionization in the air between two electrodes, allowing an electric current to flow across the gap. The source most manufacturers use is: A) Cs-137 B) Am-241 C) Ra-226 D) Pu-239 E) H-3

The correct answer is: B Am-241 half-life = 433 yrs. Alpha emitters are used in smoke detectors, Ra-226 is another source used. NCRP 56

Question Number: 574 Detection and Measurement An "acceptor" substance in a semi-conductor is a material that has: A) a loosely bound electron. B) a vacancy in the outer shell of electrons. C) same number of electrons as the conductor. D) same W value as an insulator. E) a lower resistance to current flow.

The correct answer is: B An impurity atom does not contain enough outer electrons for valence binding. This means that a vacancy now exists in what was originally a filled band. This creates a hole in the valence band. This positive hole can easily "accept" an electron from a nearby atom. This type of impurity is called "acceptor" substance. These substances are referred to as p-type semi-conductors. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg. 10-12.

Question Number: 452 Detection and Measurement Assuming a maximum permissible dose of 100 mrem, what would be the allowable working time in a radiation field consisting of 25 mrad/hr gamma, 50 mrad/hr thermal neutrons, and 15 mrad/hr fast neutrons? A) 9 minutes B) 18 minutes C) 27 minutes D) 45 minutes E) 67 minutes

The correct answer is: B Appropriate quality factors are as follows: Gamma 1 Thermal neutrons 3 Fast neutrons 10 And: Stay time = allowable dose/dose rate Therefore: Stay time = 100 mrem/[(25 * 1)+(50 * 3)+(15 * 10)]mr/h = .3077 h = 18.46 min

Question Number: 417 Detection and Measurement The quality factor refers to all of the following except: A) The factor relating absorbed dose (rads) to dose equivalent (rems) B) For all radiation sources, the constant factor which relates absorbed dose to dose equivalent C) The factor that depends on linear energy transfer (LET) D) The factor which is greater for higher LET radiation than for lower LET radiation E) The factor which depends on the characteristics of secondary charged particles liberated by the interaction of indirectly ionizing radiation in tissue

The correct answer is: B As defined in ICRP Publication 26 (1977), quality factor varies for different types of radiation depending upon the LET, thus, is not constant for all radiation sources.

Question Number: 436 Detection and Measurement The sensitivity of a pressurized ion chamber for the detection of photons can be increased by: A) increasing the applied voltage to the ion chamber. B) increasing the ion chamber fill gas pressure. C) decreasing the applied voltage to the ion chamber. D) decreasing the ion chamber gas pressure. E) None of the above

The correct answer is: B As pressure is increased, density of the fill gas is increased. Since more gas molecules are available for ionization at this higher pressure, the chamber is more sensitive.

Question Number: 608 Detection and Measurement The buildup factor used in shielding calculations is not a direct function of which of the following parameters? A) Shield thickness B) Source activity C) Gamma-ray energy D) Source geometry E) Shield material

The correct answer is: B Buildup is independent of source activity. All other choices will affect photon scatter, therefore buildup.

Question Number: 464 Detection and Measurement The approximate exposure rate (R/hr) at a point one foot from a 3.0 Ci source of Co-60 which emits two gamma photons, one with an energy of 1.17 MeV and the other with an energy of 1.33 MeV is: A) 28 R/hr B) 45 R/hr C) 21 R/hr D) 22.5 R/hr E) 24 R/hr

The correct answer is: B D = 6CEN D = 6{(3.0)[(1.17 * 1) + (1.33 * 1)] D = 45 R/hr

Question Number: 400 Detection and Measurement The sensitivity of photographic film to photons is energy dependent primarily because of: A) varying conditions of temperature and humidity during exposure. B) strong photoelectric absorption by the silver bromide in the emulsion. C) varying energies of the Compton-scattered photons. D) pair production. E) build-up.

The correct answer is: B Film is considered to be "energy dependent" since it is most efficient for photon detection when interaction is by photoelectric effect. As we know, photoelectric effect predominates only below 200 keV. This is one reason that filters are used in film badges.

Question Number: 473 Detection and Measurement Which of the following is not on a preoperational instrument check list? A) The battery voltage B) The old readings from the previous surveys C) The next calibration date on the calibration level D) The response of the instrument to a known source E) The physical damage check

The correct answer is: B Five items to be checked on a portable radiation detection instrument prior to use: Calibration valid Battery good Physical damage check Zeroed (if applicable) Response check

Question Number: 572 Detection and Measurement A semi-conductor is distinguished from an insulator or conductor by its: A) boiling point. B) band gap. C) conductivity. D) ductility. E) thermal abilities.

The correct answer is: B For semi-conductors and insulators, a gap exists between the highest filled electron band (called valence band) and the next empty band (called conduction band). This gap is called the band gap. Moving an electron into the empty band is not easy. In an insulator the gap is large, 5 eV or more. In a semi-conductor the gap is in the range of 0.7 - 2.1 eV. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg.10-10.

Question Number: 528 Detection and Measurement Which material is most likely to ionically bind with Cs-137 before it migrates to groundwater? A) Topsoil B) Clay C) Gravel D) Mud E) Sandstone

The correct answer is: B Illite clay, such as that found below pond and river beds, has a particular affinity for Cesium. It is a useful environmental indicator for Cs-137 dispersion.

Question Number: 607 Detection and Measurement The most abundant elements in soft tissue on a per atom basis are: A) Oxygen, Carbon, Hydrogen, and Nitrogen B) Hydrogen, Oxygen, Carbon, and Nitrogen C) Hydrogen, Carbon, Oxygen, and Nitrogen D) Oxygen, Hydrogen, Nitrogen, and Carbon E) Carbon, Oxygen, Hydrogen, and Nitrogen

The correct answer is: B In descending order, Hydrogen, Oxygen, Carbon, and Nitrogen are the most abundant elements found in soft tissue on a per atom basis.

Question Number: 405 Detection and Measurement What is the main advantage of using a proportional counter? A) It operates in a higher voltage region. B) It is able to differentiate between different types of radiation. C) It causes significantly more free electrons. D) It is less energy dependent than other detectors. E) It possesses higher sensitivity than other detectors.

The correct answer is: B In the proportional region, radiations with different specific ionization create pulses of different heights. By using pulse height discriminators, alpha can be distinguished from beta-gamma pulses.

Question Number: 493 Detection and Measurement The major routes of entry of radionuclides into the body are: A) absorption through the skin and inhalation. B) inhalation and ingestion. C) absorption through the skin and ingestion. D) through wounds and ingestion. E) through wounds and inhalation.

The correct answer is: B Inhalation and ingestion are the two most common routes of radionuclide intake, occupationally or otherwise. Inhalation is generally more predominant than ingestion.

Question Number: 674 Detection and Measurement If the applied voltage of a GM tube is increased, it can do all of the following EXCEPT: A) Decrease resolving time B) Result in the tube operating in the recombination region C) Result in the tube operating in the continuous discharge region D) Cause sparking/arcing in the tube E) Increase the size of the pulses

The correct answer is: B It will not result in recombination; this is at the other end of the gas amplification curve.

Question Number: 629 Detection and Measurement Which of the following is NOT a basis used for choosing environmental sampling locations? A) Meteorological data B) Population density C) Hydrological data D) Locations of main intakes of water from surrounding rivers E) Geological data

The correct answer is: B Population density is a factor considered when choosing the location for the construction of a facility, but is not as important as the other listed factors when establishing sampling locations once the facility is operational.

Question Number: 508 Detection and Measurement Obtaining reproducible results during a check of a radiation detection instrument is a measurement of: A) accuracy. B) precision. C) validity. D) conformity. E) deviation.

The correct answer is: B Precise results are those that can be corrected consistently to an accurate value through the use of the detector efficiency, a correction factor, or a calibration graph. The ability to consistently correct to an accurate value is precision.

Question Number: 688 Detection and Measurement What dosimetry would you recommend for a radiation worker near a 5 Ci PuBe sealed source? A) Film badge set up to measure the alpha particle dose from plutonium B) TLD with at least two chips, one 6Li and the other 7Li C) OSL dosimeter D) Self reading pocket dosimeter E) Dosimetry is not required.

The correct answer is: B PuBe sources emit gamma rays and neutrons, the alpha particles will be trapped inside the sealed source. OSL and the self reading pocket dosimeter are not sensitive to neutrons. See Cember, Chapter 12.

Question Number: 472 Detection and Measurement According to 10 CFR Part 20, the quality factor for high energy protons is: A) 1 B) 10 C) 20 D) 50 E) 100

The correct answer is: B Quality factors are defined in 10 CFR Part 20 (1991) in Table 1000.4(b).1. for all ionizing radiations. These follow 1977 recommendations of the ICRP.

Question Number: 537 Detection and Measurement The PRINCIPAL detriment of long bioassay sampling periods for tritium is: A) the reduced ability to estimate actual doses received by workers. B) the potential for an intake to escape detection. C) the increased cost of the detriment. D) the loss of prompt detection of tritium contamination in the work areas. E) the reduced cost of the required bioassays.

The correct answer is: B Since H-3 has a short effective half-life, the frequency of bioassay periods for occupational exposures is generally about 2 weeks.

Question Number: 478 Detection and Measurement The DAC for inert gases is based on: A) internal exposure. B) external exposure. C) both internal and external exposure. D) the DACs of their radioactive daughters. E) the "4 pi Factor".

The correct answer is: B Since inert (or noble) gases do not remain inside the body, they pose a greater external than internal hazard. The DACs for radioactive inert gases are typically based upon a 2000 hour "submersion dose" of 5 rem CEDE, or a 2000 hour shallow dose equivalent of 50 rem (ICRP 1977, 10 CFR Part 20 1991).

Question Number: 502 Detection and Measurement Ar-41 is a noble gas which decays by a 1.2 Emax beta and a 1.29 MeV gamma photon. Which of the following statements regarding exposure in a cloud of Ar-41 is INCORRECT? A) If the Ar-41 concentration is equal to the occupational DAC, the external radiation dose rate to an individual standing on the ground would be 2.5 mrem/hr. B) Since the cloud is very large, it is realistic to neglect the beta contribution to the body surface dose. C) The lung dose resulting from inhalation is small compared to the external dose received from the direct radiation from the cloud. D) The surface dose rate to the body will exceed the dose rate at any depth in the body. E) A person standing on the ground is immersed in a "semi-infinite" cloud of Ar-41.

The correct answer is: B Since only a 70 keV beta particle is required to penetrate to the basal layer of the skin, a 1.2 MeV Emax beta-emitter will be contributing significantly to the "body surface" dose. All other presented data are valid.

Question Number: 617 Detection and Measurement The dead time for proportional counters is approximately: A) 5 nanoseconds. B) 0.5 microseconds. C) 50 microseconds. D) 100 microseconds. E) 0.5 milliseconds.

The correct answer is: B Since proportional counters have such short dead times, correcting observed count rates for high activity samples is not nearly as significant as such corrections for GM detectors. GM counter dead times may exceed 100 microseconds.

Question Number: 448 Detection and Measurement The purpose of a "chi-square" test is to: A) establish a "knee voltage" for a detector. B) ensure that the instrument's results lie within a normal Gaussian distribution. C) establish the efficiency of a detector circuit. D) compare the response of an instrument to a known standard. E) calculate the average sample result obtained for a quality of radioactive material.

The correct answer is: B Since radioactive decay is a random process, a series of at least 20 counts of the same activity standard should yield a normal (or Gaussian) distribution of results. A chi-square test verifies this. If the results do not pass this "goodness of fit" check, electronic malfunction of the instrument is indicated.

Question Number: 440 Detection and Measurement A tissue-equivalent chamber must: A) be inserted into tissue. B) have walls of the same mean density as tissue. C) have a mean density of 300 gms/cubic centimeter. D) be used for depth-dose measurements. E) be used to measure dose rate.

The correct answer is: B Since the Bragg-Gray principle states that the dose to the detector wall is proportional to the dose of the detector cavity gas , constructing an ionization chamber wall from a material with the same density as tissue will produce a tissue equivalent response in the detector.

Question Number: 492 Detection and Measurement An ionization chamber which as a diameter greater than the diameter of a monoenergetic gamma beam will: A) overrespond to the beam. B) underrespond to the beam. C) respond correctly to the beam. D) alternately respond correctly and overrespond to the beam, depending upon the fill gas pressure. E) alternately underrespond and overrespond to the beam, depending upon the fill gas pressure.

The correct answer is: B Since the instrument is calibrated under a uniform field, the entire detector wall is subject to ionization. When only part of the wall is subjected to ionization, such as in this narrow beam scenario, not as much current is produced, and so, a lower response.

Question Number: 457 Detection and Measurement A worker spends 45 minutes in a room with an Iodine-131 concentration of 5.0 x 10 -8 µCi /ml. He is wearing a full plastic suit and a full-face negative pressure respirator. If the DAC for Iodine-131 is 2.0 x 10 -8 µCi /ml, how many DAC hours should the worker be assigned? A) 0.25 DAC hours B) 2.0 DAC hours C) 5.5 DAC hours D) 0.1 DAC hours E) 0.05 DAC hours

The correct answer is: B Since the protection factor of the device is 1 for I-131, the calculation is as follows: DAC fraction * time(hrs) = DAC-hours (5.0 x 10-8/2.0 x 10-8) * .75 hrs = 1.875 DAC-hrs

Question Number: 435 Detection and Measurement An accurate measurement of exposure rate can be obtained when using an air ionization chamber to measure a photon beam smaller than the detector, if: A) a scattering material is installed between the beam and the detector. B) the beam conversion factor for the instrument is used. C) the beam is collimated using a high-Z material. D) the detector fill gas pressure is increased. E) the voltage to the detector is increased slightly.

The correct answer is: B Since the small beam would not produce as much ionization in the detector as a field as wide as the detector would, the meter would under respond. This can be corrected with a beam conversion factor, if the diameter of the beam is known.

Question Number: 623 Detection and Measurement An HPGe detector is advertised as being 120% efficient. Which of the following best explains how the detector can be greater than 100% efficient? A) Each gamma interaction within the detector volume produces multiple output pulses. B) Germanium detector efficiencies are commonly stated in terms of relative efficiency as compared to a 3 x 3 inch NaI(Tl) detector. C) The detector operating voltage is so high that output pulses are amplified by a factor of 1.2. D) The germanium crystal is 120% larger than a 3 x 3 inch NaI(Tl) crystal. E) The manufacturer has produced a germanium crystal that is 1.2 times as dense as standard germanium.

The correct answer is: B The 3 x 3 inch sodium iodide scintillation detector is used as an industry standard by which other gamma spectrometer detectors are compared. Germanium detectors are less efficient than comparably-sized NaI(Tl) detectors. Gollnick, D. Basic Radiation Protection Technology (3rd ed.), Pacific Radiation Corp. pg. 273.

Question Number: 581 Detection and Measurement The response of a GM survey meter is: A) directly proportional to the energy absorbed in the sensitive volume. B) not directly proportional to the energy absorbed in the sensitive volume. C) accurate enough for use in exposure rate determination. D) slow in gamma fields > 100 keV. E) constant for any energy absorbed in the detector volume.

The correct answer is: B The GM survey meter is not an accurate instrument for exposure rate measurement. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg.12-27.

Question Number: 543 Detection and Measurement Which of the following is assumed to be a model of the human body for dosimetry calculations when made of unit density materials? A) A 15 cm by 30 cm rectangular block B) A 30 cm diameter sphere C) An ellipse with a 30 cm major diameter and a 20 cm minor diameter D) A right circular cylinder of 30 cm height and 15 cm diameter E) A right circular cylinder of 15 cm height and 30 cm diameter

The correct answer is: B The ICRU uses a 30 cm diameter sphere of unit density in its recommendations on dose equivalent calculation.

Question Number: 505 Detection and Measurement When using a TLD badge with TLD 600 and TLD 700 chips, the neutron contribution is determined by: A) subtracting the TLD 600 from the TLD 700 reading. B) subtracting the TLD 700 from the TLD 600 reading. C) averaging the response of both chips to thermal range neutrons. D) adding the response of both chips to thermal range neutrons. E) It is not possible to determine neutron dose equivalent with this configuration.

The correct answer is: B The TLD 700 chip contains natural lithium, which is mostly Li-7 and is primarily gamma responsive. The TLD 600 is natural lithium enriched in Li-6, which is neutron responsive from the Li-6(n,alpha)H-3 reaction, but contains enough Li-7 to also be gamma responsive. So, to obtain the neutron contribution, the TLD 700 (gamma only) is subtracted from the TLD 600 (neutron and gamma) reading.

Question Number: 477 Detection and Measurement A worker spends 10 minutes in a radiation field of 250 mR/hr gamma, 100 mrad/hr thermal neutrons, and 40 mrad/hr fast neutrons. The total dose equivalent to the worker for this period is about: A) 880 mrem B) 160 mrem C) 125 mrem D) 88 mrem E) 65 mrem

The correct answer is: B The appropriate quality factors (QFs) are as follows: Gamma 1 Thermal neutrons 3 Fast neutrons 10 Then: Dose equivalent(rems) = dose(rads) * QF And: dose rate * time = dose Therefore: (250* 1)+(100 * 3)+(40 * 10)mrem/hr *(10 min * 1hr/60 min) = 158.33 mrem

Question Number: 662 Detection and Measurement The most common way to determine the dose to a worker from tritium is which of the following? A) Whole body count B) Urine bioassay C) Blood sample D) TLD or OSL dosimeter E) Electronic dosimeter or TLD or OSL

The correct answer is: B The beta from H-3 is too weak to be detected outside the body, and cannot penetrate the window on TLD, OSL, or electronic dosimeters. A blood sample could work, but is not commonly used.

Question Number: 484 Detection and Measurement Albedo dosimetry will function properly if: A) the individual's body water is evaluated and fast neutrons are reflected from the body into the dosimeter. B) a cadmium filter is used between the dosimeter and the external neutron field, and neutrons are reflected from the body into the dosimeter. C) the neutron spectrum is evaluated and fast neutrons are reflected into the dosimeter. D) the individual's body water is evaluated and the neutron spectrum is evaluated. E) the individual's body water is evaluated and a cadmium filter is used between the dosimeter and the external neutron field.

The correct answer is: B The cadmium filter, which has a high capture cross section for neutrons over a fairly broad energy range, is used to shield against ambient thermal neutrons. The term "albedo" means "reflecting".

Question Number: 410 Detection and Measurement According to ANSI N323-1978, portable linear readout radiation detection instruments should be calibrated: A) at 50% of each scale to within +/- 10% of known radiation values. B) at 20% and 80% of each scale to within +/- 10% of known radiation values. C) at 20%, 50%, and 80% of each scale to within +/- 20% of known radiation values. D) at 50% of each scale to within +/- 20% of known radiation values. E) at 80% of each scale to within +/- 20% of known radiation values.

The correct answer is: B The calibration should then be checked at 50% of each scale to be used. Specifications for response are addressed in ANSI N42.17A.

Question Number: 460 Detection and Measurement What happens to the noble gases after they are inhaled? A) It takes a long time to eliminate them through the decay process. B) They do not remain inside the body. C) They remain inside the body. D) It takes a very short time for them to decay and be eliminated. E) They are absorbed by the body and excreted.

The correct answer is: B The nature of noble (or inert) gases is that they will not chemically bind with other elements. Therefore, they do not remain inside the body. They pose more of an external than internal radiation hazard, and require the calculation of "submersion dose". In fact, the DACs for the radioactive noble gases are based upon external exposure.

Question Number: 485 Detection and Measurement Which of the following detectors operates in a voltage region where gas multiplication effects are observed? A) TLD B) Proportional counter C) CsI scintillator D) Zinc-sulfide detector E) Air ionization chamber

The correct answer is: B The only two gas-filled detectors shown are the proportional counter and the ionization chamber. The ionization chamber operates in the "current" rather than the "pulse" mode, where no amplification of initial ions occurs.

Question Number: 428 Detection and Measurement How is beta exposure determined in a beta-gamma radiation field using film dosimetry? A) The beta dose is evaluated by subtracting the open window film reading from the closed window film reading. B) The beta dose is evaluated by subtracting the closed window film reading from the open window film reading. C) The beta dose is evaluated by ratioing the open window film reading to the closed window film reading. D) The beta dose is evaluated by ratioing the closed window film reading to the open window film reading. E) The beta dose is extrapolated from the beta to gamma ratio of the radionuclides present.

The correct answer is: B The open window reading yields beta and gamma effects. The closed window reading yields gamma only. Therefore: Open - Closed = beta effects

Question Number: 486 Detection and Measurement What is the ionization region? A) The region of current over which the saturation current is produced B) The region of voltage over which the saturation current is produced C) The region of voltage over which ionization is taking place D) The region of current over which ionization is taking place E) The region of current over which the saturation voltage is produced

The correct answer is: B The operation of a gas-filled detector in the "current" mode, as opposed to the "pulse" mode, places it in the ionization region of voltage in the six-region curve for gas-filled detectors. In the ionization region of voltage, one electron reaches the detector electrode (anode) for each electron released by ionization in the detector. This is called the "saturation current".

Question Number: 660 Detection and Measurement When an x-ray beam is directed at a wall, the shielding thickness must be calculated as a: A) Leakage shield. B) Primary shield. C) Secondary shield. D) Scatter shield. E) Scatter and leakage shield.

The correct answer is: B The primary shield (or barrier) is what intercepts an un-attenuated beam to reduce doses outside of the barrier. A secondary shield (or barrier) intercepts scattered or leakage radiation to reduce doses outside the barrier. See NCRP 147 for further details.

Question Number: 589 Detection and Measurement GM detectors are fairly inefficient for gamma radiation. When gamma is detected by a GM tube, the mode of interaction is most likely due to which of the following? A) A gamma photon interacting with a detector fill gas molecule causing a recoil electron which is then detected B) A gamma photon interacting with the wall of the detector and releasing an electron into the fill gas which is then detected C) A gamma photon interacting with an air molecule outside the GM window, creating a recoil electron which then enters the detector window and is then detected D) A gamma photon interacts with the anode wire creating a pulse E) GM detectors only detect the beta component of a radionuclide and not the gamma component

The correct answer is: B The probability of gamma interaction is much greater with a dense material such as the metal housing of the GM detector, rather than causing an ionization of a less dense gas.

Question Number: 467 Detection and Measurement If two gamma photons of different energies interact with a detector in a gamma spectroscopy system at the same time, the resulting spectrum will show: A) a peak at the average energy of the photons. B) a peak at the sum of the energies of the photons. C) a peak at the higher photon energy only. D) a peak at the difference of the two photon energies. E) peaks at each discrete photon energy only.

The correct answer is: B The pulse height registered in the detector will be a sum of the pulse heights of each energy photon. The probability that both photons will interact simultaneously, however, is low. More counts will be registered in the assigned channels for each energy photon, rather than in the channel representing the sum value.

Question Number: 692 Detection and Measurement A portable alpha detector must be held close to surfaces to detect contamination because the range of alpha particles in air is: A) Less than 1 mm B) 3-4 cm C) About 6 inches D) Typically 12' per MeV E) Not defined

The correct answer is: B The range of an alpha particle in air is 3 to 4 cm, whereas the range of a beta particle in air is approximately 12' per MeV. Alpha particles have a short range due to the +2 charge and their large mass. See "The Health Physics and Radiological Health" Handbook, Chapter 3, 4th edition.

Question Number: 481 Detection and Measurement The use of albedo dosimeters for fast neutron dose assessment relies on what major principle to produce a response in the dosimeter? A) Fast neutrons release photons from the hydrogenous material in the badges and these photons deposit energy in the dosimeter. B) Fast neutrons are thermalized in the body, and the thermalized neutrons are scattered partially into the dosimeter. C) Fast neutrons are moderated in the hydrogenous material of the badge and produce a response in the dosimeter. D) Radiative capture interactions in the body ionize the TLD material. E) (n,a) interactions in the body ionize the TLD material.

The correct answer is: B The term "albedo" means "reflecting". Scattering interactions with hydrogen in the body reflects thermal neutrons into the dosimeter.

Question Number: 647 Detection and Measurement Mercury-203 emits a 0.279 MeV gamma and a 70 keV photon. It is used in tracer experiments and the researcher is using a 1.5" diameter by 1" thick scintillation crystal. The RSO wants to increase the ratio of gamma ray to x-ray counts for the researcher, so he would use a: A) scintillation crystal with one that is 1.5" diameter by 0.25" thick. B) detector with a 2" diameter by 2" thick crystal. C) scintillation detector with a thin end window GM counter. D) scintillation detector with a long counter. E) different isotope. The gamma to x-ray ratio cannot be changed for any specific isotope.

The correct answer is: B The thinner crystal would increase x-ray counts; GM would do the same. Long counter is for neutrons.

Question Number: 532 Detection and Measurement Tissue dose from thermal neutrons principally as a result of: A) (n,gamma) reactions with hydrogen. B) (n,gamma) reactions with hydrogen and (n,p) reactions with nitrogen. C) (n,p) reactions with carbon. D) (n,alpha) reactions with carbon. E) (n,alpha) reactions with carbon and (n,gamma) reactions with hydrogen.

The correct answer is: B Thermal neutrons interact by absorption (capture). These are the two significant thermal neutron interactions with tissue. Fast neutrons produce dose in tissue primarily through elastic scattering interactions with hydrogen, producing recoil protons.

Question Number: 569 Detection and Measurement A gas-filled detector is collecting 100% of the ion pairs produced. It is said to be operating in the region. A) recombination B) ionization C) proportional D) limited proportional E) Geiger-Mueller

The correct answer is: B This is also known as the "saturation current". For each interaction in the detector, one electron is collected at the detector anode. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26.

Question Number: 443 Detection and Measurement The full width at half maximum peak energy for a typical HPGe detector for Cs-137 should be approximately: A) 0.3 keV B) 3 keV C) 30 keV D) 5% E) 10%

The correct answer is: B This is some ten times better resolution than a 3"x 3" Sodium Iodide detector.

Question Number: 600 Detection and Measurement The difference between the energy 1 roentgen deposits in air per gram vs. the energy 1 roentgen deposits in tissue per gram from 1 MeV photons is mainly due to: A) the difference in density of air vs. tissue. B) the difference in electron density per unit mass of air vs. tissue. C) the difference in elemental composition of air vs. tissue. D) the difference in quality factor for tissue. E) the electrical charge of an ion in air vs. the electrical charge of an ion in tissue.

The correct answer is: B Tissue has roughly 10% more electrons per gram than air. This mostly accounts for the difference in energy absorbed (87 ergs/g in air and 95 ergs/g in tissue). In the Compton Scatter region of 0.1 - 5 MeV, electron density per gram is most important.

Question Number: 456 Detection and Measurement The exposure rate from a point source is 5 R/hr at 2 feet. The expected exposure rate at 4 feet is: A) 1.00 R/hr B) 1.25 R/hr C) 2.5 R/hr D) 10 R/hr E) 20 R/hr

The correct answer is: B Use the inverse square law: 5 R/hr (2) 2 = R2 (4)2 1.25 R/hr = R2

Question Number: 649 Detection and Measurement NaI(TI) is frequently used in gamma ray scintillation detectors because it: A) transmits the gamma rays to the PMT extremely efficiently and effectively. B) is an efficient transmitter of light from the scintillations so that it is easily transmitted to a PMT. C) is an efficient absorber of light from the scintillations so that it is easily transmitted to a PMT. D) is easily activated, so that radioactive emissions can be detected by the PMT. E) is best suited to detect tritium, and is not normally used to detect gamma rays.

The correct answer is: B Transmission of light to the photomultiplier tube is critical for adequate efficiency in a NaI(Tl) detector.

Question Number: 501 Detection and Measurement The exposure rate at three feet from a 5Ci Cesium-137 point source is approximately: A) 1 R/hr B) 2 R/hr C) 3 R/hr D) 4 R/hr E) 5 R/hr

The correct answer is: B Using D = 6CEN and the inverse square law: D = [6(5)(.662)(.85)]/(3)2 = 1.875 R/hr

Question Number: 495 Detection and Measurement Bonner spheres are used to characterize neutron spectrums. This is accomplished by: A) the use of cadmium filters. B) selectively thermalizing neutrons of varying energies. C) the use of alpha spectroscopy on the B-10 (n,a) Li-7 reaction. D) comparison to Long counter results. E) the use of boronated plastic scintillators.

The correct answer is: B Using different diameter polyethylene spheres with a central BF 3 detector enables the researcher to plot the contribution of varying energy neutrons to the total spectrum. This works because it takes different thicknesses of a material to thermalize neutrons of different energies. The BF 3 detector responds only to the thermalized neutrons.

Question Number: 474 Detection and Measurement When calibrating radiation detection instruments, all of the following must be considered EXCEPT: A) Scattering B) Prevailing wind direction C) Barometric pressure D) ALARA E) Temperature

The correct answer is: B Wind direction has no bearing on the response of these instruments. It is, however, a great consideration when calculating atmospheric dispersion of radioactive materials. The other distractors are valid calibration considerations.

Question Number: 541 Detection and Measurement A sample counted for 10 minutes resulted in 1,000 counts. The background count was 250 counts in 10 minutes. Assuming negligible radioactive decay of the sample during counting, the net counting rate in counts per minute should be reported at the 95% confidence level as: A) 750 ± 35 B) 75 ± 7 C) 75 ± 10 D) 75 ± 3.5 E) 75 ± 14

The correct answer is: B net count rate = sample rate - bkg rate 2 = 1.96 [(bkg rate/bkg time) + (sample rate/sample time)]1/2 Therefore net count rate equals: = (1000/10) - (250/10) 1.96 [(250/10/10) + (1000/10/10)] 1/2 = 75 6.93 cpm

Question Number: 446 Detection and Measurement A sample counted for ten minutes resulted in 1000 counts. The background count was 250 counts over a 10 minute period. Assuming negligible radioactive decay of the sample during counting, the net counting rate in counts per minute should be reported at the 95% confidence level as: A) 750 ± 35 B) 75 ± 7 C) 75 ± 10 D) 75 ± 3.5 E) 75 ± 14

The correct answer is: B net count rate = sample rate - bkgrd rate And: 2 sigma = 1.96[(bkgrd rate/bkgrd time)+(sample rate/sample time)]½ Therefore: (1000/10)-(250/10)◌۫ .96[(250/10/10)+(1000/10/10)]½ 75 ± 6.93 cpm

Question Number: 451 Detection and Measurement Body tissue is exposed to 20 millirad per hour alpha radiation for 75 minutes. The dose equivalent to the exposed tissue would be about: A) 0.25 rem B) 0.5 rem C) 0.75 rem D) 1 rem E) 1.25 rem

The correct answer is: B rads * QF = rems (20 mrad/hr * 75 min * 1 hr/60 min) * 20 = 500 mrem = 0.5 rem

Question Number: 565 Detection and Measurement You have received a hot particle recovered from an individual. To determine the type of particle, fuel or crud, the best method to use is: A) allow the particle to decay for half-hour and recount. B) use a 90 mg/cm2 shield and observe the change in count rate. C) cover particle with plastic and recount. D) survey the particle with an alpha meter. E) use a magnet and observe particle response.

The correct answer is: B NRC Information Notice IN 90-48: crud particle betas are of a lower energy than fuel hot particles. The plastic shield will significantly reduce the crud betas while most of the fuel betas will pass through.

Question Number: 498 Detection and Measurement The net counts observed from successively counting a sample are plotted on semilog paper, and the plot forms a curved line. It is probable that: A) the counting system was not working properly. B) the sample contained more than one radionuclide. C) the effective half-life obtained from the initial counts is the correct half-life. D) the half-life obtained is the correct half-life of the longest lived radionuclide in the sample. E) the half-life cannot be determined by repetitive counts of the sample.

The correct answer is: B Since radioactive decay of a single radionuclide is a lognormal function, it appears as a straight line on a semilog graph. If two nuclides with different half-lives are present, the resulting curve is a sum of two straight lines with different slopes.

Question Number: 613 Detection and Measurement A worker wearing a respirator with a rated protection factor of 100 for particulates is exposed to a concentration of airborne particulate Co-60 at 10 times the DAC for a period of eight hours. What is the worker's calculated dose equivalent? A) 200 mrem CEDE B) 2 mrem CEDE C) 200 mrem CDE D) 0.1 mrem CDE E) 2 mrem CDE

The correct answer is: B Since the DAC for Co-60 is based on the stochastic Annual Limit on Intake (sALI), one DAC-hr represents 2.5 mrem committed effective dose equivalent (CEDE). CEDE = (DAC fraction * hrs * 2.5 mrem/DAC-hr)/PF = (10 DAC * 8 hrs * 2.5 mrem/DAC-hr)/100 = 2 mrem

Question Number: 421 Detection and Measurement A technician is working three feet from a gamma radiation point source. If the technician moves to a second location which is an additional three feet from the source, the dose rate to the technician will be reduced by a factor of: A) 2:1 B) 4:1 C) 5:1 D) 1:3 E) 3:1

The correct answer is: B The reduction factor, employing the inverse square law is: 1/(3)2 : 1/(6)2 which equals: 1/9 : 1/36 which equals: 4 : 1

Question Number: 469 Detection and Measurement The approximate exposure rate (R/hr) at a point 3 feet from a 2.5 Ci source which emits a 0.501 MeV gamma photon is: A) 0.5 R/hr B) 0.8 R/hr C) 2.5 R/hr D) 7.5 R/hr E) 29.9 R/hr

The correct answer is: B Using D = 6CEN, we must assume that N = 1 since it is not given. Then, using the inverse square law: D = [6(2.5)(0.501)(1.00)]/(3)2 = 0.835 R/hr

Question Number: 555 Detection and Measurement The reduction of counting efficiency in liquid scintillation counters because of impurities, sample solvents and other materials of poor solvent category is called: A) wavelength shift. B) photo reduction. C) quenching. D) adsorption. E) dark current.

The correct answer is: C "Quenching" refers to any colors, objects, or chemicals that reduce the amount of light that reaches the photomultiplier tubes in a liquid scintillation counting system. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 514 Detection and Measurement The full width of a given photopeak at half the maximum peak height, identified with a photon energy of 1 MeV, is 1.8 keV. The percent resolution of the detector at 1 MeV is: A) 1.8% B) 0.0018% C) 0.18% D) 18% E) 0.018%

The correct answer is: C % resolution = (FWHM/peak energy) * 100% = (1.8 keV/1000 keV) * 100% = 0.18%

Question Number: 442 Detection and Measurement The full width at half maximum peak energy for a Mn-54 photopeak obtained with a HPGe detector is 3 keV. The photopeak energy is 0.835 MeV. The percent resolution of the detection system for this energy photon is: A) 0.90% B) 3.59% C) 0.36% D) 0.23% E) 100%

The correct answer is: C % resolution = (FWHM/peak energy) * 100% = (3 keV/835 keV) * 100% = 0.359%

Question Number: 423 Detection and Measurement A radiation worker is exposed for a period of four hours to airborne radioactivity with a DAC of 1 x 10 -8 µCi / cc. What is the maximum concentration to which he could be exposed for the four hour period without exceeding 40 DAC-hours? A) 1 x 10 -8 µCi / cc B) 1.3 x 10-6 µCi / cc C) 1 x 10 -7 µCi / cc D) 5.2 x 10-6 µCi / cc E) 1.1 x 10-10 µCi / cc

The correct answer is: C (concentration/DAC) x hours = DAC-hours (concentration/1 x 10-8) x 4 = 40 concentration/1 x 10-8 = 10 concentration = 1 x 10 -7

Question Number: 414 Detection and Measurement How long must a sample with a count rate of 250 cpm be counted to give a total count rate standard deviation of 1%? A) 4 minutes B) 20 minutes C) 40 minutes D) 100 minutes E) 400 minutes

The correct answer is: C 1 sigma = (sample count rate/sample count time)1/2 And: 1 sigma = (.01)(250 cpm) Therefore: (.01)(250 cpm) = (250 cpm/sample count time)1/2 (2.5)2= (250/sample count time) 40 min = sample count time

Question Number: 654 Detection and Measurement The inverse square law is used often in ionizing radiation protection. With regard to lasers, the inverse square law: A) applies in most situations. B) applies only for visible wavelengths. C) only applies for reflected light from a diffuse reflector. D) only applies for reflected light from a specular reflector. E) applies for BOTH specular and diffuse reflected light.

The correct answer is: C A diffuse reflector will approximate a point or "kernel" source of the radiation. See calculations in ANSI Z136.1, Appendix B.

Question Number: 401 Detection and Measurement What is the effective half-life in the human body for Cobalt-60, if the biological half-life is eight days? A) 0.125 days B) 1.52 days C) 7.97 days D) 45.8 days E) 1.52 years

The correct answer is: C A good thumb rule for calculating effective half-life is that if the isotope has a half-life greater than 100 days, the effective half-life (Teff) is only a bit less than the biological half-life. The effective half-life is never greater than the biological half-life. The equation to calculate Teff is as follows: Teff = Tb * Tr / Tb + Tr Where: Tb = biological half-life Tr = radiological (physical) half-life

Question Number: 429 Detection and Measurement The average activity of Potassium-40 found in the human body is: A) 2.22 x 103 disintegrations per minute. B) 2.22 x 104 disintegrations per minute. C) 2.22 x 105 disintegrations per minute. D) 3.70 x 103 disintegrations per minute. E) 3.70 x 104 disintegrations per minute.

The correct answer is: C According to ICRP Publication 23, Reference Man contains 100 nanocuries (1 x 10 -7 curies) of K-40. Therefore: 1 x 10 -7 Ci * 2.22 x 1012 dpm/Ci = 2.22 x 105 dpm

Question Number: 658 Detection and Measurement The minimum dose required to cause permanent male sterility, according to the BEIR V report, is an acute dose to the testes of: A) 0.1 to 0.3 Gy. B) 1 Gy. C) 3 to 5 Gy. D) 5 to 7 Gy. E) 18 mGy per day for one week.

The correct answer is: C Acute doses of 3 to 5 Gy are required to cause permanent male sterility. Acute doses below this may cause temporary sterility. Note that the LD50 is approximately 3 to 5 Gy. A local dose to the reproductive organs would be implied in this question. Radiation therapy patients would be an important population to consider with this type of dose. (1990). BEIR V Report. Washington, DC., p.365.

Question Number: 626 Detection and Measurement The largest respirable particle is considered to be: A) 100 microns B) 30 microns C) 10 microns D) 1 micron E) 0.1 microns

The correct answer is: C Additionally, the most difficult particle sizes to filter are 0.2 to 0.5 microns.

Question Number: 527 Detection and Measurement Carbon dating is possible because: A) the specific activity of C-14 in living organisms has changed over time and one can identify the era of time the organism lived based on its current specific activity. B) C-14 is in secular equilibrium with its daughter. C) the specific activity of C-14 in living organisms is relatively constant through time, but decays after the death of the organism. D) the specific activity of C-14 in wood increases over time due to shrinkage of the wood. E) the specific activity of C-14 in wood decreases over time due to shrinkage in wood.

The correct answer is: C All organisms establish an equilibrium level of C-14 while alive. After death, the intake ceases and the equilibrium level decreases as a function of the decay constant. If the equilibrium level is known for certain living organisms, the time elapsed after death can be calculated.

Question Number: 540 Detection and Measurement Measurement uncertainty in a radiation measuring device is a function of: A) the method of detector operation. B) the type of radiation measured. C) both precision and accuracy in the measurement. D) the magnitude of the quantity measured. E) the significance of the hazard monitored.

The correct answer is: C Although A and B are correct responses, they are contributing factors to selection C, making it the best answer.

Question Number: 403 Detection and Measurement An individual who receives 40 DAC-hours will receive a committed effective dose equivalent of: A) 10 millirem B) 40 millirem C) 80 millirem D) 100 millirem E) 1250 millirem

The correct answer is: D Assuming the DAC is based upon the sALI, one DAC-hour is equal to a CEDE of 2.5 mrem. Therefore: 40 DAC-hrs * 2.5 mrem/DAC-hr = 100 mrem

Question Number: 595 Detection and Measurement Ultimately, absorbed dose in tissue from alpha, beta, gamma, and neutron radiation is due to: A) the damage to biological systems via direct and indirect effects. B) the chemical composition of the tissue. C) the transfer of kinetic energy to electrons. D) the transfer of energy to atoms or molecules. E) None of the above since different radiations have different interaction modes.

The correct answer is: C Although alpha, beta, gamma, and neutron radiations have different modes of interactions, absorbed dose will eventually be determined by the transfer of kinetic energy to electrons.

Question Number: 620 Detection and Measurement For a gas filled detector operating in the GM region, the detector output pulse amplitude: A) is approximately proportional to the energy of the radiation entering the detector. B) will increase proportionally with detector wall density-thickness. C) is independent of the type and energy of the radiation entering the detector. D) is dependent on the voltage applied to the detector. E) is proportional to the number of primary ion pairs produced in the fill gas.

The correct answer is: C Any number of ionizing events in the detector's fill gas will cause complete detector discharge. The output pulse amplitude is therefore independent of the type and energy of radiation entering the detector, and there is no proportionality with respect to radiation energy or number of primary ion pairs produced. In the GM region, output pulse amplitude is not significantly affected by detector applied voltage (as indicated by the "flat" GM region of the six-region curve). Gollnick, D. Basic Radiation Protection Technology

Question Number: 468 Detection and Measurement An individual breathes a concentration of 5.0 x 10 -8 µCi /ml of Cobalt-60 for one and one-half hours. If the DAC for Cobalt-60 is 9.0 x 10 -9 µCi /ml, his approximate whole body dose from this intake will be: A) 5.55 millirem B) 2.1 millirem C) 21 millirem D) 14 millirem E) 1.4 millirem

The correct answer is: C Assuming the DAC is based upon the sALI, one DAC-hour is equal to a CEDE of 2.5 mrem. Therefore: DAC-fraction * time(hrs) * 2.5 mrem/DAC-hr = CEDE (5.0 x 10-8/9.0 x 10-9) (1.5 hrs) (2.5 mrem / DAC-hr) = 20.83 mrem

Question Number: 646 Detection and Measurement From the early days of liquid scintillation counting until the 1980's, liquid scintillation counting used to require the counting apparatus be maintained at low temperatures. Given that the basic principles of liquid scintillation counting have not changed, why would this be desirable, and may even be desirable today? A) To increase the light conversion efficiency of the gamma ray peaks B) To increase the resolving time of the system C) To increase the signal to noise ratio of the counting system D) To compensate for the beta ray background E) To compensate for the gamma ray background

The correct answer is: C Cooling reduces thermionic emissions.

Question Number: 643 Detection and Measurement In the past, liquid scintillation counting required that the counting apparatus be maintained at low temperatures. Given that the basic principles of liquid scintillation counting have not changed, why would this be desirable, and may even be desirable today? A) To increase the light conversion efficiency of the gamma ray peaks B) To increase the resolving time of the system C) To increase the signal to noise ratio of the counting system D) To compensate for the beta ray background E) To compensate for the gamma ray background

The correct answer is: C Cooling reduces thermionic emissions. Knoll, Radiation Detection and Measurement.

Question Number: 695 Detection and Measurement The best way to determine if small amounts of particulate radioactivity are in a water sample is to: A) use an HPGe detector with a small vial of water centered on top of it. B) place a drop or two of water inside an LSC vial and count using an LSC. C) evaporate a large volume of water and count the residue. D) place a GM detector next to a large container of the water. E) use a ZnS detector .

The correct answer is: C Evaporating the sample will concentrate the particulate, so it may be more easily detected.

Question Number: 503 Detection and Measurement An instrument that gives a direct exposure rate reading from ionizing photon radiation is: A) a quartz fiber self-reading dosimeter. B) a liquid scintillation counter. C) an air ionization chamber survey meter. D) a silver halide film badge. E) a boron trifluoride counter.

The correct answer is: C Exposure is ionization of air by photons. The only two instruments shown which give a direct response to exposure are A and C. A quartz fiber self-reading dosimeter, however, gives an integrated reading, not a rate.

Question Number: 571 Detection and Measurement In the proportional region, the size of the avalanche in the gas-filled detector may be controlled by use of a known and stable voltage and use of a: A) stable fill gas. B) quench gas. C) cylindrical design. D) large anode. E) stable saturation current.

The correct answer is: C For a cylindrical chamber, the field strength at any radius from the needle is dependent on the voltage, the radius of the wire and the radius of the chamber. The field strength is very high near the wire, but drops off quickly as we move away from the wire. At some distance near the wire, the field strength is great enough to initiate a cascade. This means the cascade always starts the same distance from the wire for a given voltage. For a specific voltage, the size of the cascade is almost constant. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26.

Question Number: 544 Detection and Measurement When performing in-vivo measurements of personnel after a criticality accident to assess neutron dose, what is the nuclide of concern? A) I-131 B) Cs-137 C) Na-24 D) N-16 E) P-32

The correct answer is: C For in-vivo measurements of criticality accident proportions, the Na-23(n,gamma)Na-24 reaction from large blood pools in the body (armpit, abdomen) is most useful.

Question Number: 669 Detection and Measurement The concentration where the EPA recommends radon remediation in your home is which of the following? A) 1. 1.3 x 105 MeV/L air alpha B) 2. 100 pCi/L C) 3. 4 pCi/L D) 4. 3 DAC Rn-222 (including daughters) E) 5. 1 Working Level

The correct answer is: C Four pCi/L is recommended by the EPA.

Question Number: 575 Detection and Measurement A semi-conductor detector is said to be compensated when it has: A) more n-type than p-type impurities. B) more p-type than n-type impurities. C) equal number of n-type and p-type impurities. D) no p-type impurities. E) no n-type impurities.

The correct answer is: C If the number of n-type impurities is equal to the number of p-type impurities, the material is said to be compensated and the substance would be like an intrinsic semi-conductor. In this case, the impurities "compensate" for each other. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg. 10-12.

Question Number: 424 Detection and Measurement A person is standing in a semi-infinite cloud of Xenon-133 (0.081 MeV gamma) with a concentration of 3.0 x 10 -1 µCi / ml. What is the maximum time the person may stay there without exceeding a whole body gamma radiation dose of 25 rem? A) 4.1 minutes B) 24.3 minutes C) 68 minutes D) 1.5 hours E) 2.43 hours

The correct answer is: C In a semi-infinite cloud of gamma-emitting noble gases, the gamma contribution to the absorbed dose rate (D) can be estimated as: D = .25 EX Where: D = rads/sec = rems/sec E = gamma energy(MeV) * yield X = concentration (µCi/cc) And stay time is calculated as: stay time = allowable dose/dose rate Therefore: stay time = 25 rem/.25 EX = 25 rem/ .25 (.081)(3.0 x 10-1) = 4115 sec * (1 min/60 sec) = 68.59 min

Question Number: 516 Detection and Measurement In the G-M region of a gas filled type detector, the output: A) is approximately proportional to the energy of the radiation entering the detector. B) decreases to zero in a high radiation field. C) pulse height is independent of the type and energy of the radiation entering the detector. D) pulse height is independent of the voltage on the chamber over a fairly large voltage range. E) pulse is proportional to the amount of the primary ionization produced in the gas.

The correct answer is: C In the G-M region, the voltage is high enough such that one triggering event of any type of ionizing radiation will produce complete ionization of the detector fill gas, creating the same height pulse for any initiating event. Regarding choice B, modern G-M detectors are designed to fail high in high radiation fields.

Question Number: 515 Detection and Measurement In the ionization region of a gas-filled detector, the output current is approximately: A) proportional to the energy of the radiation entering the detector. B) equal to the energy of the radiation entering the detector. C) independent of the voltage over a fairly large voltage range. D) the same size regardless of the type of energy of the radiation. E) independent of the fill gas.

The correct answer is: C In the ionization region, there is a current of electrons produced which is equal to the number of initial ionizations produced in the detector. The current is independent of the voltage over a fairly broad range, the range being dependent on detector volume and fill gas characteristics.

Question Number: 434 Detection and Measurement Proportional counters operate at voltages than/as ionization chambers. A) lower B) equal C) higher D) lower and equal E) equal and higher

The correct answer is: C In the six region curve for gas-filled detectors, the regions in order of increasing voltage (the x-axis) are: Recombination Ionization Proportional Limited Proportional Geiger-Mueller Continuous Discharge

Question Number: 461 Detection and Measurement The specific gamma constant of a particular radionuclide emitting 3 MeV photons is 1 R/hr per curie at 1 m. The exposure rate at 10 cm from a point source of 10 curies is approximately: A) 10 R/hr B) 100 R/hr C) 1000 R/hr D) 3000 R/hr E) 5000 R/hr

The correct answer is: C In this calculation, the curie content is being increased by a factor of 10, and the distance decreased by a factor of 10. This results in a total increase in exposure rate of: 10 (10)2 = 1000 So: 1 R/hr (1000) = 1000 R/hr

Question Number: 690 Detection and Measurement The dose rate from a package containing Tc-99m is 16 mrads per hour at a distance of 30 cm. At what distance would the dose rate be 4 mrads per hour? A) 15 cm B) 45 cm C) 60 cm D) 75 cm E) 120 cm

The correct answer is: C Inverse square law applies, double the distance, the dose rate is reduced by a factor of four.

Question Number: 453 Detection and Measurement A ten foot long pipe containing Cobalt-60 creates an exposure rate of 20 mR/hr at twenty feet. What is the exposure rate at one foot from this pipe? A) 0.8 R/hr B) 1.3 R/hr C) 1.6 R/hr D) 1.9 R/hr E) 2.1 R/hr

The correct answer is: C L = 10 feet L/2 = 5 feet Inside L/2: R1(D1) = R2(D2) Outside L/2: R1(D1)2 = R2(D2)2 So calculate in to L/2: 20 mR/hr (20)2 = R2 (5)2 R2 at L/2 = 320 mR/hr Then calculate in to one foot: 320 mR/hr (5) = R2 (1) 1600 mR/hr = R2 1.6 R/hr = R2

Question Number: 466 Detection and Measurement What materials are most commonly used as filters in film badges? A) Paraffin, plastic, teflon B) Plastic, teflon, aluminium C) Plastic, aluminium, lead D) Cadmium, tin, paraffin E) Paraffin, polyurethane, teflon

The correct answer is: C Materials of varying density thicknesses are used as filters in film badges to correct for tissue equivalence, energy dependence, and to discriminate between types of radiation.

Question Number: 531 Detection and Measurement Which one of the following statements is TRUE regarding neutron bubble detectors? A) They are insensitive to intermediate energy neutrons. B) They are accurate within ± 30% in neutron dose rates of over 1000 rads/hr. C) They are affected by temperature. D) They cannot measure the total integrated dose. E) They are not yet commercially available.

The correct answer is: C Neutron bubble detectors rely on superheated gas molecules in a polymer matrix to expand and "pop" when exposed to the heat of the H-1(n,gamma)H-2 reaction in the detector. The events are either recorded as number of bubbles created or number of "pops" registered by transducer. Since they rely on the heat of the reaction, they are temperature sensitive.

Question Number: 509 Detection and Measurement Nominal counting efficiencies of a 2 pi proportional counter for alpha and beta sources, respectively, would be: A) 50% and 10% B) 50% and 40% C) 50% and 65% D) 75% and 50% E) 75% and 100%

The correct answer is: C Nominal efficiency in this case takes into account only geometry effects. Since one half of the sample is exposed to the detector in 2 pi geometry, the nominal efficiency for a high-LET radiation such as alpha would be 50%. Since beta particles will scatter into the detector from the sample holder, the nominal efficiency for beta particles will be greater than 50%. The answer which fits this decision logic is C.

Question Number: 412 Detection and Measurement Common radionuclides used for the calibration of portable gamma photon detectors include which of the following? A) Co-60, Cs-137, Ar-41 B) Co-60, Cs-137, Rn-222 C) Co-60, Cs-137, Ra-226 D) Cs-134, Cs-137, Ra-226 E) Co-60, Cs-134, Kr-85

The correct answer is: C Of the three, Radium is not used very frequently, although it was at one time. Sealed radium sources are susceptible to rupture due to buildup of radon gas.

Question Number: 433 Detection and Measurement A detector with a resolving time of 100 microseconds yields 175,000 net counts in one minute. What is the true count rate of the sample? A) 17,502 cpm B) 100,000 cpm C) 166,666 cpm D) 247,058 cpm E) 1,000,327 cpm

The correct answer is: D Rc = Ro /(1 - Rot) Rc = 175,000/ [1 - 175,000 (100 µsec * 1E-06 sec/ µsec * 1/60 min/sec)] = 247,058 cpm

Question Number: 465 Detection and Measurement Which of the following is a disadvantage of a TLD versus a film badge for external radiation dosimetry? A) TLDs are not weather resistant. B) TLDs cannot be reused. C) TLDs leave no permanent record. D) TLDs are less durable. E) TLDs are more awkward for personnel.

The correct answer is: C Once the TLD is annealed, the actual response in the dosimeter has been removed. If for some reason the results are not recorded properly, the data is lost. Most TLD systems have backup TL chips for this reason.

Question Number: 522 Detection and Measurement An important advantage of using a halogen quenching gas rather than an organic quenching gas in a G-M detector is: A) halogen gases have a lower ionization potential so they also have an increased sensitivity. B) organic gases corrode the detector. C) organic gases can be depleted thus losing the quenching required for the detector while the halogen is self rejuvenating. D) halogen gases are better conductors. E) it makes the instrument lighter.

The correct answer is: C Organic quench gases such as methane have a distinct life, usually expressed in total counts detected. Inorganic quench gases such as bromine are self-rejuvenating and, thus, have an indefinite life. This may be an important quality in a fixed volume, sealed detector.

Question Number: 406 Detection and Measurement What are the constituents of the fill gas P-10? A) 10% argon and 90% methane B) 50% argon and 50% methane C) 90% argon and 10% methane D) 60% argon and 10% methane E) 10% argon and 60% methane

The correct answer is: C P-10 is used in gas-filled detectors in the proportional and G-M regions. The argon serves as the ionization gas, the methane is an organic quench gas.

Question Number: 621 Detection and Measurement A detector yields a FWHM of 3 keV for the primary I-131 photopeak. The percent resolution of the detector at this energy is: A) 0.008% B) 0.08% C) 0.8% D) 8.0% E) 80%

The correct answer is: C Percent Res = (FWHM/photopeak energy) * 100% = (3 keV/364.5 keV) * 100% = 0.82% If you didn't know the I-131 peak energy, an educated guess of somewhere between 100 and 2000 keV would yield percent resolution values between 0.15 and 3. Answer C is the only choice in this range.

Question Number: 585 Detection and Measurement Radiation detectors can be operated in which of the following modes? A) Current and pulse B) Pulse and mean square voltage C) Current, pulse and mean square voltage D) Current and mean square voltage E) Current, pulse, and absolute voltage

The correct answer is: C Pulse is the most common mode of operation, allowing analysis of the energy of the radiation. Current mode is generally used in ionization chambers where the event rate in the detector is high. The mean square voltage mode is most often used in mixed radiation fields to allow discrimination between two types of radiation with high event rates where the charge produced by one type of radiation is very different from the other. Mixed neutron gamma fields are an example.

Question Number: 670 Detection and Measurement An air filled ion chamber (not pressurized) is calibrated at sea level and brought to an altitude of 7,500 feet. All readings for this ion chamber must be: A) discarded, as the altitude will cause the chamber to malfunction. B) discarded, as the increased atmospheric pressure will cause the window to bulge out, changing the volume of air. C) corrected for temperature and pressure. D) corrected for humidity. E) taken for a significantly longer time, due to slower response (resolving time) at altitude.

The correct answer is: C Readings for this ion chamber must be correct for temperature and pressure at altitude, as the quantity of air (number of air "molecules") is less at altitude, causing the ion chamber to under-respond.

Question Number: 538 Detection and Measurement Which statement is most accurate? A) It is hard to identify K-40 in the presence of 10 nCi of Co-60. B) The quantity of K-40 dose not vary by more than plus or minus 5% from individual to individual. C) K-40 has no regulatory significance in a whole body counting program but serves as an important qualitative system check. D) K-40 should be omitted from the radionuclide library for whole body counting since it is of no regulatory interest. E) A multi-detector counter will typically not identify K-40.

The correct answer is: C Since K-40 is a significant naturally occurring radionuclide, there is some level of K-40 in every individual's body. An in-vivo gamma spectroscopy result which does not show K-40 is suspect of counting error. ICRP 23 gives a value of 100 nCi of K-40 in Reference Man.

Question Number: 476 Detection and Measurement Which of the following is the best choice for measuring the dose from Kr-85? A) Criticality dosimeter B) Cutie pie C) TLD D) GM survey meter E) Vibrating reed electrometer

The correct answer is: C Since Kr-85 is a beta-gamma emitting external hazard, and dose is the quantity to be measured, the TLD is the best choice.

Question Number: 499 Detection and Measurement The most appropriate survey instrument for the detection of Pu-239 surface contamination is one which utilizes a(n): A) GM detector. B) NaI(Tl) detector. C) zinc sulfide detector. D) ionization chamber. E) boron trifluoride counter.

The correct answer is: C Since Pu-239 decays by alpha, with only a weak gamma emitted, the detector which is most efficient for alpha is chosen.

Question Number: 411 Detection and Measurement For in-vivo bioassay of a mixture of gamma-emitting radionuclides, the best detector is: A) large geometry gas-flow proportional. B) Na I. C) GeLi. D) SiLi. E) external liquid scintillation.

The correct answer is: C Since a mixture of radionuclides is specified, the detector with the best resolution is probably the "best".

Question Number: 518 Detection and Measurement Which of the following materials is commonly found in photoneutron sources? A) Tantalum B) Carbon C) Beryllium D) Cobalt E) Aluminum

The correct answer is: C Since beryllium has a low nuclear binding energy, it is often combined with gamma or alpha emitting nuclides to produce a neutron source. A typical photoneutron source is SbBe, used as a "startup source" in nuclear reactors.

Question Number: 459 Detection and Measurement The ICRP recommended in 1977 that the total effective dose equivalent should not exceed 5 rem in a year. If an individual breathed 0.2 DAC air for forty hours per week for one year and received no other internal exposure, what is the maximum external occupational exposure he could receive under this recommendation? A) 2.8 rem B) 3.2 rem C) 3.9 rem D) 4.2 rem E) 5.0 rem

The correct answer is: C Since breathing one DAC for an occupational year (2000 hours) would result in 5 rem CEDE, breathing 0.2 DAC would result in 5 rem * 0.2 = 1.0 rem. If 1 rem is being received internally, 4 rem would be allowed externally. The best answer is 3.9 rem.

Question Number: 407 Detection and Measurement You are setting up a count room for analysis of airborne and surface contamination samples at a facility where the isotopes of concern are transuranics, fission products, and activation products. Your BEST selection of instruments would be: A) Geiger-Mueller detector with scaler, zinc sulfide scintillation detector. B) Geiger-Mueller detector with scaler, GeLi detector. C) gas flow proportional counter, GeLi detector. D) zinc sulfide scintillation detector, GeLi detector. E) sodium iodide scintillation detector, gas flow proportional counter.

The correct answer is: C Since the isotopes of concern are emitting alpha, beta, and gamma radiations, a proportional counter will be necessary for its capability to distinguish between alpha and beta-gamma. Since airborne contamination is being measured, gamma spectroscopy capability (in this case GeLi has the best resolution) is required to identify radionuclides having different DACs.

Question Number: 627 Detection and Measurement A worker wearing a supplied-air full-face respirator and cotton coveralls worked in an area where the exposure without protection would have been 2,000 DAC-hours of I-131 and 1,000 DAC-hours of tritium. If the protection factor of the respirator is 1,000, the approximate intake corresponds to: A) 3,000 DAC-hours. B) 1,000 DAC-hours. C) 500 DAC-hours. D) 50 DAC-hours. E) 3 DAC-hours.

The correct answer is: C Since the maximum protection factor that can be taken for tritium is 2 ( 10 CFR Part 20, Appendix A), the calculation is as follows: (2000 DAC-hrs/1000) + (1000 DAC-hrs/2) = 502 DAC-hrs

Question Number: 470 Detection and Measurement The MOST effective bioassay method to detect uptake of tritium is: A) nasal smears. B) fecal analysis. C) urinalysis. D) liquid scintillation whole body counter. E) solid crystal scintillation whole body counter.

The correct answer is: C Since tritium is an isotope of hydrogen, it is readily taken up in body water and excreted via the urine. Urine is especially adaptable to liquid scintillation counting, which is required for tritium detection.

Question Number: 409 Detection and Measurement Why is a NaI(Tl) detector housed in a canister? A) To prevent beta particle interference in the detector B) To minimize Compton scattering in the detector C) To keep the detector dry due to its hygroscopic characteristics D) To promote bremsstrahlung for maximum efficiency E) To prevent cosmic radiation interference in the detector

The correct answer is: C Sodium Iodide will absorb moisture if left open to the atmosphere. This will cause detector decomposition and reduction in visible light transmission.

Question Number: 425 Detection and Measurement A sulphur pellet is sometimes used in a personnel dosimeter. Its purpose is to: A) measure gamma exposure. B) measure beta exposure. C) measure neutron exposure. D) measure background exposure. E) measure radon daughter exposure.

The correct answer is: C Sulfur is used in criticality accident dosimetry. The S-32(n,p)P-32 reaction produces measurable beta activity, which can be equated to neutron dose equivalent.

Question Number: 520 Detection and Measurement The average number of ion pairs produced by a 100 keV beta particle that stops in air is approximately: A) 30 B) 300 C) 3,000 D) 30,000 E) 300,000

The correct answer is: C The "W" value for air (dry air at STP) is 33.7 eV. So: (100 keV * 1 x 10 3 eV/keV)/(33.7 eV/ion pair) = 3000 ion pairs

Question Number: 684 Detection and Measurement The best way to find fixed and removable Ra-226 contamination in a lab that contains a high Co-60 background would be to use which of the following? A) Portable GM detector B) Fixed (laboratory based shielded) GM Detector C) ZnS based detector D) Liquid Scintillation Detector (LSC) E) Thin window NaI detector (0.125" thick)

The correct answer is: C The ZnS detector would be insensitive to the Co-60 gamma rays, and would detect the alpha emissions from the Ra-226. Wipes and an LSC detector would also work, but would not work with the fixed contamination.

Question Number: 496 Detection and Measurement A person is standing in a semi-infinite cloud of Krypton-88 (2.39 MeV gamma, 0.196 MeV gamma) with a concentration of 2.0 x 10 -2 µCi /ml. If the person remains there for fifteen minutes, his whole body gamma radiation dose will be: A) 2.1 rem. B) 7.7 rem. C) 11.6 rem. D) 19.6 rem. E) 21.1 rem.

The correct answer is: C The absorbed deep dose from submersion in a cloud of gamma-emitting noble gas can be estimated as: D = .25 EX Where: D = rad/sec E = gamma energy (MeV) * yield X = concentration (µCi /cc) And: Dose rate * time = dose And: yield is not given, so 1 must be assumed So: {.25[(2.39 * 1.00)+(0.196 * 1.00)](2.0 x 10 -2)} * (15m * 60s/m) = 11.64 rad And, for gamma (QF = 1) = 11.64 rem

Question Number: 450 Detection and Measurement A worker is exposed to different radiations at a work site and it is determined that he had a dose of 1 rad from fast neutrons, 1 rad from thermal neutrons, and 2 rad from gamma rays. What is the dose equivalent which should be assigned to this worker? A) 3 rem B) 7 rem C) 15 rem D) 24 rem E) 45 rem

The correct answer is: C The appropriate quality factors are as follows: Fast Neutrons 10 Thermal neutrons 3 Gamma 1 Therefore: (1 rad * 10) + (1 rad * 3) + (2 rad * 1) = 15 rem

Question Number: 506 Detection and Measurement A worker spends 90 minutes in a field of 120 mR/hr gamma, 40 mrad/hr thermal neutrons, and 80 mrad/hr fast neutrons. The total whole body dose equivalent to the worker for this period is: A) 240 mrem. B) 360 mrem. C) 1320 mrem. D) 1560 mrem. E) 1980 mrem.

The correct answer is: C The appropriate quality factors are as follows: Gamma 1 Thermal neutrons 3 Fast neutrons 10 And: rad * QF = rems And: dose rate * time = dose Therefore: [(120 * 1)+(40 * 3)+(80 * 10)] * (90 min/60 min/hr) = 1560 mrem

Question Number: 668 Detection and Measurement The dose limit to an underground miner is: A) a working level. B) four working levels. C) four working level months. D) one working level month. E) five rems per year internal inhalation of Rn-222 daughters that are in equilibrium with thoron at 4 pCi/L.

The correct answer is: C The dose limit to an underground miner is four working level months per year. See 30 CFR for limits.

Question Number: 593 Detection and Measurement Which of the following TLD phosphors exhibits an energy response most similar to that of tissue? A) CaS04:Tm B) LiF C) Li2B407:Cu D) CaF2:Mn E) CaS04

The correct answer is: C The effective Z of Li2B407:Cu is 7.4, and the effective Z of tissue is 7.5.

Question Number: 591 Detection and Measurement The effective Z of tissue is: A) 4.7 B) 5.6 C) 7.5 D) 12.3 E) 16.3

The correct answer is: C The effective atomic number of tissue is generally stated as 7.5. This value takes into account the Z of the predominant elements compromising tissue.

Question Number: 431 Detection and Measurement An intake of one non-stochastic ALI by the specified route will result in: A) 5 rem committed dose equivalent to a tissue or organ. B) 5 rem committed effective dose equivalent. C) 50 rem committed dose equivalent to a tissue or organ. D) 50 rem committed effective dose equivalent. E) 50 rem total effective dose equivalent.

The correct answer is: C The non-stochastic ALI (nALI) is that amount of radioactive material which will produce a 50 year committed dose equivalent to an individual organ or tissue of 50 rems. The stochastic ALI (sALI) will produce a 50 year committed effective dose equivalent of 5 rems.

Question Number: 691 Detection and Measurement Workers must enter a room with a 20' long pipe that contains 2 curies of Co-60 and work 40 feet from the pipe. The technician cannot remember the line source equation, so he uses the point source equation to estimate the dose rate. Which of the following is MOST correct? A) He will probably underestimate the dose. B) He will probably overestimate the dose. C) He will probably be fairly close in his estimate. D) The dose from Co-60 is only internal - it is an alpha emitter. E) Co-60 doses cannot be estimated.

The correct answer is: C The point source equation will work at distances beyond L/2. See Gollnick.

Question Number: 545 Detection and Measurement 9.25 x 1011 Bq (25Ci) of a gas, with a half-life of 2.3 hours, is uniformly distributed in the air in a 2.5m by 10m by 15m room. The effective room ventilation rate is 150m3/hr. After one hour, the activity concentration in the room is: A) 7.32 x 108 Bq/m3 B) 1.10 x 109 Bq/m3 C) 1.22 x 109 Bq/m3 D) 1.73 x 109 Bq/m3 E) 2.47 x 109 Bq/m3

The correct answer is: C The removal mechanisms from the room are by decay and ventilation. Take both of these into account when calculating the effective removal constant. Use C = Co e-(kt) and k = F/V + Therefore: C = (9.25 x 1011 Bq/375m3)e-[(150/375) + (.693/2.3)] = 1.22 x 109 Bq/m3

Question Number: 542 Detection and Measurement What is the most efficient ratio of sample counting time to background counting time given that the background counting rate is 10 counts per minute and the total counting rate with a sample is 1,000 counts per minute? A) 0.01 to 1 B) 1.0 to 1 C) 10 to 1 D) 100 to 1 E) 1,000 to 1

The correct answer is: C The statistically optimum ratio of sample count time to background count time is calculated as: sample time/bkgrd time = (sample rate/bkgrd rate)½ = (1000/10)½ = 10

Question Number: 559 Detection and Measurement Summing of gamma photons on a gamma spectrometer spectrum can also occur between: A) gamma photons and annihilation gammas. B) gamma photons and Pb x-rays. C) gamma photons and internal conversion x-rays. D) Pb x-rays and internal conversion x-rays. E) annihilation gammas and Pb x-rays.

The correct answer is: C This compilation most commonly occurs with low energy gamma processes. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 563 Detection and Measurement To avoid excessive dead time on multi-channel gamma analyzers you should keep samples below: A) 100 mr/hr at 30 cm B) 100 mr/hr at 2 inches C) 10 mr/hr at 2 inches D) 1 mr/hr at 30 centimeters E) 5 mr/hr at 1 meter

The correct answer is: C This is an industry - accepted good practice. Increasing sample activity incrementally decreases counting efficiency. EPRI Rad Waste Reference Question 1621

Question Number: 631 Detection and Measurement Which is the major factor in considering the milk-food chain when relating release of activity to the air and the dose to the population? A) Short period of time between cow exposure and retail marketing of milk B) Large volume of air the cow breathes daily C) Large concentration factor between air and milk due to the large pasture area a cow traverses to obtain food D) Large quantity of milk consumed by adults E) Large quantity of milk consumed by children

The correct answer is: C This pathway is specified in NRC Regulatory Guide 1.109 as a predominant ingestion exposure pathway. Not only is the large grazing area a factor, but also the large volume of food that the cow consumes.

Question Number: 549 Detection and Measurement Laboratories designed to evaluate environmental samples taken from locations surrounding operating nuclear power plants must be designed to measure extremely low concentrations of radioactivity. Typical MDAs required for plant effluent releases are on the order of to meet regulatory license requirements. A) 3.7 x 10-10 Bq/cm3 B) 2.2 x 10-5 Bq/cm3 C) 3.7 x 10-4 Bq/cm3 D) 2.2 x 10-3 Bq/cm3 E) 1.7 x 10-6 Bq/cm3

The correct answer is: C This quantity is approximately equivalent to one picocurie per liter. 10 CFR Part 20

Question Number: 642 Detection and Measurement Fission chambers can be used for detection of either thermal or fast neutrons. Which uranium isotope is typically used for detection of thermal neutrons in these devices? A) U-233 B) U-234 C) U-235 D) U-236 E) U-238

The correct answer is: C U-235 is used, due to its large cross section for fission, as compared to the other choices. Plutonium-239 can also be used. Knoll (1989). Radiation Detection and Measurement. Gollnick, D. Basic-Radiation Protection Technology.

Question Number: 539 Detection and Measurement The major pathway by which soluble radioactive material is removed from the body is which of the following? A) Perspiration B) Feces C) Urine D) Respiration E) Exhalation

The correct answer is: C Urine represents the largest volume of liquid excretion from the body, and therefore is responsible for the greatest removal of soluble compounds and elements. This characteristic makes urine well-suited for in-vitro bioassay sampling.

Question Number: 420 Detection and Measurement A point source of 137-Cs with an activity of 1 Ci, a photon energy of 0.662 MeV, and a photon yield of 0.85 photons/disintegration is measured at two feet. The expected exposure rate is: A) 3.38 R per hour B) 1.69 R per hour C) 0.84 R per hour D) 0.99 R per hour E) 0.90 R per hour

The correct answer is: C Use 6CEN and the inverse square law: 6CEN =(6)(1Ci)(0.662 MeV)(0.85) = 3.38 R/hr R1D12 = R2D22 (3.38 R/hr(1ft)2 = R2(2ft)2 0.84 R/hr = R2

Question Number: 513 Detection and Measurement When a radionuclide is taken into the body, the extent of damage is determined by which of the following? A) The type of radiation emitted and its half-life B) The rate at which the radionuclide is excreted from the body C) The place of deposition of the radionuclide in the body D) All of the above E) Both A and B

The correct answer is: D All of these factors must be taken into account to properly estimate the dose and resultant potential damage from a radionuclide intake.

Question Number: 579 Detection and Measurement You have two beta-gamma gas flow proportional detectors on site. One detector (1) is located in a low background building and registers 22 cpm background. The other detector (2) is located near a radioactive material storage area and registers 3 cpm background. The difference in background count rate can be explained by the use of on detector (2). I. Shielding II. Counting gas III. Coincident counter IV. Temperature V. Detector voltage A) I B) II, IV, and V C) I and III D) II, III, and V E) I, II, and IV

The correct answer is: C Using more shielding will reduce the background seen by the detector. Adding coincident circuit involves adding another detector which provides the biggest reduction in background count rate. If a count is seen in the coincident detector any counts coming from the sample detector are ignored, thus reducing the background effects by a factor of almost 10 in this example even though the detector is in a higher background. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26.

Question Number: 673 Detection and Measurement Resolving time is made up of which of the following? A) 1. Dead time B) 2. Recovery time C) 3. Resolution time D) 4. 1 and 2 E) 5. 1 and 3

The correct answer is: C Dead time + recovery time = resolving time.

Question Number: 635 Detection and Measurement The fraction of unattached radon decay products in the air depends upon all of the following EXCEPT: A) Condensation nuclei concentration B) Particle size distribution C) Radon concentration D) Diffusion coefficient of Po-218 E) Room surface plateout rate

The correct answer is: C The key word in the question is "fraction". The concentration of radon decay products in the air will depend upon the radon concentration, but the fraction is independent of the radon concentration.

Question Number: 526 Detection and Measurement The short-lived Radon (Rn-222) decay products are: A) Po-226, Bi-214, Po-218, Bi-216 B) Pb-214, Po-214, Bi-216, Po-218 C) Bi-214, Pb-214, Po-218, Po-214 D) Po-214, Ra-226, Rn-220, Pb-214 E) Po-216, Pb-212, Bi-212, Po-212

The correct answer is: C These are the nuclides that are included in the definition of "working level" and produce the majority of natural background radiation exposure by inhalation.

Question Number: 413 Detection and Measurement A detection system records 22 counts during a one minute counting period. How should the results be expressed to one standard deviation? A) 11 +/- 1.1 cpm B) 11 +/- 2.2 cpm C) 22 +/- 4.7 cpm D) 22 +/- 1.1 cpm E) 22 +/- 5.1 cpm

The correct answer is: C One standard deviation (1 sigma) represents the 68% confidence level. For this problem, it is calculated as follows: 1 sigma = (sample count rate/sample count time)1/2 = ( 22/1 )1/2 = +/- 4.69

Question Number: 628 Detection and Measurement A worker wearing a respirator with a rated protection factor of 50 is exposed to a concentration of long-lived airborne particulate activity at 10 times the DAC for a period of 10 hours. Allowing for the respiratory protection, what is the worker's calculated exposure? A) 500 DAC-hours B) 100 DAC-hours C) 20 DAC-hours D) 2 DAC-hours E) 0.2 DAC-hours

The correct answer is: D (DAC fraction/PF) * time (hrs) = DAC-hrs 10/50 * 10 hrs = 2 DAC-hrs

Question Number: 447 Detection and Measurement If the sample plus background is 1600 counts in one minute and the background is 900 counts in one minute, the net count is 700 counts per minute plus or minus counts per minute (1 standard deviation). A) 10 B) 26.5 C) 40 D) 50 E) 70

The correct answer is: D 1 sigma = [(bkgrd rate/bkgrd time)+(sample rate/sample time)]½ 1 sigma = [(900/1)+(1600/1)] ½ 1 sigma = ± 50 cpm

Question Number: 618 Detection and Measurement For general area radiation surveys, the NRC specifies measuring dose rates at what distance from a radiation source or a surface the radiation penetrates? A) 18 inches B) 30 inches C) 18 centimeters D) 30 centimeters E) 50 centimeters

The correct answer is: D 10 CFR Part 20 defines Radiation and High Radiation areas in terms of potential individual doses at a distance of 30 cm (roughly 12 in.) from radiation sources or surfaces the radiation penetrates. Very High Radiation Areas are determined based on dose rates at 1 meter.

Question Number: 426 Detection and Measurement Personnel dosimetry records must be retained: A) for the period of time it takes for the individual to reach 75 years of age. B) for a period of one year following the individual's death. C) for a period of five years following the individual's death. D) until the NRC terminates the pertinent license. E) for 50 years.

The correct answer is: D 10 CFR Part 20 requires that personnel monitoring records be maintained until the NRC license is terminated.

Question Number: 418 Detection and Measurement A proper average quality factor for estimating the dose equivalent in a radiation field consisting of an unknown spectrum of fast neutrons is: A) 1 B) 5 C) 8 D) 10 E) 15

The correct answer is: D 10 is the quality factor for neutrons of unknown energies, as represented in ICRP Publication 26 (1977) and 10 CFR Part 20.

Question Number: 677 Detection and Measurement The output signal from the amplifier of an He-3 detector is analyzed. The signal contains a 0.764 MeV peak, and two additional peaks at 573 keV and another at keV due to the . A) 1337, sum peek B) 1275, sum peak C) 253, single escape peak D) 191, wall effect E) 62, escape peak

The correct answer is: D 191 keV is the energy of the H-1 and 573 keV is the energy of the H-3 atoms. Note that the wall effect occurs when one or the other deposits energy in the wall of the detector, rather than depositing all the energy in the gas. Wall effect also occurs with BF3 detectors. The wall effect is more prominent in smaller detectors.

Question Number: 419 Detection and Measurement At what radius would you post a radiation area around a 10 Curie Manganese-54 (.835 MeV gamma) point source? (Assume 1 photon/disintegration.) A) 70 feet B) 81 feet C) 95 feet D) 101 feet E) 145 feet

The correct answer is: D According to 10 CFR Part 20, a radiation area is an area where an individual could exceed a deep dose equivalent of 5 mrem in one hour at 30 cm from the source. Using the inverse square law: R1 D12 = R2 D22 and R1 = 6CEN 6CEN = (6)(10 Ci)(0.835 MeV)(1) = 50.1 (50.1 R/hr)(1ft)2 = (0.005 R/hr)(D2)2 10020 ft2 = (D2)2 100.1 ft = D2

Question Number: 449 Detection and Measurement The quality factor for alpha particles and heavy nuclei is: A) 1 B) 10 C) 5 D) 20 E) 2

The correct answer is: D According to ICRP Publication 26 (1977) and 10 CFR Part 20, the quality factor is 20. ICRP Publication 60 (1990) has replaced the concept of quality factor with radiation weighting factor, which remains 20 for these high-LET radiations.

Question Number: 536 Detection and Measurement If the skin were contaminated by an isotope with a half-life of 8 days and assuming an exponential turnover time of the skin of 50% in 5 days, calculate the time to reduce the contaminant to 10% of the initial level. Assume decontamination has been ineffective. A) 1.1 d B) 3.1 d C) 7.1 d D) 10.2 d E) 43 d

The correct answer is: D Calculate the effective removal constant (lambda eff) and use the decay formula: eff = (0.693/8d) + (0.693/5d) = 0.225/day A = Ao e- [( eff)( t)] 0.1 = 1 e -[(0.225/day)(t)] ln(0.1) = - 0.225/day (t) 10.22 day = t

Question Number: 483 Detection and Measurement The minimum detectable activity for a counting system is: A) a measure of the efficiency of the detector. B) an indication of the range of energy response. C) a measure of the counting efficiency. D) an estimate of the lowest sample activity for which activity should be considered present. E) a time weighted average of the count rate for all samples of a specific condition at the time of counting.

The correct answer is: D Calculation of the MDA is dependent upon background count rate and count time, as well as sample count time. Increasing background and sample counting times will decrease MDA. An increase in background count rate will increase MDA.

Question Number: 566 Detection and Measurement The method used to determine the amount of uptake of C-14 is which of the following? A) Whole body count B) Urinalysis C) Blood analysis D) Breath analysis E) Fecal analysis

The correct answer is: D Capture an individual's breath with a ballon or bag and count for C-14. You are looking for CO exposed individual. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. 2 on exhalation from

Question Number: 551 Detection and Measurement Coincident circuitry is used in liquid scintillation detectors to eliminate the effects of: A) background radiation. B) light current. C) background noise. D) thermionic noise. E) tube temperature.

The correct answer is: D Circuit includes two PMTs which are used to discriminate against random noise pulses from the tubes by thermionic emission from the photocathodes of a PMT. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 663 Detection and Measurement When counting low background samples, the BEST way to increase the number of sample counts over background would be all the following EXCEPT: A) Increase sample size B) Increase count time C) Increase counter shielding D) Count samples only during the day, to minimize cosmic ray interactions E) Concentrate the sample if possible

The correct answer is: D Cosmic ray interactions might be higher during the day, and all other factors would have a greater influence.

Question Number: 455 Detection and Measurement The exposure rate from a 2 Ci source of Co-60, which emits two photons 100% of the time with energies of 1.17 MeV and 1.33 MeV is measured at 1 foot. The exposure rate is: A) 16 R/hr B) 14 R/hr C) 5 R/hr D) 30 R/hr E) 15 R/hr

The correct answer is: D D = 6CEN D = 6{(2)[(1.17 * 1)+(1.33 * 1)] = 30 R/hr

Question Number: 427 Detection and Measurement Filters are used in film badges in order to: I. Accelerate beta particles II. Correct for tissue equivalence III. Discriminate between different types of radiation IV. Correct for energy dependence of film A) I, II, and III B) II and IV C) II and III D) II, III, and IV E) I, II, III, and IV

The correct answer is: D Density thicknesses of filters are adjusted to correspond to various required measurement depths in tissue (i.e. shallow, lens, eye). "Windows" in the film badge allow for discrimination between beta and gamma radiation. Filters are also used to "soften" the energy of incident photons to promote photoelectric effect in the film, thereby increasing its efficiency.

Question Number: 454 Detection and Measurement You measure the dose rate at a job site and determine that a worker would receive a dose of 50 millirem by staying at that location for 15 minutes. The worker decides to use a long tool which makes his distance from the point source three times as far, but the work time is increased to 25 minutes. How much dose is saved using the long tool? A) 25 millirem B) 0 millirem C) 100 millirem D) 41 millirem E) 50 millirem

The correct answer is: D Dose without tool = 50 mrem Dose with tool = [50 mrem/(3)2] * (25 min/15 min) = 9.26 mrem Dose saved = (50 - 9.26) mrem = 40.74 mrem

Question Number: 578 Detection and Measurement Methods used to reduce the amount or effects of dead time in GM counters are: I. Electronic calculations using resolving time II. Quench gas III. Using a smaller detector volume IV. Increasing gas pressure V. Using shorter count times A) I, IV, and V B) I and II C) I and III D) I, II, and III E) II, III, and V

The correct answer is: D Electronic circuitry is used to calculate the true count rate. The RM-14SA uses this type of circuit to enable it to indicate 5 x 106 cpm. Decreased detector volume allows ions needing an electron a shorter path to the detector wall. Quench gas is used to provide positive ions with a source of electrons. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26.

Question Number: 676 Detection and Measurement Detectors may operate based on some basic principles. The He-3 based neutron detector is BEST described as a: A) Geiger counter. B) Scintillation detector. C) Solid state detector. D) Proportional counter. E) Ion chamber.

The correct answer is: D He-3 detectors function as proportional counters.

Question Number: 675 Detection and Measurement One method of detecting neutrons is to use He-3. The reaction that takes place is: A) 3He + 1n → 3H + 1H + 0.764 MeV B) 3He + 1n → 4He + 0.764 MeV C) 3He + 1nf → 3H + 1H + 0.764 MeV D) 3He + 1nth → 3H + 1H + 0.764 MeV E) 3He + 1n → 3H + 1H + 1.764 MeV

The correct answer is: D He-3 has a thermal neutron cross section of approximately 5330 barns, and follows the 1/v law. + 0.764 MeV is the correct answer. 3He + 1nth → 3H + 1H

Question Number: 624 Detection and Measurement What is the approximate efficiency for the radioiodines on an activated charcoal filter at the appropriate flow rate for the specific instrument used? A) 5% B) 25% C) 75% D) 95% E) 99%

The correct answer is: D If the flow rate approaches 5 liters per minute, the efficiency can be as high as 98%.

Question Number: 554 Detection and Measurement A sample containing tritium, Carbon-14, and Phosphorus-32 is counted using a liquid scintillation counter. The sample generates three peaks. The radionuclides peaks from highest to lowest were: A) P-32, H-3, C-14 B) H-3, P-32, C-14 C) C-14, H-3, P-32 D) C-14, P-32, H-3 E) H-3, C-14, P-32

The correct answer is: E Average beta energies emitted by H-3, C-14 and P-32 are 5.7 keV, 49 keV, and 694 keV. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 488 Detection and Measurement The difference between x-ray and neutron responsive films is which of the following? A) The grains are the same size and the emulsion is thicker and may be in several layers in neutron film. B) The grains are larger and the emulsion is in several layers in x-ray film. C) The grains are the same size and the emulsion is thicker and may be in several layers in x-ray film. D) The grains are smaller and the emulsion is thicker in neutron film. E) The grains are smaller and the emulsion is the same thickness in neutron film.

The correct answer is: D In neutron track film, the emulsion is about three times thicker than x-ray film and the grain size is reduced from between 1 and 2 to about 0.3 micron. These conditions enhance the production of the proton recoil tracks in the film.

Question Number: 612 Detection and Measurement BF3 gas filled detectors frequently used in neutron measuring instruments provide good discrimination against gamma radiation induced pulses because: A) B-10 has a high cross section for (n, gamma) reactions where the high energy photon causes a large pulse compared to those due to photons originating outside of the detector. B) the detectors are operated in the GM voltage region and the neutron induced pulses greatly exceed the photon induced pulses. C) the cross section for neutron scattering off the BF 3 molecule is large and the resulting pulse is very large because of the large molecule size. D) the cross section for the (n, alpha) reaction for thermal neutrons with B-10 is large and the detector is operated in the proportional voltage region. E) the abundant F atoms have a high affinity for gamma induced free electrons, thus inhibiting the detection of photons.

The correct answer is: D In proportional counters, alpha particles create a much larger output signal due to their mass and double positive charge. The alphas produced by the (n, alpha) reaction within the detector volume are easily distinguished from any pulses produced by gamma photons.

Question Number: 637 Detection and Measurement Why is the thumb rule formula X = 6CEN valid over a wide range of photon energies? A) The mass attenuation coefficients for most materials are linear over the Compton scatter region for photon energies of 0.1 - 2 MeV. B) The mass energy absorption coefficients for most materials are linear over the Compton scatter region for photon energies of 0.1 - 2 MeV. C) The photoelectric effect is linear for most materials for photon energies of 0.1 - 2 MeV. D) The mass energy absorption coefficient for air is linear over most of the Compton scattering region for photon energies of 0.1 - 2 MeV. E) The thumb rule is only a rough approximation valid to ± 70% of the actual values.

The correct answer is: D In the formula X = 6CEN, recall that: X = exposure rate at 1 ft from a point source (R/hr) C = source activity (Ci) E = photon energy (MeV) N = photon abundance (photons/disintegration) The thumb rule is valid to within 20% of actual values for photon energies of 0.1 - 2 MeV. The probability of Compton scatter is virtually independent of the "Z" (atomic number) of the absorber.

Question Number: 490 Detection and Measurement Three different labs measure the same NIST-traceable source and determine count rates to the 68.3% confidence level of 3000 ± 30, 2900 ± 35, and 3100 ± 25. How should the results be expressed? A) 3000 ± 9 B) 3000 ± 25 C) 3000 ± 30 D) 3000 ± 35 E) 3022 ± 9

The correct answer is: D In this situation, the mean of the sample value and the largest margin of error should be used to express the composite result.

Question Number: 564 Detection and Measurement You are assigned to count a number of environmental samples. To meet the required LLDs, you need to adjust a number of the counting parameters. To increase the LLD value what must you do to sample volume, count time and detector background? A) Increase sample volume, decrease count time, increase detector background B) Decrease sample volume, decrease count time, reduce detector background C) Increase sample volume, decrease count time, reduce detector background D) Increase sample volume, increase count time, reduce background E) Decrease sample volume, increase count time, increase detector background

The correct answer is: D Increasing the volume of the sample will increase the total sample activity, which is desirable for low - activity environmental samples. Increasing count time will allow a larger population of events to be collected. Decreasing background will decrease those events which are not due to sample activity. EPRI Rad Waste Desk Reference Question 1623

Question Number: 682 Detection and Measurement Which method is best suited to counting area wipes contaminated with H-3? A) Portable GM detector B) Fixed (laboratory based shielded) GM Detector C) ZnS based detector D) Liquid Scintillation Detector (LSC) E) Thin window NaI detector (0.125" thick)

The correct answer is: D LSC is the only detector suitable. The 18 keV max beta is too low of an energy to penetrate the listed detectors. See Knoll.

Question Number: 507 Detection and Measurement A sample counted for ten minutes yields 3000 counts. A 20 minute background count yields 2400 counts. The net counting rate at the 95% confidence level is: A) 240 ± 15 c/min B) 180 ± 4 c/min C) 180 ± 6 c/min D) 180 ± 12 c/min E) 180 ± 18 c/min

The correct answer is: D Net count rate = sample rate - bkgrd rate And: 2 sigma =1.96[(bkgrd rate/bkgrd time)+(sample rate/sample time)]½ Therefore: (3000/10) - (2400/20) ± 1.96[(2400/20/20) + (3000/10/10)] ½ = 180 ± 11.76 cpm

Question Number: 659 Detection and Measurement Albedo dosimetry is typically utilized to measure individual doses due to: A) Electrons (beta particles) B) Fast protons C) Thermal protons D) Neutrons E) Gamma rays (and x-rays above 60 keV)

The correct answer is: D Neutrons are thermalized by a persons body and reflected back into the albedo dosimeter.

Question Number: 656 Detection and Measurement Calculate the peak power associated with the following pulsed laser. Wavelength 1064 nm Pulse duration 15 nanoseconds 300 mJ Divergence 5 mrad Single pulse A) 60 W B) 6000 W C) 2 W D) 20 MW E) 2 × 1010 W

The correct answer is: D Peak power is the maximum output energy divided by the time duration of that energy. The result is in watts, or energy per unit (one watt = 1 joule per second = Energy/Time). Thus the solution is: Energy = 300 mJ = 0.3J Time = 15 ns = 15 x 10-9s Peak Power = Energy/Time = (0.3 J) / (15 x 10 -9s) = 20,000,000 W = 20 MW

Question Number: 487 Detection and Measurement The value used to relate the linear energy transfer of a particular type of radiation to its relative biological effectiveness is: A) collision stopping power. B) attenuation coefficient. C) absorption factor. D) quality factor. E) tissue weighting factor.

The correct answer is: D Quality factor is defined in ICRP Publication 26 (1977) as a function of the collision stopping power of a radiation in water. It has been replaced in ICRP Publication 60 (1990) with "radiation weighting factor". Quality factor and radiation weighting factor are most dependent upon the LET of the radiation.

Question Number: 687 Detection and Measurement If the voltage on a GM tube is increased too much: A) it will cause the window to melt. B) the cables may not have sufficient insulation, and "cross talk" will result in increased counts. C) the tube will be in the recombination region. D) the tube will be in the continuous discharge region. E) the anode will reverse polarity.

The correct answer is: D See the gas amplification curve in Chapter 7 of Gollnick.. A useful mnemonic is "Rest In Peace Little Grey Cat" that represent the various regions of the gas amplification curve from lowest to highest: Recombination, Ion chamber, Proportional, Limited proportional, Geiger mueller, Recombination regions.

Question Number: 432 Detection and Measurement Which of the following radionuclides is most applicable to in-vivo measurements? A) H-3 B) C-14 C) S-35 D) I-131 E) Pu-239

The correct answer is: D Since I-131 is the only significant gamma-emitting nuclide shown, it is clearly the most applicable to in-vivo measurement. NOTE: Pu-239 does emit a weak gamma. All other nuclides shown are "pure beta-emitters".

Question Number: 491 Detection and Measurement Which of the following five detectors would provide the most accurate measurement of exposure rate in a mixed energy gamma field? A) Geiger-Mueller detector B) ZnS scintillation detector C) NaI scintillation detector D) Air ionization chamber E) BF3 detector

The correct answer is: D Since exposure rate is a measurement of ionization of air, the most direct and accurate instrument would be the air ionization chamber. GM detectors do not provide a direct measurement of exposure and may overrespond at lower energies.

Question Number: 633 Detection and Measurement The most important types of environmental monitoring to perform soon after accidental release of radioactive materials to the outside air would be: A) airborne concentrations and sediment sampling. B) direct radiation levels and water sampling. C) water sampling and vegetation sampling. D) direct radiation levels and airborne concentrations. E) silt and broad-leaf vegetation sampling.

The correct answer is: D Since it is specified that the measurements will be taken soon after release, the radioactive material may still be airborne. Since exposure pathways may include both internal and external factors, measurements must be taken for both.

Question Number: 558 Detection and Measurement A gamma spectrometer spectrum of a quantity of Co-60 reveals three peaks. The smallest of the three peaks is at 2.5 MeV. This peak is the result of: A) interaction of Co-60 gammas with the lead shield. B) backscatter. C) decay of Co-60. D) summation of Co-60 gamma. E) simultaneous production of Co-60 gammas.

The correct answer is: D Sum peaks occur when gammas are emitted in very rapid succession during decay. In this problem, Co60 decays by beta - to an excited state as Ni-60. Ni-60 goes to ground state, 1.17 and 1.33 MeV gammas are emitted in very rapid succession. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 458 Detection and Measurement According to the ICRP, "ALI" stands for: A) allowable limit of isotopes. B) allowable limit on intake. C) annual limit of isotopes. D) annual limit on intake. E) accumulated limit of intake.

The correct answer is: D The ALI is defined in ICRP Publications 26 and 30 (1977). Publication 30 gives the actual values for all radionuclides.

Question Number: 653 Detection and Measurement Laser safety calculations assume that a person will only be exposed for a limited time when purposeful staring does not occur. When performing MPE calculations with continuous wave infrared lasers the time assumed is which of the following? A) 0.25 sec B) 1 sec C) 5 sec D) 10 sec E) 30 sec

The correct answer is: D The aversion response time for visible light is 0.25 seconds, for IR 10 seconds.

Question Number: 596 Detection and Measurement Which of the following has a density thickness closest to 2 cm of water? A) 1 cm of Al with a density of 2.7 gm/cm 3 B) 0.5 cm of Cu with a density of 8.96 gm/cm 3 C) 0.25 cm of Pb with a density of 11.3 gm/cm 3 D) 0.1 cm of W with a density of 19.3 gm/cm 3 E) None of the above

The correct answer is: D The density thickness of 2 cm of water = 2 cm * 1 gm/cm 3 = 2 gm/cm2. So: 0 .1 cm * 19.3 gm/cm3 = 1.93 gm/cm2

Question Number: 609 Detection and Measurement The buildup factor should only be used: A) for photons of energy below 3 MeV. B) for photons of energy above 0.5 MeV. C) in cases where the shield thickness exceeds 3 relaxation lengths. D) for situations involving broad beam or "poor geometry". E) for situations involving narrow beam or "good geometry".

The correct answer is: D The effect of photon scatter is much greater in broad beam geometries than for narrow beam situations.

Question Number: 524 Detection and Measurement The target organ for most transportable long lived alpha emitters is: A) the gonads. B) the lung. C) the gastrointestinal tract. D) the bone surfaces. E) the breast.

The correct answer is: D The heavy metals, which tend to decay by alpha emission and have long half-lives, affix themselves to the bone surfaces when taken in to the body.

Question Number: 630 Detection and Measurement The term solubility or transportability, when applied to the metabolism of radionuclides, refers to the: A) metabolic breakdown of a radionuclide- containing compound which allows its incorporation into body tissues. B) solubilization of a radionuclide-containing compound by means of hydration, ion exchange, or esterification reactions. C) translocation dissimilation of a radionuclide-containing compound by means of biological-chemical action such as enzymatic attachment and catabolism. D) property of a radionuclide-containing compound which results in its transfer across body membranes. E) translocation of a radionuclide-containing compound from one point to another under conditions of physiological dysfunction.

The correct answer is: D The more soluble, or transportable a compound is, the more likely it is to be taken up systemically in the body and transferred to a number of tissues. An example of a very "transportable" compound in the body is tritium oxide. A low-transport compound may be one containing heavy metals, such as plutonium, that tends to adhere to the bone surfaces.

Question Number: 568 Detection and Measurement In a gas filled detector, a low voltage potential will increase the time required to collect ions produced by radiation, permitting a large number to be neutralized. This process is called: A) neutralization. B) ion leakage. C) annihilation. D) recombination. E) saturation.

The correct answer is: D The recombination region of the six - region curve for gas-filled detectors does not have adequate voltage to be a useful detection region. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26

Question Number: 521 Detection and Measurement A simultaneous operating mode is used by proportional counting systems to: A) count more than one sample at a time. B) count more than one sample type. C) account for fluctuating background levels. D) count alpha and beta particles at the same time. E) count beta and gamma emitters at the same time.

The correct answer is: D The simultaneous mode uses pulse height discriminators to register alpha and beta-gamma pulses in different channels. The higher LET alpha radiation causes a higher pulse in the proportional region when counted simultaneously with beta particles.

Question Number: 616 Detection and Measurement Electrons that are initially at rest are accelerated through a voltage potential of 1,000 volts before striking a tungsten target. What energy do the electrons have upon striking the target? A) 1,000 MeV B) 10 MeV C) 0.1 MeV D) 0.001 MeV E) 0.511 MeV

The correct answer is: D The unit "electron volt" (eV) is used to quantify radiation energy. One eV is attained when accelerating an electron through an electrical potential difference of one volt. More accurately, one eV is the energy required to move an electron through a one volt potential difference. In this problem, each electron would attain an energy of 1,000 eV, or 1 keV, or 0.001 MeV. See: Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. Cember, H. Introduction to Health Physics

Question Number: 489 Detection and Measurement THe ICRP lung model has divided the respiratory tract into three compartments. They are: A) upper respiratory tract, lower respiratory tract, and alveoli. B) upper respiratory tract, tracheal/bronchial tree, and pulmonary. C) nasopharynx, pulmonary, and lymph. D) nasopharynx, tracheal/bronchial tree, and pulmonary. E) nasopharynx, tracheal/bronchial tree, and alveoli.

The correct answer is: D There are four internal models presented in the 1977 recommendations of the ICRP in Publication 30. They are the lung, gastrointestinal tract, bone, and submersion models. Typically, each relies on first order kinetics and consists of sequential compartments. The compartments for the lung model are addressed in this question.

Question Number: 482 Detection and Measurement An Airborne Radioactivity Area must be posted at one DAC or DAC-hour(s) to an individual in one week. A) 0.25 B) 1 C) 6 D) 12 E) 25

The correct answer is: D This definition of Airborne Radioactivity Area comes from 10 CFR Part 20 (1991). 12 DAC-hours in a 40-hour week can be used to establish a posting threshold of .3 DAC.

Question Number: 561 Detection and Measurement At high gamma energies, the Compton edge will occur at of the photopeak energy. A) 75% B) 95% C) photopeak energy + 150 keV D) photopeak energy - 250 keV E) 65%

The correct answer is: D This is a function of the equation used to calculate the energy of a Compton - scattered photon. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 576 Detection and Measurement The secondary emission ratio of a photomultiplier tube is the: A) number of gammas generated by bremsstrahlung. B) number of electrons freed by thermionic emission. C) number of light pulses freed by each incident electron. D) number of electrons freed for each incident electron. E) number of incident electrons that are freed by light pulses.

The correct answer is: D This ratio is also a function of the dynode surface substance, as well as the energy of electrons that bombard it. Common dynode surface materials are BeO, MgO and Cs3Sb. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26

Question Number: 586 Detection and Measurement In a photomultiplier tube with 7 dynodes and a gain of 5 electrons per dynode, the ratio of the magnitude of the output pulse to the primary photoelectron would be approximately: A) 35 B) 2,500 C) 17,000 D) 80,000 E) 1,000,000

The correct answer is: D To calculate the output pulse size, the gain is raised to the power of the number of dynodes. In this case 5 7 or 78,125.

Question Number: 512 Detection and Measurement Determine the mean of the following set of sample results: 233 cpm 270 cpm 249 cpm 239 cpm 250 cpm A) 250.2 cpm B) 251.5 cpm C) 247.8 cpm D) 248.2 cpm E) 1241 cpm

The correct answer is: D To obtain the mean, simply take the sum of n results and divide by n. So: (233+270+249+239+250)/5 = 248.2

Question Number: 605 Detection and Measurement What would be the most reliable means to quantify an individuals' tritium uptake? A) Count nasal wipes on shielded gas flow proportional counter to estimate the activity inhaled B) Well counting of a urine sample via NaI spectrometer C) Whole body counting in a shielded facility via GeLi spectrometer D) Analysis of urine samples by liquid scintillation counter E) Analysis of fecal samples by GeLi spectrometer

The correct answer is: D Tritium is very soluble and readily eliminated in the urine. Gamma spectrometers are useless for detecting the low energy beta emitted by tritium.

Question Number: 686 Detection and Measurement The OSL dosimeter is NOT sensitive to which of the following types of radiation? A) Beta B) Gamma C) Beta and Gamma D) Neutron E) Gamma rays over 1.02 MeV

The correct answer is: D Typically, the OSL dosimeter includes a plastic track etch element to measure neutron dose.

Question Number: 632 Detection and Measurement A research facility that uses tritium in levels that may pose an internal radiation hazard to workers is usually required by the NRC to have as part of their radiation safety program which of the following? A) Whole body counting of potentially exposed workers B) Air sampling and analysis for tritium in the workplace environment C) Blood tests of potentially exposed workers D) Tritium urine analysis of potentially exposed workers E) Tritium breath analysis of potentially exposed workers

The correct answer is: D Urinalysis with frequent sampling periods and liquid scintillation counting is necessary to properly assess internal dose to personnel from tritium. Since tritium is an isotope of hydrogen, the body assimilates it in its oxide form much the same as water.

Question Number: 525 Detection and Measurement Silver zeolite is the medium of choice for iodine sampling primarily because of its: A) high collection efficiency for iodine. B) long shelf life. C) low cost. D) low affinity for noble gas. E) low natural radioactivity content of silver zeolite.

The correct answer is: D When sampling for radioiodines in the presence of noble gases, such as during fission accident scenarios, the ability of silver zeolite to collect iodine with little affinity for inert fission gases is desirable.

Question Number: 517 Detection and Measurement Unless some type of quenching is used, a Geiger-Mueller Detector will re-trigger because of: A) breakdown of the detector gas caused by severe ionization. B) creation of satellite pulses. C) reduction in ion density due to recombination. D) release of electrons from the cathode during the collection of positive ions. E) release of electrons from the anode during the collection of negative ions.

The correct answer is: D When the fill gas molecule in a G-M or proportional counter is ionized, the negative ion (electron) reaches the electrode (anode) much quicker than the positive ion would reach the wall (cathode). If the positive ion did reach the wall, additional electrons would be released, causing another pulse in the detector. For this reason, quenching molecules are added to the fill gas to combine with the positive ions before they reach the detector wall.

Question Number: 553 Detection and Measurement The function of the primary solute in a liquid scintillation cocktail is to: A) remove the effects of ambient light on the scintillation process in the sample. B) suspend the scintillator in solution and absorb the energy of decay from a radioisotope. C) shift the emitted light photon wavelength so that the PMT can detect the photon. D) convert the excitation energy of the solvent molecules into a light photon. E) reduce the absorption of the light photons emitted by the scintillator.

The correct answer is: D When the solute molecules de-excite, light photons are emitted. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 408 Detection and Measurement A meter reads 40,000 net cpm and the efficiency of the detector is 40%. How many dpm does this represent? A) 10,000 dpm B) 16,000 dpm C) 10,000 dpm D) 100,000 dpm E) 1,000,000 dpm

The correct answer is: D activity(dpm) = count rate(cpm)/efficiency = 40,000 cpm/.40 = 100,000 dpm

Question Number: 445 Detection and Measurement A sample yielded 3504 counts for a five minute counting period. A background count of ten minutes yielded 220 counts. What is the net count rate and the standard deviation of the sample to the 95% confidence level? A) 3284 ± 209 cpm B) 480.8 ± 21.9 cpm C) 480.8 ± 116 cpm D) 678.8 ± 24 cpm E) 678.8 ± 26 cpm

The correct answer is: D net count rate = (sample rate) - (bkgrd rate) And: 2 sigma = 1.96[(bkgrd rate/bkgrd time)+(sample rate/sample time)]½ Therefore: (3504/5)-(220/10) ± 1.96[(220/10/10)+(3504/5/5)]½ 678.8 ± 23.39 cpm

Question Number: 480 Detection and Measurement The absorbed dose from the alpha particles emitted from Po-210 is 100 ergs in a gram of tissue. The dose equivalent in this tissue mass is: A) 1 rem. B) 10 rem. C) 10.43 rem. D) 20 rem. E) 50 rem.

The correct answer is: D rem = rad * QF And: 100 ergs/gm = 1 rad And: QF for alpha = 20 So: (100 ergs/gm * 1 rad/100 ergs/gm) * 20 = 20 rem

Question Number: 604 Detection and Measurement Given a uniform disk source of radiation, at what minimum distance from the disk source would the point source formula have only about 1% difference from the disk source formula? A) 0.7 diameters B) 1 diameter C) 2 diameters D) 3 diameters E) 4 diameters

The correct answer is: D At three diameters the exposure rate calculated from a disk source approximates the same value as the point source formula.

Question Number: 680 Detection and Measurement A University is going to purchase a 5 Ci PuBe source. In order to properly characterize the dose rates from the source upon its arrival, which of the following instruments would be necessary? A) Ion Chamber and alpha scintillator detectors B) GM tube and alpha scintillator C) Proportional counter and GM tube D) BF3 proportional counter and ion chamber E) Bonner spheres and He-3 detector

The correct answer is: D BF3 proportional counter and ion chamber are the best answer. PuBe sources emit neutrons and gammas.

Question Number: 694 Detection and Measurement Resolving time is: A) the same as dead time. B) the same as recovery time. C) recovery time minus dead time. D) recovery time plus dead time. E) dead time minus recovery time.

The correct answer is: D Resolving time = Dead time + Recovery time. Dead time is the time in which all atoms in a detector are ionized, so no signal can be produced. Recovery time is when some ions have recombined, but the resulting pulse is insufficient in magnitude to pass through a discriminator. Resolving time is the time it takes from one ionizing even until the next ionizing event produces pulses of sufficient magnitude to pass a discriminator.

Question Number: 441 Detection and Measurement According to ANSI N323-1978, portable radiation detection instrumentation should be calibrated: A) after modification or physical alteration only. B) every six month. C) every six months or after modification or physical alteration. D) annually or after modification or physical alteration. E) annually only.

The correct answer is: D The standard recommends calibration annually or after modification or physical alteration. Do not confuse this with INPO good practices or DOE MILSTD, which require semi-annual calibration for these instruments.

Question Number: 636 Detection and Measurement The primary purpose of a routine tritium urinalysis bioassay is to: A) monitor and assign doses to workers at regular intervals in order to provide feedback for determining the remaining annual allowable dose. B) verify doses estimated by the airborne concentrations and workplace stay times. C) set a bioassay time interval capable of detecting 100 mrem committed effective dose equivalent. D) comply with ANSI N477.1. E) assess the effectiveness of administrative and physical controls of the radiation protection program for tritium.

The correct answer is: E A routine bioassay program should be designed to provide a quality assurance check on the effectiveness of the radiation protection program. Event-driven bioassays are performed to determine internal doses to workers from a suspected uptake.

Question Number: 583 Detection and Measurement Consider a proportional detector operated at a constant voltage. Based only on the statistical fluctuations, which of the following fill gases would you expect to have the lowest percent resolution? A) He with a W value of 41.4 eV/ion pair B) Ne with a W value of 36.2 eV/ion pair C) Air with a W value of 33.7 eV/ion pair D) Ar with a W value of 26.2 eV/ion pair E) Xe with a W value of 21.9 eV/ion pair

The correct answer is: E As the W value decreases, the number of ion pairs created for a given amount of energy deposited in the detector gas increases. Based on statistics, the percent resolution decreases, (i.e. improves), as the number of charge carriers increases. The formula is: R = 2.35/(N)½, where N equals the number of charge carriers or ion pairs.

Question Number: 679 Detection and Measurement Neutron dosimetry is an important aspect of personnel dosimetry. Which of the following are sensitive to neutrons? A) OSL dosimetry B) TLD-100 C) TLD-200 D) TLD-700 E) CR-39

The correct answer is: E CR-39 is a track etch type detector that is sensitive to neutrons. The other detectors are only sensitive to beta and gamma radiation.

Question Number: 681 Detection and Measurement Radon is an important issue, especially in specific regions. The following devices are useful for measuring radon except: A) Working level monitors B) Lucas cells C) Charcoal canisters D) Electret ion chambers E) CR-38

The correct answer is: E CR-39 is the track etch material.

Question Number: 615 Detection and Measurement A worker has an inhalation intake of 1000 Bq of Class Y Co-60 and 6000 Bq of Class D I-131. The ICRP 30 stochastic Annual Limits on Intake for Co-60 and I-131 are 1 x 10 6 Bq and 6 x 10 6 Bq respectively. Lacking any other specific information, the worker's committed effective dose equivalent is properly estimated as: A) 2 mrem B) 4 mrem C) 6 mrem D) 8 mrem E) 10 mrem

The correct answer is: E Calculate the fraction of the ALI received: [(1000 Bq/1 x 106 Bq sALI)] + [(6000 Bq/6 x 10 6 Bq sALI)] = 0.002 sALI One sALI = 5,000 mrem CEDE Therefore: 0.002 sALI * 5,000 mrem/sALI = 10 mrem

Question Number: 611 Detection and Measurement A worker is exposed to 2,340 Bq/cubic meter (6.3 x 10 -8 µCi/cm3) Iodine-131 for 4-hours. DAC for Iodine-131 is 333 Bq/cubic meter (9.0 x 10 -9 µCi/cm3). The worker was wearing cotton overalls, rubber boots, rubber gloves, and air-purifying respirator with particulate combination cartridges. Which one of the following gives the closest numbers of DAC-hours that you would assign the worker? A) 0.5 DAC-hours B) 1 DAC-hour C) 4 DAC-hours D) 7 DAC-hours E) 28 DAC-hours

The correct answer is: E DAC-hours = (Airborne Concentration/DAC) * hours = (6.3 x 10-8 µCi/cm3)/((6.3 x 10-9 µCi/cm3)) * 4 hr = 28 DAC-hrs Note: No protection factor for iodine can be taken for charcoal cartridges. See 10 CFR Part 20, App. A)

Question Number: 678 Detection and Measurement All the following is true about He-3 detectors except: A) The cross section for neutron capture is larger for He-3 than BF 3. B) The pulses from a BF3 detector are larger than those for a He-3 detector. C) BF3 detectors can more easily be used in a high gamma flux. D) He-3 detectors can operate at lower voltages than BF 3 detectors. E) He-3 is difficult to transport as it is considered a hazardous gas by the DOT.

The correct answer is: E He-3 is not a hazardous gas. The balance of the statements are true.

Question Number: 610 Detection and Measurement The half-value thickness for 1 MeV photons in lead is approximately 1 cm. A 100 mCi Zn-65 (1.12 MeV/photon) point source produces a dose rate of 30 mR/hr at 1 meter. What is the exposure rate at 10 cm from this source with the addition of a 5 cm lead shield? (Assume a buildup factor of 2.1) A) 0.02 mR/hr B) 93.8 mR/hr C) 2.0 mR/hr D) 9.4 mR/hr E) 200 mR/hr

The correct answer is: E I = BIo (1/2)n / d2 I = (2.1) (30 mR/hr) (1/2)5 / (0.1m)2 I = 196.9 mR/hr at 10 cm (0.1 m)

Question Number: 547 Detection and Measurement Using a dual energy subtraction x-ray unit, the high contrast image of bone can be removed from the image by using the differences in: A) Compton scattering angle of the two x-rays. B) x-ray attenuation coefficients of the two x-rays. C) quality factors between the two x-rays. D) linear stopping power of the x-rays. E) x-ray absorption coefficients of the two x-rays.

The correct answer is: E In chest radiography, low energy x-ray photons, such as are generated at 70 kVp, will produce images of both soft tissues and bone. Because of its relatively high absorption coefficient for low energy x-rays, the bone image will present a high contrast relative to the surrounding tissue. A second image obtained with high energy x-ray photons (130 kVp) will show much less bone contrast because of the reduction in photo-electric absorption. By computer subtraction the bone images can be suppressed, leaving only a soft tissue image or the reverse, a bone image. Webster, Health Physics Journal, 1995, Vol 69, No5.

Question Number: 399 Detection and Measurement In NTE (nuclear track emulsion) film, the tracks are caused by: A) alpha particles. B) beta particles. C) gamma photons. D) recoil neutrons. E) recoil protons.

The correct answer is: E In this fast neutron responsive dosimeter, recoil protons from elastic scattering with hydrogen atoms in the film create short "tracks" of ionization as stable silver atoms are created. These tracks are counted either by eye or mechanically and equated to total neutron dose equivalent.

Question Number: 587 Detection and Measurement Which of the following is the best method to compensate for high background gamma radiation on a 4 π gas flow-through ion chamber designed to detect tritium? A) Use electronic pulse height discrimination. B) Shield the detector from gamma radiation with a lead housing. C) Reduce the voltage to the ion chamber to prevent the collection of ions created in the wall by gamma radiation. D) Install the instrument in the gamma field, then calibrate the ion chamber with a known concentration of tritium. E) Continuously subtract off the gamma background with an identical ion chamber not sampling tritium.

The correct answer is: E Ion chambers do not operate in the pulse mode and cannot electronically discriminate between different types of radiation. Shielding would most likely not be as practical as answer E. Answer D does not allow for changes in the gamma background once installed and would most likely be difficult to perform.

Question Number: 577 Detection and Measurement A light pipe is used in a scintillation counter to: A) shield the phosphor from outside light sources. B) illuminate the meter display. C) remove excess light from detector. D) provide a standard source of light for calibration. E) prevent the light from being trapped in the phosphor.

The correct answer is: E Lucite and quartz are substances used as light pipes. They are placed between the scintillator and photocathode and used to prevent the light from being trapped in the phosphor. Such a device doesn't eliminate the need for good optical contacts. Moe, H.J. (1992) Operational Health Physics Training ANL-88-26. pg. 10-23.

Question Number: 639 Detection and Measurement A person has asked you to determine if he has been exposed to depleted uranium. The BEST technique for determining low levels of depleted uranium exposure is: A) whole body counting using large plastic scintilators or NaI(Tl) detectors. B) breath analysis for radon decay products. C) urine sampling and subsequent analysis using an alpha proportional counter. D) urine sampling and analysis using liquid scintillation. E) urine sampling and analysis using mass spectroscopy.

The correct answer is: E Mass spectroscopy gives the best sensitivity and specificity, as the ratio of U-235 to 238 must be determined, and none of the techniques listed are able to discriminate at low levels.

Question Number: 562 Detection and Measurement To improve the efficiency of an instrument, you must create a situation where more of the source disintegrations are recorded. All of the methods below improve efficiency EXCEPT: A) Minimize self adsorption in the sample B) Change the detector type C) Increase detector size D) Change detector shape E) Move the detector farther from the source

The correct answer is: E Moving the sample closer to the detector improves efficiency. Malcome-Lawes, D.J. (1979). Introduction to Radiochemistry. Surrey. Unwin Brothers Ltd.

Question Number: 651 Detection and Measurement Irradiated samples from a reactor frequently have extremely high count rates. The samples are counted with a NaI(Tl) scintillation detector. The Radiation Safety Officer is concerned about causing fatigue of the PM tube and it is recommended that the count rate be reduced. The most effective way of reducing the count rate is: A) decreasing the total time used to count the sample. B) operating at a higher voltage to the PMT. C) minimizing the counting window. D) using integral rather than differential counting. E) using a sample aliquot.

The correct answer is: E Only by reducing the concentration of the sample can the rate of photons interacting with the tube be reduced.

Question Number: 641 Detection and Measurement All the following statements are true EXCEPT: A) 1 WLM = 1 rem CEDE B) Mining radiation exposure is regulated in 30 CFR. C) The maximum dose allowed to miners is 4 WLM per year. D) The equilibrium factor for residential spaces is 0.5. E) Pb-210 is typically included in calculations of WLM as it is an alpha emitter.

The correct answer is: E Pb-210 is not included due to its long half life.

Question Number: 697 Detection and Measurement When operating a proportional counter the high voltage channel (1800 V) reads 1200 counts in 1 minute and the low voltage channel (9500 V) reads 200 counts in a minute for the same sample, then there are: A) 200 counts due to the beta emitter present in the sample. B) 1200 counts due to the beta emitter present in the sample. C) 1200 counts due to the alpha emitter present in the sample. D) 1000 counts due to the alpha emitter in the sample. E) 200 counts due to the alpha emitter present in the sample.

The correct answer is: E Proportional counters register both alpha and beta interactions at the higher voltage, and only alpha interactions at the lower voltages. Examine the six region gas amplification curve, and the proportional region has two lines, one for alpha at the lower voltage, another for alpha plus beta at the higher voltage.

Question Number: 550 Detection and Measurement HPGe semiconductor detectors are limited by count rate due to: A) recommendation of ion pairs before electrons reach detector. B) the cold temperatures maintained in the detector area. C) the amount of lithium impurities 'drifted' into the Germanium crystal. D) coincident circuitry limitations. E) the width of the electrical pulses produced.

The correct answer is: E Pulse widths of ~100 micro seconds are common for HPGe detectors. Knoll, Radiation, Detection, and Measurement.

Question Number: 640 Detection and Measurement Air samples are taken downwind from a military base. Po-218, At-218, Pb-214, and Bi-214 are identified. The Po-218 and At-218 appear to be in transient equilibrium. This radioactivity is due to: A) a nuclear weapons accident. B) leaking uranium from a weapon. C) leaking plutonium from a weapon. D) normal off-gassing from nuclear weapons. E) normal background radiation.

The correct answer is: E Radon decays products.

Question Number: 603 Detection and Measurement In the shielding equation I = Io e(- µx), how does the shielding thickness (x) compare if (x) is calculated using the linear attenuation coefficient vs. the mass energy absorption coefficient for a 1 MeV photon? (Assume the same transmission factor value and shielding material. Neglect any build-up.) A) The shielding thickness will be about the same. The shielding thickness (x) will be thicker using the linear attenuation coefficient vs. the mass energy absorption B) coefficient because the linear attenuation coefficient is a larger numerical value than the mass energy absorption coefficient for a 1 MeV photon. C) The shielding thickness (x) will be thinner using the linear attenuation coefficient because the linear attenuation coefficient is a smaller numerical value than the mass energy absorption coefficient for a 1 MeV photon. D) The shielding thickness (x) will be thicker using the mass energy absorption coefficient because the mass energy absorption coefficient is a larger numerical value than the linear attenuation coefficient for a 1 MeV photon. E) The shielding thickness (x) will be thicker using the mass energy absorption coefficient because the mass energy absorption coefficient is a smaller numerical value than the linear attenuation coefficient for a 1 MeV photon.

The correct answer is: E Since the total linear attenuation coefficient is the sum of absorption and scattering processes, the mass energy absorption coefficient will generally be a smaller numerical value. A 1 MeV photon will most likely under go a Compton scatter interaction in most materials.

Question Number: 598 Detection and Measurement A 1kg block of ice and a 1 kg block of lead are exposed to a 1 roentgen per hour radiation field. Which object receives a greater absorbed dose after one hour if the photon energy is 0.2 MeV? A) The absorbed dose to both is the same. B) The block of ice receives a greater dose because the interaction coefficient for water is smaller than that for lead at this energy. C) The block of lead receives a greater dose because the interaction coefficient for lead is smaller than that for water at this energy. D) The block of ice receives a greater dose because the interaction coefficient for water is larger than that for lead at this energy. E) The block of lead receives a greater dose because the interaction coefficient for lead is larger than that for water at this energy.

The correct answer is: E The 0.2 MeV photons are much more likely to interact with the high density lead than the relatively low density ice.

Question Number: 683 Detection and Measurement Which of the following methods are best suited to locating a lost Am-241 source in a field of tumble weeds? A) Portable GM detector B) Fixed (laboratory based shielded) GM Detector C) ZnS based detector D) Liquid Scintillation Detector (LSC) E) Thin window NaI detector (0.125" thick)

The correct answer is: E The Thin Window NaI will be able to best detect the 60 keV photons from Am-241 at a distance, and it can be optimized to detect only those photons. The ZnS will detect the alpha emissions, but will need to be too close and the tumble weeks would probably create a hole in the detector.

Question Number: 606 Detection and Measurement A photon with a linear attenuation coefficient of .0023/cm -1 in air will travel how far before an interaction occurs? A) .0023 cm B) 2.3 cm C) 45 cm D) 230 cm E) 435 cm

The correct answer is: E The average distance a photon will travel will be the reciprocal of the linear attenuation coefficient. In this case it's 1/.0023 cm - 1 = 435 cm.

Question Number: 696 Detection and Measurement HPGe detectors occasionally have a beryllium or a carbon fiber end on them so that: A) they can be used for alpha spectroscopy. B) the germanium gases can escape, maximizing the ability of the detector to function. C) air can enter and allow for expansion when used at altitude. D) the detector is more easily heated. E) lower energy photons can enter the detector.

The correct answer is: E The beryllium or carbon fiber window will allow lower energy photons to enter the sensitive region of the detector, typically 60 keV and sometimes lower, more easily for a better low energy spectroscopy.

Question Number: 601 Detection and Measurement The term rem is a unit of dose equivalent. Which of the following is NOT a correct statement? A) A rem is the product of absorbed dose and a factor which is currently based on the collision stopping power in water. B) A rem can be considered a unit of risk relevant to late effects. C) Rems are used as units for regulatory limits. D) Rems can be converted to Sieverts. E) A dose in rems always has measurable, reproducible, and observable acute biological effects.

The correct answer is: E The quality factors used to derive dose equivalent for absorbed dose do not apply at absorbed dose rates high enough to produce these effects.

Question Number: 655 Detection and Measurement For laser safety purposes, Pulse Repetition Frequency, or PRF, is frequently used in the calculation of the maximum permissible exposure. The PRF is normally specified in terms of: A) Joules per second for the duration of the exposure in seconds. B) Joules per square cm. C) Watts per second for the duration of the exposure. D) seconds per pulse. E) Hertz.

The correct answer is: E The PRF is normally specified in terms of pulses per second. ANSI Z136.1.

Question Number: 588 Detection and Measurement A dose of 20 rem from alpha radiation to one kilogram of tissue deposits how many ergs or energy? A) 100 ergs B) 200 ergs C) 2,000 ergs D) 20,000 ergs E) 100,000 ergs

The correct answer is: E rem = rad * Q Therefore: rad = rem/Q = 20/20 = 1 (1 rad)(100 erg/gm/rad)(1000 gm/kg) = 100,000 erg/kg