chemistry chpt.5 Atomic Nucleus
97) If a material has a half-life of 24 hours, how long do you have to wait until the amount of radioisotope is 1/4 its original amount?
A) 48 hours
60) What is a half-life?
A) It is the time it takes for 1/2 of the material to undergo radiodecay.
3) When food is irradiated with gamma rays from a cobalt-60 source, does the food become radioactive? Why?
A) No. The gamma rays do not have sufficient energy to initiate the nuclear reaction in the atoms of the food.
74) Explain how radioactive decay has always warmed the earth from the inside, and nuclear fusion has always warmed the earth from the outside.
A) Radioactive elements have been within Earth since it was created while the sun is made of fusing hydrogen atoms.
51) What is the main technical difficulty in dealing with fusion reactions?
A) The amount of energy needed to overcome the electrical repulsion of the reactants is extremely high.
47) If an atom has 104 electrons, 157 neutrons, and 104 protons, what is its approximate atomic mass?
A) The approximate atomic mass is 261.
65) What does Einsteinʹs energy equation (E = mc2) say about the energy that is derived from nuclear fission reactions?
A) The energy released is due to the missing mass of the products compared to the mass of the starting materials.
18) If a nucleus of 232 90 Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons), what nucleus results?
A) Uranium-233
113) Your friend says that the helium used to inflate balloons is a product of radioactive decay. Another friend says no way. With whom do you agree?
A) Your first friend is correct. Radioactive isotopes emit alpha particles which, in turn, capture electrons and become helium atoms.
93) If three samples have the half-lives listed below, which sample would remain radioactive the longest?
A) a sample with a half-life of 20 million years
85) Which type of radiation-alpha, beta, or gamma-results in the greatest change in atomic mass number?
A) alpha radiation
43) Which of the following sources of radiation provides most of our yearly exposure?
A) background radiation
99) Which type of radiation is being emitted in the following incomplete nuclear equation?
A) beta
94) A neutron makes a better nuclear bullet than a proton or an electron because it
A) carries no electrical charge
37) After a uranium fuel rod reaches the end of its fuel cycle (typically 3 years) most of its energy comes from the fissioning of plutonium because
A) fissionable Pu-239 is formed as the U-238 absorbs neutrons from the fissioning U-235.
75) Which process would release energy from gold, fission or fusion? From carbon?
A) gold: fission; carbon: fusion
16) A sample of radium is usually a little warmer than its surroundings because
A) its atoms are continually being struck by alpha and beta particles.
12) You are given three radioactive samples (α, β, and γ) and can only dispose of one. The other two you must keep, one in your hand, the other in your pocket. How would you minimize your exposure risk?
A) keep α in hand, keep β in pocket, and dispose of γ
109) Which of the following provides the minimum amount of protection you need to block the following form of radiation? gamma
A) lead suit
20) Uranium-235 releases an average of 2.5 neutrons per fission, while plutonium-239 releases an average of 2.7 neutrons per fission. Which of these elements might you therefore expect to have the smaller critical mass?
A) plutonium-239
88) Alpha and beta rays are deflected in opposite directions in a magnetic field because
A) they have opposite charges.
112) A certain radioactive element has a half-life of one hour. If you start with a 1-g sample of the element at noon, how much of this same element will be left at 3:00 PM?
B) 0.125 gram
107) If Uranium-234 decays via alpha emission, what is the likely product of radioactive decay? (U, atomic no. = 92)
B) 230 Th 90
31) Which of the following statements best describes a critical mass?
B) A critical mass is the minimum amount of material that will undergo nuclear detonation.
80) Why is carbon better than lead as a moderator in nuclear reactors?
B) Carbon slows down the neutrons making them more effective in stimulating the nuclear chain reaction.
82) People who work around radioactivity wear film badges to monitor the amount of radiation that reaches their bodies. These badges consist of small pieces of photographic film enclosed in a light-proof wrapper. What kind of radiation do these devices monitor?
B) Gamma radiation
41) Ordinary hydrogen is sometimes called a perfect fuel, because of its almost unlimited supply on Earth, and when it burns, harmless water is the product of the combustion. So why donʹt we abandon fission energy and fusion energy, not to mention fossil-fuel energy, and just use hydrogen?
B) Hydrogen represents a viable solution for stored energy but not as a general energy source since obtaining the hydrogen from water requires more energy than is produced when you burn it.
17) Is the mass of an atomic nucleus greater or less than the sum of the masses of the nucleons composing it? Why donʹt the nucleon masses add up to the total nuclear mass?
B) Less. The individual nucleons have greater mass when separated from the nucleus. This additional mass is a result of the energy of separation.
98) If uranium were to split into three segments of equal size instead of two, would more energy or less energy be released?
B) More energy would be released because of less mass per nucleon.
92) The age of the Dead Sea Scrolls was found by carbon-14 dating. Could this technique have worked if they were carved in stone tablets? Explain.
B) No, this method of dating requires a material that was once living
49) The original reactor built in 1942 was just ʺbarelyʺ critical because the natural uranium that was used contained less than 1% of the fissionable isotope U-235 (half life 713 million years). What if, in 1942, the Earth had been 9 billion years old instead of 4.5 billion years old? Would this reactor have reached critical stage with natural uranium? Why?
B) No. The increased age of the Earth would mean that there would be a much smaller percentage of U-235, thus not enough for the reactor to reach critical stage.
104) Which of the following statements about radiation is true?
B) Radiation can be a useful tool. Like fire, it is only dangerous when misused.
21) Radium-226 is a common isotope on Earth, but has a half-life of about 1600 years. Given that Earth is some 5 billions years old, why is there any radium at all?
B) Radium-226 is a ʺdaughterʺ isotope and the result of the radioactive decay of uranium.
50) Does the average distance that a neutron travels through fissionable material before escaping increase or decrease when two pieces of fissionable material are assembled into one piece? Does this assembly increase or decrease the probability of an explosion?
B) The average distance increases while the probability of an explosion also increases.
30) Why are smaller nuclei such as carbon-14 often radioactive? (carbon-12 is the most common and most stable form of carbon.)
B) The isolated neutron is not stable and will undergo spontaneous transformation into a proton and an electron.
122) Why might the following nuclear reaction not be very good for energy production in a fission reactor?
B) The material only produces one neutron so the chain reaction will not be very efficient.
5) Which of the following statements best describes why a large nucleus is more likely to undergo radioactive decay?
B) The nuclear forces are not as strong as the repulsive electrical forces between nucleons.
84) Which of the following does not describe a nuclear fission reaction?
B) The number of nucleons in the products is different from the number of nucleons in the starting material.
57) If a fusion reaction produces no appreciable radioactive isotopes, why does a hydrogen bomb produce significant radioactive fallout?
B) The radioactive fallout is a result of the fission reaction used to ignite the thermonuclear fusion reaction.
101) How can a half-life be used to tell the age of a sample?
B) The ratio between the radioactive form and stable form varies regularly with time.
89) How can thorium be used for nuclear energy when it is not fissionable?
B) The thorium can easily be converted to U-233, which is fissionable.
78) Why is the combination of two protons and two neutrons stable, but two protons and one neutron is not?
B) There are not enough neutrons to overcome the electrical repulsion of the protons.
26) Elements above uranium in the periodic table do not exist in any appreciable amounts in nature because they have short half-lives. Yet there are several elements below uranium in atomic number with equally short half-lives that do exist in appreciable amounts in nature. How can you account for this?
B) These isotopes result from the radioactive decay of uranium.
77) Which of the following statements about radiation is true?
B) Your body contains a number of radioactive isotopes.
44) Which of the following emits more radiation?
B) a coal-fired power plant
8) Which shape is likely to need more material for a critical mass, a cube or a sphere? Why?
B) a cube because it has the greater surface area to volume ratio
22) Which of the following might be considered a viable application of a radioactive tracer?
B) adding a stream of radioisotopes to wastewater to examine where pollution goes when it flows into the ocean
52) How come an animalʹs carbon-14 levels do not start to decrease until it dies?
B) because it constantly replenishes its carbon-14 supply by eating plants with carbon-14 in them
108) What is transmutation?
B) changing one element into another by adding or removing protons from the nucleus
79) Is it at all possible for a hydrogen nucleus to emit an alpha particle?
B) no, because it does not contain enough nucleons
71) Which of the following provides the minimum amount of protection you need to block the following form of radiation?
B) suntan lotion
63) When the isotope bismuth-213 emits an alpha particle, what new element results?
B) thallium
68) Coal contains only minute quantities of radioactive materials, yet there is more environmental radiation surrounding a coal-fired power plant than a fission power plant. This indicates that A) the news media is biased in its coverage.
B) the coal-fired power plant contains none of the radiation it releases.
4) How is it possible for an element to decay ʺforward in the periodic tableʺthat is, to decay to an element of higher atomic number?
C) As a beta particle is released, a neutron transforms into a proton.
67) Light nuclei can be split. For example, a deuteron, which is a proton-neutron combination, can split into a separate proton and separate neutron. Does such a process yield energy or cost energy? Why?
C) Costs energy. This fact is consistent with the sum of the masses of the separated proton and neutron being greater than the mass of the original deuteron.
40) Why might the following nuclear reaction not be very good for energy production in a fission reactor?
C) The reactants are too small to obtain energy from the missing mass due to strong nuclear force.
23) If three samples have the half-lives listed below, which is the most radioactive?
C) a sample with a half-life of 20 minutes, shortest time line is most radioactive
87) When 218 Po 84 emits a beta particle, it transforms into a new element. What are the atomic number and atomic mass of this new element?
C) atomic number = 85; atomic mass = 218
102) When 226 88 Ra decays by emitting an alpha particle, what is the atomic number of the resulting
C) atomic number = 86; atomic mass = 222
120) Where does the earth receive most of its energy?
C) external fusion
61) Which type of radiationalpha, beta, or gammaresults in the least change in atomic number?
C) gamma radiation
9) Which type of radiation from cosmic sources predominates on the inside of a high-flying commercial airplane: alpha, beta, or gamma?
C) gamma radiation
91) The alpha particle has twice the electric charge of the beta particle but deflects less than the beta in a magnetic field because it
C) has much more inertia.
105) You and your friend journey to the mountain foothills to get closer to nature and escape such things as radioactivity. While bathing in the warmth of a natural hot spring she wonders aloud how the spring gets its heat. What do you tell her? You tell her that the hot water is the result of
C) radioactivity.
106) The isotope Cesium-137, which has a half-life of 30 years, is a product of nuclear power plants. How long will it take for this isotope to decay to about one-sixteenth its original amount?
D) 120 years
115) Complete the following nuclear equation:
D) 206 Pb 82
86) Complete the following nuclear equation:
D) 218 Po 84
118) How many alpha particles are emitted in the series of radioactive decay events from a U-238 nucleus to a Pb-206 nucleus?
D) 8
46) Why will nuclear fission probably not be used directly for powering automobiles?
D) All of the above are true. (Massive shielding would be required to protect against radioactivity exposure,Itʹs more practical for cars to use the electricity generated by nuclear fission power plants,Radioactive wastes could not be adequately controlled.)
28) Why does plutonium not occur in appreciable amounts in natural ore deposits?
D) Any plutonium initially in the earthʹs crust has long since decayed.
25) In the 19th century the famous physicist Lord Kelvin estimated the age of Earth to be much much less than its present estimate. What information did Kelvin not have to account for his error?
D) Lord Kelvin was not aware of radioactive decay, a source of energy to keep Earth warm for billions of years.
6) Why wouldnʹt you use carbon-14 dating on a piece of shell that was estimated to be 1 million years old?
D) The amount of radioactive carbon in the sample would probably too small to measure.
14) Why is the carbon-14 dating not accurate for estimating the age of materials more than 50,000 years old?
D) The concentration of carbon-14 in a body after 50,000 years is too low.
83) How do fission power plants work?
D) The heat from a nuclear reaction is used to boil water for a steam generator and turbine to turn and produce the electric power.
62) Which of the following statements about fusion is the most accurate?
D) The mass of the products is less than the mass of the reactants.
59) A pair of protons in an atomic nucleus repel each other, but they are also attracted to each other. Why?
D) The pair attract each other by nuclear force but also repel one another by a weaker electrical force.
72) Why doesnʹt uranium ore spontaneously undergo a chain reaction?
D) Uranium ore is mostly non-fissionable isotope U-238 and undergoes a chain reaction only if mixed with a moderator to slow down the neutrons.
33) What are some of the optimistic worldwide changes that may follow the advent of successful fusion reactors?
D) all of the above (Humans will have more opportunities to focus on social issues, such as world hunger,There will be fewer hostilities between nations,Economies will be geared to relative abundance rather than scarcity.)
126) In bombarding atomic nuclei with proton ʺbullets,ʺ the protons must be accelerated to high energies to make contact with the target nuclei
D) because the target nuclei are positively charged.
90) If a nucleus of 232 90 Th absorbs a neutron and the resulting nucleus undergoes two successive beta decays (emitting electrons), what nucleus results?
D) uranium-233
95) What is a rem?
E) A rem is a unit for measuring radiation exposure.
123) Which of the following is a major disadvantage of nuclear-fission-based power plants?
E) B and D (The byproducts of the fission process are radioactive and have very long half -lives,The power plants are complex and there are many safety requirements to prevent contamination of the environment)
13) Which of the following statements about chain reactions is true?
E) The key requirement for a chain reaction is that more neutrons are produced than are absorbed.
125) Why might the following nuclear reaction not be very good for energy production in a fusion reactor?
E) The reactants are too stable and it would cost energy to produce the product due to strong nuclear force.
19) Which of the following professions would likely have the highest occupational exposure to radiation per year?
E) airline pilot
114) Which of the following statements regarding a nucleon is true?
E) all of the above (Some of the mass of a nucleon can be converted into energy by breaking certain nuclei,Attraction between nucleons changes their mass,The mass of a nucleon depends on which nucleus it is in,both A and C)
103) Otto Hahn and Fritz Strassmann discovered fission by bombarding uranium with neutrons. Their discovery was made possible by finding one of the fission products, barium (Ba, atomic no. = 56). What is a reasonable explanation for why they were unable to initially observe the other product, krypton (Kr, atomic no. = 36)?
E) all of the above (The isotope of krypton generated might have a short half-life and had undergone radioactive decay to some other element,Krypton is a noble gas and it may have diffused out of the sample,Krypton is a noble gas and therefore chemically unreactive, making it difficult to characterize by chemical means,both A and B)
54) What property of half-lives makes radioactive material so problematic?
E) both A and B (There is no known way to shorten a half-life,Radioactivity is limited by the natural decay-time to stable isotopes,All half-lives are long,There is no known way to measure half-lives with any accuracy.)
69) Which of the following statements about carbon-14 dating is true?
E) none of the above (Carbon-14 dating can be used to date stone tools as well as bone,Carbon-14 can be used to date anything younger than 50,000 years,Carbon-14 dating is very accurate because the amount of carbon-14 in the atmosphere is constant,all of the above)
24) The half-life of carbon-14 is 5730 years. A sample is found to have one-eighth the original amount of carbon-14 in it. How old is the sample?
A) 17,200 years
119) Which of the following nuclear equations correctly describes beta emission?
A) 234 234 0 Th---> Pa+ e 90 91 -1
100) Which of the following nuclear equations correctly describes alpha emission?
A) 238 234 4 U---> Th + He 92 90 2
64) Just after an alpha particle leaves the nucleus, would you expect it to speed up? Why?
B) Yes. Once the alpha particle leaves the nucleus it accelerates because of mutual electric repulsion with the nucleus from which it escaped.
11) If carbon-14 is a beta emitter, what is the likely product of radioactive decay?
B) nitrogen-14
35) Does a radioactive isotope ever lose its radioactivity?
B) no
48) Complete the following nuclear equation:
C) 4 He 2
32) Which of the following statements regarding a nucleon is true in regards to nuclear reactions?
C) A nucleon inside a nucleus has a lower mass than a nucleon outside of the nucleus.
27) Which produces more energy, the fissioning of a single uranium nucleus or the fusing of a pair of deuterium nuclei? Why?
C) Fissioning a single uranium nucleus produces more energy since its mass is much greater than that of a pair of deuterium nuclei.
81) Which of the following statements about fusion is true?
C) Fusion reactions have no critical-mass requirement.
53) Which of the following types of radiation might be best for medical imaging?
C) Gamma radiation would be best because it penetrates the best.
39) What evidence supports the contention that the strong nuclear force is stronger than the electrical interaction at short inter-nuclear distances?
C) Protons are able to exist side-by-side within an atomic nucleus.
124) A friend produces a Geiger counter to check the local background radiation. It ticks. Another friend, who normally fears most that which is understood least, makes an effort to keep away from the region of the Geiger counter and looks to you for advice. What do you say?
C) The Geiger counter is detecting naturally occurring radiation from your body
96) Which of the following statements about fission is true?
C) The amount of energy released in the fission of large nuclei is very large.
15) Which of the following statements best describes the strong nuclear force?
C) The force is very strong but has a very short range.
111) Which of the following statements best describes the role of neutrons in the nucleus?
C) The neutrons stabilize the nucleus by attracting other nucleons.
117) Which of the beams is due to alpha particles?
C) c
76) Which of the following elements is the most stable from a nuclear point of view?
C) iron
121) Which of the following provides the minimum amount of protection you need to block the following form of radiation? beta
C) thick leather
7) Which of the following are advantages offered by the thorium nuclear reactor?
D) All of the above. (difficult to use for bomb making,produces isotopes of short radioactive half-lives,operates at relatively low temperatures)
42) The element uranium (U, atomic no. = 92) often has 146 (or more) neutrons but it will still undergo radioactive decay. Which statement might best describe why?
D) both A and B (The attractive force of the nucleons has a limited range,The isolated neutron is not stable and will undergo spontaneous transformation into a proton and an electron.)
36) Radioactivity is a tendency for an element or a material to
D) emit radiation.
58) To predict the approximate energy release of either a fission or a fusion reaction, explain how a physicist uses a table of nuclear masses and the equation E = mc2.
D) find the change in mass and multiply by the speed of light squared
55) Which of the following is a major advantage of nuclear-fission-based power plants?
E) A and C (The amount of energy per kilogram of fuel is greater than any other fuel source,The reactors can be used to produce their own fuel.)