Half-Life
Which isotope is the daughter isotope in this nuclear equation? 14/6 C ---> 14/7 N + 0/-1e
14/7 N (second)
A sample contains 2.2 g of the radioisotope niobium-91 and 15.4 g of its daughter isotope, zirconium-91. How many half-lives have passed since the sample originally formed?
3
A sample originally contained 1.28 g of a radioisotope. It now contains 1.12 g of its daughter isotope. How many half-lives have passed since the sample originally formed?
3
Niobium-91 has a half-life of 680 years. After 2,040 years, how much niobium-91 will remain from a 300.0-g sample?
37.5
Carbon-14 has a half-life of 5,730 years. How long will it take for 112.5 g of a 120.0-g sample to decay radioactively?
NOT 11460
The original amount of a radioactive sample should be multiplied by which expression to calculate the amount of the sample that remains after n half-lives have passed?
(1/2)^n
Samarium-146 has a half-life of 103.5 million years. After 1.035 billion years, how much samarium-146 will remain from a 205-g sample?
0.200
After 1 half life After 2 half life After 3 half life After n half life
1/2 of the original parent remains 1/4 of the original parent remains 1/8 of the original parent remains (1/2)^n of the original parent remains
How much of a sample remains after three half-lives have occurred?
1/8
radiocarbon dating
method for determining age by comparing the amount of carbon-14 to the amount of carbon-12 in a sample. uses c14.
The table below shows a list of radioisotopes and their half-lives.The radioisotope that has the longest half-life is the best to use in powering planet and space exploration vehicles because they can travel farther. Which radioisotope is the best to use?
plutonium-239
Half life importance
radioisotopes are used as tracers in nuclear scanning. short half lives avoid damaging living tissue. nuclear waste has a long half life.
In this nuclear reaction, which atom(s) are reactants? 234/91
th
Consider the image of a fossil below.How is half-life most likely used with respect to this fossil? dead fish
to find the age of the fossil
Which definition describes a half-life?
The time required for half of a radioactive sample to decay.
daughter isotope
an isotope formed from the radioactive decay of another isotope known as the parent isotope
parent isotope
an isotope that undergoes radioactive decay
An article about half-lives describes a parent isotope. What is a parent isotope?
an isotope that undergoes radioactive decay to form a more stable isotope
Radioisotopes
atoms that have unstable nuclei and undergo radioactive decay. each time it goes through radioacrive decay, it captures or releases particles to become an isotope of a different element
Leutium-176 has a half-life of 3.85 1010 years. After 1.155 1011 years, how much leutium-176 will remain from an original 16.8-g sample?
2.10
A small amount of americium-241 is used in smoke detectors. A stream of radiation flows between two electrodes. If smoke interrupts the stream, the alarm goes off. What feature of the radioisotope americium-241 would be most helpful for the smoke detector to work?
Long half life
Uranium-232 has a half-life of 68.9 years. A sample from 206.7 years ago contains 1.40 g of uranium-232. How much uranium was originally present?
11.2
Uranium-232 has a half-life of 68.9 years. A sample from 206.7 years ago contains 1.40 g of uranium-232. How much uranium was originally present?
112 g
A sample contains 2.2 g of the radioisotope niobium-91 and 15.4 g of its daughter isotope, zirconium-91.If the half-life of niobium-91 is 680 years, how long will it take for the decay described in the previous question?
2040 years
Leutium-176 has a half-life of 3.85 mc012-1.jpg 1010 years. After 1.155 mc012-2.jpg 1011 years, how much leutium-176 will remain from an original 16.8-g sample?
210 g
Carbon-14 has a half-life of 5,730 years. How long will it take for 112.5 g of a 120.0-g sample to decay radioactively?
22920
A sample contains 6.25 percent parent isotope and 93.75 percent daughter isotopes. If the half-life of the parent isotope is 58 years, how old is the sample?
232
A sample contains 6.25 percent parent isotope and 93.75 percent daughter isotopes. If the half-life of the parent isotope is 58 years, how old is the sample?
232 years
Which isotope is the parent isotope in this nuclear equation? 245/96 Cm ----> 241/94 Pu + 4/2 He
245/96 Cm (first)
A sample contains 10.5 g of the radioisotope Pb-212 and 157.5 g of its daughter isotope, Bi-212. How many half-lives have passed since the sample originally formed? 4 14 15 147.5
4
A meteorite contains 0.17 g of nickel-59, a radioisotope that decays to form cobalt-59. The meteorite also contains 5.27 g of cobalt-59. How many nickel-59 half-lives have passed since the meteorite formed?
5
Sodium-24 has a half-life of 15 hours. After 45 hours, how much sodium-24 will remain of an original 50.0-g sample?
6.25
Lanthanum-138 has a half-life of 105 billion years. After 525 billion years, how much of a 240 g sample of this radioisotope will remain?
7.5
A meteorite contains 0.3 grams of nickel-59, a radioisotope that decays to form cobalt-59. It also contains 76.5 grams of cobalt-59. How many half-lives have passed since the meteorite formed?
8
An 80.0 g sample of iodine-131 was placed in a sealed vessel forty days ago. Only 2.5 g of this isotope is now left. What is its half-life?
8
An 80.0 g sample of iodine-131 was placed in a sealed vessel forty days ago. Only 2.5 g of this isotope is now left. What is its half-life?
8 days
Argon-39 has a half-life of 269 years. How long will it take for 52.5 g of a 60.0 g sample to decay to its daughter isotope?
80.7 years
Argon-39 has a half-life of 269 years. How long will it take for 52.5 g of a 60.0 g sample to decay to its daughter isotope?
807
Rachel has an unknown sample of a radioisotope listed in the table. Using a special technique, she is able to measure the mass of just the unknown isotope as 104.8 kg at 12:02:00 P.M. At 4:11:00 P.M. on the same day, the mass of the unknown radioisotope is 13.1 kg. Which radioisotope is in the sample? Potassium-42 Nitrogen-13 Barium-139 Radon-220
Barium-139
Which of these statements about half-life is true? Check all that apply. Half-lives vary dramatically from isotope to isotope. A relationship exists between isotopes and half-lives. Half-lives are constant for a particular isotope. Half-life is an exact measure of when individual atoms will decay. Temperature, pressure, and density affect the half-life of an isotope.
Half-lives vary dramatically from isotope to isotope. Half-lives are constant for a particular isotope.
Which statement is true about radiocarbon dating?
The half-life of C-14 is 5,730 years.
Many smoke detectors use the radioisotope americium-241. A stream of radiation flows between two electrodes. If smoke enters the smoke detector, it breaks the flow of electrons, and an alarm sounds. Based on its application, would you expect the half-life of americium-241 to be relatively long (around 400 years) or relatively short (around 10 days)? The half-life of americium-24 would be expected to be relatively
long
half-life
the time required for half the radioactive nuclei in a sample to decay. all radioisotopes have a half-life. they are constant for each isotope. they vary dramatically. half-lifes are not affected by temperature, pressure, density, or concentration. it is not an exact measurement of decay of individual atom. they range in length from tiny frcations of a second to billions of years. no known relationship exists between isotopes and half-lives.
