Half-Life Answers

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Which statement is true about radiocarbon dating?

After it dies, an organism’s body continues to intake C-14.

Radiocarbon dating is useful for dating objects up to 100,000 years old.

Radiocarbon dating assumes that half-life for radioisotopes change over time.

The half-life of C-14 is 5,730 years.

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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?

5.56 g

6.25 g

16.7 g

25.0 g

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

short half-life

over-sensitive detection

less sensitive detection

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?

An article about half-lives describes a parent isotope. What is a parent isotope?

the isotope that forms from the radioactive decay of a less stable isotope

the isotope that forms from the radioactive decay of a more stable isotope

an isotope that undergoes radioactive decay to form a less stable isotope

an isotope that undergoes radioactive decay to form a more stable isotope

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?

147.5

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 g

3.00 g

5.56 g

8.40 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?

5,730 years

11,460 years

17,190 years

22,920 years

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?

3 g

18.75 g

37.5 g

100.0 g

Which definition describes a half-life?

The time required for half of a radioactive sample to decay.

The time required for half of a radioactive sample to become unstable.

The time required for all of a radioactive sample to change because of heat.

The time required for all of a sample to break down due to pressure change.

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?

5.1

5.44

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?

(one half) times n.

(StartFraction 1 over n EndFraction) squared.

(one half) superscript n.

StartFraction 1 over (2 n) EndFraction.

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?

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?

5.56 g

6.25 g

16.7 g

25.0 g

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 g

3.00 g

5.56 g

8.40 g

An article about half-lives describes a parent isotope. What is a parent isotope?

the isotope that forms from the radioactive decay of a less stable isotope

the isotope that forms from the radioactive decay of a more stable isotope

an isotope that undergoes radioactive decay to form a less stable isotope

an isotope that undergoes radioactive decay to form a more stable isotope

How much of a sample remains after three half-lives have occurred?

1/16 of the original sample

1/9 of the original sample

1/8 of the original sample

1/3 of the original sample

Consider the image of a fossil below.How is half-life most likely used with respect to this fossil?

to find the mass of the fossil

to find the age of the fossil

to determine the species shown by the fossil

to determine if radiation is being emitted from the fossil

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?