Half-Life assignment and quiz

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) x n (1/n)^2 (1/2)^n 1/(2n)

(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 g 0.400 g 20.5 g 103 g

0.200 g

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

1/8 of the original sample

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

long half-life

The table below shows a list of radioisotopes and their half-lives. mc003-1.jpg 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? lithium-5 uranium-240 carbon-14 plutonium-239

plutonium-239

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.

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

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 g

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? 2.10 g 3.00 g 5.56 g 8.40 g

2.10 g

Identify the daughter isotope in this nuclear reaction: 222/88 Ra → 218/86 Rn + 4/2 He Which is the daughter isotope? 218/86 Rn 4/2 He 222/88 Ra

218/86 Rn

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

22,920 years

Identify the parent isotope and daughter isotope in this nuclear reaction: 222/88 Ra → 218/86 Rn + 4/2 He Which is the parent isotope? 218/86 Rn 4/2 He 222/88 Ra

222/88 Ra

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

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 4 8 16

3

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? 1 5 5.1 5.44

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? 5.56 g 6.25 g 16.7 g 25.0 g

6.25 g

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?

807 years

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 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.

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

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

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

Which time frame correctly describes the range of half-lives? fractions of a second to billions of years seconds to minutes minutes to days days to millions of years

fractions of a second to billions of years

Consider the image of a fossil below. mc007-1.jpg 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

to find the age of the fossil