5.5 Mastery Check v1: Half Life

Front

What is Half-life?

Back

The amount of time it takes for half the nuclei in a sample of the isotope to decay.

Front

What is the half-life of iodine-131?

Back

8 days.

Front

If 10 mg of iodine-131 is given to a patient, how much is left after 32 days? (Half-life = 8 days)

Back

0.625 mg.

Front

After the third half-life, how much of the sample is left?

Back

1/8.

Front

The half-life of strontium-90 is 25 years. How much will remain after 100 years if the initial amount is 4.0 g?

Back

0.25 g.

Front

How do you calculate the remaining amount of a substance after a certain number of half-lives?

Back

Use the formula: Remaining amount = Initial amount × (1/2)^(number of half-lives).

Front

What happens to the amount of a radioactive substance over time?

Back

It decreases exponentially as it undergoes decay.

Front

Define radioactive decay.

Back

The process by which an unstable atomic nucleus loses energy by emitting radiation.

Front

What is the significance of half-life in radioactive dating?

Back

It helps determine the age of materials by measuring the remaining amount of a radioactive isotope.

Front

If a substance has a half-life of 10 years, how much of a 100 g sample remains after 30 years?

Back

12.5 g.