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

If the half-life of strontium-90 is 25 years, how much will remain after 100 years if you start with 4.0 g?

Back

0.25 g

Front

How many atoms of uranium-238 will remain after 4.5 billion years if you start with 50,000 atoms?

Back

25,000 atoms

Front

What is the half-life of Zn-71?

Back

2.4 minutes.

Front

If you start with 100.0 g of Zn-71, how much will be left after 7.2 minutes?

Back

12.5 g

Front

A radioactive isotope has a half-life of 10 years. If you start with 80 grams, how much will remain after 30 years?

Back

20 grams.

Front

What does it mean when we say an isotope has a half-life?

Back

It means that after one half-life, half of the original amount of the isotope will have decayed.

Front

If a substance has a half-life of 5 years, how much of a 40 g sample will remain after 15 years?

Back

5 g.

Front

What is the formula to calculate the remaining amount of a substance after a certain number of half-lives?

Back

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

Front

If the half-life of a substance is 3 years, how many half-lives are in 12 years?

Back

4 half-lives.