Author:
Michele Langhans

Students will explain the process of half-life as it relates to radioactive decay. They will also perform simple half-life calculations.

Here are your notes. Keep in mind these are just the basics.

Tutorial

What is half-life and how do you calculate it?

Source: various educators and Langhans

1. Fluorine-20 has a half life of 11.6 seconds. If you started with 100 grams of the sample of F-20, how much would remain after 11.6 seconds? After 23.2 seconds?

2. Strontium-90 has a half life of 28 days. If you started with 200 grams of the sample of Sr-90, how much would remain after 56 days?

3. C-14 has a half-life of 5730 years. If a bone originally had a mass of 1000 grams of C-14, how much would remain after 5730 years?

4. Iron-59 has a half-life of 45 days. If the original sample of Fe-59 had a mass of 2000 grams, how much would remain

a. after 45 days?

b. After 90 days?

c. After 135 days?

d. After 180 days?

5. After 1 half-life, what fraction of the sample remains? How much is decayed?

6. After 2 half-life, what fraction of the sample remains? How much is decayed?

7. After 3 half-life, what fraction of the sample remains? How much is decayed?

8. After 4 half-life, what fraction of the sample remains? How much is decayed?

9. After 5 half-life, what fraction of the sample remains? How much is decayed?

10. If I find a 100-g bone that I know is 11460 years old and the half-life of C-14 is 5730, what was the original mass of the bone?

Source: Langhans and various educators