NAME _______________________________________________ PERIOD _____ HALF-LIFE WORKSHEET
1. What is radiation?
2. What is half-life?
3. If we start with 400 atoms of radioactive substance, how many would remain after one halflife?_____ after 2 half-lifes? _____ after 3 half-lifes? _____ after 4 half-lifes? _____
4. If we start with 48 atoms of radioactive substance, how many would remain after one halflife?_____ after 2 half-lifes? _____ after 3 half-lifes? _____ after 4 half-lifes? _____
5. If we start with 16 atoms of radioactive substance, how many would remain after one halflife?_____ after 2 half-lifes? _____ after 3 half-lifes? _____ after 4 half-lifes? _____
6. If we start with 120 atoms of radioactive substance, how many would remain after one halflife?_____ after 2 half-lifes? _____ after 3 half-lifes? _____ after 4 half-lifes? _____
7. Which type of nuclear radiation (alpha particles, beta particles, or gamma rays) can be blocked by…
a. A piece of paper ________________________
b. A large block of lead _____________________
c. A thin sheet of metal _____________________
Use the following graph to answer questions 8-11
8. How long is a half-life for
carbon-14? _________________
Radioactive Decay of Carbon-14
120
9. If only 25% of the carbon-14
remains, how old is the material
containing carbon-14?
__________
% of Carbon-14
100
80
60
40
20
0
0
5370
10740
Time (years)
16110
10. If a sample originally had
120 atoms of carbon-14, how
many atoms will remain after
16,110 years? __________
11. If a sample know to be about 10,740 years old has 400 carbon-14 atoms, how many atoms were in
the sample when the organism died? ____________________
Use the following chart to answer questions 12-15
Radioactive
Substance
Radon-222
Iodine-131
Radium-226
Carbon-14
Plutonium-239
Uranium-238
Approximate Half-life
4 days
8 days
1600 years
5,370 years
24,120 years
4,470,000,000
12. If we start with 8000 atoms of radium-226, how much would remain after 3,200 years? ________
13. If we start with 20 atoms of plutonium-239, how many would remain after 48,240 years? _________
14. If we start with 60 atoms of uranium-238, how many remain after 4,470,000,000 years? __________
15. If we start with 24 atoms of iodine-131, how many remain after 32 days? __________
16. Tritium (H-3) is a radioactive isotope of hydrogen with a half-life of 12.3 years. How long would it take
for a 40.0g sample to decay down to 1.25g?
17. One-eighth of the original radioactive sample remains. How many half-lives have passed?
18. The half-life of polonium-210 is 138.4 days. How many milligrams of polonium-210 remain after 415.2
days if you start with 2.0 mg of the isotope?
19. Sodium-24 has a half-life of 15 hours. How much sodium-24 will remain in an 18.0g sample after 60
hours?
20. After 42 days a 2.0 g sample of phosphorus-32 contains only 0.25g of isotope. What is the half-life of
phosphorus-32?