Name: ______TP: ______
Different isotopes undergo radioactive decay at different rates. Some decay in a matter of seconds, but some, like uranium-238, decay very slowly and take thousands of years.1. What pattern do you notice in the picture below?
Half-Life: / % of radioactive isotope remaining: / Time elapsed:
0 / 100 / 0
1 / 50 / 10
2 / 25 / 20
3 / 12.5 / 30
4 / 6.25 / 40
5 / 3.12 / 50
6 / 1.56 / 60
7 / 0.78 / 70
8 / 0.39 / 80
9 / 0.19 / 90
10 / 0.09 / 100
/ 1. Imagine that the table to the left shows you data about Plutonium-239. Does this table show Plutonium-239 decaying? Why or why not?
2. What do you notice about the variables in the table? Use the words “increases” and “decreases” to describe your observations. / 3. What pattern do you notice in the values in the “% radioactive isotope remaining” column? / 4. What pattern do you notice in the values in the “time elapsed” column?
5. What do you think the % radioactive isotope remaining would be after the 11th half-life of Plutonium-239? Justify your answer. / 6. How much time do you think would have elapsed after the 11th half-life of Plutonium-239? Justify your answer.
7. What do you think the % radioactive isotope remaining would be after the 12th half-life of Plutonium-239? Justify your answer. / 8. How much time do you think would have elapsed after the 12th half-life of Plutonium-239? Justify your answer.
9. Use your answers to questions 1-9 to come up with a definition for “half-life.” / 10. Based on the data in the table and the definition you wrote in #10, what is the half-life of Plutonium-239? / 11. True or False: Eventually, there will be 0% of Plutonium-239 remaining. Explain your thinking.
So we sort of lied in the data above. The ½-life of Plutonium-239 (Pu-239) is actually 24,000 years. Don’t hate!
12. Pretend that you start out with 500 g of Pu-239. After 0 years, how much Pu-239 is left? / 13. How many half-lives have passed after 0 years? / 14. How much time has “elapsed”?
15. Pretend that you start out with 500 g of Pu-239. After 24,000 years, how much Pu-239 is left? / 16. How many half-lives have passed after 24,000 years? / 17. How much time has “elapsed”?
18. After 48,000 years, how much Pu-239 remains? / 19. How many half-lives have passed after 48,000 years? / 20. How much time has “elapsed”?
21. After 96,000 years, how much Pu-239 remains? / 22. How many half-lives have passed after 96,000 years? / 23. How much time has “elapsed”?
24. Use your answers to questions 12-23 to fill in the table below.
# of half-lives: / Amount of Pu-239 remaining (g): / % of Pu-239 remaining: / Time elapsed (years):
25. The half-life of 238U (Uranium-238) is 4.5 billion years. How many years would 16 grams of 238U take to decay into 0.5 grams of 238U?
26. Iodine-131 has a half-life of 8 days. If you start with a 40 g sample, how much Iodine-131 remains after 24 days?
27. Uranium-238 has a half-life of 4.56 billion years. How much time has passed when 1/16 of the original sample remains?
28. The half-life for Carbon-14 is 5730 years. A sample of wood contains 6.25% of the original carbon-14. How old is the wood sample?
29. The half-life of Polonium-210 is 140 days. How many grams of polonium-210 remain after 560 days if you start with 200 grams?
30. A 600 g sample of Nitrogen-18 decays to 75 g in 900 seconds. What is the half-life of Nitrogen-18?
31. The half-life of Potassium-42 is 1600 days. After 4800 days, you end up with 100 grams of Potassium-42. How many grams did you start with?
32. It takes 5.2 minutes for a 1-g sample of 210Fr to decay to 0.25 g. What is the half-life of 210Fr?
33. A radioactive sample contains 2.45 g of an isotope with a half-life of 3.8 days. How much of the isotope in grams remains after 11.4 days?
PUSH IT TO THE LIMIT.