1. 3.125%

2. Station __:
If we start with 120 atoms of a radioactive substance, how many will remain after 5 half lives. Show your work.

3. 3.75 atoms

4. Station __:
When you analyze a rock sample you find that only 6.25% of the original Carbon-14 remains. Knowing that Carbon-14 has a half life of 5,730 years, how old is the rock approximately? Show your work.

5. 22,920 years

6. Station __:
If a sample know to be about 11,460 years old has 400 Carbon-14 atoms, how many atoms were in the sample when the organism died? The half life of Carbon-14 is 5,730 years. Show your work.

7. 1600 atoms

8. Station __:
Sodium-24 has a half-life of 15 hours. How much sodium-24 will remain in an 18.0 g sample after 60 hours? Show your work.

9. 1.125 GRAMS

10. Station __:
After 42 days a 2.0 g sample of Phosphorus-32 contains only .25 g of the isotope. What is the half-life of phosphorus-32? Show your work.

11. 14 Days

12. Station __:
Polonium-214 has a relatively short half-life of 164 seconds. How many seconds would it take for 8.0 g of this isotope to decay to .25 g? Show your work.

13. 820 secs

14. Station __:
How many half-lives does it take for 16 g of Palladium-103 to decay to 1.0 g? Show your work.

15. 4 half lives

16. Station __:
What percentage of the original sample of Copper-66 would remain after 51 minutes if the half-life is 5.10 minutes? Show your work.

17. .1 %

18. Station __:
In 5.49 seconds, 1.20 g of Argon-35 decays to leave only 0.15 g. What is the half life of Argon-35? Show your work.

19. 1.83 secs

20. Station __:
How much of a 30.0 gram sample of a substance will be left after 2 hours if the half-life is 15 minutes? Show your work

21. .117 grams

22. Station __:
The half-life of Thorium-27 is days. How many days are require for 5.5 grams to remain if you start with 88 grams? Show your work

23. 74.88 days

24. Station __:
The half-life of Cobalt-60 is 5.26 years. If 25 grams are left after years, how many grams were in the original sample? Show your work

25. 3200 grams

26. Station __:
The half life of Zinc-71 is 2.4 minutes. If one had 100 g at the beginning, how many grams would be left after 7.2 minutes. Show work.

27. 12.5 Grams

28. Station __:
After 48 days, 2 grams of an original 128 gram sample remain. What is the half-life of the sample? Show work.

29. 8 Days

30. Station __:
The half-life of Iodine-131 is about 8 days. What percentage of an Iodine-131 sample will remain after 40 days? Show work.