1. Review

2. What type of decay will happen if the nucleus contains too many neutrons? Beta Decay

3. Alpha Decay

4. + + - - - - - - - -

5. Part II Nuclear Stability Half-Life

6. Nuclear Stability Depends on the neutron to proton ratio.

7. Band of Stability Number of Protons (Z) Number of Neutrons, (N)

8. What happens to an unstable nucleus? They will undergo decay The type of decay depends on the reason for the instability

9. Radioactive Half-Life (t 1/2 ): The time for half of the radioactive nuclei in a given sample to undergo decay.

10. Common Radioactive Isotopes Isotope Half-Life Radiation Emitted Carbon-14 5,730 years  Radon-222 3.8 days  Uranium-235 7.0 x 10 8 years  Uranium-238 4.46 x 10 9 years 

11. Radioactive Half-Life After one half life there is 1/2 of original sample left. After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

12. Graph of Amount of Remaining Nuclei vs Time A=A o e - t A

13. Example You have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. How many grams are left after one half-life? Answer:50 g How many grams are left after two half-lives?

14. Formula Amount Remaining = (Initial Amount) x (1/2) n Where: n = to the number of half lives You can calculate n by taking the elapsed time and dividing it by the duration of a half life of the substance.

15. Problem A sample of 3x10 7 Radon atoms are trapped in a basement that is sealed. The half-life of Radon is 3.83 days. How many radon atoms are left after 31 days? answer:1.2x10 5 atoms