1. Lecture 354/26/06

2. What does it mean to be radioactive? Radioactivity vs. nuclear power

5. Radioactive emissions Alpha particle (α) Helium nucleus

6. Radioactive emissions Beta particle (β) electron neutron  electron (β) + proton

7. Gamma (γ) doesn’t change atomic mass or number Radioactive emissions

9. positron (β + ) electron proton  positron (β) + neutron

10. Radioactive Electron capture Electron + proton  neutron

11. Rates of radioactive decay Decay is not affected by temperature, pressure, or state of chemical combination

13. If you start with 1.5 mg of tritium 3 H, how much is left after 49.2 years? t 1/2 =12.3 years

14. Belt of stability (empirically derived) Belt of stability ends at element 83 elements ≥ 84 protons are radioactive Type of decay nuclei above belt of stability (high N/Z) Beta emission 131 I  131 Xe + β decreases N/Z nuclei below the belt of stability (low N/Z) loss of positron of electron capture 11 C  11 B + β + or 81 Rb + e  81 Kr increases N/Z nuclei with atomic # ≥ 84 alpha emission 238 U  234Th + α

15. Belt of stability

16. Carbon dating in atmosphere t 1/2 =5730 years Ratio of 14 C/ 12 C constant until death, then 14 C/ 12 C decreases At death, 14 C has about 14 disintegrations per minute/gram (dpm/g)

17. Carbon-14 limitations 1. assume 14 C in atmosphere is constant 2. can’t date object < 100 years old 3. accuracy only ± 100 years 4. only good back to ~ 40, 000 years

22. Stability of Nuclei Out of > 300 stable isotopes: Even Odd Odd Even Z N 15752 505 31 15 P 19 9 F 2 1 H, 6 3 Li, 10 5 B, 14 7 N, 180 73 Ta