1. December 16, 2010 1.How is nuclear fusion different from nuclear fission? 2.What causes elements to be “radioactive”?

2. Goals To describe half life and solve problems using half life

3. Radioactive Decay Rates Half life- The time required for half of the sample of radioactive nuclei to decay.

4. Radioactive Decay Rates 1st half life  ½ sample remains unchanged 2nd half life-> ¼ sample remains unchanged 3rd half life -> 1/8 sample remains 4th half life - > 1/16 sample remains 1.Eventually the entire sample will decay

5. Radioactive Decay Rates 2. With each successive half life, half of the remaining sample decays to form another element. –Different radioactive isotopes have different half lives. –Half lives can last from nanoseconds  billions of years

6. Radioactive Decay Rates 3. If we know how much of the isotope is present at the beginning, we can predict how old the object is. a.Rocks 40K decays to 40Ar. b.The ratio of 40K to 40Ar is smaller in older rocks ( We have more 40Ar than 40K)

7. Radioactive Decay Rates c. We can look at the ratios between C-12 and C-14 to determine the age of animal remains or plant remains.

9. Now… Lab Parts 2 & 3 of HW pkt –Do NOT do # 3 of part 2