1. Unit 2 Notes – Radioactivity Part II Mr Nelson

2. Transuranium elements & Radioactivity Transuranium elements are just elements #93-11? (anything after Uranium!) All elements after Bismuth (Z = 83) are radioactive

3. Half Life ½ life: the time for ½ of a sample of nuclei to decay For U-238, it is 4.5 billion years Pa-234 has a ½ life of 1.2 minutes!!

4. Carbon Dating (Radioactive Dating) Based on the radioactivity of carbon-14, which decays through -particle production. Carbon-14 is continuously made in the atmosphere when neutrons from space hit the nitrogen in the air.

5. More on carbon dating: Living things always have the same amount of C-14 because they take it in through the air. As soon as a living thing dies it stops taking in carbon from the atmosphere. The C-14 decays. The ½ life of C-14 is 5730 years. If a piece of wood has ½ the C as a living tree, it is 5730 years old. What are some of the problems with this method?

6. Detecting Radiation High energy particles from radioactive decay make ions when they travel through matter. The fast particles knock electrons off the atoms they hit. A geiger counter can detect these ions through the flow of electricity

7. A geiger counter

8. Effects of Radiation Different particles penetrate in different ways energy mass How easily they make ions Chemical properties These things make radiation more or less harmful

9. Inverse Square Law Intensity =

10. Conclusions About Radiation

12. Binding Energy & Mass Defect Binding Energy – energy that holds nucleus together Mass defect – the missing mass when the mass of nucleons are added together. Example: page 14 of HW Packet

13. E = mc 2 Einsteins idea E = energy m = mass in kilograms c = speed of light 3x10 8 m/s

14. Fission and Fusion Combining two light nuclei to make a heavier nucleus is called fusion Splitting a heavy nucleus to form two nuclei with smaller masses is called fission.

15. Fission Releases a lot of energy! Can cause chain rxns

16. Chain Rxns At least one neutron must go on to split another nucleus

17. Nuclear Reactors

18. Controlling Nuclear Reactors Boron and Cadmium are used as neutron absorbers to slow down or stop the reaction.

19. Nuclear Bomb The same type of chain reaction is used in a nuclear bomb, but it is not controlled.

20. Nuclear Fusion Produces more energy than fission! Takes very high temperatures to get protons close enough to stick to each other

21. Fusion & Tokamak Reactor Fusion would be a superior method of generating power. the products of the reaction are not radioactive. The bad news is that in order to achieve fusion, the material must be in the plasma state at several million degrees.