The document discusses various topics related to radiation and nuclear physics, including: 1) The inverse-square law and how radiation intensity decreases with distance from the source. An experiment is described to demonstrate this. 2) Different types of ionizing radiation like alpha, beta, gamma rays and their properties. Experiments with shielding materials like lead are proposed. 3) Natural and medical sources of radiation and how they contribute to typical human annual radiation doses. Most exposure is from natural background sources like radon. 4) Nuclear reactions like alpha decay, neutron capture, and beta decay are explained. Isotopic notation and how the element changes during these reactions is also covered.

1. Today: Inverse-square law, shielding, sources of radiation Sources of annual ionizing radiation dose of typical human

2. Quiz results Ouch!

7. The intensity of radiation follows the inverse square law Force  Charge1 * Charge2 distance 2 Intensity of radiation  Source intensity distance 2 Remember for electric charge: If you double the distance, Intensity decreases by a factor of 4

8. Inverse-square law demo Three pieces together are a “Geiger counter” Geiger-Müller tube High Voltage Power Supply Counter Radioactive Source Holder Calibrated distance rail

9. Refresher on Geiger counter Depending on the design: Maybe detect alpha-radiation CAN detect beta-radiation Maybe detect gamma-radiation Alpha particles difficulty passing through window But can make it through mica Ionizing radiation (beta, gamma, some alpha) enter through window and create ions inside. These events are detected via the electric current and turned into audible “clicks.”

10. Inverse-square law demo Geiger-Müller tube Radioactive Source Holder Calibrated distance rail Let’s try the experiment again from last week Distance

11. Three kinds of radiation emitted via radioactive decay named before they were understood…alpha, beta, gamma Alpha particles stopped by paper alpha particles are helium nuclei Beta particles stopped by aluminum beta particles are electrons (or positrons) Gamma rays stopped by lead gamma rays are high energy photons x-rays similar, but lower energy than gamma

12. Shielding demo Geiger-Müller tube Radioactive Source Holder Calibrated distance rail Let’s try experiments with different shielding materials Place different shielding materials here

27. Parallel of electrical energy with nuclear energy Electricity and radioactivity have existed since the beginning of time So, the dangers have always been present, and always will be. Humans have learned how to harness the powers of electricity and nuclear reactions…presenting new dangers along with great benefits The task for society is to weigh the benefits against the dangers Hey toddlers! I’m your friend!

28. How to read the short-hand summary of an isotope Number of protons Atomic number (Z) Total number of nucleons (protons + neutrons) Mass number (A) Element symbol The atomic number and element symbol provide the same information. I.e., Carbon always has 6 protons. So, this isotope is also written: 12 C or Carbon-12 C 12 6

29. In chemical reactions , these items do not change Atomic number (Z) is constant Mass number (A) is constant Element does not change If any of these values change, then it is a nuclear reaction! Transmutation of an Element C 12 6

30. Examples of nuclear reactions U 238 92 Th 234 90 He 4 2 (Plus a lot of kinetic energy) Alpha-decay n 1 0 N 14 7 Neutron capture p 1 1 C 14 6 (This reaction happens in the upper atmosphere to produce Carbon-14)

33. Let’s understand beta-decay a little more by learning a bit about particle physics