Atom’s Nucleus and Radioactivity 08 October 2015

1. Atom’s Nucleus and Radioactivity08 October 2015 • Background • Radioactivity and natural background exposure • Principles of radioactivity and human health • Application of the principles of radioactivity

2. Isotopes • Atoms have specific number of protons, neutrons and electrons 8 O Oxygen-16 16 (breath deep …) • If the number of protons is unchanged but the number of neutrons goes up or down, what happens to the chemical properties of that element (i.e., Periodic Table)? 8 O Oxygen-17 17 (breath deep …)

3. Isotopes … A Bit More • Atoms of an element with same number of protons but different number of neutrons are isotopes • Conventional notation (Element - Mass) • Oxygen -17 or Oxygen -16 • Carbon -12 or Carbon -13 • Iodine -131 • Cesium -135 • Plutonium -237 • Uranium -235

4. Example: Isotopes of Hydrogen Hydrogen 11H Stable Deuterium 12H Stable Tritium 13H Unstable Proton Neutron What is a stable versus an unstable isotope?

5. Stable Versus Unstable Isotopes • Stable over time • Oxygen-16 • Carbon -12 • Carbon -13 • Unstable: “atom changes” by releasing mass and/or energy (i.e., radioactive) • Carbon -14 (radioactive carbon) • Hydrogen-3 (radioactive hydrogen/tritium)

6. Radioactive Emissions of the Nucleus • Alpha (a): 2 protons + 2 neutrons (same as the helium atom) • Beta (b): high energy electron • Gamma (g): electromagnetic radiation with very short wavelengths (not visible to eye)

7. Natural or Background Radioactivity • Sources • Cosmic rays from outer space • Soils • Water • Building materials (rock) • Nuclear sources • Examples • Radon gas (Radon-222) - soils • Beryllium (Beryllium-7) - atmosphere Annual Mean Exposure (OSU)

8. Example: Radon Exposure in the Home • Radon gas (Radon-222) • Radioactive gas • Human health effects - lungs • Human health exposure • Homes • At-risk groups: smokers • Risk mitigation - venting of basements • Geologically based radioactivity: 100% natural

9. The Essence of Being Unstable: Radioactive Decay • Uranium-238 92 protons + 146 neutrons (contrast with other atoms) • Spontaneous release of an alpha (a) particle (2 protons + 2 neutrons): atom with 90 protons and mass of 234, which is ____? • All isotopes of all elements with > 83 protons (Bismuth) are unstable and radioactively decay • Rate of decay: unaffected by the environment

10. Periodic Table

11. Types of Decay and Human Health • Alpha (a) • Two protons + two neutrons • Travel distance: stopped by sheet of paper (even air) • Beta (b) • high energy electron • Travel distance: ~10 meters; stopped by 1 cm aluminum block • Gamma (g) • high energy radiation • Travel distance: 100’s meters; stopped by 5 cm lead brick

12. Penetration of Different Types of Ionizing Radiation AlphaParticles Stopped by a sheet of paper Beta Particles Stopped by a layer of clothing or less than an inch of a substance (e.g. plastic) Radiation Source Gamma Rays Stopped by inches to feet of concrete or less than an inch of lead

13. Radioactivity: Human Health • Radioactivity in biological tissues results in atoms being ionized • Disrupts chemical bonds • DNA as primary site of action (e.g., mutations) • Disrupts biochemistry • Sensitivity greatest for actively growing cells • Blood (Strontium-90) • Bone marrow (Cesium-137) • Thyroid (Iodine-131) • Muscle (Pu-239)

14. Periodic Table

15. Radioactivity: Principles and Applications • Background • Radioactivity is natural • Quantitative analysis of radioactivity • Principles of radioactivity and human health • Application of the principles of radioactivity

16. Radioactive Decay • Rate of decay to a stable state (no more spontaneous decay): specific for each isotope • Rate: unique terminology = “half-life” • Time for ½ (50%) of atomic nuclei to decay to the stable state (abbreviated t1/2) • Range: fractions of second to billions of years (isotope specific) • Unaffected by the environment (e.g., moisture, light, pressure, etc.) • Example: M&M’s

17. Radioactive Decay

18. Application of Atomic Principles of Radioactivity • Medical science • Nuclear energy • Chernobyl Russia • Fukishima Japan • Dirty bomb

19. Medical Science: Nuclear Applications • Nuclear imaging and radio-pharmaceuticals • Injection of radioactive element • Allow for distribution in body • Imagine body for presence or absence of radioactive element • Function: assessment of functional and dysfunctional tissues (e.g., thyroid, kidneys, heart) • Examples • Iodine-131 (thyroid) • Thallium-201 (kidney)

20. Nuclear Reactor: Power Generation(read section in text) Fuel rods Moderators Coolants Steam turbines Cooling towers Nuclear waste storage Comparison with fossil fuel power generation

21. Chernobyl Reactor and Sarcophagus - April 1986 • Complete core meltdown • Sarcophagus - risk containment • Human health (~4,000 death) • Acute radiation poisoning – on site workers • Chronic exposure - residents • Iodine -131 • Thyroid cancer and leukemia • No detectable effects > 100 miles

22. Fukushima Daiichi Nuclear Power Plant Accident - March 2011

23. Atom’s Nucleus and Radioactivity08 October 2015 • Background • Radioactivity and natural background exposure • Principles of radioactivity and human health • Application of the principles of radioactivity