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Atom’s Nucleus and Radioactivity 20 October 2015

Atom’s Nucleus and Radioactivity 20 October 2015. Background Radioactivity and natural background exposure Principles of radioactivity and human health Application of the principles of radioactivity. Isotopes. Atoms have specific number of protons, neutrons and electrons 8

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Atom’s Nucleus and Radioactivity 20 October 2015

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  1. Atom’s Nucleus and Radioactivity20 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 = 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. Unstable Isotopes: Radioactive Emissions • 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 now with only 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. Question The half-life of a radioactive element is ___. A. the time it takes for 50% of the atoms in a sample to spontaneously decay B. indicates that it is capable of reducing the life of an exposed human by 50% C. describes 50% of the energy that is released when the atomic nucleus decays D. is a measure of 50% the radioactivity that is emitted from each atomic nucleus that decays

  19. Question As the temperature of a sample of radioactive element increases, the half-life will ___. A. Decrease B. Remain unchanged C. Increase D. None of the above

  20. Question There are two radioactive sources, A and B; both have the same number of unstable nuclei at the beginning. After 10 days, the number of unstable nuclei remaining for B is more than A. Which of the following statements is correct? A. The mass of A is larger than that of B B. The mass of B is larger than that of A C. The half-life (t1/2) of B is longer than that of A D. The half-life (t1/2) of A is longer than that of B

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

  22. 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, liver) • Examples • Iodine-131 (thyroid) • Thallium-201 (kidney)

  23. 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

  24. 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

  25. Fukushima Daiichi Nuclear Power Plant Accident - March 2011

  26. Question Fissionable (means what?) uranium-233, uranium-235 and plutonium-239 are used in nuclear reactors as ___. A. Coolants B. Control rods C. Moderators D. Aspirators E. Fuels

  27. Question Nuclear reactors and traditional fossil fuel combustion (gas and/or coal) plants share the following fundamental energy conversion feature. A. Nuclear reactor B. Control rods C. Power lines D. Aspirators E. Stem-driven generators to convert chemical energy to electrical energy

  28. Atom’s Nucleus and Radioactivity20 October 2015 • Background • Radioactivity and natural background exposure • Principles of radioactivity and human health • Application of the principles of radioactivity

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