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Radiation Hazards

Radiation Hazards. Nuclear Forces. At this scale, gravity is utterly insignificant Protons are repelled by electromagnetic force Two types of nuclear forces bind particles together Very short range. Nuclear Decay. Too many protons (>83, Bi): nuclear forces cannot hold nucleus together

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Radiation Hazards

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  1. Radiation Hazards

  2. Nuclear Forces • At this scale, gravity is utterly insignificant • Protons are repelled by electromagnetic force • Two types of nuclear forces bind particles together • Very short range

  3. Nuclear Decay • Too many protons (>83, Bi): nuclear forces cannot hold nucleus together • Too many neutrons also unstable • Unstable nuclei emit particles and energetic radiation (gamma rays) • Massive nuclei can sometimes split catastrophically (fission) • Natural or Spontaneous • Nuclear Reactor • Nuclear Weapon

  4. Isotopes • Atoms of element with different number of neutrons • Protons = Atomic Number • Protons + Neutrons = Atomic Weight • Example: Uranium-238 • 92 protons by definition • 238-92 = 146 neutrons • Carbon-14 • 6 protons (by definition), 8 neutrons

  5. Radioactive Decay: Half-Life

  6. Radiation and Half-Life • Decay Constant: fraction of atoms that decay/time • Half-life = 0.693/Decay Constant • Example: 10% decay per hour: Half Life = 0.693/(0.1/hour) = 6.9 hours • Shorter Half Life = More Radiation Per Unit Time • Generally more energetic

  7. Curie • Unit of radioactivity • 3.7 x 1010 decays/second • Rn-222 3.8 days .000006 grams • Co-60 5.26 yr .0013 grams • Sr-90 28 yr .007 grams • Ra-222 1600 yr 1 gram • Pu-239 24400 yr 16 grams • U-238 4.5 b.y. 3,000,000 gm (3 tons)

  8. Radiation Hazards • Three Mile Island: 50 curies • About ½ gram • Chernobyl (1986) 50,000,000 curies • About 500,000 grams (half a ton) • Russian Deep Waste Injection Program: 3,000,000,000 curies

  9. Half-Life and Hazard • Very short half-life (days or less) • Extremely high radiation hazard • Decays very quickly • Probably won’t move far during lifetime • Extremely long half-life (geological) • Radiation hazard negligible • Chemical toxicity is worst hazard • Daughter products (radon) can be a problem • Medium half-lives (years to 1,000’s years) • Last long enough to migrate

  10. Types of Radiation • Alpha (helium nucleus) • Beta (electrons) • Neutron (nuclear fission only) • X-rays (energetic electromagnetic radiation) • Gamma (more energetic than X-rays)

  11. Hazards of Radiation • Direct damage to organic molecules • Creation of reactive molecules and free radicals • DNA mutations • Birth Defects • Sterility • Cancer • Dangers of Radiation Types • Penetrating Ability • Ability to create electric charges (ionize)

  12. Alpha Radiation • Given off by decay of uranium and thorium and daughter products (including radon and radium) • Cannot penetrate skin • +2 electric charge = high ionizing ability • Least dangerous externally, most dangerous internally

  13. Beta Radiation • Given off by light and medium nuclei, including most fission products (fallout and reactor waste) • Can penetrate a few mm into tissue • Electrons, -1 charge = moderately high ionizing ability • Minor external hazard, fairly serious internal hazard

  14. Gamma Rays • Produced by all nuclear decays • Need not be accompanied by particle emission • Penetrates tissue easily, requires 1 cm lead to reduce by ½ • Most serious external hazard

  15. Units of Radiation Dose • Roentgen – Ability to create a specified electric charge per volume of air • Gray (Gy): 1 Joule/kg = 100 Rad (Radiation absorbed dose) • Sievert (Sv)= Biological Effect of 1 Gray of X-Rays = 100 Rem (Roentgen equivalent man) • For general human exposure, Gray and Sievert are roughly equivalent

  16. Background Radiation • Cosmic Rays • Solar Wind • Decay of Natural Radioactivity • Typical Doses • Global Average 1 mSv (0.1 rem)/year (80% natural) • Some areas up to 10 mSv (1 rem)/year • Ramsar, Iran: up to 0.26 Sv (26 rem)/year

  17. Human Radiation Sources • Nuclear Fallout from Atmospheric Testing (US and Russia, 1963; France, 1974; China, 1980) • Chernobyl 1986, Fukushima 2011 • Uranium Mining • Radon release from construction and earth-moving • Conventional power plants

  18. Human Survival Limits • 2 Sievert = 200 rem (whole body): few immediate fatalities • 5 Sievert = 500 rem (whole body): 50% fatalities • 10 Sievert = 1000 rem (whole body): No survivors

  19. Chain Reaction

  20. Nuclear Fission • Chain reaction requires a critical mass to proceed • 10 kg U-235 = 2.5 x 1025 atoms • 1,2,4,8 … 2.5 x 1025 = 85 steps • @ 1/1,000,000 sec per step = 1/10,000 sec • After 64 steps, T = 10,000 K (twice as hot as sun) • Have only completed 1/1,000,000 of fission

  21. Nuclear Weapons To get a nuclear explosion, you have to • Assemble a critical mass in millionths of a second • Retain a high percentage of the neutrons • Hold the material together against temperatures hotter than the Sun • Imposes limits on yield of weapon • Unless something is specifically designed to be a nuclear weapon, it will not explode

  22. Yields of Nuclear Weapons • Kiloton = 1000 tons of explosives = 4.2 x 1012 joules (1 trillion calories) • Texas City, Texas, April 16-17, 1947 • Collapse of World Trade Center • Impact of 10-m asteroid • Megaton = 1,000,000 tons of explosives = 4.2 x 1015 joules (1000 trillion calories) • Magnitude 7 earthquake • Impact of 100-m asteroid

  23. Largest Chemical Explosions • Many Chemical Explosions Have Overlapped Nuclear Weapon Yields • Wartime Events • Ammunition Handling Mishaps • Disposal of Explosives • Simulation of Nuclear Explosions • Excavation • Industrial Accidents

  24. “Das war keine gute Idee”

  25. Effects of Nuclear Weapons • Direct ionizing radiation • Heat (Fireball) • Rising fireball sucks dust upward, creates “mushroom cloud” • Any large explosion will create a “mushroom cloud” • Blast (Expansion of Fireball) • Fallout

  26. Nuclear Winter • Publicized by Carl Sagan and others in 1980’s • Global nuclear exchange would raise large amounts of dust and soot into upper atmosphere • Would absorb or reflect sunlight, cooling the surface • Would be above most precipitation processes • Did not happen in Gulf War 1991

  27. Controlled Nuclear Fission • Barely achieve critical mass • Absorb most neutrons • Moderator: water, graphite • Allow just enough fissions to occur to keep chain reaction running • Heat used to run steam turbines • Failure of moderator or coolant can result in meltdown

  28. Nuclear Waste • Spent Fuel • Breeder Reactors • On-site storage • Geological storage (100,000 + years) • Decommissioned Power Plants • Neutrons make reactor walls radioactive • Low-Level Waste • Medical • Universities • Smoke detectors (Exempt)

  29. Fusion • Natural: how stars (and the sun) generate energy • Artificial and uncontrolled: Thermonuclear Weapon (hydrogen bomb) • Fusion Reactor: controlled • “Energy source of the future. Always has been, always will be.”

  30. Uncontrolled Fusion • We cannot achieve T and P necessary to use ordinary hydrogen • Have to use H-2 (deuterium) or H-3 (tritium) • Still need T = 1,000,000 K+ • Initiated by a nuclear (fission) weapon • Fission weapons yield up to 20 kilotons • Fusion (hydrogen or thermonuclear) weapons yield up to 20 megatons

  31. Controlled Fusion • Temperatures too high for any material • Need to contain by magnetic fields, achieve small-scale reactions for short periods • Have not achieved break-even • Apparatus will be incredibly complex and expensive • Reactions give off neutrons: there will still be radioactive waste • No spent fuel or fissionable residue

  32. Plutonium • At 24,400 years half-life, much less radioactive than radium (1600 y) or radon (3 days) • Not highly soluble • Chemical toxicity comparable to many other heavy metals • Concentrates in bone marrow • Allowed occupational exposure 10-3 microcuries (1.6 x 10-8 gm) per quarter • Compare Be, Rh (10-9 gm/m3 of air)

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