A Nuclear Primer

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A Nuclear Primer

• When energy leaves an atom, its usually called
  radiation that scares civilians.
• Caused by electrons light, x-rays, low energy
  electrons
• Caused by nuclear processes
• ? helium nucleus
• ? electron or positron
• ? high energy photon
• p,n proton or neutron
• Other energetic particles possible

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Radiation Units

• Geiger counter video - watch dial
• curie (Ci) and becquerel (Bq) are certain numbers
  of decays per second
• rad and gray (Gy) measure how much energy is
  deposited in a kg of tissue.
• rem and sievert (Sv) measure how much damage is
  done. 1 Sv 100 rem
• rem rad RBE
• Its rems that harm you

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Radiation Sickness

• Consider whole body doses
• lt 100 rem no short-term illness
• 100 - 200 nausea, hair loss
• 300 LD50
• gt 1000 survival unlikely
• Alexander Litvinenko

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Cancer and the linear hypothesis

• 2500 rem whole body gives 100 chance of excess
  cancer
• So 25 rem whole body gives 1 chance of excess
  cancer
• Give 100 people 25 rem each, expect one extra
  cancer (20 from other causes)
• Most people assume linear hypothesis at all dose
  levels, so 25 mrem gives 0.001 chance of excess
  cancer.

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Fission and fusion energy

• Fission occurs when a nucleus splits
• Fragments have less mass than the original
  nucleus E mc2
• Fusion occurs when two lighter nuclei fuse into a
  single heavier nucleus.
• Again, mass goes missing and comes out as energy
  (lots of it)
• How can this happen in both cases?

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• Fusion generates lots of relatively clean power,
  but requires high temperature and probably
  magnetic confinement
• Fusion is the power source of stars
• Fusion bombs are the most powerful ever made

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Chain reactions

• The power of repeated doubling
• Neutrons initiate fission, and fission creates
  more neutrons
• Runaway chain reaction is a bomb
• Critical mass is required (15 kg for U-235, 5 kg
  for Pu-239) to ensure enough neutrons are
  absorbed
• Make critical mass with gun or with implosion

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How to make a bomb

• Enrich uranium to increase U-235
• Gas centrifuges
• Modern, efficient, but need strong material for
  their construction
• Calutrons
• Slow but sure Saddam tried this method
• Use plutonium
• Implosion must be used hard to do
• Use fission bomb to start a fusion reaction
  (H-bomb)

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Bomb damage

• 20 kiloton about a mile away
• Light/x-ray pulse
• Thermal pulse
• Blast wave
• Radioactive fallout
• New York City example
• The only winning move is not to play the game

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A reactor hodge-podge

• Fast vs. slow neutrons
• Bombs need fast neutrons to get enough doublings
  in a short time
• Reactors generally use slow neutrons, since they
  are absorbed more readily by the smaller fraction
  of U-235
• Moderators
• Used to slow the neutrons down - thermal
• Water, heavy water, graphite

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A reactor hodge-podge, p.2

• Control rods
• Absorb neutrons to control the reaction
• Neutron absorbed by U-238 gives Pu-239 --
  breeder reactor
• Sometimes uses fast neutrons. Less safe but more
  efficient.
• Depleted uranium bullets