Radiation Hazards

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

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 wont 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 1,000s 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
• Rem (Roentgen equivalent man) Biological effect
  of one roentgen of X-rays
• Rad (Radiation absorbed dose) Energy
  absorption 400,000 rads heat H2O 1 deg
• For general human exposure, these units are
  roughly equivalent

16
Background Radiation

• Cosmic Rays
• Solar Wind
• Decay of Natural Radioactivity
• Typical Doses
• Global Average 0.1 rem/year (80 natural)
• Some areas up to 1 rem/year
• Ramsar, Iran up to 26 rem/year

17
Human Radiation Sources

• Nuclear Fallout from Atmospheric Testing (US and
  Russia, 1963 France, 1974 China, 1980)
• Chernobyl 1986
• Uranium Mining
• Radon release from construction and earth-moving
• Conventional power plants

18
Human Survival Limits

• 200 rem (whole body) few immediate fatalities
• 500 rem (whole body) 50 fatalities
• 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
• _at_ 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
• 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
• Magnitude 7 earthquake
• Impact of 100-m asteroid

23
Das war keine gute Idee
24
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

25
Nuclear Winter

• Publicized by Carl Sagan and others in 1980s
• 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

26
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

27
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)

28
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.

29
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

30
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

31
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)