Physics 31: Nuclear Energy - Effects and Uses of Radiation

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Physics 31 Nuclear Energy - Effects and Uses of
Radiation

• Christopher Chui

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Nuclear Reactions and the Transmutation of
Elements

• Nuclear reaction n 147N?146C p
• Conservation of energy a X ?Y b
• Reaction energy, Q-value(MaMX-Mb-MY)c2
• If Qgt0, the reaction is exothermic or exoergic
• If Qlt0, the reaction is enthermic or endoergic
• Neutron capture n 23892U ? 23992U
• Beta decay 23992U ? 23993Np e- n
• Beta decay 23993Np ? 23994Pu e- n

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Nuclear Fission Nuclear Reactor

• Neutron bombards n 23592U?14156Ba 9236Kr
  3n
• Energy/fission (0.9MeV/nucleon)(236nucleon)200M
  eV
• Sustaining chain reaction? bomb or nuclear
  reactor
• In nuclear reactors, moderators such as heavy
  water or graphite (C-12) to slow down reactions
• Critical mass must be maintained for nuclear
  fission
• Control rods are used to maintain critical mass
• Delayed neutrons allow control rods to operate
• A breeder reactor breeds new fuel, 23994Pu, from
  23892U

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Fusion

• Nuclear fusion builds larger nuclei by combining
  smaller nuclei, up to about A 60
• Producing deuterium n 11H?g 21H 2.22 MeV
• Fusion reactor 21H 21H ? 31H 11H 4.03 MeV
• Fusion reactor 21H 21H ? 32He n 3.27 MeV
• Fusion reactor 21H 31H ? 42He n 17.59 MeV
• Temperatures required for fusion to occur 108 K
• Two forms of fusion reactors magnetic
  confinement and inertial confinement

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Magnetic and Inertial Confinement Fusion

• Russian tokamak uses two magnetic fields to
  confine plasma
• Lawson criterion ion density x time gt 3x1020
  s/m3
• Temperatures of 4x108 K have been obtained
• Inertial confinement deuterium and tritium
  pellets are bombarded with several high power
  lasers. Lawson criterion was achieved, but not
  hot enough
• NOVA lasers deliver 105J in 10-9 s?1014W, which
  is more all US power plant capacity

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Radiation Damage

• Ionizing radiation are charged particles which
  ionize atoms or molecules of any object
• Alpha and beta rays have energies of 1 Mev and
  atoms and molecules ionize at 10 eV
• Damage to cells due to ionization
• All forms of radiation can ionize atoms by
  knocking out electrons
• Damage to DNA is more serious somatic and genetic

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Dosimetry-1

• Strength of a source at a given time is source
  activity
• 1 Ci 3.70 x 1010 disintegrations/sec
• 1 Bq 1 disintegration/sec
• Source activity DN/Dt lN 0.693N / T1/2
• Absorbed dose is the effect on the absorbing
  matter. 1 R 1.6x1012 ion pairs/gm of dry air
• 1 R 0.878 x 10-2 J/kg of air
• 1 rad 1.00 x 10-2 J/kg in any absorbing
  material
• 1 Gy 1 J/kg 100 rad

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Dosimetry-2

• Relative biological effectiveness or quality
  factor is the number of rads of X or g radiation
  that produces the same biological damage as 1 rad
  of radiation
• Effective dose in rem dose in rad x QF
• Effective dose in Sv dose in Gy x QF
• We all receive a low-level natural
  radiation0.36rem/yr. Government allows 0.5rem/yr
• Radiation film badge monitors radiation absorbed
• Radiation sickness includes nausea, fatigue, etc

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Radiation Therapy and Tracers

• The treatment of disease, mainly cancer, using
  6027Co or X-rays in the range of 200 keV to 5 MeV
• The diagnosis of disease, such as 13153I, 99m43Tc
• Tracers are isotopes for research in biology and
  medicine. 146C or 31H are tagged to molecules to
  study pathway
• Autoradiography uses film to detect isotopes
• Single photon emission tomography uses g camera
  to image whole body patients
• Positron emission tomography uses positron
  emitters, 116C, 137N, and 189F. After absorption,
  g are emitted and detected
• PET and SPET give images related to biochemistry,
  metabolism, and function, while X-ray CT scans
  give anatomy

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NMR and MRI

• NMR requires a ring circular magnetic field and
  and RF coil. A RF pulse of EM radiation is
  applied to the sample. If hf DE kBT, then the
  photons will be absorbed, exciting many
  nuclei?resonance
• For 11H, f 42.58 MHz for a field BT 1.0 T
• NMI is to image NMR to give 2D and 3D images
• Typical resolutions X-rays ½ mm nuclear
  medicine 1 cm SPET 1 cm PET 3-5 mm, NMR ½ -1
  mm ultrasound 2 mm