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Physics 31: Nuclear Energy; Effects and Uses of Radiation

Physics 31: Nuclear Energy; Effects and Uses of Radiation. Christopher Chui. Nuclear Reactions and the Transmutation of Elements. Nuclear reaction: n + 14 7 N  14 6 C + p Conservation of energy: a + X Y + b Reaction energy, Q-value=(M a +M X -M b -M Y )c 2

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Physics 31: Nuclear Energy; Effects and Uses of Radiation

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  1. Physics 31: Nuclear Energy; Effects and Uses of Radiation Christopher Chui Nuclear Energy; Effects and Uses of Radiation - C. Chui

  2. Nuclear Reactions and the Transmutation of Elements • Nuclear reaction: n + 147N146C + p • Conservation of energy: a + X Y + b • Reaction energy, Q-value=(Ma+MX-Mb-MY)c2 • If Q>0, the reaction is exothermic or exoergic • If Q<0, the reaction is enthermic or endoergic • Neutron capture: n + 23892U  23992U • Beta decay: 23992U  23993Np + e- + n • Beta decay: 23993Np  23994Pu + e- + n Nuclear Energy; Effects and Uses of Radiation - C. Chui

  3. Nuclear Fission & Nuclear Reactor • Neutron bombards: n + 23592U14156Ba + 9236Kr + 3n • Energy/fission = (0.9MeV/nucleon)(236nucleon)~200MeV • 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  4. 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  5. Magnetic and Inertial Confinement Fusion • Russian tokamak uses two magnetic fields to confine plasma • Lawson criterion: ion density x time > 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  6. 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  7. 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  8. 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 radiation~0.36rem/yr. Government allows 0.5rem/yr • Radiation film badge monitors radiation absorbed • Radiation sickness includes nausea, fatigue, etc Nuclear Energy; Effects and Uses of Radiation - C. Chui

  9. 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

  10. 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 Nuclear Energy; Effects and Uses of Radiation - C. Chui

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