Physics 6 Spring 2005 Some concepts covered since second exam fission neutrons isotopes - 235 and 238 Uranium - separation - thermal separation chain reaction - neutrons per fission ~= 2.3 scattering - elastic, inelastic capture cross section energy - 200 MeV per breakup of U critical radius (or mass) and mean free path Other terms: isotopes, curve of binding energy, mass defect mass-energy, kinetic energy energy units: Joule (MKS system), eV, MeV, kiloton (kT) 1 .6 × 10-19 J = 1 eV, 1 MeV = 10 6 eV, 1 kT= 4.2 × 10 12 J radiation, radioactivity, radionuclide, alpha, beta, gamma half-life, exponential decay activity = (0.69/T 1/2 ) N (N=number of decaying nuclei) activity is in units of disintegrations per second or Becquerel (Bq) Radiation units : Curies (1 Ci = 3.7 × 10 10 decays/sec, 1 decay/sec=1 Bq), Roentgens, rads, rems (see Lecture 21) If needed on the Final the radiation order of magnitude “Rules of Thumb” will be given: a. 1 gram of Ra or a 1 Ci source produces 1 R per hour at 1 meter distance;
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