P461 - decays III1 Gamma Decays If something (beta/alpha decay or a reaction) places a nucleus in an excited state, it drops to the lowest energy through.

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P461 - decays III1 Gamma Decays If something (beta/alpha decay or a reaction) places a nucleus in an excited state, it drops to the lowest energy through gamma emission excited states and decays similar to atoms conserve angular momentum and parity photon has spin =1 and parity = -1 for orbital P= (-1) L first order is electric dipole moment (edm). Easier to have higher order terms in nuclei than atoms

P461 - decays III2 Mossbauer Effect Gamma decays typically have lifetimes of around sec (large range). Gives width: very precise if free nuclei decays, need to conserve momentum. Shifts gamma energy to slightly lower value example. Very small shift but greater than natural width

P461 - decays III3 Mossbauer Effect II Energy shift means an emitted gamma won’t be reabsorbed but if nucleus is in a crystal lattic, then entire lattice recoils against photon. Mas(lattice)-->infinity and Egamma=deltaM. Recoiliess emission (or Mossbauer) will have “wings” on photon energy due to lattice vibrations Mosbauer effect can be used to study lattice enrgies. Very precise. Use as emitter or absorber. Nary energy by moving source/target (Doppler shift)

P461 - decays III4 Nuclear Reactions, Fission and Fusion 2 Body reaction A+B->C+D elastic if C/D=A/B inelastic if mass(C+D)>mass(A+B) threshold energy for inelastic (B at rest) for nuclei relativistic usually OK

P461 - decays III5 Nuclear Reactions A+B->C+D measurement of kinematic quantities allows masses of final states to be determined (p,E) initial A,B known 8 unknowns in final state (E,px,py,pz for C+D) but E,p conserved. 4 constraints->4 unknowns measure E,p (or mass) of D OR C gives rest or measure pc and pd gives masses of both often easiest to look at angular distribution in C.M. but can always convert

P461 - decays III6 Fission A->B+C A heavy, B/C medium nuclei releases energy as binding energy/nucleon = 8.5 MeV for Fe and 7.3 MeV for Uranium spontaneous fission is like alpha decay but with different mass, radii and Coulomb (Z/2) 2 vs 2(Z-2). Very low rate for U, higher for larger A induced fission n+A->B+C. The neutron adds its binding energy (~7 MeV) and can put neclei in excited state leading to fission even-even U(92,238). Adding n goes to even-odd and less binding energy (about 1 MeV) even-odd U(92,235), U(92,233), Pu(94,239) adding n goes to even-even and so more binding energy (about 1 MeV) --> 2 MeV difference between U235 and U238 fission in U235 can occur even if slow neutron