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Compound Nucleus Reactions

Compound Nucleus Reactions. Direct. Time. Energy. CN decays. Two-step reaction. CN “forgets” how it was formed. Decay of CN depends on statistical factors that are functions of E x , J . Low energy projectile, medium or heavy target. E a CM. Q CN. Compound Nucleus Reactions.

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Compound Nucleus Reactions

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  1. Compound Nucleus Reactions Direct • Time. • Energy. CN decays • Two-step reaction. • CN “forgets” how it was formed. • Decay of CN depends on statistical factors that are functions of Ex, J. • Low energy projectile, medium or heavy target. EaCM QCN Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  2. Compound Nucleus Reactions Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  3. Compound Nucleus Reactions • Considerp + 63Cu at EpCM= 20 MeV. • Calculate Ep + [m(63Cu) + m(p) – m(64Zn)]c2. • Divide by 64  available energy per nucleon << 8 MeV. • Multiple collisions  “long” time  statistical distribution of energy  small chance for a nucleon to get enough energy Evaporation. • Higher incident energy  more particles “evaporate”. See also Fig. 11.21 in Krane. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  4. Direct Reactions • Random collisions  nearly isotropic angular distribution. • Direct reaction component  strong angular dependence. See also Fig. 11.20 in Krane. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  5. Direct Reactions • Peripheral collision with surface nucleon. • 1 MeV incident nucleon   ??  more likely to interact with the nucleus  CN reaction. • 20 MeV incident nucleon   ??  peripheral collision  Direct reaction. • CN and Direct (D) processes can happen at the same incident particle energy. Distinguished by: • D (10-22 s) CN (10-18-10-16 s). [Consider a 20 MeV deuteron on A=50 target nucleus]. • Angular distribution. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  6. Direct Reactions • (d,n) stripping (transfer) reactions can go through both processes. • (d,p) stripping (transfer) reactions prefer D rather than CN; protons do not easily evaporate (Coulomb). [(p,d) is a pickup reaction]. • What about (,n) transfer reactions? HW 36 Show that for a (d,p) reaction taking place on the surface of a 90Zr nucleus, and with 5 MeV deuterons, the angular momentum transfer can be approximated by l = 8sin(/2), where  is the angle the outgoing proton makes with the incident deuteron direction. (Derive a general formula first). J(90Zrgs) = 0+ J(91Zr) = l ± ½, = (-1)l Fig. 11.23 in Krane. Optical model, DWBA, Shell model, Spectroscopic Factor. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  7. Neutron-induced Reactions X(n,b)Y b(Q+En) n(En) Probability to penetrate the potential barrier Po(Ethermal) = 1 P>o(Ethermal) = 0 For thermal neutrons Q >> En b(Q)  constant Non-resonant Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

  8. Neutron-induced Reactions Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

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