Compound Nucleus Reactions

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Presentation transcript:

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).

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

Compound Nucleus Reactions Consider p + 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).

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).

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).

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. l 1 2 3  0º 14.4º 29º 44º Optical model, DWBA, Shell model, Spectroscopic Factor. Nuclear and Radiation Physics, BAU, First Semester, 2007-2008 (Saed Dababneh).

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).

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