Energetics of Nucleon and Photon Emission from Compound Nuclei: Angular Distributions ofCu61Recoil Products

We report the results obtained from a detailed study of the ${\mathrm{Mn}}^{55}({\mathrm{B}}^{11},p4n){\mathrm{Cu}}^{61}$ reaction. The excitation function has a maximum cross section of about 130 mb at an energy corresponding to 6.2 MeV of available energy per nucleon emitted, and is in good agreement with the compound-nucleus reaction mechanism inferred earlier on the basis of recoil-range data. We have measured angular distributions of ${\mathrm{Cu}}^{61}$ at 10 bombarding energies over the region 53 to 114 MeV, covering all but the lowest-energy portion of the excitation function. These experiments have been analyzed to yield information on the average total energies of particles and photons emitted in the de-excitation of the compound nuclei. Above about 20 MeV of available energy, gamma-ray emission becomes significant and accounts for about 14 MeV of de-excitation energy at the higher bombarding energies. The amount of energy dissipated as gamma radiation is larger than nucleon binding energies, and indicates substantial competition between particle and photon emission in the de-excitation process. Our results are in very good agreement with the less specific but more direct gamma-ray measurements of other investigators.