Angular Distributions of Products from Reactions of Copper Isotopes withHe4Ions

Abstract

Angular distributions of the recoil products of the ${\mathrm{Cu}}^{63}(\ensuremath{\alpha},n)$ reaction as well as of the ($\ensuremath{\alpha},2n$), ($\ensuremath{\alpha},3n$), ($\ensuremath{\alpha},2p$), and ($\ensuremath{\alpha},\ensuremath{\alpha}n$) reactions of ${\mathrm{Cu}}^{65}$ have been measured over the energy range of 20-43 MeV. The results have been compared with a Monte Carlo evaporation calculation and good agreement has been obtained for a reasonable choice of the level-density parameter for all but the ($\ensuremath{\alpha},n$) and ($\ensuremath{\alpha},\ensuremath{\alpha}n$) reactions at the higher energies. The discrepancies observed for the latter are indicative of a direct-interaction mechanism. Average properties of the angular distributions have been used to obtain the average values of particle and photon energies for the various reactions. The information obtainable from transformations of the angular distributions between the laboratory and center-of-mass systems has been explored. It was found that, on the assumption that the distribution of evaporation recoil velocities is isotropic and Gaussian, the laboratory distributions could be characterized by two parameters, namely the most probable evaporation velocity and a Gaussian width parameter. The latter could in turn be used to obtain average nucleon and photon energies.