Al(α,α′)Al*Compound-Nucleus Reactions

The energy and angular distribution of $\alpha$ particles inelastically scattered from Al have been measured from 30 to 170° for 20.0- and 27.5-MeV bombarding energies. Angular distributions of the inelastic $\alpha$ particles corresponding to residual nuclei excited to the continuum are found to be symmetric around 90°. For a number of angular distributions, the magnitude of the anisotropy is large; i.e., the ratio of differential cross sections at 170 to 90° is greater than 2.5. In the interpretation of the experimental results, the nuclear-level-density parameter and the spin cutoff parameter are derived by application of the semiclassical compound-nucleus theory of Ericson and Strutinski. This cutoff parameter is consistent with the rigid-rotor model of the nucleus. In order to obtain agreement between the magnitudes of the calculated and the experimentally measured cross sections, it was necessary to incorporate nuclear shell effects into the statistical-theory calculations.