Energy Dependence of Angular Distributions of the Reaction Al²⁷(<i>p</i>, α)Mg²⁴ in the Energy Region between 10.5 and 14.5 Mev

Abstract

The angular distributions of the reactions Al 27 ( p , α)Mg 24 resulting in the ground and first excited states of Mg 24 were measured at 37 energies between 10.5 and 14.5 Mev, making use of proportional counters. Similar behaviour was obtained for both reactions. The variation of the shape of the angular distributions with the bombarding energy is rather smooth in the higher energy region, but becomes rapid with decreasing the bombarding energy. There appear some resonance-like peaks and valleys in the excitation curves at laboratory angles of 50°, 90° and 130° but their positions are not coincident with one another and in the higher energy region these peaks disappear in the excitation curves for the total cross sections. The variations of the excitation curves for the total cross sections and of the shape of the angular distributions with energy in the lower energy region may be due to the fluctuations in the number or properties of the compound nucleus levels and to the interference between the compound nucleus and direct interaction processes. The smoothing-outs of the excitation curves for the total cross sections and of the variation of the shape of the angular distributions in the higher energy region seem to be due to the effects of decreasing level spacing in the compound nucleus and of increasing contribution from the direct interaction process. However, in the entire energy region, the interference between the compound nucleus and direct interaction processes and some contribution from the heavy particle stripping process cannot be neglected.