Energy and Angular Dependence of Differential Cross Sections for theO16(O16,α)Si28Reaction

Abstract

Excitation functions for elastic scattering and $\alpha$-particle emission have been measured for 35-39-MeV oxygen projectiles incident on an oxygen target. Differential cross sections for $\alpha$-particle emission to the ground and first excited states of ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ are approximately 10-100 μb/sr. The angular distribution at 36-MeV laboratory bombarding energy indicates that $J=12\mathrm{}$ angular momentum states of the compound nucleus are the dominant contributors for $\alpha$ decay to the ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ ground state. The fluctuation width obtained from both the elastic and the $\alpha$-particle-emission channel is 76±17 keV. Neither the fine nor gross structure in the elastic scattering excitation function is correlated with fluctuations in the cross section for $\alpha$-particle emission from the compound nucleus. The level density of spin-12 states of the ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ compound nucleus at an excitation energy of 34.2 MeV has been determined to be 2000 levels per MeV. Statistical-model calculations of the level density, average cross sections, and fluctuation widths require a value of the nuclear level-density parameter $a$ between $\frac{A}{7}$ and $\frac{A}{9}$.