Emission of alpha particles in statistical multistep compound reactions

Abstract

Excitation functions and angular distributions of alpha particles emitted from the $^{27}\mathrm{Al}(^{3}\mathrm{He}, \ensuremath{\alpha})$ and $^{27}\mathrm{Al}(\mathrm{p}, \ensuremath{\alpha})$ reactions are measured at a composite nucleus excitation energy of about 30 MeV. The experimental results together with the widely varying correlation widths extracted from the fluctuation analysis are successfully interpreted on the basis of the statistical multistep compound emission mechanism. Confirmation is found of the interpretation of each experimental correlation width in terms of a coherent sum of the widths of the relevant stages of the reactions, previously proposed in the case of proton channels. Moreover, the $\ensuremath{\alpha}$-spectrum shape and the correlation width values are shown to be consistent with an $\ensuremath{\alpha}$ preformation picture of the target nuclei considered.NUCLEAR REACTIONS $^{27}\mathrm{Al}(^{3}\mathrm{He}, \ensuremath{\alpha})$ $E=8.2\ensuremath{-}13$ MeV; $^{27}\mathrm{Al}(\mathrm{p}, \ensuremath{\alpha})$, $E=18.5\ensuremath{-}25.6$ MeV; measured $\ensuremath{\sigma}(E;\ensuremath{\vartheta})$; statistical multistep compound emission, calculated $\ensuremath{\sigma}(E)$, $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}})$; generalized autocorrelation analysis, extracted coherence widths; suggested $\ensuremath{\alpha}$ preformation.