Pre-equilibrium alpha emission induced by different incident channels: Evidence for alpha preformation in nuclei

Abstract

A study of $\ensuremath{\alpha}$ emission induced by different incident channels has been undertaken. Measurements of energy spectra and angular distributions of $\ensuremath{\alpha}$ particles emitted in proton-, deuteron-, $^{3}\mathrm{He}$-, and $\ensuremath{\alpha}$-induced reactions were performed. An analysis in the frame of the pre-equilibrium model succeeds in giving an over-all description of all particle spectra. The $\ensuremath{\alpha}$ particle being in this approach considered as an exciton, a preformation factor around 0.2 for four nucleons to be correlated as an $\ensuremath{\alpha}$ particle has been obtained. The $\ensuremath{\alpha}$ preformation probability deduced from this analysis is independent of the proton, deuteron, $^{3}\mathrm{He}$ incident channel, incident energy, and mass of target nuclei.NUCLEAR REACTIONS $^{57}\mathrm{Fe}$, $^{58}\mathrm{Co}$, $^{66}\mathrm{Zn}$, $^{118}\mathrm{Sn}$, $^{209}\mathrm{Bi}(p, \ensuremath{\alpha})$; $^{56}\mathrm{Fe}(d, \ensuremath{\alpha})$; $^{55}\mathrm{Mn}$, $^{57}\mathrm{Fe}$, $^{207}\mathrm{Pb}(^{3}\mathrm{He}, \ensuremath{\alpha})$; $^{56}\mathrm{Fe}$, $^{63}\mathrm{Cu}$, $^{115}\mathrm{In}$, $^{206}\mathrm{Pb}(\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}})$ measured $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}}, \ensuremath{\theta})$ deduced reaction mechanism.