Preequilbrium alpha emission from proton, deuteron, $sup 3$He and alpha induced reactions: evidence for alpha preformation in nuclei

Measurements of continuous energy spectra and angular distributions of alpha particles emitted in proton, deuteron, $sup 3$He and alpha induced reactions were performed. An analysis using the preequilibrium model succeeds in giving an overall description of particle spectra. The alpha particle in this approach being considered as an exciton, a preformation factor around 0.2 for four nucleons to be correlated as an alpha particle is found. The alpha preformation probability deduced from this analysis is independent of the proton, deuteron $sup 3$He incident channel and target nucleus mass. (auth)