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The intrinsic reaction mechanism of proton-induced composite particle pre-equilibrium emission is well known to be a statistical multistep process. However, until recently it was still not clear how important the competition between pickup and knockout is to produce a composite ejectile in the multistep sequence. An evaluation of recent (p , α) results at incident energies from 65 to 160 MeV and on representative target nuclei is presented. The virtue of analyzing power angular distributions to unravel the details of the reaction mechanism is discussed and future possible avenues of investigation are explored. [ABSTRACT FROM AUTHOR]

The reaction mechanism of pre-equilibrium proton-induced α-particle emission from 93Nb at an incident energy of 100 MeV was investigated with polarized projectiles. A formalism based on the statistical multistep direct emission model of Feshbach, Kerman, and Koonin was found to give a reasonably good reproduction of cross section and analyzing power angular distributions at various emission energies. Existing experimental distributions for the same reaction at an incident energy of 65 MeV were also analyzed with the same model. The incident-energy variation from 65 MeV up to 160 MeV was found to be consistent with the predictions of the basic model. However, whereas knockout of an α cluster is the dominant reaction mechanism in the final stage at the lowest and highest incident energies, at 100 MeV a pickup process competes with comparable intensity in yield. [ABSTRACT FROM AUTHOR]