(p, α) Reactions inLi7,Be9, andC12at 15.0-18.6 MeV

Abstract

Angular distributions of alpha particles from the ${\mathrm{Li}}^7(p, \alpha ){\mathrm{He}}^4$ reaction were measured at bombarding energies of 15.0 and 18.6 MeV, and ${\mathrm{Be}}^9(p, \alpha ){\mathrm{Li}}^6$ and ${\mathrm{C}}^{12}(p, \alpha ){\mathrm{B}}^9$ angular distributions were each measured at 15.6 and 18.6 MeV. Absolute cross sections were measured for all of the reactions. The main features of the ${\mathrm{Li}}^7(p, \alpha ){\mathrm{He}}^4$ angular distributions, which are symmetric about 90 deg, can be reproduced by the appropriately symmetrized triton pickup theory. The ${\mathrm{Be}}^9(p, \alpha ){\mathrm{Li}}^6$ ground state and ${\mathrm{Be}}^9(p, \alpha ){\mathrm{Li}}^{6*}$ (2.2 MeV) reactions exhibit backward peaking which suggests a possible contribution from heavy particle stripping. The ${\mathrm{C}}^{12}(p, \alpha ){\mathrm{B}}^9$ angular distributions are oscillatory but cannot be fitted satisfactorily using the plane wave triton pickup or knock-on theories. The oscillations in the ${\mathrm{Li}}^7(p, \alpha ){\mathrm{He}}^4$ and ${\mathrm{C}}^{12}(p, \alpha ){\mathrm{B}}^9$ angular distributions do not shift in angle as the bombarding energy is changed, so that the value used for the interaction radius must be decreased as the proton energy is raised. None of the angular distributions are strongly energy dependent, and all of the cross sections decrease with increasing bombarding energy.