Evidence for Surface alpha Particle Clusters in (nat)AG(197)Au from the (e,alpha)Reaction

摘要

The (nat) Ag and (197) Au (e,p) and (e, alpha) energy and angular distributionswere measured at 6 electron bombarding energies between 50 and 115 MeV at the National Institute of Standards and Technology. The (nat) Ag and (197) Au (e,p) angular distributions exhibit an asymmetric component which increases from 0 to 50% as the proton energy increases from the proton Coulomb barrier to 26 MeV. The (nat) Ag and (197) Au (e, alpha) angular distributions exhibit an asymmetric component which increases from 0 to 30% as the alpha energy increases from the alpha particle Coulomb barrier to 26 MeV. The authors conclude that the asymmetric component of the proton and alpha particle yields are the result of direct or semidirect processes rather than resonance processes and hence, because of the short mean free paths of alpha particles in nuclear matter, give evidence for the existence of alpha particle clusters in the nuclear surface.