Imaginary potential in resonating-group calculations for the α + α system

Abstract

Resonating-group calculations have been quite successful in describing the α + α system below the reaction threshold of 17.36 MeV (c.m.). In order to extend these calculations to energies above this threshold, a local, phenomenological, imaginary potential is introduced into the usual resonating-group formulation; the purpose being to account approximately for the influence of reactions on the elastic scattering. It is found that a simple, surface-peaked, imaginary potential with a strength which varies smoothly with energy is quite adequate to reproduce the imaginary parts of the experimentally determined α + α phase shifts from 25 to 60 MeV (c.m.). The introduction of such a potential is found to cause only a small change in the calculated real parts of the α + α phase shifts. The agreement of these calculated real phases with those determined from experiment is better below the reaction threshold than above it. A discussion is given of α + α effective potentials, and the influence of the imaginary potential on the real, effective potential is investigated.