Coulomb and nuclear effects in direct breakup of 54-MeV 7Li+12C, 197Au.

Abstract

Direct breakup of {sup 7}Li{r arrow}{alpha}+{ital t} was measured for 54-MeV {sup 7}Li+{sup 12}C, {sup 197}Au reactions. The breakup products were detected in coincidence using a close-geometry detection system, and small scattering angles forward of grazing, were investigated. The direct-breakup cross sections for {sup 12}C ({sup 7}Li, {alpha}{ital t}){sup 12}C{sub g.s.} exhibit significant enhancements beyond predictions of simple {ital E}1 Coulomb-breakup calculations, indicating the importance of the nuclear field. Direct-breakup yields in {sup 197}Au({sup 7}Li,{alpha}{ital t}) quasielastic reactions are sensitive to detector geometry, with the asymptotic fragment energies exhibiting target-proximity effects. Three-body classical trajectory calculations are found to provide qualitative agreement with these observations, provided the projectile is treated as an extended object. These strong Coulomb and nuclear effects severely complicate the extraction of radiative-capture cross sections and low-energy astrophysical {ital S} factors.