Kinematically complete study of the 7Li(p, gamma )8Be*-->2 alpha reaction at Ep=25 MeV.

Abstract

A kinematically complete study of the $^{7}\mathrm{Li}$(p,\ensuremath{\gamma}${)}^{8}$${\mathrm{Be}}^{\mathrm{*}}$\ensuremath{\rightarrow}2\ensuremath{\alpha} reaction at ${\mathit{E}}_{\mathit{p}}$=25 MeV is described. An upper limit of d\ensuremath{\sigma}/d\ensuremath{\Omega}0.04 \ensuremath{\mu}b ${\mathrm{sr}}^{\mathrm{\ensuremath{-}}1}$ is reported for the ${\mathrm{\ensuremath{\theta}}}_{\ensuremath{\gamma}}$=90\ifmmode^\circ\else\textdegree\fi{} capture cross section to the ${2}^{+}$ states at 16.62 and 16.93 MeV, which is five times smaller than published results. This new datum is shown to be more consistent with a semidirect reaction mechanism involving the giant dipole resonance built on the $^{8}\mathrm{Be}^{\mathrm{*}}$ 2.94-MeV state than the previously proposed direct reaction mechanism.