Alpha capture into the giant quadrupole resonance inSi28

Abstract

Angular distributions have been studied in the $^{24}\mathrm{Mg}(\ensuremath{\alpha}, {\ensuremath{\gamma}}_{0})^{28}\mathrm{Si}$ reaction in fine energy steps for excitation energies $14\ensuremath{\lesssim}{E}_{x}\ensuremath{\lesssim}22$ MeV. Absolute cross sections were determined with errors smaller than 10% and were found to be substantially lower than previously determined. A total $E2$ strength of (3.7\ifmmode\pm\else\textpm\fi{}0.4)% of the energy weighted sum rule was observed, in good agreement with results obtained from ($\ensuremath{\alpha}, {\ensuremath{\alpha}}^{\ensuremath{'}}{\ensuremath{\alpha}}_{0}$) coincidence experiments. Strong interference effects as well as other deviations from statistical model expectations are interpreted as due to nonstatistical preequilibrium effects in both $E1$ and $E2$ channels.NUCLEAR REACTIONS $^{24}\mathrm{Mg}(\ensuremath{\alpha}, {\ensuremath{\gamma}}_{0})^{28}\mathrm{Si}$, $E=4.3\ensuremath{-}14.0$ MeV; measured $\ensuremath{\sigma}(E, {E}_{\ensuremath{\gamma}}, {\ensuremath{\theta}}_{\ensuremath{\gamma}})$. $^{28}\mathrm{Si}$ deduced $E1$, $E2$ strengths. Enriched target. Compared decay strengths with Hauser-Feshbach estimates, including effects of isospin.