Experimental determination of the resonance width and the branching ratio Γp1/Γp0 for the 19.40-MeV state in Be8 for studying the Be7(n,p1)Li*7 reaction relevant to the cosmological lithium problem

Abstract

The $^{7}\mathrm{Li}(^{3}\mathrm{He},d)^{8}\mathrm{Be}^{*}(p)^{7}\mathrm{Li}$ reaction was measured at ${E}_{\mathrm{lab}}(^{3}\mathrm{He})=28$ MeV for studying the $^{7}\mathrm{Be}(n,{p}_{1})^{7}\mathrm{Li}^{*}$ reaction, which is a $^{7}\mathrm{Be}$ destruction reaction in the big bang nucleosynthesis. Resonant states at 18.9--20.1 MeV in $^{8}\mathrm{Be}$ were populated by the $^{7}\mathrm{Li}(^{3}\mathrm{He},d)^{8}\mathrm{Be}^{*}$ reaction and decay protons to the ground (${p}_{0}$) and first-excited states (${p}_{1}$) in $^{7}\mathrm{Li}$ were well separated and measured. The resonance width $\mathrm{\ensuremath{\Gamma}}$ and branching ratio ${\mathrm{\ensuremath{\Gamma}}}_{p1}/{\mathrm{\ensuremath{\Gamma}}}_{p0}$ for the 19.40-MeV state in $^{8}\mathrm{Be}$ were deduced to be $342\ifmmode\pm\else\textpm\fi{}112$ keV and $11.2\ifmmode\pm\else\textpm\fi{}3.5\ifmmode\pm\else\textpm\fi{}5.0$ (syst.)%, respectively. The $^{7}\mathrm{Be}(n,{p}_{1})^{7}\mathrm{Li}^{*}$ reaction cross section was deduced.