Experimental study of the \nΓp1/Γp0\n ratios of resonance states in \nBe8\n for deducing the \nBe7(n,p1)Li*7\n reaction rate relevant to the cosmological lithium problem

Abstract

The $^{9}\\mathrm{Be}(^{3}\\mathrm{He},\\ensuremath{\\alpha})^{8}\\mathrm{Be}^{*}(p)^{7}\\mathrm{Li}$ reaction was studied at ${E}_{\\mathrm{lab}}{(}^{3}\\mathrm{He})=30$ MeV to deduce the branching ratios of ${\\mathrm{\\ensuremath{\\Gamma}}}_{p1}$/${\\mathrm{\\ensuremath{\\Gamma}}}_{p0}$ of resonant states at 18.91--20.1MeV in $^{8}\\mathrm{Be}$, which are necessary to extract the $^{7}\\mathrm{Be}(n,{p}_{1})^{7}\\mathrm{Li}^{*}$ reaction rate relevant to the $^{7}\\mathrm{Be}$ destruction in the big bang nucleosynthesis, from the $^{7}\\mathrm{Li}(p,{n}_{0})^{7}\\mathrm{Be}$ reaction cross section. The decay protons from $^{8}\\mathrm{Be}^{*}$ to the ground and first excited states in $^{7}\\mathrm{Li}$ were well-separately measured. The ${\\mathrm{\\ensuremath{\\Gamma}}}_{p1}$/${\\mathrm{\\ensuremath{\\Gamma}}}_{p0}$ ratio of the 19.235-MeV state was deduced to be $3.4\\ifmmode\\pm\\else\\textpm\\fi{}1.9$ %. The 19.86- and 20.1-MeV states were found to decay dominantly into the first excited and ground states of $^{7}\\mathrm{Li}$, respectively.