Be7(n,p)7Li total cross section from 25 meV to 13.5 keV

The total ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(n,p${)}^7$Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T=2.9×${10}^{\mathrm{-}7}$ to 0.16 GK. For thermal neutrons the cross sections to the ground state ($p_0$) and the first excited state (${\mathit{p}}_1$) of ${}_{}{}^7{}_{}{}^{}\mathrm{BLi}$ are 38 400±800 b and 420±120 b, respectively. This result for the total ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(n,p${)}^7$Li thermal cross section is about 25% lower, and is approximately a factor of 10 more precise than previous published measurements. For energies above 100 eV, a significant departure from a 1/v shape for the total cross section is observed. The data were analyzed using a single-level approximation, and were also analyzed together with other data using multilevel-multichannel R-matrix theory. Results are presented for the properties of the $2^{\mathrm{-}}$ threshold state and for a possible nearby $2^{\mathrm{-}}$ state. The astrophysical reaction rate, $N_A$〈σv〉, was calculated from the measured cross sections for the combined $p_0$ and $p_1$ transitions. The resulting reaction rate is approximately 60–80 % of the rate currently in use. This reduction in the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}$(n,p${)}^7$Li reaction rate could result in a calculated increase in the production of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ during the big bang by as much as 20%.