Be7(n,p)7Li

Abstract

The total 'Be(n, p)'Li cross section has been measured from 25 meV to 13.5 keV. These energies correspond to temperatures of T =2.9)& 10 ' to 0.16 GK. For thermal neutrons the cross sections to the ground state (po) and the first excited state (p, ) of 'Li are 38400+800 b and 4202120 b, respectively. This result for the total 'Be(n, p)'Li thermal cross section is about 25%%uo 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/u 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 threshold state and for a possible nearby 2 state. The astrophysical reaction rate, N~(nv ), was calculated from the measured cross sections for the combined po and pl transitions. The resulting reaction rate is approximately 60-80% of the rate currently in use. This reduction in the Be(n,p) Li reaction rate could result in a calculated increase in the production of 'Li during the big bang by as much as 20%.

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