Astrophysical reaction rate for the ⁸Li(n, γ)⁹Li reaction

An attempt was made to measure the excitation function of the cross section for the ⁸Li(n, γ)⁹Li reaction by performing the inverse reaction ⁹Li(γ,n)⁸Li, with the equivalent photons in the electric field of nuclei in a Pb target providing the γ rays for the reaction. The energy spectrum of lithium nuclei in coincidence with neutrons had no discernible peak where any beam-velocity ⁸Li's would be located. Statistically, a Gaussian-shaped ⁸Li peak could have been present with 30±29 counts, which we interpreted as consistent with zero, with a two-standard-deviation upper limit of 87 counts. Using the fact that neutron capture on ⁸Li must be dominantly s-wave capture, and applying detailed balance, we obtained, with E in eV, σ_{n, γ}<930E^-1/2 μb. The corresponding limit on the astrophysical reaction rate is <790 cm³ mol^-1 s^-1. Theoretical predictions of the reaction rate have exceeded our upper limit by factors of 3-50.