$^{7}$Be(n,p)$^{7}$Li Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN

We report on the measurement of the $^{7}$Be(n, p)$^{7}$Li cross section from thermal to approximately 325 keV
neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This
reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard
cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover
the energy window of interest for BBN, and they showed a large discrepancy between each other. The
measurement was performed with a Si telescope and a high-purity sample produced by implantation of a
7Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low
energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with
the values inferred from the time-reversal $^{7}$Li(p, n)$^{7}$Be reaction, thus yielding only a relatively minor
improvement on the so-called cosmological lithium problem. The relevance of these results on the nearthreshold
neutron production in the p + $^{7}$Li reaction is also discussed.