​The chemical composition of certain stars is very close to the early universe. While their content in hydrogen and helium is in perfect concordance with theoretical predictions, their content in lithium (⁷Li, the most common stable isotope) is approximately three times smaller than expected. A team of researchers has been seeking to determine if this anomaly could be explained by a deficit in the precursor of this nucleus, a radioactive isotope of beryllium (⁷Be). To do so, they studied the capture of a neutron by ⁷Be, producing helium-4 and an α particle.

At a new experimental area of CERN, the neutron Time-Of-Flight (n_TOF) collaboration bombarded a sample of ⁷Be with neutrons and measured the neutron capture rate by ⁷Be as a function of the energy of incident neutrons. Their results are consistent with the theory. The cosmological lithium anomaly therefore remains unsolved.

This work was achieved using a new neutron source, more intense than the preceding one, in partnership with INFN, Italy, and the Institute for Nuclear Physics at Université Paris Saclay (IPN), in particular. The beryllium-7 nuclei were produced by Institut Paul Scherrer, Switzerland.