Beta-Decay Experiment for Rapid Neutron-Capture Process Nucleosynthesis*

The rapid neutron capture process (r-process) is a nucleosynthesis process responsible for about half of the abundances of elements heavier than iron in the universe. Its astrophysical site is not uniquely identified. The observation of elemental abundances in halo stars shows a good agreement with solar system r-process abundances for Z≥52, but not for the lighter elements 38≤Z≤47. There might be another nucleosynthesis process, for example the weak r-process, which produces medium mass neutron-capture elements around Zr. The recently observed kilonovae after the detection of the neutron star merger event GW170817 provides strong evidence that this is a site of the r-process. However, we need more nuclear and astronomical data to identify the site of weak r-process. In this work, the β-decay half-lives and β-delayed neutron emission probability (P_n) of neutron-rich isotopes in the region of mass A = 100 have been measured. The experiment was performed in the Radioactive Ion Beam Factory (RIBF) at RIKEN in Japan, in 2017. Thanks to the state-of-the-art instrumentation of the β-delayed neutron detector at RIKEN (BRIKEN), we will be able to provide P_n values of very short-lived isotopes for the first time.