β-delayed neutron emission from r-process nuclei along the N=82 shell closure
Item statusRestricted Access
Embargo end date25/07/2021
Hall, Oscar Benjamin
The rapid-neutron capture process (r -process) is thought to be responsible for the production of around half the elements heavier than iron. Despite first being proposed almost six decades ago, the astrophysical site of the r-process remains an open question. The multi-messenger observation of gravitational waves originating from a binary neutron star merger (GW170817) and its electromagnetic counterpart provided evidence indicating that a possible r-process had occurred, providing a possible answer to this question. The accurate modelling of the nucleosynthesis processes taking place in such mergers requires precise nuclear input data, including nuclear masses, β-decay half-lives, and β-delayed neutron emission probabilities. A challenge here is that for the exotic neutron-rich nuclei that are of importance to the r-process, relatively few values are known experimentally. There is, therefore, high demand for experimental measurements along the r-process path which can be used as inputs in r-process calculations. In addition to being used as inputs in nucleosynthesis calculations, experimentally measured values act as reference points for the development of theoretical models in regions far from stability. This thesis presents the first measurement of the β-delayed neutron emission probabilities of 21 neutron-rich isotopes and improves upon the precision of a further four. In addition to this, measurements of the half-lives of 31 neutron-rich isotopes are presented. These neutron-rich isotopes are located along the N = 82 shell closure, a region that has been highlighted as being important in the production of the r-process A = 130 peak. These values, therefore, represent a significant contribution to the experimental data available for use in r-process calculations. The measurements were carried out at the Radioactive Ion Beam Factory in Japan, where the β-decays of neutron-rich ions were measured using the Advanced Implantation Detector Array in coincidence with their β-delayed neutrons that were measured using the BRIKEN neutron counter array.
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