Impact of Newly Measured β-Delayed Neutron Emitters around 78Ni on Light Element Nucleosynthesis in the Neutrino Wind Following a Neutron Star Merger

Abstract

<p>Neutron emission probabilities and half-lives of 37 β-delayed neutron emitters from 75Ni to 92Br were<br>measured at the RIKEN Nishina Center in Japan, including 11 one-neutron and 13 two-neutron emission<br>probabilities and six half-lives for the first time that supersede theoretical estimates. These nuclei lie in the<br>path of the weak r process occurring in neutrino-driven winds from the accretion disk formed after the<br>merger of two neutron stars synthesizing elements in the A ∼ 80 abundance peak. The presence of such<br>elements dominates the accompanying kilonova emission over the first few days and have been identified in the AT2017gfo event, associated to the gravitational wave detection GW170817. Abundance calculations<br>based on over 17 000 simulated trajectories describing the evolution of matter properties in the merger<br>outflows show that the new data lead to an increase of 50%–70% in the abundance of Y, Zr, Nb, and Mo.<br>This enhancement is large compared to the scatter of relative abundances observed in old very metal poor<br>stars and thus is significant in the comparison with other possible astrophysical processes contributing to<br>the light-element production. These results underline the importance of including experimental decay data<br>for very neutron-rich β-delayed neutron emitters into r-process models.<br></p>