Mass measurements of neutron-rich A≈90 nuclei constrain element abundances

Abstract

Atomic masses of the neutron-rich isotopes 83,84Ga, 82–86Ge, 82–89As, 82,84–91Se, 85,86,89–92Br, 89,91,92Kr, and 91Rb have been measured with high precision and accuracy using the multi-reflection time-of-flight mass spectrograph at the RIBF facility. The masses of 88,89As were measured for the first time and the mass uncertainties of 86Ge and 90,91Se were significantly reduced from several hundred keV to below the 10 keV scale. Investigation of shell evolution and potential subshell closures are proceeded by analysis of two-neutron separation energy systematics. As a result of the precise mass measurements, no prominent change on the slope of the two-neutron separation energy beyond N=56 is observed in Se isotopes, indicating the subshell closure effect at N=56 of Se does not exist. Also, various leading mass models are compared with the measurements. The impact of the more precisely known data on r-process nucleosynthesis calculations is investigated in light of these new mass measurements, showing a remarkable reduction of reaction-rate uncertainties.