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

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.