Mass measurements of neutron-rich Rb and Sr isotopes

We report on the mass measurements of several neutron-rich Rb and Sr isotopes in the A≈100 region with the TITAN Penning-trap mass spectrometer. By using highly charged ions in the charge state q=10+, the masses of Rb98,99 and Sr98–100 have been determined with a precision of 6–12 keV, making their uncertainty negligible for r-process nucleosynthesis network calculations. The mass of Sr101 has been determined directly for the first time with a precision eight times higher than the previous indirect measurement and a deviation of 3σ when compared to the Atomic Mass Evaluation. We also confirm the mass of Rb100 from a previous measurement. Furthermore, our data indicate the existence of a low-lying isomer with 80keV excitation energy in Rb98. We show that our updated mass values lead to minor changes in the r process by calculating fractional abundances in the A≈100 region of the nuclear chart.