Mass measurements of neutron-rich Rb and Sr isotopes

TL;DR

This study provides precise mass measurements of neutron-rich Rb and Sr isotopes near A=100, improving data accuracy for r-process nucleosynthesis models and revealing a possible isomer in Rb-98.

Contribution

First direct measurement of Sr-101 mass with significantly improved precision and identification of a low-lying isomer in Rb-98.

Findings

Masses of Rb-98,99 and Sr-98-100 determined with 6-12 keV precision.

First direct measurement of Sr-101 mass, 8 times more precise.

Evidence of an 80 keV isomer in Rb-98.

Abstract

We report on the mass measurements of several neutron-rich $\mathrm{Rb}$ and $\mathrm{Sr}$ isotopes in the $A \approx 100$ region with the TITAN Penning-trap mass spectrometer. Using highly charged ions in the charge state $q=10+$, the masses of $^{98,99}\mathrm{Rb}$ and $^{98-100}\mathrm{Sr}$ have been determined with a precision of $6 - 12\ \mathrm{keV}$, making their uncertainty negligible for r-process nucleosynthesis network calculations. The mass of $^{101}\mathrm{Sr}$ has been determined directly for the first time with a precision eight times higher than the previous indirect measurement and a deviation of $3\sigma$ when compared to the Atomic Mass Evaluation. We also confirm the mass of $^{100}\mathrm{Rb}$ from a previous measurement. Furthermore, our data indicates the existance of a low-lying isomer with $80\ \mathrm{keV}$ excitation energy in $^{98}\mathrm{Rb}$. We show that our updated mass values lead to minor changes in the r-process by calculating fractional abundances in the $A\approx 100$ region of the nuclear chart.