Mass Measurements of Neutron-Deficient Y, Zr, and Nb Isotopes and Their Impact on $rp$ and $\nu p$ Nucleosynthesis Processes

TL;DR

This study measured the masses of specific neutron-deficient isotopes using advanced spectrometry, providing more accurate data that impacts models of nucleosynthesis processes like the rp- and νp-processes.

Contribution

First-time mass measurements of $^{82}$Zr and $^{84}$Nb, and refined masses of $^{79}$Y, $^{81}$Zr, and $^{83}$Nb, clarifying nuclear properties relevant to astrophysical processes.

Findings

New masses of $^{82}$Zr and $^{84}$Nb measured with ~10 keV uncertainty.

Refined masses of $^{79}$Y, $^{81}$Zr, and $^{83}$Nb differ from previous values.

Results suggest the Zr-Nb cycle in the rp-process is unlikely, affecting nucleosynthesis models.

Abstract

Using isochronous mass spectrometry at the experimental storage ring CSRe in Lanzhou, the masses of $^{82}$Zr and $^{84}$Nb were measured for the first time with an uncertainty of $\sim 10$ keV, and the masses of $^{79}$Y, $^{81}$Zr, and $^{83}$Nb were re-determined with a higher precision. %The latter differ significantly from their literature values. The latter are significantly less bound than their literature values. Our new and accurate masses remove the irregularities of the mass surface in this region of the nuclear chart. Our results do not support the predicted island of pronounced low $\alpha$ separation energies for neutron-deficient Mo and Tc isotopes, making the formation of Zr-Nb cycle in the $rp$-process unlikely. The new proton separation energy of $^{83}$Nb was determined to be 490(400)~keV smaller than that in the Atomic Mass Evaluation 2012. This partly removes the overproduction of the $p$-nucleus $^{84}$Sr relative to the neutron-deficient molybdenum isotopes in the previous $\nu p$-process simulations.