Probing the N=104 midshell region for the r process via precision mass spectrometry of neutron-rich rare-earth isotopes with the JYFLTRAP double Penning trap

TL;DR

This study provides high-precision mass measurements of neutron-rich rare-earth isotopes near N=104, refining r-process models and revealing differences from previous mass evaluations, with implications for astrophysical nucleosynthesis.

Contribution

First high-precision mass measurements of several neutron-rich rare-earth isotopes near N=104, improving constraints on r-process nucleosynthesis models.

Findings

New mass values for $^{169}$Tb, $^{170}$Dy, $^{171}$Dy, $^{169}$Dy, and $^{169-171}$Ho.

Resolved isomeric states in $^{170}$Ho with excitation energy 150.8 keV.

Updated r-process abundance calculations showing a steeper minimum at A=170, differing by 15-30% from previous models.

Abstract

We have performed high-precision mass measurements of neutron-rich rare-earth Tb, Dy and Ho isotopes using the Phase-Imaging Ion-Cyclotron-Resonance technique at the JYFLTRAP double Penning trap. We report on the first experimentally determined mass values for $^{169}$Tb, $^{170}$Dy and $^{171}$Dy, as well as the first high-precision mass measurements of $^{169}$Dy and $^{169\text{-}171}$Ho. For $^{170}$Ho, the two long-lived ground and isomeric states were resolved and their mass measured, yielding an isomer excitation energy of $E_\text{exc}=150.8(54)$~keV. In addition, we have performed independent crosschecks of previous Penning-trap values obtained for $^{167\text{,} 168}$Tb and $^{167\text{,} 168}$Dy. We have extended the systematics of two-neutron separation energies to the neutron midshell at $N=104$ in all of the studied isotopic chains. Our updated and new mass measurements provide better mass-related constraints for the neutron-capture reaction rates relevant to the astrophysical rapid neutron capture (r) process. The r-process abundances calculated with the new mass values seem to produce a steeper minimum at A=170 and differ by around 15-30\% from the abundances computed with the Atomic Mass Evaluation 2020 values.