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

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.

10 pages, 7 figures