Exploration for Astromers near $^{132}$Sn with the Canadian Penning Trap

TL;DR

This work uses the Canadian Penning Trap at CARIBU to perform high-precision mass measurements of ground and isomeric states near $^{132}$Sn, extracting excitation energies $E_x$ for $^{129}$Sn, $^{131}$Sn, and $^{132}$Sb. The authors integrate these masses into the PRISM astrophysical network to evaluate how isomer populations and thermalization temperatures $T_{ ext{th}}$ affect neutron-capture rates in $i$- and $r$-process environments, finding that $^{129m}$Sn behaves as an astromer in both processes while $^{131m}$Sn and $^{132m}$Sb do not. The results refine the treatment of astromers in reaction networks and highlight the need for spectroscopy of higher-lying states to better constrain feeding and depopulation pathways. Overall, the precise mass determinations substantially improve the accuracy of nucleosynthesis models in neutron-rich, near-$^{132}$Sn nuclei.

Abstract

Nuclear isomers can have significant impacts on astrophysical nucleosynthesis processes, with recent efforts demonstrating that the population of isomeric states with different half-lives may require separate treatment in reaction networks to accurately capture the differences in heating or in identifiable electromagnetic signals. Several potential so-called ``astromers'' in tin and antimony isotopes near doubly-magic $^{132}$Sn were identified and direct mass measurements of their ground and isomeric states were performed with the Canadian Penning Trap at Argonne National Laboratory's CARIBU facility, and their impact on astrophysical reaction rates and in reaction networks calculated. It was found that $^{129g,m}$Sn, with measured mass excesses of $-80 593.2(25)$ keV and $-80 557.4(25)$ keV, respectively, and an excitation energy of $35.8(35)$ keV, behaves as an astromer during neutron capture in the $i$-process and in the $r$-process.

Figures (7)

• Figure 1: A histogram of detected ion locations for a sample $^{129g}\text{Sn}^+$ final phase measurement with phase accumulation time $t_{\text{acc}}=450.894$ ms. The locations of the four species captured in the trap, which separate due to differing mass-based phase accumulations, are labeled.
• Figure 2: Measured $\nu_c$ values for $^{129m}\text{Sn}^+$ at eight distinct $t_{\text{acc}}$ values between 450.019 ms and 451.022 ms. The dashed line represents a fit of the model described in Ref. Orford20 to the data, and the solid line and bar the true $\bar{\nu}_c$.
• Figure 3: Astromer diagram for $^{129}$Sn. The solid line indicates transition from the ground state to isomeric state and the dotted line indicates the reverse. Rates of $\beta$-decay for the two states are shown with dashed lines. With present data the $\beta$ decay thermalization temperature, indicated by the vertical grey dashed line, is estimated to be 30 keV, below which the nucleus may need to be treated as two separate species in astrophysical reaction networks.
• Figure 4: Astromer diagram for $^{132}$Sb. Lines are the same as in Fig. \ref{['fig:129Sn']}. With present data the $\beta$-decay thermalization temperature is estimated to be 15 keV, below which the nucleus may need to be treated as two separate species in astrophysical reaction networks.
• Figure 5: Astromer diagram for $^{131}$Sn. Lines are the same as in previous two figures. With present data the $\beta$-decay thermalization temperature is estimated to be 77 keV, below which the nucleus may need to be treated as two separate species in astrophysical reaction networks.