The stellar beta-decay rate of 134Cs and its impact on the Barium nucleosynthesis in the s process

TL;DR

This study calculates a new stellar beta-decay rate for 134Cs using advanced shell model methods, significantly impacting barium nucleosynthesis predictions in the s process and aligning with meteoritic data.

Contribution

The paper introduces a more accurate beta-decay rate for 134Cs based on shell model calculations, revising previous estimates and improving nucleosynthesis models.

Findings

New decay rate is ten times lower than previous estimates at s-process temperatures.

Revised rate explains meteoritic Ba isotope ratios without invoking the i process.

Suggests a minimum of 28 million years elapsed since the last AGB event polluting the early Solar System.

Abstract

We have calculated the stellar $\beta$-decay rate of the important s-process branching point ${}^{134}$Cs based on the state of the art shell model calculations. At typical $s$-process temperatures ($T\sim$ 0.2-0.3 GK), our new rate is one order of magnitude lower than the widely-used rate from Takahashi and Yokoi (hereafter TY87). The impact on the nucleosynthesis in AGB stars is investigated with various masses and metallicities. Our new decay rate leads to an overall decrease in the ${}^{134}$Ba/${}^{136}$Ba ratio, and well explains the measured ratio in meteorities without introducing the $i$ process. We also derive the elapsed time from the last AGB nucleosynthetic event that polluted the early Solar System to be $>$28 Myr based on the ${}^{135}$Cs/${}^{133}$Cs ratio, which is consistent with the elapsed times derived from ${}^{107}$Pd and ${}^{182}$Hf. The $s$-process abundance sum of ${}^{135}$Ba and ${}^{135}$Cs is found to increase, resulting in a smaller $r$-process contribution of ${}^{135}$Ba in the Solar System.