Reanalysis of the (J = 5) state at 592 keV in 180Ta and its role in the neutrino-process nucleosynthesis of 180Ta in supernovae

TL;DR

This study reevaluates the impact of a low-lying 592 keV state on the production of 180Ta in supernovae, finding its effect is minimal and supporting the neutrino-process origin of 180Ta and 138La.

Contribution

It provides a more accurate estimate of the transition width for the 592 keV state, refining the understanding of 180Ta nucleosynthesis in supernovae.

Findings

The 592 keV state causes only a slight reduction in the isomer population ratio.

The revised ratio is R=0.38, close to previous estimates, not the more drastic reduction previously suggested.

Supports the coproduction of 180Ta and 138La via neutrino nucleosynthesis with kT~4 MeV.

Abstract

We analyze the production and freeze-out of the isomer 180Tam in the neutrino-process. We consider the influence of a possible low-lying intermediate (J = 5) state at 592 keV using a transition width estimated from the measured half-life. This more realistic width is much smaller than the previous estimate.We find that the 592-keV state leads only to a small reduction of the residual isomer population ratio from the previous result; that is, considering this better estimate for the transition width, the isomer population ratio changes from R = 0.39 to R = 0.38, whereas previously it was estimated that this transition could reduce the ratio to R = 0.18. This finding strengthens the evidence that 138La and 180Ta are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of kT~4 MeV.