Reanalysis of the (J=5) state at592keV inTa180and its role in theν-process nucleosynthesis ofTa180in supernovae

Abstract

We analyze the production and freeze-out of the isomer $^{180}\mathrm{Ta}$${}^{m}$ in the $\ensuremath{\nu}$-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 $\mathcal{R}=0.39$ to $\mathcal{R}=0.38$, whereas previously it was estimated that this transition could reduce the ratio to $\mathcal{R}=0.18$. This finding strengthens the evidence that $^{138}\mathrm{La}$ and $^{180}\mathrm{Ta}$ are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of $\mathit{kT}\ensuremath{\approx}4$ MeV.