Speaker
Description
$^{205}$Pb has been proposed as a cosmochronometer for the early solar system as it is only produced in the s-process and has a half-life of 17 My. This half-life can change dramatically in the stellar environment depending on the ionization stage of $^{205}$Pb and $^{205}$Tl and the thermal population of excited nuclear states. $^{205}$Pb has an excited 1/2$^-$ state at 2.3 keV that shortens its half-life by six orders of magnitude. On the other hand $^{205}$Pb can be produced by bound-state beta decay of highly ionized $^{205}$Tl. To reliably model the synthesis of $^{205}$Pb in AGB stars therefore requires a consistent treatment of both electron capture rates in $^{205}$Pb and bound-state beta decay rates in $^{205}$Tl for a wide range of temperatures and densities. Compared to previous work by Takahashi and Yokoi we could improve the rates by using an experimentally determined value for the bound-state beta decay of $^{205}$Tl that has been measured recently by the E121 collaboration at GSI. We also improved the description of the interaction between ions and plasma and used Dirac-Hartee-Fock calculations for the spectra and wave functions of the $^{205}$Pb and $^{205}$Tl ions.
Supported by the Deutsche Forschungsgemeinschaft – Project-ID 279384907 – SFB 1245.
