Speaker
Description
Bound-state β−-decay is a rare radioactive process where the created electron is trapped in an atomic orbital instead of being emitted. It can be observed in highly ionized atoms in particular when normal beta-decay is energetically forbidden, but bound-state decay is still possible. An extremely challenging measurement of the bound-state $\beta^-$ decay of the fully ionized $^{205}$Tl was conducted at GSI using storage ring measurement$^1$. The decay rate is observed as $2.76(25)_{\rm stat}(13)_{\rm syst} \times 10^{-8} {\rm s^{-1}}$, which corresponds to a half-life of 291(+33-27) days and a log$ft$ = 5.91(5). The relevant transitions involve first-forbidden $\beta^-$ decays, including both unique and non-unique transitions. These transitions are significantly more challenging to describe theoretically than allowed decays because their decay rates depend sensitively on nuclear matrix elements and on the detailed structure of the shape factors. Reliable predictions therefore, require a microscopic treatment of nuclear structure combined with a consistent description of the lepton phase space and bound-electron wave functions.
We investigate the $\beta_b$ decay rate of $^{205}$Tl using a theoretical framework analogous to that employed for electron capture, treating the process as the time-reversed analogue of electron capture. The nuclear matrix element is evaluated employing the nuclear shell model configuration interaction approach with a refined effective interaction. We obtain a good agreement between the measured and calculated half-life for $^{205}$Tl. The developed framework can be extended to additional isotopes and higher-order forbidden transitions, contributing to more precise modeling of weak-interaction processes under extreme conditions.
1. G. Leckenby et al., Nature 635, 321 (2024)
| Contribution category | Theory |
|---|---|
| Presenter status | Postdoc |