Observation of Bound-State ${\mathit{\beta }}^{-}$ Decay of Fully Ionized ${}^{187}$Re: ${}^{187}$Re${-}^{187}$Os Cosmochronometry

We observed the bound-state ${\beta }^{-}$ decay of fully ionized ${}^{187}$Re nuclei circulating in a storage ring. With two independent methods the time dependent growth of hydrogenlike ${}^{187}$Os ions has been measured and a half-life of $32.9\pm 2.0\mathrm{yr}$ for bare ${}^{187}$Re nuclei could be determined, to be compared with 42 Gyr for neutral ${}^{187}$Re atoms. With the resulting $\log \mathrm{ft}$ value of $7.87\pm 0.03$ the half-life of ${}^{187}$Re ions in any ionization state can be calculated. Thus one can correct the ${}^{187}$Re${-}^{187}$Os galactic chronometer calibration, by taking account of the ${\beta }^{-}$ decay enhancement in stellar interiors, which will lead to a more accurate estimate of the galactic age.