Observation of bound-state β- decay of bare 187Re using magnetic analysis

We observed the bound-state beta- decay of fully ionized Re-187-nuclei circulating in the experimental storage ring ESR at GSI. Re-187 ions were accelerated in the GSI accelerator complex to a final energy of 347 MeV/u, fully stripped and injected into the ESR. During storage times of up to four hours, several hundred Os-187(75+) ions were produced via bound-state beta- decay of Re-187(75+) ions and circulating on almost the same orbit. To separate the Os-187 ions from their mother nuclei, an internal Ar gas jet target was used to strip off the last electron and produce Os-187(76+). AS a result Of the higher charge state the Os-187 ions now were stronger deflected by the following dipole magnet, and detected in a position sensitive microstrip-gas-counter. The determined half-life is T-1/2 = 31.2(-2.5)(+3.0) yr. With the now measured Re-187 half-life the Re-187/Os-187 cosmochronometer can be recalibrated. By taking into account the beta(-) decay enhancement in stellar interiors, this 'clock' will lead to a more accurate estimation of the Galactic age.