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

Abstract

We observed the bound-state β − decay of fully ionized 187Re-nuclei circulating in the experimental storage ring ESR at GSI. 187Re 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 187Os 75+ ions were produced via bound-state β − decay of 187Re 75+ ions and circulating on almost the same orbit. To separate the 187Os ions from their mother nuclei, an internal Ar gas jet target was used to strip off the last electron and produce 187Os 76+. As a result of the higher charge state the 187Os 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 187Re half-life the 187 Re 187 Os cosmochronometer can be recalibrated. By taking into account the β − decay enhancement in stellar interiors, this ‘clock’ will lead to a more accurate estimation of the Galactic age.