Two-body beta decay of stored few-electron ions

The combination of the projectile fragment separator FRS and the cooler-storage ring ESR at the accelerator facility of GSI Darmstadt offers the unique opportunity to study beta decay of stored highly-charged ions. Basic nuclear properties such as masses and half-lives are measured by applying the mass- and time-resolved Schottky Mass Spectrometry (SMS). The relative mass-to-charge ratio is directly correlated to the relative revolution frequency. The SMS is sensitive to single stored ions and the decay of each stored ion can be precisely determine by steady monitoring of the corresponding revolution frequencies. On this basis the single particle decay-spectroscopy has been developed which allows for an unambiguous time-resolved and background-free identification of a certain decay branch. In this contribution we discuss experiments on the orbital electron capture (EC) of radioactive ions in the ESR. Fully ionized, hydrogen- and helium-like 140Pr and 142Pm ions have been selected for these studies. These nuclei decay to stable daughter nuclei via either the three-body β + - or the two-body EC-decay by a single allowed Gamow–Teller (1 +  →0 + ) transition.