Orbital electron capture of stored H-like ions

The accelerator facility of GSI Darmstadt with the heavy ion synchrotron SIS coupled via the projectile fragment separator FRS to the experimental storage ring ESR offers the unique opportunity to study the beta decay of highly ionized atoms. It is possible to produce, separate, and store for extended periods of time exotic nuclei with a well-defined number of bound electrons. Basic nuclear properties such as masses and lifetimes are measured by applying the mass- and time-resolved Schottky Mass Spectrometry (SMS). The change of the mass in a radioactive decay is evidenced by a corresponding correlated change of the revolution frequency. The area of the Schottky frequency peak is proportional to the number of stored ions and to the square of the atomic charge state, q2. This allows us to precisely determine the fate of each stored ion. In this contribution we discuss experiments performed at the FRS-ESR on orbital electron capture (EC) decay of hydrogen-like 140Pr, 142Pm, and 122I ions. Decay events accounting for nuclear electron capture processes have been unambiguously identified and the time between production and decay has been measured. The obtained results show a significant deviation from the expected exponential decay. The interpretation of this effect is widely disputed in literature and is discussed. The status of the data analysis, and future perspectives are outlined.