Experiments with relativistic exotic nuclei at the FRS-ESR facilities

Abstract

The status and the upgrade of the secondary nuclear beam facility FRS at GSI are outlined. Besides its main task to provide monoisotopic spatially separated fragment beams, the FRS has been successfully used as a high-resolution energy-loss spectrometer. Precise momentum measurements contribute to the study of neutron-halo nuclei and lead to the identification of the extended proton distribution in the 8B nucleus. First experiments with stored radioactive beams on direct mass and lifetime measurements of fully ionized atoms are presented. Measurements were performed with relativistic Ni, Au, and Bi projectile fragments separated by the FRS and injected into the storage-cooler ring ESR. For the first time the mass difference of ground and isomeric states for cooled secondary beams has been measured. About 37 new masses have been measured for a large region of elements 52≤Z≤85 using Schottky spectrometry. The accuracy was about (50 – 200) keV and the resolving power 4.7·10 5. Lifetimes of stored and cooled bare nuclei have been measured to study the influence of the atomic charge states on the β decay.