Fission isomer studies with the FRS

Abstract

The ‘island’ of fission isomers identified in the actinide region (Z = 92 - 97, N = 141- 151) originates from multi-humped fission barriers, which can be described as the result of superimposing microscopic shell corrections to the macroscopic liquid drop barrier. For the first time, populating fission isomers by using the fragmentation of 1 GeV/u $^{238}$U projectiles was tried rather than light particle induced reactions so far in use. Projectile fragmentation gives access to isotopes that are hard or impossible to reach by light particle reactions. In-flight separation with the fragment separator FRS allows to study fission isomers with half-lives as short as 100 ns. Most importantly, it provides beams with high purity and enables an event-by-event identification. Different detection methods, such as decay and mass spectrometry, have been used in the experiment to search for fission isomers within a half-live from 100 ns to 50 ms. The experiment to study fission isomers with the FRS at GSI has been performed within the framework of FAIR Phase-0.