Direct measurement of the 4.6 MeV isomer in stored bare 133Sb ions

Abstract The core-excited isomer in fully-ionized 133 Sb has been directly studied for the first time by applying the novel technique of isochronousmass spectrometry at GSI. The neutron-rich nuclidesin high charge states were produced by projectile fission of 411 MeV A 238 U ions, separated in flight by the fragment separator (FRS) and stored in the isochronous storage ring(ESR). The measured excitation energy is 4.56(10) MeV. The neutral-atom half-lifeis known to be 17 μs. This is the shortest-lived isomer measured directly with mass spectrometry techniques. The extended in-flight half-lifeof the bare ions in the ESR, which is due to the exclusion of the strong internal conversion, demonstrates that there should be another nuclear level above that identified from isomer-decay spectroscopy, in support of shell-model calculations. This measurement opens up a new half-lifedomain for storage-ringmeasurements.