On the β-decaying (21+) spin gap isomer in 94Ag Original Research Article

The β decay of 94Ag, a nucleus with three proton and three neutron holes with respect to 100Sn, was investigated at the GSI on-line mass separator by using an array of germanium and silicon detectors. On the basis of a βγγ coincidence measurement, the previously reported decay scheme has been considerably improved and evidence is presented for a spin–gap isomer with a spin-parity assignment of (21+), i.e., the highest spin ever observed in β decay. The half-life of the low-spin isomer (7+) was remeasured to be 0.59(2) s, whereas the half-life of the high-spin isomer was determined as 0.47(8) s. For the states in 94Ag and 94Pd, large-scale shell-model calculations that include up to 4p–4h excitations across the N=Z=50 shell gap and employ a realistic interaction were carried out. These core excitations play a crucial role in generating the E4 isomerism required for the interpretation of the long half-life of the (21+) state in 94Ag.