First Measurement of the g Factor in the Chiral Band: The Case of the Cs 128 Isomeric State

The g factor of the 56 ns half-life isomeric state in Cs128 has been measured using the time-differential perturbed angular distribution method. This state is the bandhead of the positive-parity chiral rotational band, which emerges when an unpaired proton, an unpaired neutron hole, and an even-even core are coupled such that their angular momentum vectors are aplanar (chiral configuration). g-factor measurements can give important information on the relative orientation of the three angular momentum vectors. The measured g factor g=+0.59(1) shows that there is an important contribution of the core rotation in the total angular momentum of the isomeric state. Moreover, a quantitative theoretical analysis supports the conclusion that the three angular momentum vectors lie almost in one plane, which suggests that the chiral configuration in Cs128 demonstrated in previous works by characteristic patterns of electromagnetic transitions appears only above some value of the total nuclear spin.