Investigation of A=155 and A=151 nuclides: Identification of the 155Tm s1/2 isomer and of the 155Yb β-decay branch

The decay properties of 155Lu, 155Yb, 155Tm, and of the α-decay daughters 151Er and 151Ho were investigated following the on-line mass separation of A=155 nuclides produced in 64Zn irradiations of 95Mo. In the study, the half-life of the low-spin isomer in 155Lu was measured to be 140±20 ms, the β-decay branch of 155Yb was identified by observing daughter γ rays and Tm K x rays, and the existence in 155Tm of an s1/2 isomer (T1/2=44±4 s), in addition to the h11/2 ground state (T1/2=21.6±0.2 s) was established. Schemes for the β decays of 155Yb, 155Tm, and 151Er are proposed. New information on 151Er decay establishes the s1/2 isomer in 151Ho to be 41.1±0.2 keV above the h11/2 ground state. Also, branchings of 90±5, 28±7, and 80-20+15% were determined for the α decays of 155Yb, 151Ho, and 151Hom, respectively