Decay of the 9/2- isomer in 181Tl and mass determination of low-lying states in 181Tl, 177Au, and 173Ir

A detailed spectroscopic study of the neutron-deficient isotope Tl-181 and the daughter of its alpha decay, Au-177, has been performed in the complete fusion reaction Ca-40+Sm-144 -> Pb-184(*) at the velocity filter SHIP (GSI). The mass excess, excitation energy, and decay scheme of the isomeric 1.40(3) ms, 9/2(-) intruder state in Tl-181 have been established for the first time. These results solve a long-standing puzzle of the unrealistically large reduced alpha-decay width of this isomer. Based on this, the previously unknown masses of the long-lived isomeric states in Au-177 and Ir-173 have been derived. In turn, it now allows the excitation energies of previously identified bands in Au-177 and Ir-173 to be deduced and compared with theoretical predictions. First measurements of alpha-decay branching ratios for Tl-181(m) and Au-177(m,g) are also reported.