Decay modes of the 9/2(-) isomeric state in Tl-183

The internal transition decay and alpha decay of the T-1/2 = 53.3 ms, 9/2(-) isomeric state in the neutron-deficient isotope, Tl-183, have been studied using the Resonance Ionization Laser Ion Source and the Windmill detection setup at the ISOLDE facility at CERN. Clean samples of Tl-183m were produced by selective laser ionization and subsequent mass separation. An internal transition cascade of 356.5-272.2 keV gamma rays has been identified. Multipolarities of these transitions have been determined by means of simultaneous gamma-ray and conversion- electron spectroscopy. Improved data for the fine structure of the Tl-183m -> 179 Au decay were deduced. This involves a 6058 keV alpha-decay transition, which populates a previously unknown state in Au-179, that is tentatively assigned as a (9/2(-)). It is interpreted as a coupling of the 1h(9/2) proton-intruder with the excited 0(+) state in the Pt-178 core.