Decay modes of the $9/2^-$ isomeric state in $^{183}$Tl

The internal transition decay and α decay of the $T_{1/2} = 53.3$ ms, $9/2^-$ isomeric state in the neutron-deficient isotope, $^{183}$Tl, have been studied using the Resonance Ionization Laser Ion Source and the Windmill detection setup at the ISOLDE facility at CERN. Clean samples of $^{183}$Tl 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 $^{183}$Tl → $^{179}$Au decay were deduced. This involves a 6058 keV $\alpha$-decay transition, which populates a previously unknown state in $^{179}$Au, 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 178Pt core.