β-delayed fission of 180 Tl

The detailed analysis of the β-delayed fission data of 180 Tl is presented. The experiment was performed by producing a pure beam of 180 Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE (CERN, Geneva) isotope separator. A surprising asymmetric mass distribution of fission fragments from 180 Hg, the daughter of 180 Tl β decays, was observed. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments’ energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise β-delayed fission probability PβDF( 180 Tl) = 3.2(2) × 10 −3 % was deduced.