<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math>-delayed fission of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow/><mml:mn>180</mml:mn></mml:msup></mml:math>Tl

The detailed analysis of the $\ensuremath{\beta}$-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 $\ensuremath{\beta}$ 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 $\ensuremath{\beta}$-delayed fission probability ${P}_{\ensuremath{\beta}\text{DF}}{(}^{180}\text{Tl})\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}3.2(2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}%$ was deduced.