Effect of final-state interactions in allowed β decays. II. Reliability of the β-decay spectrum forT2

The final-state distribution of ${\mathrm{HeT}}^{+}$ resulting from the β decay of molecular tritium has been investigated with particular emphasis on its reliability in connection with the interpretation of the tritium neutrino-mass experiments. This investigation concentrates on two aspects. First, the reliability within the sudden approximation is examined. This includes the extension of previously calculated final-state distributions to a larger range of energy transfer, i.e., to an excitation energy of 800 eV, the investigation of the effect of nuclear motion on the continuous electronic spectrum, and the use of improved basis sets. Second, the molecular transition-probability spectrum (including electronic bound and continuous states) has been calculated for the first time in a beyond sudden-impulse approximation. It is concluded that the concomitant corrections are too small to explain the problems of recent experiments difficulties to extract the neutrino mass out of the β spectrum of ${\mathrm{T}}_2.$