On the β-Transition of 205T1 to 205Pb
Some first forbidden β-decays in nuclei near 208 Pb have low ft-values. The large matrix elements corresponding to these were interpreted long ago as due to purity of shell model configurations at the closed proton and neutron shells . On the basis of this information it was suggested to build a low energy neutrino detector . A neutrino with energy higher than 62 keV could be absorbed by 205 Tl nucleus in its 1/2+ ground state resulting in a 1/2- state, 2.3 keV above the 205 Pb ground state.