POSSIBILITY OF OBSERVING MASSIVE NEUTRINO ADMIXTURES IN NUCLEAR ORBITAL ELECTRON-CAPTURE RATES

The unusual case in nuclear orbital electron capture whereby either a neutrino in a weak interaction eigenstate or in a mass eigenstate is emitted by the same nucleus is examined. The case of the low-energy Q value nuclear electron capture decays is considered where, for at least one electronic shell, the emission of a weak eigenstate neutrino having an admixture of a second mass eigenstate neutrino (with mass in the keV/c2 range) is energetically prohibited. This feature, in particular, opens the possibility for a new approach to searching for massive neutrino admixtures using relative electron capture rates. Five candidates are specifically identified, of which one, Tb-157, is conceivably of immediate interest to the 17 KeV/c2 neutrino mass question. Finally experimental prospects and limitations are described.