Spectroscopic studies of two beta-rays from 100Mo are shown to be of potential interest for investigating both the Majorana neutrino mass by neutrinoless double beta-decay and low energy solar neutrino's by inverse beta-decay. With a multi-ton 100Mo detector, coincidence studies of correlated beta-beta from neutrinoless double beta-decay, together with the large Q value, permit identification of the neutrino-mass term with a sensitivity of ~ 0.03 eV. Correlation studies of the inverse beta and the successive beta-decay of 100Tc, together with the large capture rates for low energy solar neutrino's, make it possible to detect in realtime individual low energy solar neutrino in the same detector.