Two measurements of the β spectrum of ${}_{}{}^{35}{}_{}{}^{}\mathrm{S}$ have been made using a windowless Si(Li) detector. The data show a clear threshold anomaly at Q-17 keV which is consistent with the emission of a 16.9±0.4 keV neutrino with a mixing probability of (0.73±0.09±0.06)%. All values of mixing probability <0.26% are rejected at the 99% confidence level.

• Received 9 September 1988

DOI:https://doi.org/10.1103/PhysRevD.39.1825