Measurement of the neutrino mass using the inner bremsstrahlung emitted in the electron-capture decay of 163Ho.

An experimental investigation of the spectrum of x rays emitted in the electron-capture decay of /sup 163/Ho is described. The data obtained are analyzed to determine their sensitivity to the value of the neutrino mass. At a 95% confidence level, an upper limit of 225 eV is set for the electron neutrino mass. No evidence for a finite value is found. Using available photon detectors, further improvements of this result are severely limited by uncertainties in atomic interference effects inherent to the decay.