Positron Spectrum ofO15

The positron spectrum of ${\mathrm{O}}^{15}$ has been investigated with two iron-free magnetic spectrometers. One measurement, performed with an intermediate-image spectrometer and a solid source, gave an end-point energy of 1.723±0.005 Mev. The other measurement, performed with a thin-lens spectrometer and a gaseous source, gave an end-point energy of 1.736±0.010 Mev. These values, which are approximately 0.050 Mev higher than the only previously reported spectrometer measurement, are in good agreement with the end point predicted from ${\mathrm{N}}^{15}(p, n){\mathrm{O}}^{15}$ threshold determinations. The $\mathrm{ft}$ value calculated from an average end-point energy of 1.733±0.005 Mev derived from the beta spectra and the ($p, n$) threshold measurements is 4280±100 seconds. This new value brings the ${\mathrm{O}}^{15}$ decay into good agreement with the $B-x$ analysis of the 0-0 spin change and the "doubly closed shell plus or minus one nucleon" beta transitions.