Neutrino Recoils Following the Capture of Orbital Electrons inA37

The energy spectrum of the recoil nuclei resulting from orbital electron capture in ${\mathrm{A}}^{37}$ has been determined by a time-of-flight measurement of the recoil ions. ${\mathrm{A}}^{37}$ disintegrations occurred within a gas-filled source volume, where the total pressure was approximately ${10}^{-5\mathrm{}}$ mm of Hg. The time-of-flight distribution, as measured by a multichannel delayed-coincidence technique, has a definite maximum time limit. Furthermore, the shape and extent of the distribution correspond to that expected from monoenergetic recoils, originating in an extended source and having an energy of 9.7 ev as predicted by the single neutrino hypothesis. Zero and short time coincidences were observed in addition to the above distribution. Further measurements indicate these to be the result of electron scattering associated with ${\mathrm{A}}^{37}$ decays not originating in the source volume.