Longitudinal Polarization ofO14Positrons

The longitudinal polarization of positrons from the pure Fermi transition of ${\mathrm{O}}^{14}$ has been studied by the method of Bhabha scattering. A prismatic beta-ray spectrometer selected 1.0-Mev positrons which then were focused by a solenoidal magnetic lens on a Supermendur foil magnetized by the lens. Scattered positrons and recoil electrons were detected in fast coincidence. The scattering asymmetry observed upon reversal of the lens magnetic field was (4.16±0.80)%, which corresponds to positron longitudinal polarization + (0.97±0.19) v/c.