Radiations from High-Energy Positrons Incident on a Beryllium Target

The energy spread and yields of nearly monoenergetic photons of various energies produced by the annihilation in flight of relativistic positrons have been experimentally determined using a 6-in.-long by 5-in.-diam NaI (Tl) crystal spectrometer. Photon lines with an energy spread of a few percent are reported. Yields of positrons and monoenergetic photons in the energy range from 2 Mev to 14 Mev have been measured. The bremsstrahlung spectra from 8.5-Mev positrons and electrons were compared and the yields and spectral distributions were found to agree within the experimental error.