Opening angles of electron–positron pairs

Abstract

G-5, 200 μm, nuclear emulsion plates were exposed to a bremsstrahlung photon spectrum of known intensity, produced by 100 MeV electrons at the Saskatchewan Linear Accelerator. The emulsions were later scanned for electron–positron pairs. Measurements were made such that the pair opening angle could be determined. From the resulting distribution of angles, the photon spectra predicted by the theories of Borsellino and Olsen, relating the most probable photon energy to a measured opening angle, were calculated. These spectra were compared to the experimental photon spectrum for the energy interval 50 to 100 MeV. Agreement was obtained for the theory of Olsen, within experimental error.