Contributions of Bremsstrahlung Conversion in Trident Experiments

Abstract

Determinations of the cross section for the direct creation of electron pairs by energetic charged particles in nuclear emulsions are dependent on the experimental criteria by which the observations are accepted, phenomenologically, as tridents. This paper discusses the extent to which materialization of a bremsstrahlung photon close to the path of the parent particle becomes experimentally indistinguishable from direct pair production. A study of 200 pairs arising from the conversion of bremsstrahlung photons from electrons with energies between 0.1 and 10 Bev leads to the conclusion that about 6 percent of the pairs materialize so close to their parent that they would be interpreted as tridents. An extension of the analysis to electrons of incident energy 100 Bev demonstrates that under typical experimental conditions about 70 percent of such secondary pairs would be accepted as tridents. Recently reported experiments which indicate a cross section for direct pair production by fast electrons much larger than that predicted by theory are discussed.