Electron Tridents between 0.1 and 10 Bev

Data on the direct production of pairs by fast electrons of the cosmic radiation have been collected in nuclear emulsions by a track-following method. Multiple-scattering measurements were made on the secondaries of 61 tridents with energies between 0.1 and 10 Bev; of these, 14 originated on arms of pairs. A mean free path of 134±{}42 cm was deduced for the latter, corresponding to a cross section of 0.92±{}0.29×{}10^-25 cm². An appropriate statistical treatment for small numbers has been adopted, and a correction has been made for the inclusion of pseudo-tridents. The theoretical cross sections of Bhabha and Racah, which apparently disagree by a factor of about 2 in this energy region, have been shown to be consistent. The theoretical cross section averaged over the experimental energy distribution is 0.82×{}10^-25 cm². The distributions in fractional energy transfer to the created pair and internal energy partition in the pair have been derived and are compared with our observations. It is concluded that trident theory is in agreement with this experiment.