A total of 50 knock-on electrons with emission angles less than or equal to 10° were located by along-the-track scanning of 105.4 m of 16.2-GeV/c negative-pion track in nuclear emulsion. The measured electron energies were found to be in agreement with kinematics. The spectrum of these high-energy $\delta$ rays is in agreement with both theory and previous bubble chamber results. A serious scanning deficiency at small angles in along-the-track scanning was found, and its implications for experiments searching for anomalous scattering on electrons are discussed.

• Received 17 April 1970

DOI:https://doi.org/10.1103/PhysRevD.2.1820