Longitudinal Behavior of Electromagnetic Showers

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Abstract
The need to establish recognition patterns for high-energy photons and electrons in cosmic-ray work, and more recently, around high-energy accelerators, has stimulated theoretical and experimental investigations into the properties of electromagnetic cascades. The most recent results of statistical computations, for longitudinal development and for lateral and angular spread, are in large part inconsistent with earlier published data. In order to study the longitudinal behavior of electron-induced showers, measurements have been made with a monoenergetic electron beam (energies 100-1000 MeV) at the 1.5-BeV CIT electron synchrotron. Buildup and energy dissipation were investigated, through the sampling of showers generated in lead of variable thicknesses, by means of a Lucite Čerenkov counter. Average numbers of shower particles with energies above 10 MeV are given for these incoming energies and penetration depths up to 10 radiation lengths; also, shower fluctuations are presented for the same points. The results of this experiment can readily be compared with the data recently computed by Crawford and Messel. Agreement appears to be satisfactory.