EXPERIMENTAL DETERMINATION OF TRANSITION EFFECT IN ELECTROMAGNETIC CASCADE SHOWERS

The transition effect that occurs when an electromagnetic cascade crosses the boundary between different materials has been measured. This transition effect is a rapid change in the numbers and spectra of electrons and photons which constitute the cascade, and in the resultant energy deposition. The magnitude of this effect depends on the age of the shower at the discontinuity in the critical energies. In the present experiment, 1-GeV cascade showers were developed in glass, iron, and lead, and 5-GeV showers in lead, each followed by a second medium of Plexiglas. The energy deposited as a function of position in the Plexiglas has been measured for a variety of shower ages and for thicknesses of the transition region between 0 and 1 radiation length. The results show a smaller transition effect than predicted by Approximation B of the cascade theory developed by Rossi and Greisen, but the measured transition effect is sufficiently rapid to cause systematic errors on the order of 20% in cascade measurements in some cases. © 1969 The American Physical Society.