Measurement of photon showers in lead produced by electrons of 150 MeV

The photon energy spectra induced by 150 MeV electrons in lead were measured in the energy range from 40 MeV up to the primary electron energy. The target thickness was varied between 0.1 and 2.5 radiation lengths X0. The photons were analyzed by use of a technique based on deuteron photodisintegration. Differential and integral shower spectra are presented and compared with Monte Carlo calculations of Nagel and Messel et al., both interpolated to our primary energy of 150 MeV. The measured spectra show good agreement with these Monte Carlo calculations for the thickest target of 2.5X0 and with calculated bremsstrahlung spectra for the thinnest target of 0.1X0. Considerable discrepancies, however, are found for medium target thicknesses in the range <1.5X0. Around the shower maxima, the shower spectra are narrower and the maxima are shifted about 0.3-0.4X0 to lower target thicknesses, furthermore the number of photons at the shower maxima are up to 50% higher than calculated. (Auth.)