Electron-Induced Cascade Showers in Copper, Tin, and Lead

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Abstract
Electromagnetic cascade showers induced by 900-MeV electrons have been studied in copper, tin, and lead targets. A small, parallel incident beam with negligible background contamination was employed to achieve good resolution and undistorted development of the shower. The three-dimensional spatial distribution of energy deposition was measured with a CsI(Tl) detector placed at various positions in a small hole in an otherwise solid block of material. Measurements were extended to radii of 7 Molière lengths and depths of 30 or more radiation lengths. Additional data for showers induced by 200-MeV electrons incident on lead are also presented. The results of this experiment are compared with the results of previous experiments and with the predictions of recent Monte-Carlo calculations. The measured longitudinal distribution of energy is in good agreement with theoretical predictions, while the radial distributions show an unpredicted dependence on the atomic number of the target material.