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Using high-resolution semiconductor detectors, a study was made of the large I&ionization cross sections of atoms over a wide range of atomic numbers (Z=29-83) and of incident electron energies (E= 150-900 MeV). For the higher-Z elements (Z&60), the L x-ray cross sections were also measured over the incident electron energy range. Ratios of the relative intensities of various distinct lines were determined and compared to recent low-energy work. The results of the K-ionization experiment are compared to the recent relativistic calculations of Kolbenstvedt.The experimental K-ionization cross sections for each incident electron energy appear to fit a power-law dependence on the atomic number. The Kolbenstvedt theory also exhibits a power-law dependence and is in good agreement with this experiment. All differential x-ray cross sections were found to be isotropic. The L x-ray cross sections measured for four high-Z elements increase with atomic number and incident electron energy.The Ip/I n, Iy/I n, and K/I. intensity ratios are also given. A search for nuclear y rays produced by high-energy electron scattering was also undertaken in this work. No nuclear y-ray lines were detected. Recent theoretical calculations show that the expected cross sections are below the minimum observable levels in these experiments. However, a 511-keV p line was observed. This line wRS RssociRted with positron annihilation and was apparently produced in the target.

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