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The occupation length of channeled 17-MeV electrons and 54-MeV electrons and positrons in silicon has been determined by measuring the intensity of the emitted channeling radiation. For 17-MeV electrons the measured 1/e occupation lengths are approximately 16 pm for the (100) plane and 20 pm for the (110) plane. For 54-MeV electrons the occupation lengths are 24 pm for the (100) plane and 36 pm for the (110) plane. For 54-MeV positrons the occupation lengths are 40, 60, and 42 pm for the (100), (110), and (111)planes, respectively. In all cases, the bound-state populations remain equal relative to one another throughout the thickness of the crystal. Multiple scattering appears to modify positron channeling radiation spectra slightly, but multiple scattering has no perceptible inhuence upon electron channeling radiation spectra.

The absolute differential production efficiencies (photons/eV sr electron) for x rays emitted from each of three transition radiators were measured for incident electron-beam energies of 17.2, 25, and 54 MeV. The radiators were made of stacks of 1.0-pm-thick foils: 18 foils of beryllium, 18 foils of carbon, and 30 foils of aluminum. The radiation spectra were most intense between 0.5 and 2.5 keV, peaking at 0.8, 1.3, and 1.3 keV, respectively. The angular distribution of the transition radiation from the beryllium-foil stack was measured for the three electron-beam energies and found to agree well with theoretical predictions. Owing to K-shell absorption, the photon-energy spectra from the carbon and aluminum stacks are narrowed. Theoretical calculations, which include both the twosurface interference and photon attenuation in the foil material, agree well with these data. A method of enhancing output using a split-foil stack is considered; cursory experiments with a split stack of Mylar foils showed enhanced emission. The use of transition radiation as a source of x rays for lithographic purposes may be practical.

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