High pressure Xe and Ar were excited by high-current relativistic-electron bursts. The spectral and temporal characteristics of the uv continua, centered near 1700 A. in Xe and 1260 A in Ar, were measured. The maximum of the Xe spectral distribution shifted from 1690+ 9 to 1710+9 A. , and the spectral width decreased from 150+ 3 to 110+3 A. when the pressure was raised from 2 to 34 atm. The shift of the Ar continuum centered at 1260+ 9 A was negligible and the spectral width decreased from 130+ 3 to 90+ 3 A when the pressure was raised from 2 to 61 atm. Exponential time constants for the buildup and decay of the Xe and Ar continua were obtained. They are characterized by aP t 5 pressure dependence below 3 atm. Pressure-independent decay time constants of 4+ 1, 16+ 2.5, and about 280 nsec were obtained for Xe at high pressure. For Ar the pressure-independent decay time constants were 6+ 1.5, 30+ 5, and about 230 nsec. The efficiency for conversion of electron kinetic energy to uv energy was 10+ 4% in Xe and 15+ 7% in Ar.

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.

Vacuum ultraviolet (VUV) emission characteristics of xenon for pressures from 15 to 450 psi are presented. Stimulated emission was observed above 200 psi. Experiments were run both with and without mirrors. Without mirrors, the emission was 150 Å wide centered at 1700 Å, and the mean radiative lifetime was 2×10−8. The energy conversion efficiency was ∼ 20%. With mirrors above 200 psi the emission width narrowed to 17 Å centered at 1716 Å, and the output was highly directional. The pulse width narrowed from 50 to ∼ 3 nsec.

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