Angular Distribution and Thickness Dependence of Transition Radiation from Thin Aluminum Foils

Abstract

The angular distribution of photons emitted from Al foils 320 Å in thickness bombarded with 80-keV electrons, and the dependence of the peak intensity on foil thickness, have been determined experimentally in the wavelength region from 650 to 1100 Å. The absolute efficiency of the optical spectrometer was determined in the visible-wavelength region from a standard lamp and extrapolated into the vacuum ultraviolet-wavelength region using the measured grating efficiency and quantum efficiency of sodium salicylate. Experimental photon intensities were found to be approximately one half of the theoretical photon intensities. The intensity at the peak wavelength had a maximum at 22° and 157° from the foil normal, with zero intensity at 0°, 180°, and 90°. The angles for which the theoretical curves exhibit maximum intensity are 15 and 168°. The wavelength for which the experimental curves exhibit maximum intensity was found to decrease as the angle of observation increased from 0° to 40° or decreased from 180° to 140°. The plasma wavelength and energy, 835 Å and 14.9 eV, respectively, were obtained by extrapolating to 0°. The intensity at the wavelength of maximum emission was found to decrease rapidly as the foil thickness was increased from 180 to 435 Å and then to remain fairly constant out to 700 Å.