The angular and spectral distribution of transition radiation from thin silver foils

Abstract

The angular and spectral distributions of photons emitted by Ag foils 660 Å and 1 980 Å in thickness when bombarded by 40 keV electrons have been determined experimentally in the wavelength region from 2 500 A to 5 600 Å. The spectral distribution of light polarized in the plane of incidence showed a sharp peak at 3 300 Å ± 12 Å, this value being an average over photon directions from 10° to 50° from the foil normal. In addition to the peak, the spectrum showed a continuum which decreased slowly with increasing wavelength and a deep minimum at 3 200 Å with a rise in the shorter wavelengths. The angular distribution of photons emitted at the peak wavelength showed a maximum at 30° from the foil normal with zero intensity at 0° and near 90°, whereas the photons emitted at other wavelengths in the continuum, e.g., 2 700 A and 4 500 Å, were most intense at 50° from the foil normal. The absolute photon yield was determined by calibrating the spectrometer, analyzer, and photomultiplier with a tungsten filament lamp obtained from the U. S. National Bureau of Standards. For photon directions from 10° to 40° the photon yield was found to agree with the theoretical predictions in all respects at all wavelengths except at that of the sharp peak where the experimental values were about 30 % lower