Transition Radiation from Relativistic Electrons Crossing Dielectric Boundaries

A coincidence technique has been used to observe transition radiation from fast electrons crossing the boundary between a vacuum and a dielectric. Gold, nickel, aluminum, and Mylar were the dielectrics used. A photomultiplier was used to count single photons in coincidence with the arrival of the electron at the boundary, as observed with a lithium-drifted germanium detector. The electrons were from a cesium-137 source. The relative photon yields for the three metals were: Al yield/Au yield=1.03±0.22, Ni yield/Au yield=0.61±0.09. The absolute yield for gold was (10±3)×${10}^{-3\mathrm{}}$ photons per electron, in agreement with theory. The results with Mylar are complicated by fluorescence effects, but there is evidence that the transition-radiation yield is of the same order of magnitude as the yield in gold. The yield was measured as a function of electron energy; it is a monotonically increasing function of the energy from 0.33 MeV to 0.662 MeV, in qualitative agreement with theory.