Measurements of the spectrum and energy dependence of x-ray transition radiation

We present the results of experiments designed to test the theory of x-ray transition radiation and to verify the predicted dependence of the characteristic features of the radiation on the radiator dimensions. We have measured the x-ray frequency spectrum produced by 5- to 9-GeV electrons over the range 4 to 30 keV with a calibrated single-crystal Bragg spectrometer, and at frequencies up to 100 keV with an NaI scintillator. The interference pattern in the spectrum and the hardening of the radiation with increasing foil thickness are clearly observed. We have also studied the energy dependence of the total transition-radiation intensity using a radiator with large dimensions designed to yield energy-dependent signals at very high particle energies, up to $\frac{E}{m{c}^2}\approx {10}^5$. The results are in good agreement with the theoretical predictions.