A coincidence measurement of the fully differential cross section for atomic field bremsstrahlung

Abstract

A coincidence measurement of the absolute cross section for electron atomic field bremsstrahlung, differential in photon energy, photon emission angle, and electron scattering angle, was performed. The incident electron energy was 140 keV and the scattering materials were thin films of aluminum and gold. Measurements were made for the following cases of electron scattering angle (theta_ei), photon emission angle (theta_gamma i)' and photon energy (k): theta_ei = 15°, theta_gamma i = 270°, and k = 30 and 70 keV; theta_ei = 30°, theta_gamma i = 270°, and k = 20 and 70 keV; and theta_ei = 30°, theta_gamma i = 30°, and k = 20, 30, 50, and 70 keV. The data, expressed in a form so as to emphasize the photon energy dependence of the cross section, were compared to the two available theoretical calculations - that of Elwert and Haug and that of Bethe and Heitler. Both theories gave satisfactory agreement for aluminum. The Elwert-Haug theory was somewhat more accurate for gold, although neither theory agreed with the data at the kinematic point of theta_ei = 30°, theta_gamma i = 270°, and k = 70 keV. Also a discrepancy between theory and experiment for both gold and aluminum was found to exist for very low photon energies for the case of both the electron and photon being emitted at 30°. No conclusions could be reached with respect to atomic electron screening effects because of the relatively large uncertainties involved in the experiment.