Double bremsstrahlung

Abstract

The cross-section for double bremsstrahlung has been measured for 75 keV incident electron energy utilizing thin film targets of silver, terbium, gold, and uranium. Double bremsstrahlung is defined here to be any inelastic scattering process which produces correlated emission of two photons. Measurement of the cross-sections was accomplished with a modified Fast-Fast coincidence technique. Results are fully differential with respect to the emitted photons, but neglects energy and angle of the scattered electron. A pair of solid state detectors arranged at 90 and 270 degrees relative to the incident beam direction recorded the two-photon events. An energy window for one detector was held fixed at 20 keV, while the second detector's window was allowed to vary from a minimum of 10 keV to a maximum of 50 keV, near the kinematic endpoint. Behavior of the cross-section as a function of photon energy and atomic number is discussed. A comparison between experiment and the theoretical result of Smirnov('1) shows poor agreement, with the data being several orders of magnitude larger than theory. The theoretical result is a relativistic treatment in the first Born approximation, requiring (alpha)Z/(beta) << 1. Experimental conditions were such that (alpha)Z/(beta) (TURNEQ) 1, which suggests that the double bremsstrahlung process is very sensitive to higher order terms. ('1)A. I. Smirnov, Sov. J. Nucl. Phys. 25, 548 (1977).