Bremsstrahlung Cross-Section Measurements for 50-kev Electrons

The dependence of the bremsstrahlung differential cross section on photon energy and angle for 50-kev electrons (${\beta }_0\approx 0.4$) incident on a 10-μg/${\mathrm{cm}}^2$ gold target and a 17-μg/${\mathrm{cm}}^2$ aluminum target has been determined from measurements made with a scintillation spectrometer at angles ranging from 10 to 140 degrees. The experimental results are compared with the Sommerfeld-Kirkpatrick-Wiedmann cross sections multiplied by the relativistic correction factor ${(1-{\beta }_{0}cos\theta )}^{-2\mathrm{}}$. For high photon energies (45 kev), the experimental results show good agreement with the theory at the peak intensity angles, approximately 50 and 60 degrees for gold and aluminum, respectively, but at the extreme angles there are differences of about 50% with the theory. For low photon energies (10 kev), discrepancies with the theory also increase at the extreme angles, with maximum differences of about 30% for aluminum and 40% for gold. Good agreement is obtained between theory and experiment over the whole angular range for 45-kev photons emitted from the aluminum target, when rough estimates of retardation and screening effects are also included in the theory. The experimental values for the Heitler parameter, $\frac{{\phi }_{\mathrm{rad}}}{\overline{\phi }}$, are 5.5±0.6 and 6.7±0.7 for aluminum and gold respectively, compared to the theoretical value (including the above relativistic correction factor) of approximately 6.9 for both aluminum and gold.