Differential Cross-Section Measurements of Thin-Target Bremsstrahlung Produced by 2.7- to 9.7-Mev Electrons

Abstract

The electron beam removed from a 50-Mev betatron and a total absorption scintillation spectrometer containing a sodium iodide crystal 5 in. in diameter and 9 in. long were used for the measurement of brems-strahlung cross sections that are differential in photon energy and angle. Thin targets of beryllium, aluminum, and gold were bombarded by electrons with kinetic energies of 2.72, 4.54, and 9.66 Mev. The bremsstrahlung spectra from thick tungsten targets were also studied.The results were compared with the differential cross-section predictions of Sauter, Schiff, and Gluckstern and Hull. The spectral shapes obtained with the beryllium and aluminum targets agreed with those expected from theory for the electron energies of 2.72 and 4.54 Mev. The 9.66-Mev experiment gave 20% more low-energy than intermediate-energy photons when compared with theory. For gold the experimental cross sections for the high photon energies are larger than theory with the differences increasing with decreasing electron primary energy. Evidence for electron-electron bremsstrahlung is obtained from the absolute magnitude of the differential cross sections, which are $\frac{(Z+1)}{Z}$ times larger than theory within the experimental errors. The thick-target tungsten spectra produced by 9.66-Mev electrons decreased more rapidly with increasing photon energy than did the thin-target cross sections derived by Schiff.