Coincidence measurement of the fully differential cross section for atomic-field bremsstrahlung

A coincidence measurement of the absolute cross section for electron-atomic-field bremsstrahlung, differential in photon energy, photon-emission angle, and electron scattering angle, is reported. 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 (${\theta }_{\mathrm{ei}}$), photon-emission angle (${\theta }_{\gamma i}$), and photon energy ($k$): ${\theta }_{\mathrm{ei}}=15\mathrm{}°$, ${\theta }_{\gamma i}=270\mathrm{}°$, and $k=30\mathrm{} \mathrm{and} 70$ keV; ${\theta }_{\mathrm{ei}}=30\mathrm{}°$, ${\theta }_{\gamma i}=270\mathrm{}°$, and $k=20\mathrm{} \mathrm{and} 70$ keV; and ${\theta }_{\mathrm{ei}}=30\mathrm{}°$, ${\theta }_{\gamma i}=30\mathrm{}°$, and $k=20, 30, 50, \mathrm{and} 70$ keV. The data are compared to the theoretical calculations of Elwert and Haug and of Bethe and Heitler. Both theories give generally satisfactory agreement for aluminum. The Elwert-Haug theory is somewhat more accurate for gold, although neither theory agrees with the data at ${\theta }_{\gamma i}=270\mathrm{}°$ and $k=70\mathrm{}$ keV. A discrepancy between theory and experiment for both gold and aluminum also appears to exist for low photon energies ($k=20\mathrm{}$ keV) for the case of both the electron and photon being emitted at 30°.