ZDependence and Angular Distribution of Bremsstrahlung from 17-Mev Electrons

Abstract

The relative bremsstrahlung cross section for the upper portion of the spectrum as a function of $Z$, for 17-Mev electrons from a 22-Mev betatron, has been measured. The radiation was detected by means of the ${\mathrm{Cu}}^{63}(\ensuremath{\gamma},n)$ induced activity, which has a 10.9-Mev threshold. The effect of atomic screening is small for the quantum energies to which this detector responds, but was taken into account. The results are in agreement with the Bethe-Heitler theory for electron-nuclear interactions within 1 percent. Electron-electron interactions give 0.75 times the intensity for electron-proton interactions, as measured with a copper detector.The total cross section for radiative energy loss of electrons has been measured with an ionization chamber. The experimental $Z$ dependence of the relative cross section indicates that the yield from gold for a given $N({Z}^{2}+Z)$ is somewhat less than that from low $Z$ elements. This discrepancy might be accounted for by improved corrections for screening, and by more accurate consideration of the radiation produced by electron-electron impacts. Rough measurements of the absolute cross section are in agreement with the Bethe-Heitler theory.The intrinsic angular distribution of bremsstrahlung, produced in a small amount of cellophane and air, was measured by film and ion chamber, and was found to fit a $\frac{1}{{[1+{(\frac{E\ensuremath{\theta}}{\ensuremath{\mu}})}^{2}]}^{2}}$ distribution. The angular distribution was measured with three detectors, for one Be and several Au targets. The results are in agreement with calculations in which the above intrinsic distribution and Moli\`ere's multiple scattering theory are used.The central intensity of bremsstrahlung as a function of target thickness, measured with a small ion chamber, is in approximate agreement with a calculation in which the energy loss of the primary electrons has been taken into account.