Determination of atomic form factors by means of coherent bremsstrahlung.

Abstract

A method has been developed by means of coherent bremsstrahlung from a single crystal for the determination of atomic form factors. This method employs a precise measurement of energy spectra of \ensuremath{\gamma} rays in the several-hundred-MeV region produced by 1.2-GeV electrons from single crystals as a function of the relative angle between a definite crystal axis and the incident-electron beam. It is shown that the spectra contain the electron-screening effect around the target nuclei and give information on the atomic form factor mainly at small momentum transfers. Possible problems with this method have been examined with this experiment using a silicon crystal. A method to analyze the experimental results has been established and with this method the deviation of atomic form factor from theoretical calculation is detectable at a level of down to a few percent. The present experimental data for a silicon crystal are consistent with the form factor obtained by the Pendello$uml---sung method, which shows small deviations from the Hartree-Fock model at small momentum transfers. The accuracy attained in this method has been shown not to be too much affected by the imperfections of the crystal, at least for dislocation densities of up to ${10}^{4}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$.