Measurement of Multiple Scattering of 15.7-Mev Electrons

Abstract

The angular distribution of electrons scattered by thin Be and Au foils has been measured for angles where the multiple scattering is important. The $\frac{1}{e}$ widths of the distributions obtained with Au foils of 18.66 and 37.28 mg/${\mathrm{cm}}^{2}$ are 2.58\ifmmode^\circ\else\textdegree\fi{} and 3.76\ifmmode^\circ\else\textdegree\fi{}, respectively. These widths are about 10 percent narrower than those calculated from the theories of Williams or of Goudsmit and Saunderson but are in good agreement with the calculations of Moli\`ere.The $\frac{1}{e}$ widths obtained with Be foils of 257 and 495 mg/${\mathrm{cm}}^{2}$ are 3.06\ifmmode^\circ\else\textdegree\fi{} and 4.25\ifmmode^\circ\else\textdegree\fi{}. These widths are about 5 percent smaller than those given by Moli\`ere's theory increased by ${(1+\frac{1}{Z})}^{\frac{1}{2}}$ for the contribution of electron-electron collisions. The discrepancy may be qualitatively explained by the fact that the Thomas-Fermi screening used in the calculation is different from the effective screening in the Be metal.The scattering from the two Au foils was measured for larger angles where the scattering can be considered as single scattering modified by the effect of multiple scattering. The ratio of the scattering from the thick to the thin foil can be represented by the relation $2+\frac{95}{{\ensuremath{\theta}}^{2}}$ from 9\ifmmode^\circ\else\textdegree\fi{} to 30\ifmmode^\circ\else\textdegree\fi{}, and is in fair agreement with theoretical expressions for this ratio.