Elastic scattering of intermediate-energy electrons by Ar and Kr

Abstract

Using the relative-flow technique elastic differential cross sections ${\ensuremath{\sigma}}_{\ensuremath{\theta}}(\mathrm{Ar}\mathrm{or}\mathrm{Kr})$ for Ar and Kr relative to ${\ensuremath{\sigma}}_{\ensuremath{\theta}}(\mathrm{He})$ have been measured at impact energies of 3, 5, 7.5, 10, 15, 20, 30, 50, 75, and 100 eV. The angular range covered is from 20\ifmmode^\circ\else\textdegree\fi{} to 135\ifmmode^\circ\else\textdegree\fi{}. These ratios have been multiplied by the recently measured values of ${\ensuremath{\sigma}}_{\ensuremath{\theta}}(\mathrm{He})$ to obtain ${\ensuremath{\sigma}}_{\ensuremath{\theta}}(\mathrm{Ar}\mathrm{or}\mathrm{Kr})$. The differential cross section curves for both Ar and Kr show deep minima. The positions of these minima have been obtained with an accuracy of \ifmmode\pm\else\textpm\fi{}2\ifmmode^\circ\else\textdegree\fi{}. The cross sections in the angular regions lying between 0\ifmmode^\circ\else\textdegree\fi{} and 20\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{} and 180\ifmmode^\circ\else\textdegree\fi{} could not be measured owing to instrumental limitations. In these regions estimates of the shapes of differential cross section (DCS) curves have been made by fitting the data obtained from 20\ifmmode^\circ\else\textdegree\fi{} to 135\ifmmode^\circ\else\textdegree\fi{} with a phase-shift analysis, while the normalization to the absolute scale was obtained by normalizing these fits to the relative flow measurements. From these estimates and the measured values of the differential cross section, integral and momentum-transfer cross sections have been obtained. The error limits for the differential, integral, and momentum-transfer cross sections have been estimated as 20, 30, and 30%, respectively.