Measurement of the Total, Differential, and Exchange Cross Sections for the Scattering of Low-Energy Electrons by Potassium

Abstract

An atom beam recoil technique has been used to determine the total, $Q$, differential, $\ensuremath{\sigma}(\ensuremath{\theta})$, and differential exchange, ${\ensuremath{\sigma}}_{e}(\ensuremath{\theta})$, cross sections for the scattering of low-energy electrons by potassium. The method consists of observing the angular distribution of atoms scattered from a potassium atom beam which has been cross fired by an electron beam. Relative values of $\ensuremath{\sigma}(\ensuremath{\theta})$ are then obtained by transforming to electron scattering angles. An inhomogeneous magnet and collimating channel are used as a velocity filter for the atom beam. Curves representing the variation of $\ensuremath{\sigma}(\ensuremath{\theta})$ with $\ensuremath{\theta}$ between approximately 15\ifmmode^\circ\else\textdegree\fi{} and 60\ifmmode^\circ\else\textdegree\fi{} are presented for various electron energies between 0.6 and 9.0 ev.The magnet also serves to polarize the beam. Relative values of ${\ensuremath{\sigma}}_{e}(\ensuremath{\theta})$ were determined by observing the amount of depolarization of the beam in the scattering region, using a second inhomogeneous magnet as an analyzer. Over the observed range of angles, exchange accounts for approximately one third of the scattering. Bounds on the total exchange cross section, ${Q}_{e}$, are also tabulated for energies between 0.5 and 4.0 ev. The bounds on ${Q}_{e}$ at 0.5 volt are $0.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14} {\mathrm{cm}}^{2}<{Q}_{e}<1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14} {\mathrm{cm}}^{2}$.