THE ELASTIC-SCATTERING OF 20-EV ELECTRONS FROM MAGNESIUM

A modulated crossed-beam technique has been used to measure the differential cross section for elastic scattering of electrons from the 3(1)S state in magnesium at an impact electron energy of 20 eV. The cross section was measured over a range of scattering angles from 15 degrees to 130 degrees. Our results agree with the previous experimental cross sections of Williams and Trajmar within the combined uncertainties, however, the present data reduce the uncertainty by about an order of magnitude, thereby allowing a meaningful comparison to be made with the predictions of the various theories. At this time no theory accurately predicts the behaviour of the elastic differential cross section over the whole angular range. A complex phase-shift analysis is applied to the present data to derive the 20 eV integral elastic cross section. This integral cross section is also compared with the results of previous experiment and theory.