Electron scattering in helium

Abstract

Scattering of electrons in helium has been carefully investigated by (among others) Kollath, who measured the scattering at electron velocities corresponding to 1 to 40 volts. To test the formula for scattering, which Mott has deduced by means of Born’s method, it was of interest, as was also emphasised by the work of Moller, to get measurements at higher velocities. Earlier measurements, e. g ., those by Dymond and Watson and by McMillen have given the scattering as a function of the angle of scattering. In the present paper are given the results for scattering at a fixed angle of 90° and for different electron velocities corresponding to from 40 to 300 volts. The measurements were carried out with an arrangement, of which the principal part is shown schematically in fig. 1. From the heated tungsten filament G-, which had a potential —V volts relatively to the tube H, an electron beam of small circular section passed through H into the upper tube R. During the experiment, H and R were kept at the same potential. Electrons, which at 0 are deflected through 90°, will pass through a ring-slit S II and another ring-slit into the Faraday-chamber E II , where the amount of electrons is measured by a Lindeman electrometer connected to the chamber. The direct beam of electrons hits the small circular hole S I , through which the electrons pass into the Faraday-chamber E I . E I is connected to a second Lindeman electrometer, which permits a measurement of the direct beam.