MEASUREMENTS OF ELASTIC ELECTRON-SCATTERING IN THE BACKWARD HEMISPHERE

A new experimental method is described which allows the range of scatt ering angles to be extended to cover the whole of the backward hemisph ere, i.e. up to 180 degrees, in measurements of elastic electron scatt ering. This is achieved by adding a localized magnetic field to the in teraction region of a conventional electrostatic electron spectrometer . Measurements are presented of the differential cross section from 30 -180 degrees for elastic scattering of electrons by argon at an energy of 10 eV, and of the resonance structures due to the P-2(3/2,1/2) sta tes of Ar- at the fixed scattering angles of 110 degrees, 150 degrees and 180 degrees.