Measurement of total cross sections for low energy positron-helium collisions. (Positron backscattering from metal surface)

Abstract
An efficient method for the conversion of the high energy positrons emitted by Na22 into slow positrons of energy about 1 eV has been developed using the backscattering of positrons from a gold surface coated with magnesium oxide powder. These positrons have been used for the measurement of the total cross section for positron-helium collisions at energies between 2 eV and 20 eV. A preliminary value for the positron-argon cross section at 8 eV is also given.