Positron-Gas Scattering Measurements

A 4.75 MeV proton beam from a Van de Graaff accelerator is used to generate an 11C positron source by making use of the 11B(p, n) 11C reaction. Moderated, low energy positrons emerging from the boron target are then electrostatically focussed into a beam which is used in positron-gas scattering experiments. Total scattering cross sections have been measured for 0.3 to 800 eV positrons scattering from several atoms and molecules. Comparisons of these measurements with the corresponding electron total scattering cross section measurements (made with the same apparatus and technique) reveal many interesting similarities and differences. Positronium formation has been found to play an important role in positron scattering from the gases that have been studied.