Electron and positron scattering by gasses

Total scattering cross sections for positrons by various gasses were measured by time of flight method (TOF). The vibrational excitation cross-section for CO2 molecules was compared between electron and positron beams. The broad 'unscattered peak' in the energy spectrum observed by TOF shifted slightly due to the inelastic scattering induced by the collisions of electrons or positrons to CO2 molecules. An α-value, which is defined as the ratio of the shift due to the inelastic scattering to the total inelastic scattering, was estimated. The magnitude of the inelastic scattering for the vibrational excitation was deduced from the shift and the α-value. Consequently, the magnitude for the inelastic scattering by positron scattering was an order of magnitude larger than that by electron scattering. This result agreed well with the recent theory. (Y. Kazumata)