Total scattering cross sections for low-energy positrons in the molecular gases H2, N2, CO2, O2and CH4

The method described by Charlton et al. (1980) to measure total cross sections for the scattering of electrons from helium and argon has been used for similar measurements with positrons in the molecular gases H 2 , N 2 , CO 2 , O 2 and CH 4 over an energy range from 2 to 20 eV. The apparatus used is, with minor modifications, the same as that of Charlton et al. and incorporates a localised scattering cell close to the slow positron source which requires the measured attenuations to be normalised to previously known absolute cross sections. The apparatus used in this study, together with the normalisation procedure and the method of data analysis, is described in detail.