EXCITATION AND IONIZATION CROSS-SECTIONS OF HE, NE AND AR BY POSITRON-IMPACT

Excitation and ionization cross sections of He, Ne and Ar atoms by positron impact have been presented in the energy range from the respective thresholds up to 100 eV using a time-of-flight (TOF) method. These data were compared with the theoretical and experimental data. For excitation, the present data for Ar in the whole range and for Ne in the range 50-100 eV coincide roughly with the electron impact data of de Heer and co-workers. However, for He the present data are much smaller than the electron data above 30 eV, but in good agreement with the theoretical data of Varracchio below 35 eV. The present data for the ionization cross section for He coincide well with the experimental data of Fromme et al in the range less than 100 eV.