Total scattering cross sections have been measured in the same apparatus for positrons and electrons colliding with helium, neon, and argon atoms in the energy range from 15 to 800 eV using a beam-transmission technique. These measurements reveal a merging of the positron and electron cross-section curves for helium at energies above 200 eV while the available theories predict this merging to occur at considerably higher energies. For neon and argon the positron and electron total-cross-section curves are slowly approaching each other at the highest energies. The present experimental approach is analyzed with regard to the discrimination against small-angle forward elastic scattering, and estimates are made of other potential errors in the measured total cross sections. The present results are used to test the zero-energy sum rule, obtained from forward dispersion relations, and it is found that these data are consistent with prior measurements in that the sum rule is found to fail for electron scattering and to be valid for positron scattering.

• Received 28 August 1979

DOI:https://doi.org/10.1103/PhysRevA.24.725