Differential cross-section measurements in positron–argon collisions

Differential cross sections for elastic scattering and ionization in positron-argon collisions as a function of energy (40-150 eV) are reported at 60 degrees. Of particular interest is the energy range 55-60 eV, where earlier measurements by the Detroit group found a drop in the elastic-scattering cross section of a factor of 2. This structure has been tentatively attributed to a cross channel-coupling effect with an open inelastic-scattering channel, most likely ionization. Our results indicate that ionization remains an important channel over the same energy range and only begins to decrease at an energy above 60 eV.