By establishing coincidences between target ions and scattered projectiles, and coincidences between target ions, scattered projectiles and ejected electrons, triply differential (TDCS) information was generated in terms of projectile energy loss and scattering angles for interactions between 1 keV positrons and electrons and Ar atoms. The conversion of the raw experimental information to TDCS is discussed. The single ionization TDCS exhibit two distinguishable regions (lobes) where binary and recoil interactions can be described by two peaks. A comparison of the positron and electron impact data shows that the relative intensity of both binary and recoil interactions decreases exponentially as a function of the momentum transfer and is larger when ionization is induced by positron impact, when compared with electron impact.

Triply differential electron emission cross sections are measured for single ionization of argon by 500 eV positrons. Data are presented for coincidences between projectiles scattered into angles of 3 degrees and electrons with emission energies less than 10 eV that are observed between 45 and 135 degrees along the beam direction. For interpretation, these are compared to cosine squared representations of the binary and recoil lobes which are convoluted over experimental parameters. Singly differential electron emission data for double and triple ionization by positrons are also presented.

Double-to-single-ionization ratios for electron emission as a function of the angle are measured for 200, 500, and 1000 eV positron and electron impact on argon. Both the sign of the projectile charge and the impact energy are shown to influence the angular dependences. By combining these ratios for positron and electron impact, information about how first-and secondorder double-ionization mechanisms interfere and contribute to the total differential electron emission at different collision velocities is obtained.

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