POSITRON-IMPACT IONIZATION OF ATOMS

Experimental data are presented for the single (sigma(i)(+)) and the r atio of double to single (R-2) ionisation cross sections for e(+) impa ct on Ne, Kr and Xe from near threshold to 1000 eV. The ratio between e(+) and e(-) sigma(i)(+) maxima was generally seen to be lower for ta rgets with higher atomic number (Z), as would be expected from the eff ect of the increasing static interaction between the projectile and un distorted target. For double ionisation, the importance of inner-shell ionisation followed by Auger decay is manifest at high velocities for the higher Z targets. Preliminary measurements of the total ionisatio n cross section(sigma(T)(+)) in e(+)-D collisions are also presented a nd are found to disagree with recent results. (C) 1998 EIsevier Scienc e B.V. All rights reserved.