IONIZATION OF HELIUM AND MOLECULAR-HYDROGEN BY SLOW ANTIPROTONS

Measurements of the cross sections for single and double ionization of helium as well as for the creation of H-2 and H+ ions from H-2 for im pact of antiprotons in the energy range 13-500 keV are presented. The results are compared with our earlier, less accurate data and with dat a for equivelocity proton impact. The single ionization cross section of helium agrees remarkably well with a continuum distorted wave (CDW EIS) calculation. The ratio between the double and the single ionizati on cross sections of helium increases dramatically with decreasing pro jectile energy. New theoretical calculations are called for.