Low energy positron-induced ionization of He and Ne

Following the preliminary results of Szłuińska and Laricchia [Nucl. Instr. and Meth. B 221 (2004) 100], further investigations of ionization have been carried out below the positronium formation threshold of He and Ne. Within the present experimental sensitivity, no significant signal is observed for He. Additionally, the residual signal previously observed in Ne is found to be due principally to contaminants rather than annihilation from this atom.