POSITRON IONIZATION MASS-SPECTROMETRY .2. IONIZATION BY FAST POSITRONS

The ionization of polyatomic molecules in their interaction with positrons is discussed with respect to the likely mechanisms expected at various positron kinetic energies and the rationale behind the study of these processes. These mechanisms include impact ionization, those that involve the formation of positronium, and those that involve capture of the positron without positronium formation. Data are shown for ionization by fast positrons. These results constitute the first examples of the mass analysis of ions from polyatomic molecules ionized by fast (3-keV) positrons. Mass spectra derived from the bombardment of several different targets with 3-keV positrons, 70-eV electrons, and 2.7-keV electrons are compared. These comparisons support the expectation that the underlying mechanism for ionization in this collision energy region is very similar for electrons and positrons. © 1990.