ABSTRACT
Positronium is formed in collisions of slow positrons with atoms of matter, followed by the capture of an electron by positron from atoms of the medium. Positrons passing through a solid or gas lose some of their energy due to ionization of the medium. In addition to the ionization process, the formation of positronium atoms is significantly affected by the excitation of electronic levels of atoms in a solid. Moreover, there is a significant decline in the probability of positronium formation, when the positron energy exceeds the
excitation energy of the first electronic level * E . Recall that the
energy * E is always lower than the ionization potential Vion.
