Correlations between ionization cross sections and threshold energies in electron-, positron-, proton- and antiproton-atom collisions

Abstract

Strong correlations between the direct single-ionization cross sections and the target ionization energies are found for electron, positron, proton and antiproton impact on the noble gases. These correlations, extending from near threshold to high projectile energies, are similar to those previously observed for positronium formation, namely σ = A exp(−BE th ), where σ is the cross section for each process, E th is the relevant threshold energy and A and B are functions of the excess energy of the projectile. The generality of this form for the four projectiles is suggestive of a common underlying fundamental aspect of the collisions.Recent investigations of positronium (Ps) formation in positron-atom collisions have revealed a strong correlation between the Ps formation cross section σ Ps and the corresponding threshold energy E Ps = (E i − 6.8) eV (E i being the single-ionization threshold of the target and 6.8 eV the binding energy of Ps) [1,2]. The data for Ps formation in single ionization for both the noble gases and the alkalis were shown to fit the relation

Regularities in positronium formation for atoms and molecules

“…When this scaling is applied to the total Ps formation cross section, clear differences are observed in the atomic and molecular cases. In an effort to determine an empirical scaling law for the total Ps formation cross section applicable to both atoms and molecules, we have modified equation (1) above [12,13,21,22]. The resulting equation is known as the surge function…”

Positron and electron-impact multiple-ionization

“…The energy threshold in MI is a key point that has deserved much theoretical and experimental effort [17,[42][43][44][45][46]]. If we Figure 1.…”