title: Spin-orbit quenching of positronium during atomic collisions.
abstract: When positrons are injected into a gas, 75% of the positronium (Ps) is likely to be formed as long-lived ortho-Ps. The main decay mechanisms for the ortho-Ps have been assumed to be natural decay of ortho-Ps and pickoff annihilation of the positron during Ps-atom collisions. A third possibility for annihilation is ortho-Ps-->para-Ps conversion due to the spin-orbit interaction between the atom and colliding Ps. This extra quenching mechanism may explain a number of phenomena observed in the annihilation spectrum of Kr and Xe, including the very small Ps fraction of 3% seen for Xe.
authors.affiliation: Faculty of SITE, Northern Territory University, Darwin NT 0909, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Mitroy
authors.forename: S A
authors.initials: SA
authors.lastname: Novikov