Electron emission due to positronium annihilation in solid Ar, Kr, and Xe

We present measurements of positron and electron emission by solid rare-gas surfaces implanted with low-energy positrons. The electron yield exhibits a 0.5-eV-wide peak at a positron energy just above the threshold for positronium (Ps) formation, but below the electron-hole--pair threshold. A similar peak in the fraction of the incident positrons annihilating in the sample leads us to conclude that (1) slow Ps has an anomalously short diffusion length possibly due to self-trapping, and (2) energetic electrons are liberated from Ps atoms following annihilation of the positrons with valence electrons. The energy spectrum of the emitted electrons should contain information about the internal Ps wave function in the solids.