Time-domain observation of the slowing-down of positronium in condensed matter

The capability of positron AMOC (age-momentum correlation) spectroscopy to measure the momentum distribution of annihilating positron-electron pairs as a function of the positron age is used to investigate the slowing-down of positronium in condensed matter. The measured AMOC reliefs are analyzed in terms of a model that is based on the assumption that Ps thermalization proceeds via inelastic phonon scattering. Quantitative data are presented on the initial kinetic energy of Ps after its formation and the Ps slowing-down time in fused quartz (Suprasil and Herasil), polyvinyltoluene (Pilot-U), tetramethylsilane, and benzene.