On the Anomalous Broadening of the Positronium Peak in NaF: Possibility of Metastable Self-Trapped Positronium State

Abstract

Recently observed anomalous temperature dependence of the width of the positronium peak in NaF is interpreted in terms of metastably self-trapped positronium. Analysis of the data indicates that there exists metastable self-trapped state of positronium at about 0.1 eV above the ground state of free positronium.