Momentum Distributions of Ortho-Positronium Dependent on Electronic State at Free Volume Walls in Insulators

Age-momentum correlation (AMOC) spectroscopy, which can sensitively probe momentum distributions of positrons and positronium (Ps), was conducted for studying the pick-off process of the triplet bound state ortho-Ps (o-Ps) with electrons at the walls of the free volume holes. Influences of different chemical elements forming free volume and the size of the free volume are investigated. It is found that the momentum distribution of o-Ps pick off annihilation sensitively depends on the electronic state. The feasibility of the chemical analysis relevant to the free volume in insulating materials is discussed.