Experimental investigation of ortho-positronium?surface interactions

Abstract

In an effort to measure absolute positronium formation cross-sections for positrons scattered by various target atoms and molecules, we detect coincidences of the two 511 keV γ rays produced by the decay of para-Ps and by the interaction of ortho-Ps with the walls of our scattering cell, and also coincidences of 2 of the 3 γ rays with energies between 300 and 460 keV produced by ortho-Ps decay. The ratio of the coincidence signals (3γ/2γ) plotted as a function of positron energy has a number of interesting features that we believe may provide useful information on ortho-positronium–surface interactions.