Efficient Positronium Formation by Slow Positrons Incident on Solid Targets

Abstract

A beam of slow positrons in the few-eV region is directed at bakable solid targets in a vacuum of (2-4) × ${10}^{-8\mathrm{}}$ Torr. Measurements of the $\frac{2\gamma }{3\gamma }$ annihilation-yield ratio indicate the conversion of the incident positrons into positronium. The conversion efficiency depends on the target material and incident positron energy, varying from less than 25% at 300 K to 40-85% at 900 K.