Abstract
Energy and angular distributions of the positronium emitted from single-crystal samples of the alkali halides LiF, NaF, KCl, KBr, and KI following bombardment of the surfaces with 0.1--4-keV positrons are reported. Energetically narrow positronium distributions were formed at the positron implant depth, and this hot positronium diffused to the surface, losing energy in the process. An analysis of the data using a diffusion model yields an estimate of the strength of the positronium-phonon coupling. This coupling is found to be energy dependent, with the effective deformation potential decreasing as the positronium energy increases. Positronium work functions and binding-energy estimates are also given. The angular distributions of the emitted positronium from all samples except LiF were sharply peaked in the forward direction. The energy distributions from the LiF samples also differed from those of the other alkali halides by showing two distinct energy components instead of a single peak.
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