Positronium velocity distributions using the time-of-flight technique have been determined for positronium emitted from clean, well-annealed, single-crystal samples of Al(111), Cu(100), Ni(100), and Au(100). The positronium energy distribution had a similar shape for all samples and was consistent with the hypothesis that positronium formation leaves behind a single electron hole in the conduction band of the metal. This was verified by explicit calculation for Ni, the first d-band metal to be studied by this technique.

• Received 24 October 1986

DOI:https://doi.org/10.1103/PhysRevB.35.5303