Inelasticity of the positron-surface interaction at low energies

Slow positron emission and reflection from clean single crystals of W and Cr are observed. The broad emitted-positron-energy distributions and the absence of reflections at incident energies below the bulk penetration threshold imply that strong inelastic processes operate in the surface region. These results contradict single-particle-potential models and demonstrate that many-body effects dominate positron-surface interactions. © 1983 The American Physical Society.