Relative probabilities of work-function and epithermal positron re-emission from silver

Experimentally determined values for the relative probabilities for work-function and epithermal positron re-emission from silver are reported as a function of incident positron energy E. The method involves the comparison of absolute slow-positron yields from a polycrystalline Ag sample with a very small negative work function with the epithermal yields from an Ag(100) sample having a small positive work function. The results show that the epithermal fraction increases steeply from almost zero as E decreases below 2 keV, tending to almost 100% as E approaches 0.