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Positron backscattering probabilities from solid surfaces at 2-30 keV

A measurement of the total positron backscattering probabilities using a magnetically guided positron beam is reported. Backscattering yields were measured as a function of the incident positron energy in the range 2-30 keV and the atomic number Z of the target (6<or=Z<or=79). Absolute backscattering probabilities extracted from the annihilation count rates at the target are compared with doubly differential measurements at 35 keV. The total backscattering ratios from these two measurements agree with the experimental uncertainties. The experimental backscattering probabilities compare well with Monte Carlo simulations of keV positron slowing in solids.