Satisfactory random backscattering yields from crystals can be obtained by tilting the sample and rotating about its normal to obtain an average over 2π in azimuthal angle. The influence of the tilt angle α on this yield has been studied, and in addition to effects due to the scattering geometry there is a further contribution if the secondary electron suppression is incomplete due to the angular dependence of the emission coefficient δ. For 1.9 MeV α-particles on amorphous silicon, δ was typically 4.6 for normal incidence and increased with angle as (cos α)-1. Measurements also showed that the averaged scattering yield from silicon crystals was between 1% and 2% lower than from amorphous material. Analysis of averaged backscattering spectra from K-β-alumina, (1+ χ) K2 O·11Al2 O3, gave a potassium content of (1+χ)=1.26 in good agreement with chemical and X-ray determinations. This contrasts with the value (1+χ)=1.14 derived from an apparently good random spectrum obtained at a single angle of incidence.
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