Experimental findings in 180° backscattering enhancement from solids

Abstract

We use a backscattering assembly developed recently to investigate the enhanced backscattering from polycrystalline materials near 180\ifmmode^\circ\else\textdegree\fi{}. The nominal scattering angle can be continuously varied between exactly 180.0\ifmmode^\circ\else\textdegree\fi{} and 178.5\ifmmode^\circ\else\textdegree\fi{}. It is shown that the stochastic model of flux peaking, though its predictions are surprisingly consistent with experimental results, either does not apply to real measurements or does only take account of a negligible fraction of the effect, which cannot be documented by experiment. The energy loss of He projectiles along correlated inward and outward trajectories turns out to be the same as in any random direction. To get the enhancement factor unaffected from detector resolution we measured the integrated backscattering yield from a number of targets with different thickness and deduced the yield by two different methods. For 400 keV He projectiles scattered from partly oxidized Ta a maximum enhancement factor of 2.8 is found.