The observation of structure in the dependence of the 1 keV positron backscattering coefficient on target atomic number

The total backscattering coefficient eta + has been measured for 1 keV positrons incident normally on a number of elemental targets with atomic numbers Z in the range 6-82. The measurements require the minimization of surface contamination on the samples and as a result data analysis has to allow for the formation of positronium at the sample surface. Pronounced structure in eta +(Z) is observed, and it is suggested that this may be correlated with the effective atomic electron density.