Assessment of the normalization procedure used for interlaboratory comparisons of positron beam measurements

Variable-energy positron annihilation data from ion implanted and unirradiated Si and SiO2 were obtained at five separate laboratories. Line-shape analysis of the 511 keV annihilation γ rays yielded normalized S parameter signatures for radiation defect distributions in both types of samples. Laboratory-to-laboratory variations are found which, although small, lie outside the expected range of reproducibility. Large variations found in the extracted values for positron diffusion lengths L+ in silicon are identified and thought to arise from differences in sample surface conditions. Possible sources of the observed discrepancies are discussed, together with methods for reducing them.