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

Variable-energy positron annihilation data from ion implanted and unirradia ted Si and SiO2 were obtained at five separate laboratories. Line-shape ana lysis of the 511 keV annihilation gamma rays yielded normalized S parameter signatures for radiation defect distributions in both types of samples. La boratory-to-laboratory variations are found which, although small, lie outs ide the expected range of reproducibility. Large variations found in the ex tracted values for positron diffusion lengths L+ in silicon are identified and thought to arise from differences in sample surface conditions. Possibl e sources of the observed discrepancies are discussed, together with method s for reducing them. (C) 1999 American Institute of Physics. [S0021-8979(99 )01413-9].