An analysis of the causes of discrepant results in proficiency tests in a testing laboratory

We present an analysis of the results reported in the framework of proficiency tests performed in the years 2003–2007 in a gamma-ray spectrometry laboratory. Measurements of 102 samples and 622 results reporting the activities or activity concentrations of 39 gamma- or X-ray emitters are included in the study. A total of 61 results were found to be in disagreement with their target values. The cause of the disagreement was not found for only 21 discrepant results.