Evaluation of EC interlaboratory comparison on radionuclides in soil

A comparison was organised by the Institute for Reference Materials and Measurements among 73 environmental radioactivity monitoring laboratories for the determination of 15 radionuclides in soil. The reference material IAEA-375 Soil was reprocessed by IRMM to provide the comparison material and reference values traceable to SI units and SIR were established at IRMM. The analytical procedures used by participating laboratories are described. A robust evaluation of the performance of laboratories is performed using three different approaches: relative deviations, En numbers and PomPlots. The performance of the participating laboratories varied depending on the radionuclide determined and method used. Gamma-ray spectrometry with respect to 137Cs and 40K is well controlled. The determination of 90Sr proved difficult for about two-thirds of the participants, which submitted results outside the acceptable range. These laboratories need to review their analysis procedures. Several laboratories need to improve their analytical procedures for the uranium isotopes and 226Ra. Moreover, the results for thorium isotopes are far from satisfactory mainly for the 230Th. The use of the En criterion revealed that the uncertainty estimation of many participating laboratories is poor.