Evaluation of the 2014 EC measurement comparison on simulated airborne particulates : 137Cs in air filters

In 2014, the European Commission Directorate-General Joint Research Centre, Institute for Reference Materials and Measurements (JRC-IRMM) organized on request of the Directorate-General Energy an interlaboratory comparison (EC ILC) exercise on 137Cs measurement in air filters; a similar exercise was organized in 2003. This report describes the full life cycle of the above mentioned comparison among 76 European laboratories monitoring radioactivity in the environment. JRC-IRMM provided the comparison samples which were prepared individually for each laboratory using a gravimetrically diluted 137Cs solution standardised by JRC-IRMM. The samples were made by gravimetrically dispensing the necessary activity amounts close to those the laboratories routinely measure. Reference values were fully documented and available to all participants and nominating national authorities after completion of the comparison. A robust evaluation of the individual performance using three different approaches, percentage difference (D%), En numbers and PomPlots, is presented. Finally, the performance of laboratories which have participated in both the 2003 and the 2014 137Cs measurement in air filters exercises are compared. The majority of the laboratories reported reliable measurement results; only 5 out of 76 participants reported values with a percentage difference larger than ±33% of the reference value. Furthermore, 23 laboratories did not fulfil the criterion of the compatibility test based on En numbers. These results point out eventual problems with radioactivity measurements in the air filters and estimation of uncertainty which need to be addressed by the concerned laboratories