First intercomparison among laboratories involved in COST Action-TU1301 "NORM4Building": Determination of natural radionuclides in ceramics.

This work describes the outcomes of the COST Action-TU1301 "NORM4Building" intercomparison on the determination of natural radioactivity in ceramics. Twenty-two laboratories involved in the intercomparison are evaluated for their performance using robust statistics. The reference values of Ra (Bi and Pb) are determined to be 122 ± 11 Bq kg and 124 ± 14 Bq kg, respectively and in secular equilibrium in the uranium chain while the reference values of Th (Ac) is determined to be 61 ± 6 Bq kg and that of K was determined to be 955 ± 40 Bq kg. Although the aim of the exercise was to determine the activity concentration of Ra, Th and K and evaluation of the "Activity Concentration Index", laboratories were asked to report complete characterization of natural radionuclides. The results of this exercise pointed out a good performance among laboratories since the percentage of the acceptable results were above 90% for the radionuclides of interest. Based on these results, considering the systematic rejection of the results reported from a few laboratories we emphasize the need for quality control procedures.