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 226Ra (214Bi and 214Pb) are determined to be 122 ± 11 Bq kg-1 and 124 ± 14 Bq kg-1, respectively and in secular equilibrium in the uranium chain while the reference values of 232Th (228Ac) is determined to be 61 ± 6 Bq kg-1 and that of 40K was determined to be 955 ± 40 Bq kg-1. Although the aim of the exercise was to determine the activity concentration of 226Ra, 232Th and 40K 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.