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Comparisons: International Comparisons for Air-Kerma and Absorbed Dose to Water from Gamma-ray Beams


A bilateral comparison was conducted between NIST and the International Atomic Energy Agency (IAEA) to support international efforts for harmonizing radiation protection measurements around the world, ensuring the safety of radiation workers and the public.


The air kerma national standards from 137Cs and 60Co beams were compared at both the IAEA and NIST. The work started in the second half of 2009 and was completed in January 2010 and the results were published in a special issue of Metrologia. Two reference class chambers with volumes of 100 cm3 and 1000 cm3 owned by the IAEA were used during the comparison. Calibration coefficients for the two chambers were determined at NIST and at the IAEA in both 137Cs and 60Co beams. A quite good agreement of within less than 0.30 % for the air kerma from both gamma-ray beams was obtained.

In April 2010 the results of the EUROMET key comparison project 813 were published in a special issue of Metrologia. This work supports international efforts for harmonizing radiation measurements that are routinely made in the medical field. NIST represented the U.S. as one of 26 countries that participated in this long term project that was carried out over a period of 4 years and was completed at the end of 2008. The radiation quantities absorbed dose to water and air kerma from 60Co gamma ray therapy level beams were compared in a blind test format. In addition, NIST served as the host laboratory for participants in the Sistema Interamericano de Metrología (SIM) regional metrological organization comprised of national standards laboratories in the American continent. The results of this work are also available from the BIPM Key Comparison Database.

Website (comparison identifiers EUROMET.RI(I)-K1 and EUROMET.RI(I)-K4) at:;

Created April 13, 2011, Updated April 27, 2021