Performance of Whole-Body Counters at IGCAR in an Intercomparison Exercise

The Canadian National Calibration Reference Centre for in vivo Monitoring (NCRC), and United States Department of Energy (USDOE) periodically conduct intercalibration and intercomparison exercises with the aim of evaluating the relative performances of whole-body counting systems in various countries. In continuation of their earlier exercises they initiated another exercise in 1996. The exercise consists of identifying and quantifying the unknown radionuclides deliberately included inside the phantom chosen for calibration. The exercise was carried out with a resin-filled, ICRP standard, adult female BOMAB phantom. Each participating laboratory was given seven days for measurement and evaluation of the results irrespective of the number of counting systems they possessed. Health and Safety Division (HASD), Indira Gandhi Centre for Atomic Research (IGCAR) received the phantom during April 1997 and correctly identified the radionuclides. The activity estimate has a bias of 3% and a measurement precision better than 1%. It is interesting to see such close agreement in the prediction of activity of the radionuclides, even though the whole-body counting systems are calibrated with a masonite cut-sheet phantom whose size, shape and weight are quite different from that of the BOMAB phantom used in the present exercise. The details of the exercise, the phantom used, the measurements made and the results obtained are discussed.