9TH INTERNATIONAL MINI INTERCOMPARISON OF ENVIRONMENTAL DOSIMETERS - A FURTHER ANALYSIS OF THE DATA

Eight previous intercomparisons conducted since 1974 show, on average, a 5% under-response of TLDs calibrated with Cs-137 relative to those calibrated with Co-60. As reported previously, a 9th international int ercomparison involving 43 participants from 25 countries who were able to calibrate their dosemeters with both Cs-137 and Co-60 was held in 1987 specifically to investigate this phenomenon. The dosemeters were irradiated at the US National Institute of Standards and Technology wi th Co-60 and Cs-137, and at the Environmental Measurements Laboratory with Cs-137 using collimated beams for all irradiations. Three experim ents were conducted so that Co-60 and Cs-137 were used in different co mbinations of calibration and irradiation nuclides. The results indica ted an average under-response of 5.3% for the caesium calibrated dosem eters. In the present study, the results of the ninth intercomparison were further analysed for correlation to preparation protocols, and ca libration and readout techniques. While the data indicated that indivi dually calibrated dosematers reveal the under-response more clearly th an do batch calibrated dosemeters, no correlations were found that pro vide a physical explanation for the caesium under-response.