Ninth international 'mini' intercomparison of environmental dosemeters: a further analysis of the data

Eight previous intercomparisons conducted since 1974 show, on average, a 5% under-response of TLDs calibrated with 137Cs relative to those calibrated with 60Co. As reported previously, a 9th international intercomparison involving 43 participants from 25 countries who were able to calibrate their dosemeters with both 137Cs and 60Co was held in 1987 specifically to investigate this phenomena. The dosemeters were irradiated at the US National Institute of Standards and Technology with 60Co and 137Cs, and at the Environmental Measurements Laboratory with 137Cs using collimated beams for all irradiations. Three experiments were conducted so that 60Co and 137Cs were used in different combinations of calibration and irradiation nuclides. The results indicated an average under-response of 5.3% for the caesium calibrated dosemeters. In the present study, the results of the ninth intercomparison were further analysed for correlation to preparation protocols, and calibration and readout techniques. While the data indicated that individually calibrated dosemeters reveal the under-response more clearly than do batch calibrated dosemeters, no correlations were found that provide a physical explanation for the caesium under-response. (author)