Results from the First Annual Aarst Radon Measurement Intercomparison Exercise

The First Annual AARST Radon Measurement Intercomparison Exercise was conducted at the radon calibration laboratory at Bowser-Momer, Inc. in November and December, 1997. There were thirty-two participants involved in the exercise, including Bowser-Momer. For grab radon measurements, the Environmental Measurements Laboratory (EML) sent samplers to be filled in the Bowser-Morner chamber simultaneously with the filling of scintillation cells from participants. For this measurement device type, therefore, the EML value was the reference for the exercise. Sets of three to four scintillation cells were filled simultaneously with EML's samplers for each of seven participants, including Bowser-Morner. The average relative differences from EML's value for these seven participants ranged from -12.4% to 7.3% and averaged -0.3%. Bowser-Morner's chamber values were the references for all other device types. Eighteen sets of five charcoal devices were exposed in the chamber for periods of time ranging from two to seven days, during which the radon concentration was held relatively constant. The average relative differences from the chamber values for these eighteen sets ranged from -16.0% to 19.5% and averaged 0.6%. Seven sets of five short-term electret ion chamber devices were exposed for two days. The average relative differences from the chamber values for these seven sets ranged from -9.3% to 3.3% and averaged -1.0%. Eight continuous monitoring devices were exposed for periods ranging from two to nine days. The relative differences from the chamber values for these eight devices ranged from -16.7% to 2.3% and averaged -4.6%. Three participants submitted sets of five alpha-track devices, and three participants submitted sets of five long-term electret ion chamber devices. Because of the small numbers of each of these two types of devices, they were combined into one category for reporting purposes. These six sets of devices were exposed simultaneously in the Bowser-Morner chamber for a period of 31 days, during which the radon concentration varied significantly. The average relative differences from the chamber value for these six sets of devices ranged from -3 1.5% to 27.3% and averaged -3.0%. These results of measurements over a cross-section of the radon industry, using various types of devices, generally were in good agreement with each other and with the reference values. The average of the relative differences from the reference values for each device category was in the range of L5%. However, some individual groups of devices were not in as close agreement with the reference value as would be desired, particularly in the long-term 1998 International Radon Symposium 111 3.1 measurement category. More participants with long-term devices are needed in future exercises so that alpha-track devices and long-term electret ion chamber devices can be categorized individually.