AN INTERNATIONAL MARINE-ATMOSPHERIC RN-222 MEASUREMENT INTERCOMPARISON IN BERMUDA .2. RESULTS FOR THE PARTICIPATING LABORATORIES

As part of an international measurement intercomparison of instruments used to measure atmospheric Rn-222, four participating laboratories m ade nearly simultaneous measurements of Rn-222 activity concentration in commonly sampled, ambient air over approximately a 2 week period, a nd three of these four laboratories participated in the measurement co mparison of 14 introduced samples with known, but undisclosed (''blind '') Rn-222 activity concentration. The exercise was conducted in Bermu da in October 1991. The Rn-222 activity concentrations in ambient Berm udian air over the course of the intercomparison ranged from a few hun dredths of a Bq . m(-3) to about 2 Bq . m(-3), while the standardized sample additions covered a range from approximately 2.5 Bq . m(-3) to 35 Bq . m(-3). The overall uncertainty in the latter concentrations wa s in the general range of 10%, approximating a 3 standard deviation un certainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the stand ard additions, and almost within expected statistical variations. Thes e same two laboratories, however, at lower ambient concentrations, exh ibited a systematic difference with an averaged offset of roughly 0.3 Bq . m(-3). The third laboratory participating in the measurement of s tandardized sample additions was systematically low by about 65% to 70 %, with respect to the standard addition which was also confirmed in t heir ambient air concentration measurements. The fourth laboratory, pa rticipating in only the ambient measurement part of the intercompariso n, was also systematically low by at least 40% with respect to the fir st two laboratories.