An international marine-atmospheric Rn-222 measurement intercomparison in Bermuda. II - Results for the participating laboratories

As part of an international measurement intercomparison of instruments used to measure atmospheric Rn-222, four participating laboratories made nearly simultaneous measurements of Rn-222 activity concentration in commonly sampled, ambient air over approximately a 2-wk period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed ('blind') Rn-222 activity concentration. The exercise was conducted in Bermuda in October 1991. The overall uncertainty in the latter concentrations was in the general range of 10 percent, approximating a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions, and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an averaged offset of roughly 0.3 Bq/cu m. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65 to 70 percent, with respect to the standard addition which was also confirmed in their ambient air concentration measurements. (Author)