An international marine-atmospheric {sup 222}Rn measurement intercomparison in Bermuda. Part 1: NIST calibration and methodology for standardized sample additions

As part of an international {sup 222}Rn measurement intercomparison conducted at Bermuda in October 1991, NIST provided standardized sample additions of known, but undisclosed (blind) {sup 222}Rn concentrations that could be related to US national standards. The standardized sample additions were obtained with a calibrated {sup 226}Ra source and a specially-designed manifold used to obtain well-known dilution factors from simultaneous flow-rate measurements. The additions were introduced over sampling periods of several hours (typically 4 h) into a common streamline on a sampling tower used by the participating laboratories for their measurements. The standardized {sup 222}Rn activity concentrations for the intercomparison ranged from approximately 2.5 Bq {center_dot} m{sup {minus}3} to 35 Bq {center_dot} m{sup {minus}3} (of which the lower end of this range approached concentration levels for ambient Bermudian air) and had overall uncertainties, approximating a 3 standard deviation uncertainty interval, of about 6% to 13%. This paper describes the calibration and methodology for the standardized sample additions.