An International Radon-in-Air Measurement Intercomparison Using a New Transfer Standard

Abstract A new secondary measuring system for 222 Rn-in-air that can be used as a very efficacious transfer calibration standard for measurement intercomparisons between laboratories has been developed and extensively tested. The system is based on measurements of the photon emission rate of radon samples contained in spherical 35-mL glass ampoules with a NaI(Tl) well counter. The system is calibrated against the NIST pulse-ionization-chamber (PIC) national radon measuring system, and has an overall uncertainty of approximately 2 percent. An international intercomparison of 11 laboratories, including NIST, using this system was performed.