Nist Traceable Radon Calibration System for Calibrating

The NIST (National Institute of Standards and Technology) has recently made available 222Rn emanation standards for test and evaluation. The NIST certified parameters include the ^ ~ a strength and the emanation coefficient. When such a source is loaded into a radon leak tight enclosure of a known volume, 222~n accumulates over time and it is possible to calculate precisely the time integrated average radon concentration after any given accumulation time. For example, if 25 Bq(676pCi) NIST source is loaded into a jar with an air volume of 3.72 liter, the time integrated average radon concentration is 973 Bq m'3 (26.3 pCi after an accumulation time of exactly two days. If the radon detector placed in the jar is non-radon absorbing and a true integrator, the radon detector must yield the theoretically predicted results. The paper describes a study involving 30 randomly chosen E-PERM% and 15 NIST sources in 15 different calibration jars. The study indicated that E-PERM% give results within about 5 % of the predicted results. The study also shows how a NIST source can be used in practice. Theavailability of N1ST sources in the future with precisely known radon emanation characteristics is considered to be a major advancement in radon metrology.The methodology is within the reach of any quality conscious radon measurement laboratory.