Radon monitor calibration using NIST radon emanation standards: steady flow method.

The National Institute of Standards and Technology (NIST) polyethylene-encapsulated 226Ra/222Rn emanation (PERE) standards (old SRM 4968 and new SRMs 4971, 4972, and 4973) provide precise radon emanation rate, certified to a high degree of accuracy (approximately to 2%). Two new SRM 4973 standards containing totally 1036 Bq (0.028 microCi) of 226Ra, emanate 0.114 Bq (3.08 pCi) of 222Rn per min. Air passing over such sources at a flow rate of 1 l min(-1) will have a radon concentration of 114 Bq m(-3) (3.08 pCi l(-1)). This paper describes a practical calibration system and the actual calibration verification data obtained at different flow rates, for E-PERM passive radon monitors, Femto-Tech and Alpha Guard Continuous Radon Monitors. The use of such an affordable and easy to use system by the manufacturers and users of radon measurement devices will bring uniform standards with traceability to a NIST standard source and is considered an important step in standardising radon measurement methods.