This primary radon measurement system consists of 4 pulse ionization chambers and ancillary gas handling and gas purification equipment. All of the radon measurements made at NIST and radon transfer calibration standards and calibration services provided at NIST are directly related to this national radon standard.
Reference: The NIST Primary Radon-222 Measurement System. R. Collé, J.M.R. Hutchinson, and M.P. Unterweger. J. Res. Natl Inst. Stand. Technol. 95, 155 (1990).