NIST 222Rn emission standards

NIST radon standards are hermetically sealed polyethylene capsules filled with 226Ra solution. Recently, four new series of standards with activities 5, 50, 500, and 5000 Bq were prepared. The measured emanation fraction agrees with a calculation that accounts for the radon accumulated inside the polyethylene walls of the capsule. Obtained solubility of radon in polyethylene is approximately 45 of the solubility of radon in water. The radon diffusion coefficient in low-density polyethylene is 7.2×10-8cm2/s.