Background: Standard reference of 220Rn activity concentration is essential for 220Rn measuring device calibration. Purpose: A well performance standard reference of 220Rn activity concentration is imperative for 220Rn measurement device calibration in China. Methods: For this purpose

analytically pure Th(NO3)4 ·4H2 O which had been preserved for more than 40 years was used for producing 220Rn source with stable exhalation rate. An inner source 220Rn chamber was designed and constructed with temperature

humidity and airflow control system to ensure the stability and homogeneity. The 220Rn activity concentration was adjustable through changing different activity 220Rn sources. A measuring device using Lucas scintillation cell whose calibration coefficient was determined by both theoretical method and calibration test in PTB was developed to determine the 220Rn activity concentration in the chamber. Results: It was shown that both the short-term(more than two days) and long-term(half a year) stability of our standard reference performed very well. The heterogeneity of our standard reference in the chamber was less than 5.5%. By changing different 220Rn sources

the adjustable range of our standard reference was 500–20 000 Bq·m-3. The calibration coefficient of the Lucas scintillation cell was confirmed as 53.02 Bq·m-3·min in PTB calibration test. Conclusion: A standard reference of 220Rn activity concentration which is accurate

stable

uniformly distributed and concentration adjustable is established in this study.