In the calibration and development of instruments for measuring radioactive gases, calibration chambers serve as efficient and convenient environments for testing. For 220 Rn (Thoron), which has a notably short half-life of 55.6 seconds, its markedly non-uniform spatial distribution within the chamber can compromise the accuracy of activity concentration calibrations. This study developed a numerical model that integrates dilute species transport with fluid dynamics, based on the 220 Rn calibration chamber at the China Institute of Atomic Energy, to simulate the spatial distribution of 220 Rn activity concentration within the apparatus. The model’s validity was confirmed through comparison of simulated results with empirical measurements obtained from eight sampling locations. Based on the simulated distribution data, areas exhibiting less than a 5% variation in activity concentration were delineated and classified as uniform regions. Subsequently, the original sampling port configuration was optimized accordingly. Experimental validation demonstrated that the optimized sampling scheme reduced the relative standard deviation of measurement results from 5.3% to 3.5%, thereby enhancing the representativeness of sampling and the reliability of the calibration process. This numerical model thus offers a theoretical framework and empirical support for the performance assessment and structural optimization of 220 Rn calibration chambers. • A numerical model coupling dilute species transport and fluid dynamics was developed for 220 Rn calibration chambers. • Spatial distribution characteristics of 220 Rn activity concentration in the calibration chamber were simulated and analyzed in detail. • Simulated 220 Rn activity concentration values show good agreement with experimental measurement results. • Optimization of measurement point layout significantly improved the uniformity of 220 Rn concentration distribution.
Zhou et al. (Wed,) studied this question.