Implementation and testing of steady-state operating mode of the radon chamber

The Slovak Institute of Metrology has developed a system for the metrological testing and calibration of instruments designed to measure the volumetric activity of radon. The system comprises the AiRneSt radon calibration chamber and RF-type dry flow sources containing ²²⁶Ra salts. The chamber, with an internal volume of approximately

1 m³, enables the generation of ²²²Rn concentrations ranging from 100 Bq/m³ to 100 kBq/m³.

At present, the chamber operates in a self-decay mode, in which it is filled with radon of a precisely defined initial concentration that decreases naturally due to radioactive decay. This mode is particularly suited for accurate determination of radon decay curves and verification of reference values.

The objective of this study is to develop and validate a method enabling the transition from the self-decay regime to a stationary operating mode. The proposed approach is based on a model with constant radon supply and controlled ventilation. The temporal evolution of the radon volumetric activity , is described as an exponential increase toward a steady-state value, governed by the decay constant (), ventilation coefficient (), radon input rate (), and chamber volume ().

Implementation of the stationary regime ensures stable radon concentrations and consistent airflow during measurements, thereby enhancing the reproducibility and accuracy of exposures and related measurement parameters.