²²²Rn/²²⁰Rn and their daughters are widely present in the atmosphere and indoor environment. The presence of high-concentration ²²⁰Rn can affect the accuracy of ²²²Rn concentration measurements.

This study aims to measure radon concentration more accurately by investigating the variation in the response coefficients of the AlphaGUARD PQ2000 radon monitor to ²²⁰Rn under thoron gas concentrations with different wind speeds and directions within a standard radon chamber.

The single-scintillation proportional counter flow gas static method was employed to determine the thoron concentration in this study. Firstly, a self-made and stable high emissivity solid ²²⁰Rn source at the University of South China was applied to the generation of ²²⁰Rn gas in the chamber, a temperature and humidity control system was adopted to regulate the inside temperature and humidity of ²²⁰Rn whilst the wind speed was controlled by changing the operating frequency of the variable frequency fan. Then, the readings of the AlphaGUARD PQ2000 were observed at various wind speeds and directions under controlled temperature and humidity conditions. Subsequently, the response coefficients of the AlphaGUARD PQ2000 to thoron in diffusion mode were calculated according the observed results.

When the wind speed increases from 0.05 m·s^-1 to 3.50 m·s^-1, the response coefficient of AlphaGUARD PQ2000 to ²²⁰Rn increases from 0.044 to 0.126. When there is no wind, the response coefficient is 0.049. When the wind speed is fixed at 0.71 m·s^-1 and the angle between the wind direction and AlphaGUARD PQ2000 diffusion window changes from 0° to 180°, the response coefficient decreases from 0.083 to 0.051. When the wind speed is fixed at 1.43 m·s^-1 and the angle between the wind direction and AlphaGUARD PQ2000 diffusion window changed from 0° to 180°, the response coefficient is reduced from 0.115 to 0.081.

The response coefficients obtained in this study can provide a reference for correcting the interference of ²²⁰Rn in the measurement results of the diffusion mode of the AlphaGUARD PQ2000 radon detector.