Radon release from building materials in Hong Kong

Area of Science:

• Environmental Science
• Radiological Protection
• Building Physics

Background:

• Indoor radon (222Rn) is a significant contributor to public radiation exposure, particularly in high-rise buildings.
• Radon originates from the decay of naturally occurring radioactive materials (NORMs) within building materials.
• Understanding radon sources and transport mechanisms is crucial for mitigating indoor air quality issues.

Purpose of the Study:

• To investigate the radionuclide content of typical building materials used in Hong Kong.
• To measure physical properties influencing radon transport in these materials.
• To assess factors affecting indoor radon exhalation rates, including surface coatings and temperature.

Main Methods:

• Gamma spectrometry was employed to determine the concentrations of radium-226 (26Ra), thorium-232 (232Th), and potassium-40 (40K).
• Emanation coefficients and radon diffusion coefficients were measured.
• Radon exhalation rates were quantified under varying conditions, including the application of surface coatings and temperature changes.

Main Results:

• Hong Kong concrete exhibits the world's highest average concentrations of 226Ra, 232Th, and 40K.
• Measured physical properties (emanation and diffusion coefficients) were comparable to international values.
• Surface coatings reduced radon exhalation by 2-68%, and exhalation rates increased with temperature, up to fourfold at 50°C compared to 20°C.

Conclusions:

• The exceptionally high radionuclide content in Hong Kong concrete is a primary driver of elevated indoor radon levels.
• While material properties are similar globally, local radionuclide concentrations are a critical factor.
• Temperature significantly enhances radon exhalation, necessitating consideration in building design and climate control.