Abstract: Radon is a major contributor to human exposure to natural radiation, and radon exhalation from building materials is an important contributor to indoor radon concentrations. Fired common brick is extensively used in residential buildings in rural areas in China and remains a predominant wall material. In this study, a total of 14 fired common brick samples were collected from 10 provinces in China. The ²²⁶Ra content of the samples was determined using a GC3018 low-background HPGe γ-spectrometer, while porosity was measured using a BSD-TD-K fully automated true density and open porosity analyzer. The radon exhalation rate and radon emanation fraction were measured using the activated carbon sealed chamber method. The radon diffusion length and diffusion coefficient were determined by controlling the thickness of the building material samples using an integrated system including a source chamber, diffusion window, accumulation chamber, and RAD7 radon detector. The mean ²²⁶Ra content of fired common brick was 48 ± 9 Bq/kg, and the mean porosity was 38%±3%. The mean surface radon exhalation rate was 0.03 ± 0.02 mBq·m^-2·s^-1, and the radon emanation fraction was 2.2%±1.1%. The mean radon diffusion length was 0.44±0.10 m, and the radon diffusion coefficient was (0.403±0.165)×10^-6 m²·s^-1. Based on the measured radon exhalation parameters, an indoor radon concentration prediction model was applied to estimate the indoor radon concentration attributable to radon exhalation from building materials. Indoor radon concentrations were also measured in the investigated rooms to quantitatively evaluate the contribution of building materials to indoor radon. The results showed that the average contribution of radon exhalation from building materials to the measured indoor radon concentration was 41%±9% across the six rooms. The contribution of radon exhalation from building materials was lower on the first floor than on the second floor, indicating that first-floor rooms were more strongly affected by radon originating from the underlying soil.

Key words: indoor radon, radon exhalation rate, building materials, fired common brick