Field assessment of radon exposure in three zirconium and titanium mineral processing plants: radon concentrations, individual progeny concentrations, size distributions, etc.

Naturally-Occurring Radioactive Materials (NORM), such as uranium, radium, and thorium, can lead to elevated radon exposure among workers and the public. In certain mineral processing facilities-such as those handling zirconium and titanium-exceptionally high concentrations of uranium and thorium are present, necessitating field surveys and radon exposure assessments from a radiation protection management perspective. This study investigated three typical factories in Qinzhou, southern China. Measurements were conducted in workplaces for gamma dose rates, radon and thoron progeny concentrations, and key physical characteristic parameters of radon-thoron progeny. Dose conversion factors (DCFs) for radon and thoron were calculated using the TAURUS software. Results indicate an average radon activity concentration of 14.67 ± 0.39 Bq/m3, while the average equilibrium equivalent radon concentration (EERC) and equilibrium equivalent thoron concentration (EETC) were 2.64 ± 0.09 Bq/m3 and 2.45 ± 0.07 Bq/m3, respectively. Elevated gamma dose rates were observed in some workplaces. For characteristic parameters, the average activity median diameter of attached radon/thoron progeny (AMDa) was 218 nm and 206 nm, with geometric standard deviations (GSDa) of 1.7 and 1.8, respectively. The average activity median diameter of unattached progeny (AMDu) was 1.32 and 2.18 nm, with GSDu values of 1.3 and 1.2. The DCF for radon progeny was calculated as 32.5 nSv/(Bq·m-3·h), and for thoron progeny as 149 nSv/(Bq·m-3·h). In workplaces, the estimated annual effective dose for workers primarily stems from gamma radiation and thoron exposure, with contributions of 0.67 and 0.44 mSv, respectively. In contrast, radon exposure contributed only 0.11 mSv. When both workplaces and dwellings are considered, the total estimated annual effective dose was 3.59 mSv, with gamma radiation, radon, and thoron making comparable contributions on average.