Abstract: Objective To systematically reveal the distribution law of underground radon concentration in metal mines under the coupled effects of depth gradient,ventilation conditions and occupational exposure,accurately identify high-risk areas and exposed populations,and carry out dosimetric attribution and risk assessment.Methods A retrospective analysis was performed on 62 groups of underground monitoring data collected from underground metal mines in the Gannan area of Jiangxi Province.A RAD7 radon detector was adopted for field measurement.The UNSCEAR recommended model was used to estimate miners’annual effective dose.Normality test and homogeneity of variance test were conducted to verify the applicability of the data,and analysis of variance as well as multiple linear regression models were applied to analyze the multi-factor coupling effects. Results The arithmetic mean of underground radon concentration was(499±632)Bq/m³ with a median of 285 Bq/m³,and 16.1%of the measuring points exceeded 1 000 Bq/m³.Radon concentration increased significantly with the rise of mining depth(P＜0.001).The average radon concentration at mining depth≥400 m was(1 422±919)Bq/m³,which was 6.9 times that of shallow areas(depth＜100 m).There was a significant negative correlation between effective ventilation rate and radon concentration(P＜0.001).When the ventilation rate was less than 60%,the average radon concentration reached(2003±900)Bq/m³,while it decreased to(128±59)Bq/m³ when the ventilation rate was≥90%.There were significant differences in exposure levels among different occupational groups(P＜0.001).The median annual effective dose of extraction workers was 3.917 mSv.The data passed normality and homogeneity of variance tests and met the prerequisites for analysis of variance.The adjusted R² of the multiple linear regression model was 0.68.The annual effective dose increased by 0.65 mSv per 100 m increase in mining depth,and decreased by 2.70 mSv per 10%improvement in effective ventilation rate. Conclusion Radon pollution in underground metal mines is characterized by“generally controllable with partial over-limit areas”.The coupling of deep mining,low ventilation efficiency and long-term exposure of extraction workers is the core cause of high radiation dose.Differentiated and targeted ventilation optimization and occupational health management strategies should be implemented for deep mining areas(≥400 m)andextraction workers.

Key words: metal mine, radon concentration, depth gradient, ventilation conditions, occupational exposure