Miners' exposure to radon and its decay products in some Iranian non-uranium underground mines

Measurements of radon, radon decay products and gamma exposure rate in 12 non-uranium underground mines have been carried out in order to estimate the occupational radiation exposure of miners. Continuous measurements of radon using pulse ionisation chambers and scintillation cell techniques were employed for these studies. Progenies of radon were collected on filter paper, and then a three-count procedure was used for the measurement. The equilibrium state between radon and its decay products has been determined. Concentrations of natural radionuclides (Ra-226, Th-232 and K-40) in ore and soil samples taken from various locations in each mine have been measured using a Canberra High Purity Germanium detector. Based on these measurements two ranges of dose were evident. Doses ranged from 0.1 to 1.52 mSv y(-1) for nine mines and from 10 to 31 mSv y(-1) for the other three mines. A separate grouping of the mines was recognised from radon concentrations, which varied from 2 Bq m(-3) to 10 kBq m(-3). In three of these mines, working level (WL) concentrations of the order of 36-1771 mWL were determined in different working areas. In all other mines, the concentrations were observed to be < 45 mWL.