A study of radiation parameters in an open-pit mine.

Radiation parameters associated with the open pit mining of a small (10,000 tonnes), but high grade (2%) uranium deposit at Nabarlek, N.T., have been investigated in detail. External radiation levels, radon emanation rates and radon daughter levels were measured systematically during the development of the mine, and are correlated with ore grade, properties of the host rock and atmospheric conditions. Significant radon daughter concentrations were observed only under stable atmospheric conditions, usually during the might and were invariably associated with thermal inversions. The mean cumulative exposure to radon daughters was estimated from the measured levels to be 0.065 Working Level Months for employees working in the pit for the entire four and a half months of mining. The mean cumulative external gamma ray exposure for the same employee group was measured using thermoluminescent dosimeters to be 2.3 mSv (230 mrem). For most other employees, however, exposures were much lower. Data on long lived radionuclides in dust and on particle size distribution are also presented.