RADIUM-226 IN COAL-MINE EFFLUENT, PERRY COUNTY, OHIO

Coal and the associated bituminous shale in the Pennsylvanian System of Ohio contain uranium (U) and thorium (Th) in concentrations ranging from 1 to 5 ppm. The radioactive daughters of these elements have been released into aqueous solution as a consequence of open-pit mining. The most abundant radionuclide is Ra-226 because it has a comparatively long half-life of 1600 years. This and other radionuclides form cations which are sorbed to ferric hydroxide that precipitates from the mine effluent as the pH rises. Radium-226 decays by alpha emission to radon-222 followed by a 0.184 MeV gamma ray with a frequency of 3.3%. Therefore, the Ra concentrations of solid ferric hydroxide in Rush Creek and its tributaries near New Lexington, Perry County, were measured by gamma-ray spectrometry. In a typical experiment, 15 g of air-dried ferric hydroxide were counted for 64 hours yielding a decay rate of 1.1 x 10^-5 micro Curies and a Ra-226 concentration of 23 picograms per gram. The Ra concentrations determined in this way range up to 590 pg/g depending on the U concentration of the source, on the pH of the water, and on the fraction of Ra removed from the water by sorption upstream of the collecting sites. The total gamma-ray flux caused by the decay of Ra-226 and other daughters of U and Th in the ferric hydroxide ranges up to 40 MeV/g/s which corresponds to less than 2 x 10^-2 Rems/100g/y (4p geometry) and does not exceed the maximum permissible dose of 0.5 Rems/y per person.