Modes of occurrence of Ra-226 and its immediate daughter products in uranium tailings samples from the Monticello Mill, Utah

A nuclear-emulsion feasibility study of the modes of occurrence of 226Ra and its immediate alpha-emitting daughter products has been completed. The study involved approximately 40 samples of drill core from the Monticello Mill, Monticello, Utah. The drill core was studied using the dispersed-grain nuclear-emulsion technique, a micro-autoradiographic procedure which permits the direct observation of the alpha activity of these radionuclides and their association with individual mineral grains or particles. This work was undertaken because nuclear-emulsion techniques have not been used in the study of uranium-mill-tailings and because it was important to explore the possible contributions that these untried techniques might make to the remedial-action program. Specifically, it was hoped that it would be possible to supplement the bulk measurements of uranium, radium, radon, and other radionuclide concentrations in the tailings with information on how these radionuclides are distributed, i.e., their modes of occurrence, mineralogy, and relative mobility. Four modes of occurrence of 226Ra and its immediate daughter have been described and photographed. The most abundent phase is believed to be a chemical combination of radium with sulfate most probably as a surface reaction with the mineral (Ra,Ba)SO4. The second mode of occurrence is characterized by point sources of alpha activity which are not associated with visible grains or particles. The third mode is less common and is characterized by the association of relatively intense 226Ra alpha activity with deposits of very fine red particles frequently attached to the surface of quartz grains. The fourth mode is characterized by the presence of two-, three-, and four-track alpha stars whose vertices appear to lie on grain surfaces