Analysis of trace level thorium and uranium in drainage from a radioisotope laboratory by particle-induced X-ray emission

A procedure has been developed and tested for particle induced X-ray emission (PIXE) analysis for thorium and uranium in drainage from the radioisotope laboratory at Tohoku University. Two kinds of targets were prepared and analyzed by PIXE under the condition of 3-6 μC irradiation of 3 MeV protons. Concentrations higher than 40 ppb, regardless of the chemical forms of thorium and uranium ions in a sample solution, were determined for targets prepared by deposition of 0.15 ml solution containing Ga-internal standard on a thin polycarbonate film. Uranium was analyzed quantitatively down to 5 ppb with good precision by a pre-concentration method of dibenzyl-dithiocarbamate complexation combined with subsequent condensation into dibenzylidene-D-sorbitol gels. The PIXE analysis for these two kinds of targets can be applied to routine work for contamination control of drainage from a radioisotope laboratory using extremely long-lived actinides such as thorium and natural uranium in various experiments.