Application of the fission track method for the determination of uranium absorbed on filter paper

The fission track method has been used for the determination of uranium in solid samples, but it has been hard to apply to the solution sample and to the solid sample in which uranium distributes heterogeneously. In the present study, we contrived the following sample preparation to give homogeneous distribution of uranium on the surface of a filter paper. GSJ rock samples (50 ∼ 100 mg) were dissolved in a mixed acid of hydrofluoric acid, nitric acid, hydrochloric acid and perchloric acid. The solution was evaporated to dryness, and the residue was taken up with 1 M nitric acid to prepare the sample solution. An aliquot (100 μl) of the sample solution was put on a filter paper (1.3 x 1.3 cm) and dried up. This filter paper was contacted with a mica detector (5 x 5 mm) that had been annealed for 6 h at 600degC and etched by hydrofluoric acid for 2 ∼ 3 h at 25degC in advance, and irradiated for 5 ∼ 90s at a neutron flux of 4.5 x 1013 cm-2s-1. After irradiation, the mica detector was etched again. Double-etched latent tracks were more enlarged and therefore we could distinguish easily the latent tracks from the neutron induced ones. Track densities were determined using an optical microscope of 150 ∼ 600 magnification. Calibration curve was prepared with standard solutions. Then we determined uranium concentrations of GSJ rock samples and the values were in good agreement with reference values reported by Geological Survey of Japan. (author)