STUDY OF INTERACTION BETWEEN ACTINOIDS AND COLLOIDAL MATTER IN GROUND WATER

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Understanding the sorption mechanism of actinoids having long-term radiological toxity onto colloidal matter in aground water is central to the safety assessment of underground disposal of radioactive wastes. In order to develop a methodology for analyzing compositions of colloids sorbing actinoids without disturbing conditions of an experimental system, a vertical in-air Particle Induced X-ray Emission (PIXE) system has been installed at a single-ended type Dynamitron accelerator in Tohoku University, and we have developed a method for auto-analysis of PIXE spectrum. The air offers a good heat removal from a delicate specimen containing a volatile component. Endurance of Kapton foil used as an exit window of in-air PIXE system for beam irradiation was analyzed in consideration of beam current, diameter and energy loss, which enables us to estimate the lifetime of the Kapton foil under various irradiation conditions. A procedure has been developed and tested for PIXE analysis of solubl … More e and insoluble constituents in a water sample. Three kinds of targets were prepared and analyzed with the PIXE system of 3-MeV proton beam. Insoluble components were filtered on a Nuclepore filter of 0.4-pm pores, and the lower detection limit for ferric hydroxide colloids was a few tens of ppb at an accumulated charge of 3 muG.The concentrations of thorium and uranium higher than 40 ppb were precisely determined by 3-muG irradiation on targets which were made from a 0.12-ml solution containing Ga-internal standard evaporated on a user-madepolycarbonate foil. Uranium(VI) ions in a 25-mi sample were preconcentrated into a thin uniform target containing Pd as an internal standard by means of a combination of dibenzyldithiocarbamate complexation with subsequent condensation into dibenzylidene-D-sorbitol gels, and the low concentration of 4 ppb was easily determined by the PIXE measurement. However this method did not work for concentrating trace thorium ions. The widespread concentrations (several tenths of ppb to a few tens of ppm) of -24 elements from Na to Pb were determined simultaneously in a precision sufficient to reveal the elemental distribution between the soluble and insoluble fractions of riverwaters. The methodology also had good sensitivity and precision enough to detennine concentrations of thorium and uranium lower than their permissible concentrations in drainage from a radioisotopelaboratory. Less