Abstract
The 238U, 234U and 226Ra in the river-bed soil were investigated on those adsorption and contents. The soil samples were taken from the upstream area of Yoshii-River in Okayama Prefecture. In this area, uranium mine has been developed and nuclear fuel plants have been operated for producing uranium enriched by centrifugation of UF6. The radioactive waste effluent has been released into the river. Six soil samples were sieved into six fractions according to particle-size, respectively. The preliminary experiment concluded that the concentrations of the three nuclides increased with decrease in particle-size of soil on all samples, though the particle-size distributions varied with both sampling location and date. Thus the concentration of each nuclide in a fine river-bed soil was found to show effectively the latest level of pollution in the river water. The concentrations of 238U in each fraction of the two samples were measured by γ-ray spectrometer with intrinsic Ge-detector and 226Ra also with Ge(Li)-detector. The soil surface-area of each fraction was measured by B. E. T. method. The con-centrations of each nuclide in the soil were directly proportional to the specific surface-area. The concentrations of both nuclides adsorbed on the soil and the 226Ra/738U ratio were estimated with respect to the specific surface-area in each fraction. It was found to be useful for monitoring of nuclear fuel plants to pay attention to the 226Ra/238U ratio as well as the 234(235)U/238U ratio.
