Investigation of the migration of Np-237 in loess by direct gamma-ray method

The migration of Np-237 in an undisturbed Chinese loess column was investigated by direct gamma-ray method. The column was taken from a field test site and installed in a laboratory simulation hall. Radionuclide Np-237 in the form of neptunium nitrate, mixed with quartz, was introduced into the column and covered with loess. Artificial rainfall was applied to the column for about 3 years and, the counting rates of Np-237 in the column from 56 to 616 days at different vertical positions were detected with a gamma-ray detection system. Based on the counting rates of Np-237 in the simulation column at different vertical positions and the distance from the source layer, the relationship of the mass center of Np-237 in the column at different experimental periods to the experimental time was established, C-m = 0.36 log(t)-2.75. Here C-m is the mass center of Np-237 in the column, cm, and t is the experimental time in days. Based on this relationship, the mass center of Np-237 for the 1,073-day experiment was predicted and compared to that obtained with the final destructive method. The good agreement between the prediction and the experimental values indicates that the direct gamma-ray method could be used to predict the migration of strongly adsorbed radionuclides such as Np-237 in environmental media with the help of laboratory simulation columns.Chemistry, AnalyticalChemistry, Inorganic & NuclearNuclear Science & TechnologySCI(E)0ARTICLE1161-16627