Separation of Ultratraces of Radiosilver from Radiocesium for Environmental Nuclear Forensics

The presence of environmental radiosilver and the investigation of the 108mAg/110mAg isotopic ratio in the aftermath of a nuclear power plant accident provide valuable information on the condition of the control rods of pressurized water reactors. However, the detection of minute amounts of the γ-emitting radiosilver isotopes is often thwarted by the presence of concomitant and dominating γ emitters, primarily 137Cs, which results in increased detection limits in the γ spectra. We developed a rapid and robust separation protocol for trace silver extraction in the presence of overwhelming activities of 137Cs via the autodepostion of silver on a copper plate. This method achieved a quantitative removal of interfering 137Cs in the deposition product and proved to be very efficient (yields >70% for aqueous samples), rapid (results within 4 h), and robust with respect to varying salinities and composition of the water samples. The autodeposition approach is also applicable for organic samples after acid-assisted microwave digestion. By applying the established sequential extraction protocols for soil, the fate of freshly deposited radiosilver and radiocesium in soil was investigated. Silver showed a high affinity to the soil with a pronounced (>90%) accumulation in the residual fraction after the sequential extraction, whereas radiocesium exhibited higher mobility, allowing for the extraction of major fractions in the first extraction steps. The composition of the aqueous contamination matrix (CaCl2 or Ca­(NO3)2) had a significant influence on the binding properties of cesium on soil.