Determination of plutonium and its isotopic ratio in marine sediment samples using quadrupole ICP-MS with the shield torch system under normal plasma conditions

摘要

An analytical method for determining ~(239)Pu and ~(240)Pu in marine sediment samples, which uses quadrupole ICP-MS, was developed in this work. A simple anion-exchange chromatography system was employed for the separation and purification of Pu from the sample matrix. A sufficient decontamination factor of 1.4×10~4 for U, which interferes with the determination of ~(239)Pu, was achieved. High sensitivity Pu determination was obtained, which led to an extremely low concentration detection limit of ～8 fg/ml (0.019 mBq/ml for ~(239)Pu; 0.071 mBq/ml for 240Pu) in a sample solution, or an absolute detection limit of 42 fg in a 5 ml sample solution, by using the shield torch technique. Analytical results for the determination of the ~(239+240)Pu and the ~(240)Pu/~(239)Pu ratio in IAEA 368 (ocean sediment) reference material indicated that the accuracy of the method was satisfactory. The method developed was successfully applied to a study of Pu behavior in the sediments from Sagami Bay, Japan. The observed high ~(240)Pu/~(239)Pu ratio in the sediment core indicated that there was additional Pu input derived from close-in fallout in addition to the global fallout.