Determining ~(241)Pu in environmental samples: case studies in alpine soils

摘要

A procedure was developed for determining ~(241)Pu activity in environmental samples. This beta emitter isotope of plutonium was measured by ultra low level liquid scintillation, after several separation and purification steps that involved the use of a highly selective extraction chromatographic resin (Eichrom-TEVA). Due to the lack of reference material for ~(241)Pu, the method was nevertheless validated using four IAEA reference sediments with information values for ~(241)Pu. Next, the method was used to determine the ~(241)Pu activity in alpine soils of Switzerland and France. The ~(241)Pu/~(239)Pu,~(240)Pu and ~(238)Pu/~(239)Pu,~(240)Pu activity ratios confirmed that Pu contamination in the tested alpine soils originated mainly from global fallout from nuclear weapon tests conducted in the fifties and sixties. Estimation of the date of the contamination, using the ~(241)Pu/~(241)Am age-dating method, further confirmed this origin. However, the ~(241)Pu/~(241)Am dating method was limited to samples where Pu-Am fractionation was insignificant. If any, the contribution of the Chernobyl accident is negligible.