| Popis: |
Benefits of the use of environmental concentrators include improved measurement sensitivity and, in some cases, matrix materials that are present in smaller quantities and with less varied composition than in soil samples. Actinides are frequently present only in small quantities in the environment, yet accurate determination of their source and isotopic composition is of great importance for purposes ranging from gauging the impact of industrial accidents to monitoring compliance with the terms of international nuclear nonproliferation agreements. Two concentrators of actinides are discussed in this work: rusty metal and lichens. It was demonstrated that rusty metal samples can be used to identify plutonium attributable to a specific source term and its distribution throughout a specific site. This was achieved by analysis of plutonium isotopes present in rusty metal samples collected in the area of the former Mound site in Southwestern Ohio. Comparison of the results with previous measurements made by Oldham, et al. shows the influence of environmental factors on the adsorption of plutonium by rusty metal. A new preconcentration method for rusty metal samples that avoids the use of harsh reagents (hydrofluoric acid) and that has potential application for multielemental analysis without requiring the sample to be divided is also presented. It was demonstrated that this method can provide comparable plutonium measurement results to preconcentration by lanthanum coprecipitation. The use of lichens for monitoring of anthropogenic radionuclides contained in airborne particulates is evaluated as well. Lichens collected from trees function as adventitious air filters and can be used to identify the composition of anthropogenic radionuclides that are likely to continue to be transported in the environment. An existing lichen reference material certified for composition of stable elements, prepared for use in support of air quality studies, was determined to also provide a suitable benchmark for measurements of key anthropogenic radionuclides including uranium, plutonium, neptunium, and cesium. Quantity and isotopic composition of these nuclides was determined to be consistent with what was known about the time period and location during which the lichen was collected. |
