COMPARATIVE ASSESSMENT OF DIGESTION METHODS FOR SOIL SAMPLES DURING THE RADIOCHEMICAL DETERMINATION OF ^239+240Pu

A great many nuclear tests of different types and yields were conducted at the Semipalatinsk Test Site (STS). That has lead to the formation of radioactively contaminated areas within it, which differed from one another in the pattern, levels and the isotopic composition. At the same time, technogenic radionuclides are oftentimes in the soil cover of STS in tightly bound and slightly soluble forms, which hampers their complete extraction from samples for a subsequent quantitative analysis. Typically, the extraction process is carried out in open systems using solutions of hydrofluoric acid (HF) and other mineral acids. However, this technique is time-consuming, requires a great many reagents and may result in the loss of elements to be assayed as well as in a possible cross contamination of samples. Autoclave digestion can be an alternative to acid digestion in open systems. This method, on the one hand, is devoid of the disadvantages inherent in open decomposition, on the other hand, it has an undoubted advantage, which consists in accelerating the decomposition process due to an increase in the boiling point of acids. As demonstrated by experimental findings, measurements of 239+240Pu activity concentration in soil samples obtained from a complete acid and autoclave decomposition, in most cases, agree well enough with one another (the existing discrepancies are within the measurement error). Analysis of a radioactivity reference standard using the autoclave decomposition technique showed satisfactory results. The deviation from a certified value was in the order of 5%.

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