Comparison of two methods to determine ~(129)I in charcoal cartridge samples by AMS

摘要

To investigate the short- and long-term accumulated emissions from a nuclear facility, charcoal air filter cartridges were exposed at a reactor site for seven days. The short-lived ~(131)I adsorbed in these filters was measured by gamma counting immediately after the samples were retrieved. The very long-lived ~(129)I was analyzed later by AMS. For this purpose, two methodologies were developed: an extraction method and direct analysis, i.e., inserting an aliquot of the filter carbon directly into the target piece. The former method used a system designed to avoid sample loss resulting from the high I_2 species volatility. Iodine-125 was used as a tracer to monitor the efficiency of this extraction process. The direct method was based on our experience with charcoal in the analysis of ~(14)C in Cs sputter ion sources. In this direct analysis, charcoal samples were first spiked with a known quantity of stable iodine (~(127)I), in an excess over the quantity naturally present in the filter, and then pressed into targets. In this way, ~(129)I concentrations from all the charcoal samples were quickly determined. In both methods, it was found that the atom concentration of ~(129)I in these samples exceeded that of the ~(131)I by 2-3 orders of magnitude. These studies demonstrate the effectiveness of the charcoal capture method as a diagnostic tool for monitoring the emissions from nuclear facilities. This approach may be extended for the detection of other long-lived radioactive isotopes, which would further expand the scope of such monitoring studies.