Development of a field method for the detection of technetium-99 in soil

Technetium-99 is a pure beta emitter with a maximum beta energy of 292 keV. Detection of technetium-99 in soil is dependent on efficient and selective chemical separation of technetium from other soil components. Previous methods for the chemical separation of technetium are not suitable for use in the field due to the chemicals used, the waste produced, the time required, or the need for an experienced chemist to run the procedure. This research has a produced a technique that is rapid, chemically simple, inexpensive, and that produces little waste.

A 1.00 g soil sample is leached with 20.0 mL of 10% sodium hypochlorite and centrifuged. The soil is then leached with another 20.0 mL of 10% sodium hypochlorite and centrifuged. The hypochlorite solutions are combined and treated with 10.0 mL of 30% hydrogen peroxide. Technetium in the soil will be promoted to the plus seven oxidation state by this procedure. When in the plus seven state, technetium forms a very stable and soluble ion, pertechnetate. After the peroxide treatment, the solution is evaporated at 80°C to decrease the volume. After this solution has cooled, it is mixed with 10.0 mL of cyclohexanone.. Cyclohexanone is insoluble in the aqueous solution, and, as a result, two layers are formed. The pertechnetate ion forms a complex with cyclohexanone. Therefore, technetium in the aqueous phase is efficiently transferred to the cyclohexanone phase. Other beta emitters common in contaminated soil are not transferred to the cyclohexanone, so the technetium has been isolated. The cyclohexanone extraction is repeated twice to increase the yield and the sample can be counted using either gas proportional counting or liquid scintillation counting. This procedure is currently yielding efficiencies of 93±2%. Reproducibility errors are below ±5%. With a low background liquid scintillation counter and a 1 hour counting time, the detector controlled potential lower limit of detection is approximately 0.04 Bq/g of soil (1 pCi/g).

This procedure has been tested by an outside laboratory, Oak Ridge Institute of Science and Energy Energy/Environment Systems Division( ORISE EESD). This laboratory reported average efficiencies of 97%. ORISE EESD is using gas proportional counting instead of liquid scintillation counting. In all other ways, the procedure is identical to the one described in this thesis. This procedure has been implemented asORISE EESD's standard operating procedure for the detection of technetium-99 in soil sample.