A new very sensitive LSC procedure for determination of Tc-99 in environmental samples

Abstract

A new method for the determination of Tc-99 in different environmental samples has been developed. The sample is carefully ashed in a muffle furnace and then fused with Na₂CO₃ and K₂CO₃. The first step is an enrichment and purification of TcO ₄ ⁻ on an anion exchange resin. The Tc is desorbed as a cationic thiourea complex, which is held on a cation exchange resin. The complex is destroyed by oxidation to TcO ₄ ⁻ with (NH₄)₂S₂O₈ in sulfuric acid. From this solution TcO ₄ ⁻ is extracted into TBP/toluene and the organic phase is mixed with a scintillation cocktail and counted in an anticoincidence shielded LSC. Tc-99m is used as a chemical yield tracer. The decontamination factors for all important fission and activation products and naturally occurring radionuclides are in the range between > 10⁵ and > 10⁸. The detection limit is about 5 mBq per sample at a counting time of 1000 minutes. The maximum sample amount of plants is 500 g dry weight and therefore the lowest detection limit achievable is 10 mBq/kg. Ashing and dissolution of the samples takes 24 h and 4 analyses are performed by one technician in 8 hours. The chemical yield ranges from 50 to 80%.