Rapid radiochemical analysis of 131I in environmental samples using a well-type Ge-detector

Large-scale production of 131I in a nuclear reactor, the gaseous nature of 131I, and its selective uptake by the human thyroid gland, make this radioisotope a health hazard in the event of a nuclear accident. The maximum concentration of 131I in drinking water has been set at 1 pCi/l. Human ingestion of 131I through the grass-cow-milk pathway makes milk an environmentally significant matrix to be monitored for. A simple and a rapid radiochemical procedure for the analysis of 131I in water and milk samples is reported. A quick single-step separation on anion-exchange resin concentrates radioiodine from large sample volumes. The resin is then directly counted in the cavity of a low-background well-type HPGe detector that has high counting efficiency for X-rays and low-energy γ-radiation. Chemical recovery is evaluated from the intensity of the 29.6 keV X-rays of the 129I spike, and 131I is assayed through the intensity of its 364.5 keV γ-peak. The method's minimum detection limit is 0.5 pCi 131I based on a 1 liter sample and a 200-minute count. (author)