Determination of the loss of 129I from milk during storage using neutron activation analysis

Abstract

¹²⁹I is a long-lived radionuclide (T_1/2 = 1.6. 10⁷ y) present in Sellafield aerial emissions which transfersthrough the air–grass–cow–milk pathway. Concentrations of ¹²⁹I in milk are regularly monitored and they are also predicted bymodeling, the results of which are used to set limits on the discharges fromSellafield. It has been suggested that the analysis may under-estimate theconcentration of ¹²⁹I in milk due to a “loss” of thisradioisotope during storage of the milk before analysis takes place. Thisstudy used neutron activation analysis to determine ¹²⁹I in a milksample obtained from a farm downwind of the Sellafield site, over a periodof ten weeks. Sub-samples of milk were removed from storage and analyzed after0, 3, 7, 14, 28, 49 and 70 days. A mean concentration of 4.4 mBq . l ^—1 was determined in the milk and analysis of the results showedthat there was no discernible loss of ¹²⁹I from the milk over the10-week storage period. The stable iodine content of the milk was also determinedand was found to be within the “normal” range quoted in the literatureof between 0.01 and 1 mg . l ^—1 .