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

I-129 is a long-lived radionuclide (T-1/2 = 1.6(.)10(7) y) present in Sellafield aerial emissions which transfers through the air-grass-cow-milk pathway. Concentrations of I-129 in milk are regularly monitored and they are also predicted by modeling, the results of which are used to set limits on the discharges from Sellafield. It has been suggested that the analysis may under-estimate the concentration of I-129 in milk due to a "loss" of this radioisotope during storage of the milk before analysis takes place. This study used neutron activation analysis to determine I-129 in a milk sample obtained from a farm downwind of the Sellafield site, over a period of ten weeks. Sub-samples of milk were removed from storage and analyzed after 0, 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 showed that there was no discernible loss of I-129 from the milk over the 10-week storage period. The stable iodine content of the milk was also determined and was found to be within the "normal" range quoted in the literature of between 0.01 and 1 mg(.)l(-1).