Determination of 129I and 127I at natural levels by neutron activation analysis

129I is a long-lived (Tsub(1/2) = 1.6 x 107 a) radionuclide which occurs in nature as the result of spontaneous fission of heavy elements and of cosmic-ray reactions. As a fission product it is also produced in nuclear reactors and can be released either at the reactor or later at the fuels reprocessing plant. Because of its long half-life it becomes a permanent contaminant once incorporated into the environment. A combination of neutron activation and gamma-ray coindcidence counting techniques has been used to determine the concentration of 129I and the isotope ratio 129I/127I in mammalian thyroids and various commercial iodine chemicals. Analytical procedures and coincidence counting techniques are presented. The thyroids show an average value of 129I/127I = 21 x 10-9 and 129I concentrations of 22 x 10-4 pCi per g of thyroid. (orig.)