Iodine-129: its occurrence in nature and its utility as a tracer.

Natural production rates of the 16 million-year iodine-129 from spontaneous fission and from cosmic-ray reactions are estimated to contribute a steady-state concentration of more than 10(-14) gram of I(129) per gram of I(129) to the hydrosphere, the atmosphere, and the biosphere. These concentrations are expected to be detectable by neutron-activation analysis in natural materials that concentrate iodine. Substantial additional contributions have been made by fission-produced I(129) in fallout, serving as an intrinsic tracer for natural iodine kinetics. Iodine-129 activation analysis has advantages as a tracer technique.