Intrinsic Tracers Research Articles

Impurity diffusion in transition-metal oxides

Intrinsic tracer impurity diffusion measurements in ceramic oxides have been primarily confined to CoO, NiO, and Fe 3O 4. Tracer impurity diffusion in these materials, and TiO 2, together with measurements of the effect of impurities on tracer diffusion (Co in NiO and Cr in CoO), are reviewed and discussed in terms of impurity-defect interactions and mechanisms of diffusion. Divalent impurities in divalent solvents seem to have a weak interaction with vacancies whereas trivalent impurities in divalent solvents strongly influence the vacancy concentrations and significantly reduce solvent jump frequencies near a trivalent impurity. Impurities with small ionic radii diffuse more slowly with a larger activation energy than impurities with larger ionic radii for all systems considered in this review. Cobalt ions (a moderate-size impurity) diffuse rapidly along the open channels parallel to the c axis in TiO 2 whereas chromium ions (a smaller-sized impurity) do not.

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.