Initial distribution and chemical state of 131IO3- dopants in solid periodate matrices

The initial distribution and chemical state of 131IO3- dopants, prepared from 131I-, are investigated in NaIO4 and KIO4. Previous analytical procedures are modified towards more reliable results. Doping by rapid cyrstallization from hot saturated solutions produces well calibrated crystallite (50μm). Except for the outer layers of the crystallites, the activity distribution is roughly uniform in NaIO4 and KIO4. The initially exchanged fraction, E, depends drastically on the dopant concentration, Cd, with a sharp maximum at 25 ppm iodate. Data from positron annihilation techniques point to positronium formation in the doped samples and confirm a marked anomaly at 25 ppm iodate. The peculiar shape of the variation of E with Cd can be explained supposing that the exchange occurs whenever two or more dopant ions aggregate at nearby lattice sites during the doping process. The defect associated with a single dopant ion, presumably an oxygen vacancy, would be responsible for the positronium formation. 17 refs