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G. J. Beyer, G. Pimentel-Gonzales

Physicochemical and radiochemical aspects of separation of radioiodine from TeO₂-targets

The radio-isotopes of iodine with mass-numbers 120, 123, and 124 are available via proton or deuteron induced reaction on enriched TeO2 targets with medical PET cyclotrons. The radioiodine can easily be separated from irradiated TeO₂ targets using a dry thermo-chromatographic process. The half-time for the release of radioiodine from molten TeO₂ samples as a function of the sample geometry and temperature has been studied systematically. Only 2 minutes are needed to release the radioiodine with >95% yield. Another 10 minutes are needed to trap the released iodine from the gas phase. An Al₂O₃ filter can be used to trap the released iodine intermediately and to clean the iodine from traces of evaporated TeO₂. The activation energy for the release process has been determined to be QA = (170±30) kJ/mol which indicates, that convection contributes significantly to the release. For the adsorption-desorption process of iodine from Al₂O₃ the activation energy was measured to be Q_ad = (90±14) kJ/mol. The desorption half-time was <5 sec for T = 800°C. Dry Al₂O₃ columns can be used as a thermochromatographic ¹³²Te-¹³²I generator. The released iodine exhibits electrophilic properties, suitable for labelling procedures directly from the gas phase. Most likely the iodine is transported in the gas phase in the form of free radicals I*.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 88, 03/2000
Pages: 175

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