CHARACTERIZATION OF 126I-LABELED FULLERENES BY MULTIPHOTON DETECTION. Michael G. Mitch, Lisa R. Karam, and Bert M. Coursey, Ionizing Radiation Division, NIST, Gaithersburg, MD, USA.

Iodine radionuclides are important in nuclear medicine for both imaging and therapy. The entrapment of such a chemically reactive species within fullerenes may allow the development of a new family of radiotracers and, with the appropriate biomolecule derivative, site-specific radioimagers. We have attempted to encapsulate iodine within fullerenes by high-current arc-burning of graphite rods doped with iodoform (CHI3) in a helium atmosphere. Following removal of excess iodine from the resulting soot by solvent wash and heating methods, fullerenes were extracted by stirring in CS2 and purified by High Performance Liquid Chromatography (HPLC). Iodine present in HPLC fractions was activated using gamma photons from the Medical Industrial Radiation Facility (MIRF) through the reaction 127I(gamma, n)126I. The radiolabel was identified by MultiPhoton Detection (MPD) and Fuji plate phosphoimaging. Activation following soot processing has allowed the development of a protocol for fullerene encapsulation of iodine which will be applied to the direct encapsulation of 123I and 125I, radionuclides currently used in nuclear medicine. Although designed for ultra-low level detection of 125I, the efficiency of the MPD for 126I was determined by measurements of Na126I samples by both an HPGe detector of known efficiency and the MPD. The photonuclear isotope production yield of 126I by the MIRF at 25 MeV was determined, as well as the lower limits of 126I detection for the MPD and Fuji plate.