Nuclear medicine program progress report for quarter ending September 30, 1993

Processing of enriched tungsten-186 oxide targets after long irradiations (> 2 cycles) in the ORNL High Flux Isotope Reactor (HFIR) has resulted in specific activities significantly lower than the theoretical values, with the concomitant formation of varying amounts of highly radioactive black insoluble material to total tungsten-188 yield, 5% sodium hypochlorite solution has been found to dissolve this black material. Yields for longer irradiation periods (> 2 cycles) have nearly doubled. As an alternative, more simple approach, enriched tungsten-186 metallic targets have also now been irradiated. Following irradiation, these targets were dissolved in hydrogen peroxide/NaOH solution with no evidence of any residual black insoluble material remaining. Yields for a 2-cycle (e.g. 42 days) HFIR irradiation have thus now significantly increased, for example, from 5--6 mCi {sup 188}W/mg of {sup 186}W, to 10 mCi/mg (43 days) and 12.9 mCi/mg (53 days). Large clinical scale (< 1 Ci) generators fabricated from tungsten-188 prepared from such metal targets have exhibited the expected high {sup 188}Re yield and low {sup 188}W breakthrough. Also during this period, a systematic evaluation of the production yields of a number of radioisotopes of current interest in nuclear medicine were evaluated by irradiation of targets in the Hydraulic Tubemore » Facility (HT) of the ORNL High Flux Isotope Reactor (HFIR). Small samples were irradiated for short periods, and the radioactive contents of the sealed sources then analyzed by gamma spectroscopy.« less