PROCESSING OF REACTOR-PRODUCED W-188 FOR FABRICATION OF CLINICAL-SCALE ALUMINA-BASED W-188/RE-188 GENERATORS

The traditional technique for processing of reactor-irradiated W-186-enriched tungsten oxide (WO3) targets involves formation of W-188-sodium tungstate solutions by target dissolution in 0.1 M NaOH. Following long irradiations (>21 days) in the ORNL High Flux Isotope Reactor (HFIR) the (WO3)-W-186 targets contain a NaOH-insoluble W-188-labeled black solid (approx. 30-50% of total activity) which decreases the yield and specific activity of the processed W-188 (e.g. 5-6 mCi/mg W-186 for a 79-day irradiation). The black material is postulated to represent a ''tungsten blue'' insoluble polymeric form of tungsten oxide, which we have now found to dissolve in 0.1 M NaOH containing 5% sodium hypochlorite solution. Complete dissolution results in a significant increase in the yield and specific activity of sodium W-188-tungstate. As an alternative approach, irradiated W-186-enriched metal targets dissolve in sodium hydroxide solution by cautious addition of <30% hydrogen peroxide. Sodium W-188-tungstate solutions prepared from processing of such metal targets show no evidence of residual black insoluble material. Specific activity values for completely dissolved HFIR-irradiated W-186 targets have increased to 10 mCi/mg (43.5 days) and 12.9 mCi/mg (49.2 days). Large clinical scale (>1 Ci) generators prepared from hypochlorite-processed W-186 oxide or peroxide-processed W-186 metal targets exhibit the expected Re-188 high yield and low W-188 breakthrough.