Production of [13N]ammonia applicable to low energy accelerators

We have developed a technique for the rapid conversion of the nitrogen-13 induced in a graphite target into nitrogen oxides. This was accomplished by heating the graphite target in a stream of pure oxygen at 800 degrees C. Less than 20% of the radioactivity was found in the form of [13N]nitrogen. The rest of the radioactivity was efficiently trapped in a solid-phase medium that consisted of an aqueous solution of 5% NaOH dispersed in silica gel. The radioactivity from this solid-phase medium was eluted with water (94% recovery) and found to be in the form of 13NO2- (99%). This was subsequently converted to [13N]ammonia with Raney-nickel, either by a conventional liquid-phase reduction with an overall conversion efficiency to ammonia of 45%, or by an incorporation of the Raney-nickel into the solid-phase medium. The latter system resulted in an overall conversion efficiency to ammonia of 37 +/- 9%, with a radiochemical purity of nearly 100% and a synthesis time under 17 min.