Production of high yield [13N] ammonia by proton irradiation from pressurized aqueous solutions

The method of direct production of large quantities of [13N] ammonia in the cyclotron water target for clinical cardiac studies by PET or synthetic uses was considered. Two main approaches based on the proton irradiation either of dilute aqueous ethanol solution under helium pressure or pure water pressurized by hydrogen were evaluated. Using ethanol as a target additive at the relatively low helium pressure of 400 KPa up to 22.2 GBq (600 mCi, EOB) of final product can be produced with radiochemical purity of more than 98%. Under comparable conditions the water target pressurized by hydrogen was about two times less effective for production of [13N]NH3 because of the formation of considerable amounts of [13N]N2. A possible mechanism of labelled nitrogen production was discussed. (author). 16 refs., 1 fig., 3 tabs