In-target production of high specific radioactivity [15O]nitrous oxide by deuteron irradiation of nitrogen gas.

A simple and rapid production method for high specific radioactivity [15O]N2O has been developed based on the 14N(d,n)15O reaction on high-purity nitrogen gas in a flow-through target irradiated with a 0.5 microA beam of 7 MeV deuterons. The [15O]N2O formed during irradiation is selectively concentrated from the target effluent by adsorption on a zeolite during 150 s and subsequently released by rapid heating into a pulse with a full width at half maximum of 3.5 s. The radioactivity and specific radioactivity in the pulse amount to 4 MBq [15O]N2O and 4.5 x 10(13) Bq/mol respectively with a radiochemical purity >99.95%. A tenfold higher specific radioactivity may be feasible at larger beam currents. It was shown that stable N2O was also formed during irradiation. Based on responses to variations in various parameters during irradiation and on analyses performed on the products, an explanation is given on the mechanisms of in-target [15O]N2O and N2O formation, involving reaction of a particular excited state of O3 with N2.