Yield ratio of [11C]-CO2, [11C]-CO and [11C]-CH4 from the irradiation of N2/H2-mixtures in a gas target

The¹⁴N/p, /¹¹C-reaction was studied in different N₂/H₂-mixtures. The products are ¹¹C]-CO₂, ¹¹C]-CO and ¹¹C]-CH₄. The yield ratio may be controlled by varying the bombardment conditions. High pressure, high H₂-content, high beam current and high proton energy shift the ratio towards ¹¹C]-CH₄. Lower beam current and lower proton energy increase the yield of ¹¹C]-CO₂. The production of ¹¹C]-CO is constant over a wide range of conditions /about 10%/. For the production of ¹¹C]-CH₄ in good yield a target gas holder for high pressures has been developed. Details are given in Fig. 7. This target gas holder was filled with 5% H₂ in N₂ at 3×10⁶ Pa. Proton irradiation of the mixture gives a typical yield of ¹¹C]-CH₄ of 400–500 mCi at a beam current of 15–20 A within 20 min. Only traces of other¹¹C-labelled compounds could be detected under these conditions.