On the chemistry of 11C recoil atoms in alkyl halogenides and hydrogen halides

The gas phase reactions of 11C recoil atoms which were produced by the nuclear reaction 14N(p,α)11C, were investigated in this present work in mixtures of N2 with CH3Cl, CH3Br and CH3I as well as with HCl, HBr and HI. The radiochemical yields of the gaseous reaction products were determined by radiogaschromatography. By using different columns, the carrier-free compounds produced could be clearly identified. Higher boiling products which occured in the present systems as wall activities were detected in some cases by means of high-pressure liquid chromotography. The formation of the products is discussed in the light of known recoil chemical reactions (abstraction, insertion) where attention is paid to the influence of O2 inhibitors and radiation dose effects. The quite considerable radiochemical yield of 11C-labelled methyl iodide in the N2/HI system enables the development of an on-line system for the recoil synthesis of larger amounts of activity of this important methylating agent for fast 11C labelling. A system was thus developed consisting of a gas dosing unit, target, gas purification system, and collector apparatus which enables the optimization of the product conditions by varying different parameters (proton energy, beam intensity, gas composition) and which enables the production of 11CH3-I activity quantities upto 90 mCi within a radiation and collecting time of 40 minutes at beam intensities of 20 μa and a proton input energy of 16 to 20 MeV. Specific activities of approx. 300 mCi/μmol are achieved. (orig.)