Operating a colutron ion source with reactive gases

The discharge ion source of a colutron isotope separator is particularly suitable for ion-impact studies because of the (1) high beam intensities (2) small energy spread of the ion beam; and (3) simplicity of realization. However the operation and stability of this ion source depend considerably on the nature of the gas admitted to the discharge chamber. In particular, difficulties arise when operating with reactive gas (instability of the discharge, short lifetime of the filaments). High beam intensities of, for example halogen and sulphur positive-ions have been obtained by diluting the reactive gas with an inert support (helium, argon, krypton); in certain cases a carburization agent, usually C2H4, is required to improve the electron emission of the filament. Preferential ionization of the reactive gas has been observed in most cases; both excitation energy transfers and charge transfers occuring between the rare-gas atoms and atoms of molecules of the reactive gas may be invoked to describe this phenomenon. (Auth.)