A NEW CONCEPT TANDEM THERMAL DISSOCIATOR ELECTRON IMPACT IONIZATION SOURCE FOR RIB GENERATION/

An innovative thermal dissociation/electron impact ionization positive ion source is presently under design at the Oak Ridge National Labora tory for potential use for generating RIBs at the Holifield Radioactiv e Ion Beam Facility (HRIBF). Because of the low probability of simulta neously dissociating and efficiently ionizing the individual atomic co nstituents with conventional, hot-cathode, electron-impact ion sources , the ion beams extracted from these sources often appear as a mixture of several molecular sideband beams. In this way, the intensity of th e species of interest is diluted. We have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high efficiency characteristics of an electron im pact ionization source. If the concept proves to be a viable option, t he source will be used as a complement to the electron beam plasma ion sources already in use at the HRIBF. The design features and principl es of operation of the source are described in this article.