A Negative Surface Ionization Source for Generation of Halogen Radioactive Ion Beams

A simple and efficient negative surface ionization source has been designed, fabricated and initially tested for on-line generation of radioactive ion beams of the halogens (Cl, Br, I, and At) for use in the nuclear-structure and nuclear-astrophysics research programs at the Holifield Radioactive Ion Beam Facility. The source utilizes a solid, spherical geometry LaB6 surface ionizer for forming highly electronegative atoms and molecules. Despite its widely publicized propensity for being easiiy poisoned, no evidences of this effect were experienced during testing of the source. A nominal efficiency of 15% for Br- beam generation is obtained during off-line evaluation of the source with AlBr3 feed material when account is taken of the fractional dissociation of the molecule. Principles of operation, design features, operational parameter data, initial performance results, and beam quality data (emittance) are presented in this article. I. INTRODUCTION The Holifield Radioactive Ion Beam Facility (HRIBF) utilizes negative ion beams for post acceleration to research energies (l). Because of the restricted number of elements with high electron affinities, this type of surface ionization source is highly selective and can be used to great advantage for radioactive ion beam (RIB) applications to eliminate isobaric contaminants that may compromise experimental results. For these reasons, a negative surface ionization source was designed and characterized for on-line use in generating radioactive ion beams (RIBS) of the halogen elements for the nuclear-structure and nuclear-astrophysics experimental programs at the HRIBF. These sources are characterized by high beam purity (chemical selectivity), low thermal energy spreads (-2 kT<更多