A Negative Surface Ionization Source for RIB Generation

Abstract. An efficient negative surface ionization source has been designed, fabricated, and initial tests begun for potential on-line use in generating radioactive ion beams of members of the group VIIA elements (F, Cl, Br, I, and At) for the Holifield Radioactive Ion Beam Facility research program. The source utilizes direct-surface ionization to form negative-ion beams resulting from interactions between highly electronegative atoms or molecules and a spherical-sector surface LaB6 surface ionizer maintained at ~1722 °C. Despite its widely publicized propensity for being easily poisoned, no evidences of this effect were experienced during testing of the source. The source has been extensively evaluated off-line in terms of ionization efficiency for generating beams of Br − by feeding AlBr3 vapor at low feed rates into the source. The results of initial testing indicate that the source is reliable, stable and easy to operate, with nominal efficiencies of 15 % for Br − beam generation when account is taken of the fractional thermal dissociation of the AlBr3 carrier molecule. The design features and principles of operation of the source are described and initial performance, operational parameter and beam quality (emittance) data are presented in this article