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A high efficiency, kinetic-ejection negative ion source for RIB generation

 

作者: G. D. Alton,   Y. Liu,   C. Williams,   S. N. Murray,  

 

期刊: AIP Conference Proceedings  (AIP Available online 1999)
卷期: Volume 473, issue 1  

页码: 330-340

 

ISSN:0094-243X

 

年代: 1999

 

DOI:10.1063/1.58953

 

出版商: AIP

 

数据来源: AIP

 

摘要:

Chemically active radioactive species, diffused from RIB target materials, often arrive at the ionization chamber of the source in a variety of molecular forms. Because of the low probability for simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecules with conventional hot-cathode electron-impact ion sources, the species of interest are often distributed in several mass channels in the form of molecular side-band beams and consequently, their intensities are diluted. The sputter negative ion beam generation technique offers an efficient means for simultaneously dissociating and ionizing highly electronegative atomic species present in molecular carriers. We have incorporated these principles in the design and fabrication of a kinetic ejection negative ion source and evaluated its potential for generating17,18F−beams for the Holifield Radioactive Ion Beam Facility astrophysics research program. The source utilizesCs+beams to bombard condensable fluorine compounds that emanate from a target material, such asAl2O3,and are transported to the cooled inner surface of a conical-geometry cathode where they are adsorbed. The energeticCs+beams efficiently dissociate these molecules and sputter their constituents. Since the work functions of cesiated surfaces are low, highly electronegative species such as fluorine are efficiently ionized in the sputter-injection process. Measured efficiencies for ionizing atomic fluorine, dissociated from condensable compounds that are formed by reactions ofSF6with fibrousAl2O3material, exceed 6.5&percent;. In this report, we describe the mechanical design features and principles of operation, and present emittance,F−yield and ionization efficiency data derived from off-line, experimental evaluation of the source. ©1999 American Institute of Physics.

 

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