A MICROBEAM CS ION-SOURCE FOR ACCELERATOR MASS-SPECTROMETRY

A negative ion sputter source incorporating a microbeam Cs+ source int ended for application in accelerator mass spectrometry (AMS) has been developed from a General Ionex HICONEX 834(TM) source. (HICONEX is a t rade mark of High Voltage Engineering Europa,) The source is part of a microbeam AMS system, designed for in situ microanalysis of geologica l samples known as AUSTRALIS (AMS for UltraSensitive TRAce element and Isotopic Studies) recently developed at the Heavy Ion Analytical Faci lity laboratory. With requirements of precise beam positioning on mine ralogical samples, a high magnification sample viewing system is a vit al part of the source, enabling live observation of the sputtering pro cess and visual tuning of the primary beam. Microbeam of Cs+ of 30 mu m in diameter can be produced routinely with adequate intensity for a number of applications. The ''screen'' electrode in the secondary ion extraction system facilitates steering of the primary beam affected by the extraction field, back into the geometric center of the sample. T he injector system includes high resolution electric and magnetic anal yzers, improving the background suppression before injection into the accelerator. (C) 1998 American Institute of Physics. [S0034-6748(98)64 402-6].