The CSIRO/GEMOC Nuclear Microprobe: A High-Performance System based on a New Highly Integrated Design

Chris G. Ryan1,3, David N. Jamieson2, William L. Griffin3,1, Soey H. Sie1, Gary Cripps1 and Gary F. Suter1, 1. CSIRO EM 2. School of Physics, Microanalytical Research Centre, University of Melbourne, 3. GEMOC Macquarie.

In response to a shift in emphasis in geoscience applications of the Nuclear Microprobe (NMP) to complement new techniques such as LA-ICP/MS, a new NMP has been developed at the CSIRO, in collaboration with GEMOC and the Microanalytical Research centre, University of Melbourne, to better exploit advanced trace-element techniques that are unique to the NMP such as real-time high-resolution quantitative elemental imaging, non-destructive fluid and solid inclusion analysis, light element microanalysis using PIGE, and impurity atom lattice location using ion micro-channeling.

The new probe uses a highly integrated design approach and a new focusing lens system design based on a quadrupole quintuplet (detailed elsewhere in this conference). The design goal has been to optimise beam-optical performance at the same time as maximising detection geometry and the provision of high-quality microscope optics and sample manipulation. This has been achieved by designing the whole probe as a 3D computer model which permits detailed shaping of components to tackle the conflicting space requirements of lens system, detector system, microscope optics and sample manipulation.

The key to achieving high demagnification of the lens system is a small working distance. This has been achieved by a combination of shaped quadrupole yokes with pole-tip extensions which bring the quadrupole fields 30 mm closer to the target, and access cut-outs in the yokes that accommodate unrestricted detector access at 135¯ to the beam; four cut-outs are used to maintain four-fold symmetry. The result is an effective working distance of 80 mm.

Further features of the new probe include: CanberraTM 100 mm2 germanium X-ray, 30% g-ray and PIPS detectors, digital signal processors, electrostatic on-demand beam-switching and scanning, QuestarTM long-range microscope for normal sample viewing, sample goniometer (X,Y,Z,q,f) and vacuum-lock, anti-vibration mounting, and computer-controlled object and divergence limiting slits. This paper will describe the new system, its operation, performance and sensitivity, and its anticipated areas of application in geology.

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