The new CSIRO-GEMOC nuclear microprobe: First results, performance and recent applications

A new nuclear microprobe (NMP) has been designed and built at the CSIRO featuring: (1) a quadrupole quintuplet lens system with a demagnification of 67 and 80 mm working distance; (2) a close detection geometry for Ge X-ray, 30% Ge γ-ray and particle detectors; (3) a high-quality normal-viewing microscope, coaxial with the beam; (4) computer-controlled beam-shaping and 5-axis sample stage; (5) scanning for imaging to >5×2 mm²; and (6) a vibration isolated mounting. Most design goals have been successfully achieved. On the first day of operation, a spot size of 1.3μm was obtained at a beam current of 0.5 nA, suitable for fluid inclusion analysis and imaging. The spot size grows to just 1.8μm at 8 nA (3 MeV protons) and 2μm at 10 nA, despite the low brightness of our tandem accelerator (1.2pA μm^-2 mrad^-2 MeV^-1). This beam current is ideal for geological samples with PIXE detection limits down to 0.2 ppm (Br) achieved in silicates (39 pp b (Ge) in diamond at 22-25 nA) in quantitative, high resolution, trace element images.