Martin John Whitehouse oral presentation (OA1-Tue2-2-1)
Ion imaging with large-geometry SIMS – novel applications in geochemistry, cosmochemistry and environmental sciences
Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden
The ion optical design of the CAMECA large-geometry SIMS instruments provides a unique combination of direct (ion microscope) and scanning ion image (SII) modes as well as high-spatial resolution point analysis (ion microprobe). While the latter is the mode most commonly utilized with these instruments, providing high precision isotope ratio analysis, SII is increasingly being used both as a reconnaissance method to identify targets of interest for subsequent point analysis, for example U particle analysis in nuclear safeguards, and as an analytical tool in its own right, using dedicated image processing software to generate accurate, high-precision isotope ratios from user-defined regions of interest in an imaged sample.
This presentation will first review the key design features of the instrument that enable operation in SII mode at high mass resolution and the inherent limitations that have to be considered in designing an SII routine. It will then present a number of case studies from geochemistry, cosmochemistry and environmental sciences, undertaken using the IMS1280 instrument at the NordSIMS facility, illustrating the utility of this approach. These case studies include (1) Pb-isotope imaging of zircon, the most widely used mineral in geochronology; (2) full U-Pb analysis from complex imaged zircon grains from the early Earth and the Moon; (3) S-isotope analysis of sulphides from the deep biosphere revealing fine-scale zoning and extreme fractionation; (4) C-, N-, and Fe-isotope analysis of biological samples, for example diatoms and cyanobacteria. The potential for future progress in both instrument design and data processing software will also be reviewed.