New capabilities for small-scale and high-precision SIMS analyses

Abstract

Secondary ion mass spectrometry (SIMS) has wide application for in situ geochronology, trace element and isotope analysis. Despite the strengths of SIMS techniques, their usefulness has been limited for many problems by the relatively coarse scale of analysis (~10-30 µm), and poor precision for element abundance ratios (~1-10 %, relative). Three recent innovations in SIMS instrumentation have improved capabilities in both regards, creating opportunities for new kinds of applications: (1) The NanoSIMS provides a reduced primary beam size (typically 100-300 nm; as small as 10's of nm). A conventional SIMS instrument equipped with a Gallium source can achieve similar resolutions, though at the cost of significantly reduced sensitivity. (2) The NanoSIMS is also the first ion microprobe capable of simultaneous detection of elements differing greatly in mass (up to a factor of 22; e.g., ^(12)C and ^(238)U). This allows for multi-collection of most element ratios, much as isotope ratio multi-collection is done on lower-dispersion mass spectrometers. (3) The ims-7f Geo provides a 'pseudo multi-collection' capability. This is intended as a poor-man's instrument for high-precision isotope ratio analysis, but also permits element ratio measurements at greater than normal speed and precision.

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