Instrument Description The UCLA Cameca ims 1270 is a new generation, high-resolution / high-sensitivity ion microprobe (or Secondary Ion Mass Spectrometer: SIMS) designed specifically for microscale isotopic and elemental analysis of complex minerals. It is an extremely versatile tool, capable of analyzing either conducting or insulating samples for elements ranging from H through U.

Configuration For the following discussion consult the plan view of the Cameca ims 1270. The instrument is equipped with both Cs+ and duoplasmatron (16O-) primary ion sources which can be focussed to produce ion beams as small as 1 mm diameter, although ~10 mm sputter craters are more typical for isotopic analyses. A large-radius triple-focusing mass spectrometer maintains high transmission even at the high mass resolving power (MRP ~ 6,000) required for Pb isotopic analysis of zircon. As with other Cameca ims instruments, the 1270 also functions as an ion microscope by direct ion imaging of the sample (with ~0.5 mmlateral resolution), enabling precise location of small inclusions for isotopic analysis (e.g., microfossils). A normal incidence electron flood gun provides charge compensation which enables analysis of electonegative elements (e.g, carbon and oxygen isotopic ratios) in thin-sectioned samples of (electrically insulating) rocks. Isotope ratios are measured either by rapid field switching with a laminated magnet, or by simultaneous multiple collection of up to 5 ion beams. The forward geometry design of the mass spectrometer enables energy filtering as well as multiple isotope collection. The multiple collection may be achieved with either Faraday cup detectors, or with discrete dynode electron multipliers for ion counting applications. Low (2000), moderate (4000), or high (6000) mass resolution modes are available in multicollection, whereas continously variable MRP (~1000 to ~15000) may be achieved with the off-axis monocollector. Isotopic precision achieved is typically in the range of 1 permil but is highly sample and element dependent: see specific application notes.