|Ion Imaging/Depth Profiling||Trace Elements|
|Various materials and isotopes||Various materials and isotopes|
Two broad applications have been developed for the ims 1270, a large-radius, triple-focusing mass spectrometer: U-Th-Pb measurements of accessory minerals, and stable isotopic analysis of insulators.
U-Th-Pb analysis is conducted using a beam of negative oxygen ions that can be focused to spots from 1 to 30µm on 1" polished thin sections or grain mounts. A slit-lens transfer optical system and the 585mm radius magnet achieve high secondary ion transmission at the mass resolving power of ~5,000 required for these analysis. Isotopic ratios are measured by rapid peak-switching in to a pulse-counting electron multiplier. Measurements of U-Th-Pb systematics of zircon [e.g. X. Quidelleur et al., The thermal evolution and slip history of the Renbu Zedong Thrust, southeastern Tibet. J. Geophys. Res. 1997] and monazite [e.g., Harrison et al., Earth Planet. Sci. Lett. 133, 271, 1995] yield high Pb sensitivities (up to 20 cps/ppm/Pb/nA) and typical age accuracy of ±2%.
Stable isotope measurements of oxygen and carbon in insulating specimens are undertaken using a Cs+ primary beam which can be focused to a diameter between 0.2 and 30µm. Carbonates and silicates, for example, have yielded typical δ18O precisions of 1.0‰ for 10 min analysis times and, typically, 15µm diameter analysis areas [e.g. L.A. Leshin et al., The oxygen isotopic composition of olivine and pyroxene from CI chondrites. Geochim. Cosmchim. Acta 1997]. The same precision has been obtained for δ13C in carbonates under similar analytical conditions.