Ion microprobe technique

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

By the late 1980s ion microprobe techniques had become sufficiently refined to search for 26A1 in chondrules, the dominant component of chondrites. A few studies showed positive results, such as a feldspar-bearing clast chondrule from Semarkona that gave an initial ratio of 7.7 x 10 fi (Hutcheon and Hutchison, 1989). However many did not. Eventually, it was shown that feldspar and glass in chondrules are easily affected by parent body... 

Since then Mojzsis et al. (1996) have used in situ ion microprobe techniques to measure the isotopic composition of carbon in Isua BIF and in a unit from the nearby Akilia Island that may be BIF. in carbonaceous inclusions in the BIF ranged from —23%o to —34%o those in carbon inclusions occluded in apatite micrograins from the Akilia Island BIF ranged from —2l%o to —49%c. Since the carbon grains embedded in apatite were small and irregular, the precision and accuracy of the individual measurements... 

Near-surface diffusion in single crystals and thin amorphous films was studied by means of charged-particle Rutherford back-scattering and ion microprobe techniques at 200 to 450C. It was found that the former results could be described by ... 

Scanning Auger Electron Spectroscopy (SAM) and SIMS (in microprobe or microscope modes). SAM is the most widespread technique, but generally is considered to be of lesser sensitivity than SIMS, at least for spatial resolutions (defined by primary beam diameter d) of approximately 0.1 im. However, with a field emission electron source, SAM can achieve sensitivities tanging from 0.3% at. to 3% at. for Pranging from 1000 A to 300 A, respectively, which is competitive with the best ion microprobes. Even with competitive sensitivity, though, SAM can be very problematic for insulators and electron-sensitive materials. 

There are two principal sources of reliable partitioning data for any trace element glassy volcanic rocks and high temperature experiments. For the reasons outlined above, both sources rely on analytical techniques with high spatial resolution. Typically these are microbeam techniques, such as electron-microprobe (EMPA), laser ablation ICP-MS, ion-microprobe secondary ion mass spectrometry (SIMS) or proton-induced X-ray emission (PIXE). 

Fortier SM, Cole DR, Wesolowski DJ, Riciputi LR, Paterson BA, Valley JW, Horita J (1995) Determination of the magnetite-water equilibrium oxygen isotope fractionation factor at 350°C a comparison of ion microprobe and laser fluorination techniques. Geochim Cosmochim Acta 59 3871-3875 Friedman I, O Neil JR (1977) Compilation of Stable Isotope Fractionation Factors of Geochemical Interest. US Geol Surv Prof Paper 440-KK... 

The importance of surface analysis for evaluating the environmental effects of toxic substances is becoming more apparent as the result of recent work in this field. Chapter 9 describes ESCA, Auger, Ion Microprobe, and SIMS surface analysis techniques for atmospheric particulates. These techniques overcome the obvious limitations of bulk analysis, that is, the wide variability in the physicochemical characteristics of different particles. 

Microanalytical techiuques such as laser microprobe (Kelley and Fallick 1990 Crowe et al. 1990 Hu et al. 2003 Ono et al. 2006) and ion microprobe (Chaussidon et al. 1987, 1989 Eldridge et al. 1988, 1993) have become promising tools for determining sulfur isotope ratios. These techniques have several advantages over conventional techniques such as high spatial resolution and the capability for in-situ spot analysis. Sulfur isotopes are fractionated during ion or laser bombardment, but fractionation effects are mineral specific and reproducible. 

The distributions of trace elements between minerals and within a suite of related rocks provide powerful tools for constraining the origin and history of rocks and meteorites. Trace-element abundances for rocks typically are part of the data set collected when determining bulk compositions. Trace element compositions of minerals require more powerful techniques such as the ion microprobe or the laser-ablation inductively coupled plasma mass spectrometer (ICPMS). 

Advances in techniques for handling and analyzing very small particles have allowed detailed examination and characterization of IDPs. Especially useful instruments include the transmission electron microscope ( ), synchrotron facilities, and the ion microprobe. 

The ion microprobe has also been applied in a preliminary fashion to the rubidium-strontium dating technique. The correlation of the ion mieroprobe results with the independently determined isochron indicates that it may be possible to obtain useful results for samples on a micrometer scale from this dating technique. 

Direct Characterization Techniques. The in situ analysis of elemental composition of coals by ion microprobe was first demonstrated by Dutcher t al. (85). Raymond (86) has applied this technique to examine the variation in composition of coal macerals which has been especially effective for looking at sulfur distribution. An example of the organic sulfur distribution for two bituminous coals is shown in Table II which is taken from reference (86). Note that the liptinites contain the... 

Megaelectron volt (MeV) ion beam techniques offer a number of non-destructive analysis methods that allow to measure depth profiles of elemental concentrations in material surfaces. Elements are identified by elastic scattering, by specific nuclear reaction products or by emission of characteristic X-rays. With nuclear microprobes raster images of the material composition at the surface can be obtained. Particle-induced gamma-ray emission (PIGE) is especially suited for fluorine detection down to the ppm concentration level. 

PIXE is the analogue to EDX/WDX (energy/wave dispersive analysis of X-rays) done with electron microprobes. Elements in the sample are identified by the characteristic X-rays emitted during MeV particle bombardment. PIXE is not well suited for fluorine detection because of the low energy of the corresponding X-rays. However, it is often performed simultaneously with other ion beam techniques and gives very valuable information on the bulk composition and other trace element concentrations in the sample. 

The ion microprobe has been widely applied to the analysis of trace elements in a variety of geological materials, as the excellent spatial resolution provides the ability to study either elemental zoning patterns in a large mineral or to analyze phases that are too fine-grained (or are too limited in quantity) to make separation and bulk analysis practical. In comparison to other techniques, the ion probe also of-... 

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