X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Patent
1998-06-08
2000-06-06
Church, Craig E.
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
378 71, G01N 2330
Patent
active
060728531
DESCRIPTION:
BRIEF SUMMARY
This invention relates to material analysis, and concerns in particular methods of analysing crystalline mineral materials using X-ray diffraction pattern techniques.
It is common to analyse crystalline materials using a technique that involves making an X-ray diffraction pattern from the material and comparing this with similar, reference patterns derived from known materials. The diffraction pattern for any crystalline substance is characteristic of the atomic elements making up the substances, the ways these are regularly arranged within the crystal (the crystal lattice), and the overall structure of the crystal (the various lattice planes therewithin, and especially the distance of separation between these). The lattice forms a diffraction grating the spacing of which is of a size that will result in the diffraction of very short wavelength, very high frequency electromagnetic radiation passing through the crystal; indeed, the grating size is so small that a useful diffraction pattern can only be obtained using X-rays, photons which have wavelengths of the order of 1 nanometre (10.sup.-9 metre) and below.
The use of this X-ray diffraction pattern technique is of particular value in the analysis of multi-phasic materials--that is, materials which are compositions of several different sorts of substances--where it is required to identify the individual phases and determine how much of each is present. Typical solid multi-phasic materials that can be handled by the technique are both natural bodies such as rocks and also artificial substances such as cements, ceramics, and metals and their alloys.
At present it is routine to make X-ray diffraction patterns using versions of this method that differ essentially only in employing one or other of two basic physical forms of material and looking either at transmitted (forward scattered) or reflected (backward scattered) X-rays. In the first version, which is perhaps conceptually the simplest, a spot on the face of a very thin slice of the material under study is illuminated by a narrow, parallel (collimated) beam of monochromatic (single wavelength) X-rays, and the diffracted X-rays transmitted (forward scattered) through the slice and coming out from the spot at different angles are picked up and measured (as regards their intensity) by a detector that scans slowly across the fan of X-rays emanating from the sample's reverse face. The manner in which the intensity of the transmitted X-rays varies as the scanner moves, and the angle changes, forms the desired diffraction pattern, and is, as noted above, characteristic of the material. In the second version of the method a sample of the material, commonly but not necessarily in the form of a compressed powder, is similarly illuminated, and the fan of reflected X-rays is similarly scanned (most rocks are effectively compressed or compacted powders; provided the illuminated spot includes a sufficiently large number of randomly-oriented individual crystallates, a powder material is, on the atomic scale involved, little different for this purpose from a simple slice, and is often much more convenient to prepare and deal with). The second version permits the surface identification of a thick sample (such as a rock drill core), but because of the very limited penetration ability of the X-rays presently used provides no information about the material within the sample.
Analysis by X-ray diffraction pattern has been very effectively utilised for many years. In the oil industry, for instance, it has been employed to determine the precise nature of the formations through which an oil well borehole is to pass (drill core samples are advantageously analysed using this technique). There are, nevertheless, serious problems with the present implementations of the procedure. Firstly, the method is a destructive one, for it necessarily involves the original material sample--a drill core, for instance--being structurally destroyed, by being either cut into slices or powdered. In itself, such destruction means that the sample in
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Batzer William B.
Church Craig E.
Schlumberger Technology Corporation
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