JPS6123501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the identification of diamonds, particularly gem-quality diamonds.

Gem-quality diamonds, of course, have great value for perennial ornamental and investment purposes. The value of these diamonds continues to increase,
This increase has created various problems for police authorities and insurance companies. If a gemstone diamond is lost or stolen, the properties of the diamond may change, especially as these can change in appearance through techniques such as repolishing, recutting and irradiation.
Law enforcement has difficulty identifying recovered diamonds as stolen or lost diamonds.

Identification of recovered diamonds has been accomplished in the past by assembling "finger prints" of the diamond's easily recognized features. Such characteristics include the diamond's carat weight, cut, clarity and color, among others are various physical tests performed on the diamond. The latter feature can be achieved by measuring surface irregularities using e.g. Nomarski's differential interference contrast, or e.g. by fluorescence,
Includes methods for measuring the average properties of diamond, such as magnetic, optical absorption, and electron spin resonance measurements. However, such diamond fingerprints are sufficient for authorities to identify a particular diamond when it is recovered, but only if the diamond's properties have not been altered as described above. It is possible. Furthermore, this fingerprint technique is generally only performed on cut diamonds and is inappropriate for rough diamonds. However, safety agreements at diamond mines and diamond processing plants require that all rough, semi-finished and processed diamonds passing through them be verified. Although there is currently no technology available to identify specially cut diamonds from processed rough diamonds, there is a clear need for such a method.

It has now been discovered that the application of topography can provide a fingerprint of rough and processed diamonds, which remains unchanged even if the diamond is repolished, recut and/or irradiated. The fingerprint changes only when the characteristic crystallinity of the diamond is significantly altered by its conversion, for example to amorphous carbon. Topography is a technique that depicts some characteristic of a sample point-by-point throughout its entire volume. The study of this topography will always be of special value whenever sample heterogeneity is important (E.G. Lang, et al.
“Modern Diffraction and Imaging Techniques
in Material Sinse.”Narth−Halland Publishing
Co., Amsterdam-London.407 (1970)).

The method of the invention uses X-ray topography to create a record of one or more internal defects in a diamond, and by comparing the record thus made with similar records made from known diamonds. , including determining whether a diamond is the same or different from a known diamond. Preferably, the recording is made using X-ray diffraction at the Bragg angle. Here, the term "Bragg angle" means an angle that satisfies the equation 2d _hkl sinθ=ηλ, which is known as Bragg's law. In this equation, d _hkl is the internal spacing between these crystal lattice planes, and the orientation of the crystal lattice is the index
Denoted by hkl, the angle θ is the angle that the beam of X-rays makes with the plane, η is an integer, and λ is the wavelength of the X-rays. X-ray diffraction transmission photographs taken at the Bragg angle (also called X-ray diffraction topographs) show characteristic patterns that differ in such a way that no two diamonds have exactly the same fingerprint, especially If a series of X-ray diffraction transmission photographs were taken at various planes and using Bragg reflection angles, the result would be as shown above. The recording is an X-ray diffraction or an absorption topography, preferably a diffraction topography.

The expression "using X-ray diffraction at the Bragg angle" is used here in a general sense. If the sample has a very different orientation with respect to other parts of the crystal, then the projection onto the crystal
The wavelengths contained within the ray beam are limited to a narrow enough range, the angular differences between the X-ray beams incident on the sample are sufficiently small, and some crystal sites satisfactorily satisfy Bragg's law, while others do not. Actual projection
The above law is not satisfied at a given angular setting of the crystal with respect to the average orientation of the line beam. Such misorientations within the sample are recorded and are assumed to include, in effect, the X-ray topographic recording of internal defects in the diamond. Sensitivity of the contrast, nature of the contrast (i.e. excess or deficiency of diffracted intensity)
And the reference range over which these misorientations (and small misorientations such as those related to displacements of individual crystal lattices) are recorded varies according to the degree of collimation and wavelength of the X-rays incident on the sample. In this way, the contrast characteristics of an X-ray topography generally depend on the
Depending on whether the line radiation is collimated by a slit or collimated and/or monochromated by a previous blurred reflection by a so-called "monochromator" crystal, or even if the radiation source Depends on whether it is a conventional X-ray generator or a synchrotron source. It is understood that such practical variations and subdivisions are included within the expressions ``using X-ray diffraction at the Bragg angle'' and ``satisfying Bragg's Law'' as used herein. By the way.

In the method of the invention, crystals with different orientations and/or internal spacings are produced by projection and/or cross-sectional topography in a predetermined procedure designed to maximize the information content regarding the internal distinguishing features of the crystal.
Plug reflections from one or more crystal lattice planes can be used. The use of this X-ray topography technique detects imperfections in the crystal lattice, such as crystal lattice displacements, growth bands, stacking faults and twins in diamond.
etc. can be identified.

As can be seen from the Bratz law equation, if the x-ray radiation is monochromatic (or nearly monochromatic), then the crystal will have at least a Bratz law equation for the directional range of rays contained within the projected It is necessary to set an angle that satisfies one crystal lattice plane (hkl). In this case, the X-ray topography is recorded in series. On the other hand, if the X-ray radiation is not monochromatic, such as so-called "white radiation" emitted from X-rays, or X-rays generated from a synchrotron, each angle setting of the crystal with respect to the projection beam Bragg reflection groups arising from crystal lattice planes with different orientations are described by Guinier and
Tennevin, Acta, Acta
Crystallographica. 1949, Vol. 2, pp. 133-8. Depending on the characteristics of the X-ray source used, the Bragg reflections are recorded as a series (using X-rays of a given wavelength) or simultaneously as a group, as in the method of Guinier and Tennevin above. is a matter of choice. When using the latter method, it is advantageous to record reflection groups when the axis of symmetry is oriented parallel to the axis of the projected X-ray beam. for example,
The reflection groups are recorded for each group by one of three equiaxed crystal axes oriented parallel to the beam.

A series of diffraction transmission photographs can be taken using the crystallographic equivalent of reflection as described above. The simplest procedure when using monochromatic radiation is to choose three equiaxed crystal planes on which four transmission photographs are taken on each plane, and between each transmission photograph the crystal is rotated around the perpendicular line. Rotated 90 degrees to give a full view of the gem.

The topography is permanently or semi-permanently recorded by conventional techniques such as X-ray polaroid method, X-ray sensitive photographic emulsion, xerography and electronic techniques. Such electronic technologies include electronic image intensifiers (which may or may not include television equipment), and position-sensitive gas-filled or solid-state X-ray photon detection devices (single or arrayed). . This recording is, for example, in the form of a magnetic tape. The x-ray source (which needs to be collimated) is obtained from a conventional x-ray tube or a synchrotron, which is a highly collimated and highly powerful x-ray source.

Synthetic and natural diamonds can be distinguished by this topographic technique, in part because currently available synthetic diamonds have a type that contains metal impurities that are not present, for example, in natural diamonds.

Some diamonds, especially rough diamonds from e.g. alluvial sources, have surface damage, so
It is desirable to remove as much surface damage as possible before taking a line topographic record or a diamond record. Removal of surface damage more clearly reveals the diamond's internal signature features and contrast in the X-ray topography. Surface damage can be caused by e.g. gas under controlled temperature and pressure,
It is removed by etching using gases, stirred liquids and fast ions and atoms in the presence of electric current.

If a rough diamond has a coating, an X-ray topography can indicate whether the rough diamond is worth the expense and effort of opening it.

Insurance companies and law enforcement agencies develop X-ray topographic indicia of known diamonds, and such indicia form part of the present invention. Indicators are, for example, stacking disturbances, twinning, slip bands or small angle grain boundaries (misorientation) and especially strain fields in combination with lattice dislocations, growth stratification and semi-trace inclusions or precipitates recorded in X-ray topography. (strain field)
Contains a summary, summary, or codification describing one or more types of internal defects, such as.

The attached topograph (Reference Figures 1 and 2) is an X-ray diffraction diagram of one carat of brilliant diamond. Reference figure 1 is a projected topograph (Long
Acta Crystallographica, 1959, 12 volumes,
249-250), and the almost elliptical one in Reference Figure 2 is an X-ray cross-sectional topograph (this technique is described by Lang,
Acta Metallurgica. 1957, Vol. 5, 358-364) describes a brilliant diamond as having its widest cross section parallel to the upper table, i.e. parallel to the equator. This is a cross-sectional topograph cut almost in parallel. This cross-sectional topography shows very sharp detail, ie, a high degree of uniqueness, as it shows only one cut through the crystal. This is somewhat less sharp since the projected topograph shows an image of the entire volume of the crystal. This particular diamond is rather pathological in terms of crystal growth (although its internal structure is not so rare in appearance). This is therefore not an easy problem for fingerprints, since they contain a large number of imperfections. However, this image is believed to constitute a unique and distinct fingerprint from the many more images on the same right, which cannot be replaced by any method that does not destroy the stone itself.

In one example of the invention, X-ray diffraction topographs were taken of three rough diamonds without any visible defects or microscopically visible identifying features.
In order to obtain a reasonably complete diffraction topographic record of the rough stone for "fingerprinting" purposes, yet to minimize the number of topographs, we use a minimum number of shapes, i.e., a regular hexahedron {100} reflections, and this shape It was decided to obtain a projected topograph using each of the three independent planes that . The lowest order reflection from this shape that is allowed by the symmetry of the space group to which the diamond belongs, ie O ⁷ _h ), is of type 400.
Therefore, each plane (400), (040) and (004) was used in sequence. Furthermore, since no easy or other "fingerprints" could be foreseen, it was decided to take four topographs using each of the three planes of {400}, so that each reflection could We obtained four different figures or aspects of the equation. The final record was thus 12 diffraction topographs for each stone. _M.O.K. radiation was used throughout, and the procedures for each topography were standard. The three rough stones were then cut and polished into brilliant shapes, an operation which completely changed their size and shape. X-ray diffraction topographs of three cut brilliant diamonds have been taken, and there is no difficulty in using the topographs of a given stone to match the rough and final conditions, thereby determining which rough diamond it came from. Each brilliant diamond formed is uniquely identified. Reference FIGS. 3 and 4 are topographs taken of one of the diamonds before and after cutting, respectively, as an example. Identical numbers were used on the diagrams to indicate common features, allowing unique identification of the source of the cut and polished diamonds.

The method of the invention can also be used to "fingerprint" other gemstones such as rubies, emeralds or saphires.

The main aspects of the embodiments of the present invention will be explained as follows.

1 The record was made using X-ray diffraction at the Bragg angle. Claimed method.

2. Recording of the sample (or said selected portion thereof) by projecting the sample onto it such that a portion of the volume of the sample (or said selected portion thereof) essentially satisfies the X-ray diffraction conditions at the Bragg angle. It is created by orienting the X-rays contained in the X-ray beam to the orientation range. Claimed method.

3. A record of the sample (or said selected region) is made by illuminating the sample with an X-ray beam, and records the spectral distribution of said X-rays and their orientation with respect to the sample (or said selected region). The range is selected such that a portion of the sample (or said selected region) deviates by a certain small angle from the exact satisfaction of the conditions of X-ray diffraction at the Bragg angle. Claimed method.

4. A method according to claim 1 or any of the preceding clauses, wherein surface damage is removed from the diamond before the record is made.

5. The method of item 3 above, wherein the surface damage is removed by etching.

6. The method according to claims 1 to 5 above, wherein the recording is an X-ray topography.

7. The method according to any of the claims or the preceding paragraphs, wherein the known diamond is an uncut diamond.

8. Indices of known diamond records produced by X-ray topography and for use in the claims or in any of the preceding paragraphs.

Claims (1)

[Claims] 1. A diamond, characterized in that it uses X-ray topography to make a record of one or more internal defects in the diamond, and that the record thus made is compared with similar records made from known diamonds. How to determine whether a diamond is the same or different from a known diamond.