A METHOD OF GENERATING A FINGERPRINT FOR A GEMSTONE USING X-RAY IMAGING

Abstract

The present invention provides a method of generating a fingerprint for a gemstone (5), for example a diamond, using x-ray imaging. The fingerprint comprises a three-dimensional map of a crystal or crystals present within the gemstone (5) including internal imperfections of the crystals and may also comprise further information about the gemstone (5). The method comprising the steps of: mounting the gemstone (5) in a sample holder (4) of an imaging apparatus, the imaging apparatus comprising a detector (6), a sample holder (4) mounted on a sample stage (3), an x-ray source (1), the sample holder (4) and the x-ray source (1) aligned along an optical axis, wherein the sample holder (4) is movable relative to the at least one x-ray source (1) and the detector (6); exposing the gemstone (5) to x-ray radiation from the x-ray source (1), whilst moving the sample holder (4) according to a search strategy that is predetermined for the gemstone (5) based on known physical characteristics of the gemstone (5); using the detector (6) to locate diffraction and/or extinction spots generated by the lattice of the crystals; utilising the located diffraction and/or extinction spots to calculate information about the position, orientation, and phase of the crystals; generating a suitable x-ray diffraction scanning strategy from the calculated information, the strategy including moving the sample holder (4) relative to the x-ray source (1) and the detector (6) and exposing the gemstone (5) to appropriate x-ray radiation as the sample holder (4) is moved, wherein the strategy is generated to locate and classify internal imperfections in the at least one crystal; scanning the gemstone according to the scanning strategy and recording the diffraction and/or extinction images using the detector (6); and generating a fingerprint from the recorded diffraction and/or extinction images.

Claims

1-59. (canceled)

60. A method of generating a fingerprint for a gemstone using x-ray imaging, wherein the fingerprint comprises a three-dimensional map of at least one crystal present within the gemstone including internal imperfections of the at least one crystal; the method comprising the steps of: mounting the gemstone in a sample holder of an imaging apparatus, the imaging apparatus comprising a sample holder mounted on a sample stage, at least one x-ray source, the sample holder and the at least one x-ray source aligned along an optical axis, wherein the sample holder is movable in at least one degree of freedom relative to the at least one x-ray source and at least one detector; exposing the mounted gemstone to x-ray radiation from the at least one x-ray source, while moving the sample holder relative to the at least one x-ray source and the at least one detector according to a search strategy that is predetermined for the gemstone based on known physical characteristics of the gemstone; using the at least one detector to locate diffraction and/or extinction spots generated by the lattice of the at least one crystal; utilizing the located diffraction and/or extinction spots to calculate information about the position, orientation, and phase of the at least one crystal; generating a suitable x-ray diffraction scanning strategy from the calculated information, the strategy including moving the sample holder relative to the at least one x-ray source and the at least one detector and exposing the gemstone to appropriate x-ray radiation from the at least one x-ray source as the sample holder is moved, wherein the strategy is generated to observe a sufficient number and quality of diffraction and/or extinction images for specified lattice planes of the at least one crystal to locate and classify internal imperfections of the crystal lattice; scanning the gemstone according to the scanning strategy and recording the diffraction and/or extinction images using the at least one detector; and generating the fingerprint from the recorded diffraction and/or extinction images.

61. A method according to claim 60, wherein the sample holder is movable in at least two degrees of freedom relative to the at least one x-ray source and the at least one detector.

62. A method according to claim 61, wherein the sample holder is movable in at least three degrees of freedom relative to the at least one x-ray source and the at least one detector.

63. A method according to claim 60, wherein the fingerprint further comprises a map of surface defects of the gemstone.

64. A method according to claim 60, wherein the fingerprint further comprises classification information about the internal imperfections.

65. A method according to claim 60, wherein the at least one x-ray source produces either a polychromatic spectrum or a monochromatic spectrum.

66. A method according to claim 60, wherein the imaging apparatus further comprises a processing unit and the processing unit controls the steps of: exposing the mounted gemstone to x-ray radiation from the at least one x-ray source, whilst moving the sample holder according to a search strategy that is predetermined for the gemstone based on known physical characteristics of the gemstone; using the at least one detector to locate diffraction and/or extinction spots generated by the lattice of the at least one crystal; utilizing the located diffraction and/or extinction spots to calculate information about the position, orientation, and phase of the at least one crystal; generating a suitable x-ray diffraction scanning strategy from the calculated information, the strategy including moving the sample holder relative to the at least one x-ray source and the at least one detector and exposing the gemstone to appropriate x-ray radiation from the at least one x-ray source as the sample holder is moved, wherein the strategy is generated to observe a sufficient number and quality of diffraction and/or extinction images for specified lattice planes of the at least one crystal to locate and classify internal imperfections in those lattice planes; scanning the gemstone according to the scanning strategy and recording the diffraction and/or extinction images using the at least one detector; and generating the fingerprint from the recorded diffraction and/or extinction images.

67. A method according to claim 60, wherein the scanning strategy includes a topo-tomographic scan.

68. A method according to claim 60, wherein the imaging apparatus is a forward diffraction scanner.

69. A method according to claim 60, wherein the sample stage has at least three degrees of translational freedom and three degrees of rotational freedom.

70. A method according to claim 60, wherein the imaging apparatus is one of: a compact instrument comprising a sample stage, a fixedly mounted high-resolution detector, and a fixedly mounted polychromatic x-ray source that provides an effective source size smaller than 100 micrometers and a divergent beam; wherein the sample stage is rotatable around at least two axes; a section topography apparatus comprising a single detector that is positioned off the optical axis and is oriented toward the sample stage such that it can detect diffracted beams from a gemstone such that an adequate spatial representation of lattice defect within an irradiated section of the gemstone can be obtained; and an x-ray tomography apparatus that records extinction spots in a direct x-ray beam and no diffraction spots.

71. A method according to claim 60, wherein the fingerprint contains information about the orientation and location of the fingerprint relative to one or more of: a surface model of the gemstone; a volume model of the gemstone; flat facets of the gemstone; visible points of reference of the gemstone.

72. A method according to claim 60, wherein the fingerprint includes one or more of: a direct grayscale reconstruction of the internal structure of the at least one crystal; unclassified local defects of the internal structure of the at least one crystal; classified local defects of the internal structure of the at least one crystal; local defect statistics; and information on strain, stress or similar deformation fields within the at least one crystal.

73. A method according to claim 60, comprising the steps of: comparing the generated fingerprint with one or more of the previously generated fingerprints; wherein the comparison step comprises a correlation step wherein the generated fingerprint is compared to previously generated fingerprints using information on some or all of the internal imperfections in the generated fingerprint and a confidence metric is produced for the correlation between the generated fingerprint and the previously generated fingerprints to identify a gemstone.

74. A method according to claim 60, comprising evaluating features of the fingerprint to determine whether they are characteristic of a natural or a synthetic gemstone.

75. A method according to claim 60, comprising using evaluation features of the fingerprint to determine whether the gemstone has any features characteristic of one or more particular physical treatments in the current observed state of the gemstone, or when compared to a previously generated fingerprint of the same stone to determine whether a gemstone has undergone a physical treatment.

76. A method according to claim 60, wherein the generated fingerprint is used to produce a computer model and rendering of the gemstone simulating the visual appearance of the gemstone when examined visually.

77. A method according to claim 60, comprising devising a cutting plan on the basis of the fingerprint of the gemstone for use in cutting a design of a gemstone.

78. A method according to claim 60, wherein information on internal imperfections of the gemstone from the fingerprint is combined with a surface or volume model of the gemstone to inform an assessment of a value of the gemstone.

79. A method according to claim 60, wherein a 4C assessment is predicted from information in the fingerprint.

80. A method according to claim 60, where the fingerprint is generated in an audited procedure and used to confirm the natural origin of the gemstone as a proof of location and circumstances of the extraction of the gemstone in a mining process and/or to confirm the artificial/man-made/synthetic origin of the gemstone as a proof of location and circumstances of the production of the gemstone in a controlled industrial process.

Description

DRAWINGS

[0223] FIG. 1 is a schematic diagram of an imaging apparatus that may be used in a method according to the present invention; and

[0224] FIG. 2 is a schematic diagram of an alternative imaging apparatus that may be used in a method of the present invention

[0225] FIG. 1 shows an embodiment of an imaging apparatus that may be used in the method of the present invention. The imaging apparatus is a forward diffraction scanner and comprises an x-ray source 1, beam defining slits 2, a sample stage 3, a sample holder 4, a detector 6 and a processing unit 7. During use a gemstone 5 is mounted in the sample holder 4 which is mounted on the sample stage. The sample stage 3 can be controlled to vary the rotational position of the gemstone 5. The processing unit 7 controls and records position information from the source 1, the beam defining slits 2, the sample stage 3 and the detector 6, and it receives recorded images from detector 6. In addition, the processing unit 7 receives and processes commands from a user or another unit, processes the recorded images and received data and information, determines a scanning strategy, generates a fingerprint and additional data, and transmits the fingerprint and additional data to a database.

[0226] The method of the present invention is carried out using the imaging apparatus in the following manner. First the gemstone 5 is mounted in the sample holder 4. There is no requirement for the gemstone 5 to be mounted in any specific orientation. Then the x-ray source 1 is controlled to emit a direct x-ray beam that propagates towards the beam defining slits 2. The beam defining slits 2 constrain the cross-section of the direct x-ray beam to irradiate the gemstone 5 and to shield the detector 6 from the direct x-ray beam. The direct x-ray beam leaving the beam defining slits 2 propagates towards and irradiates the gemstone 5. The sample stage 3 is controlled to vary the rotational position of gemstone 5 in a way that some of the irradiating direct x-ray beam is diffracted from a lattice plane in a crystal within the gemstone 5 towards the detector 6, which detects and records the resulting diffraction image. This is done according to a predetermined search strategy based on known physical characteristics of the gemstone 5, such as material. The processor 7 then uses the recorded diffraction images to generate a scanning strategy for the gemstone 5. The imaging apparatus is then controlled to carry out the generated scanning strategy and the resulting diffraction images are recorded by the detector 6 and sent to the processor. The processor 7 then generates a fingerprint for the gemstone from the diffraction images generated when the generated scanning strategy is carried out.

[0227] FIG. 2 shows an alternative imaging apparatus that can be used in the method of the present invention. The imaging apparatus of FIG. 2 is section topography apparatus. The apparatus comprises an x-ray source 1, beam defining slits 2, a sample stage 3, a sample holder 4, a detector 6 and a processing unit 7. During use a gemstone 5 is mounted in the sample holder 4.

[0228] When operated according to the method of the present invention. The x-ray source 1 is controlled to emit a direct x-ray beam, which propagates towards the beam defining slits 2 and the gemstone 5. The beam defining slits 2 constrain a cross-section of the direct x-ray beam to a narrow horizontal line at the position of gemstone 5. The direct x-ray beam reaches and irradiates a narrow section of the gemstone 5. The gemstone 5 is mounted on the sample holder 4 which is mounted on the sample stage 3. The sample stage 3 is controlled to change the rotational position of gemstone 5 relative to the direct beam in such a way that a narrow wavelength range in the irradiating direct x-ray beam is diffracted from a lattice plane in a section of a crystal within the gemstone 5. The diffracted beam propagates towards and is detected by the detector 6. The processing unit 7 controls and records position information from source 1, beam defining slits 2, sample stage 3 and detector 6, and it records images from detector 6. In addition, the processing unit 7 receives and processes commands from a user or another unit, processes the recorded and received data and information, determines the scanning strategy, computes the fingerprint and additional data, and transmits the fingerprint and additional data to a database.

[0229] In the imaging apparatus of FIG. 2, the angle between the diffracted beam direction and the direct x-ray beam irradiating the gemstone 5 is around 90° (45° Bragg angle). The diffracted beam represents a projection of the irradiated section of the crystal. The method of the present invention is carried out using the imaging apparatus of FIG. 2 in substantially the same manner as the set out above for the imaging apparatus of FIG. 1 with the exception that when the generated scanning strategy is carried out diffraction images (section topographs) are recorded from parallel sections of the crystal by translating the gemstone 5 perpendicular to the x-ray beam and the sections. Detector 6 records images in a synchronised manner with the translation of sample stage 3 and gemstone 5. This procedure is repeated for all crystals of interest within the gemstone 5. A fingerprint is then constructed from the imaged sections.