Patent Publication Number: US-2023146198-A1

Title: Multi-fraction sample holder for 3D particle analysis

Description:
RELATED APPLICATIONS 
     This application claims the benefit under 35 USC 119(e) of U.S. Provisional Application No. 63/263,625, filed on Nov. 5, 2021, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Various imaging modalities have been used to identify and visualize mineral content of rocks, both in two dimensions (2D) and in three dimensions (3D). For example, these imaging modalities can analyze rock samples and determine comminution statistics for the mining industry. In more detail, in mining and material processing in general, the particle size of materials is reduced often by crushing, grinding, cutting, vibrating, and/or other processes. This is an important operation in mineral processing, ceramics, electronics, and other fields. 
     In typical operation, these imaging modalities create image datasets such as 3D volumes or 2D images. Image analysis techniques are then employed to assess particle sizes and size distributions and mineral content of the particles from the volumes and the images. 
     X-ray computed tomography (CT) microscopy systems are a common imaging modality. These systems irradiate the samples with x-rays, typically in a range between 1 and several hundred keV. 2D projection images are collected at multiple angles and 3D volumes of the sample are reconstructed from these projections. 
     SUMMARY OF THE INVENTION 
     It can often be important to analyze many samples in an automated fashion. Multiple size fractions need to be analyzed per sample and multiple samples per system in order to get a statistically representative description of particle behavior. Automated sample loaders can help alleviate this problem to some degree by automatically mounting a sequence of samples onto the sample stage, but are limited in terms of the maximum number of samples that they can mount. 
     In general, according to one aspect, the invention features a sample assembly for an x-ray microscopy system, comprising an outer tube and a bottom plug sealing an inner bore of the outer tube, wherein the outer tube contains powder to be analyzed by the x-ray microscopy system. 
     In embodiments, spacers are inserted into the outer tube for separating multiple samples in the outer tube. As a consequence, the outer tube may hold three or more samples. A top plug is useful for sealing a top of the outer tube. 
     In use, the outer tube holds different samples with different particle sizes along a length of the tube, such as from a mining operation. 
     In terms of construction, the outer tube can is constructed from plastic and can be less than 5 millimeters in diameter with an inner bore of the outer tube is less than 3 millimeters in diameter. 
     In general, according to another aspect, the invention features an x-ray microscopy system, comprising a source of generating x-rays, a sample holder for holding samples in the beam, a sample assembly held by the sample holder, including an outer tube that contains powder samples, and a detector for detecting the beam after interaction with the samples. 
     A positioning stage can be useful for moving the sample holder in a y-axis direction and the sample assembly holds different samples distributed along the y-axis. 
     In general, according to another aspect, the invention features a method of operation of an x-ray microscopy system. The method comprises generating x-rays, holding samples in the beam with a sample assembly including an outer tube containing powder samples, and detecting the beam after interaction with the samples. 
     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale; emphasis has instead been placed upon illustrating the principles of the invention. Of the drawings: 
         FIG.  1    is a side cross-sectional view of sample assembly include a mounting tube containing five samples, according to the present invention, for use in the x-ray CT system; and 
         FIG.  2    is a perspective view of the samples, mounting tube, and sample holder; and 
         FIG.  3    is a schematic diagram of an x-ray CT system with the mounting tube. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the singular forms and the articles “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms: includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Further, it will be understood that when an element, including component or subsystem, is referred to and/or shown as being connected or coupled to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
       FIG.  1    shows a sample assembly  114  that has been constructed according to the principles of the present invention. This concerns an inexpensive and easy technique that allows for multiple size fractions of powder to be mounted in a single sample holder and thereby analyzed in an automated sequential way without having to remount the sample. 
     In general, the sample assembly  114  comprises an elongate outer mounting tube  12 . This outer tube  12  is hollow with a preferably circular cross-section and a circular cross-section inner bore. It is preferably constructed from a low-Z material such as polyimide, Polytetrafluoroethylene (PTFE) or Polyether ether ketone (PEEK) tubing or other plastic. An outer diameter of the outer mounting tube  12  can be a few millimeters in diameter such as less than 5 millimeters (mm), or preferably around 2 mm. The inner diameter of its inner bore can be less than 3 mm in diameter and is preferably about 1 mm. 
     Multiple samples S 1 , S 2 , S 3 , S 4 , S 5 , possibly with different size fractions or even multiple individual samples, are usually mounted in the hollow inner bore  12 B of the outer mounting tube  12 . The samples are spaced from each other along the axis of the mounting tube  12  by short lengths of solid cylindrical spacers SP 1 , SP 2 , SP 3 , SP 4  that seal against the inner bore to separate the discrete samples. The bottom end of the mounting tube is sealed with a bottom plug B and the top of the mounting tube  12  is sealed by a top plug T. Typically, the spacers SP 1 , SP 2 , SP 3 , SP 4 , bottom plug B, and top plug T are all composed of a low Z material such as graphite so as to not significantly interfere with the x-ray imaging process. 
     In the example shown above, samples S 1 , S 2 , S 3 , S 4 , S 5  are preferably arranged in size order, arranged from the coarser near the base such as samples S 1  and S 2  to the finest samples S 4 , S 4  near the top. This allows for easy fraction indexing of each sample during tomography setup. 
     During setup, in a preferred embodiment, the graphite rod sections are used and spacers SP 1 , SP 2 , SP 3 , SP 4  are inserted into the mounting tube  12  sequentially, clearing the mounting tube of any residual powder adhering to the tube&#39;s inner bore wall, minimizing cross contamination of size fraction samples. The same graphite rod sections are also used as the top plug T and the bottom plug B to allow mounting into a pin-vice sample holder  112  and closure of the top. 
     It should be noted that the total length L of the sample being mounted in a single outer tube  12  should be less than this maximum vertical (y-axis) travel of the rotation and positioning stage  110  of the x-ray imaging system. Thus, L will often be less than 5 centimeters. 
     The bottom graphite plug B is first bonded inside the inner bore of the outer mounting tube  12 . Often this is a 1-2 centimeter length of graphite that is inserted inside the plastic outer tube  12 , then is sealed/attached to the base of the plastic outer tube  12  with epoxy such as a UV curing epoxy. Preferably, about half the length of the graphic bottom plug extends beyond the end of the outer tube to interface with the sample holder  112 . 
     Then, the first sample S 1  is introduced into the inner bore of the outer tube and packed against the top end of the bottom plug B. 
     Then the spacer SP 1  is placed in the outer tube  12  over the first sample S 1 . Often this is a small length of graphite, 1-2 millimeters in length. 
     This process is repeated adding the samples S 2 -S 5  with the intervening spacers SP 2 -SP 4 . Finally, the top plug T is sealed in place. 
       FIG.  2    shows a sample assembly  114  containing four samples S 1 -S 4 . It is held in the sample holder  112 . Specifically, a pin vise  112 P of the sample holder clamps onto the length of the bottom plug B that extends from the outer mounting tube  12 . 
       FIG.  3    is a schematic diagram of an x-ray CT system  100  for analyzing the sample in the sample assembly  114 . 
     In general, the x-ray CT system  100  includes an x-ray source system  102  that generates an often polychromatic x-ray beam  104  and a rotation and positioning stage  110  with sample holder  112  for holding the sample assembly  114  in the x-ray beam  104 . Images or x-ray projections are captured by a detector system  118 . The x-ray source system  102 , the rotation and positioning stage  110 , and the detector system are mounted to a base  108  of the x-ray CT system  100 . 
     A computer system  200  typically receives and processes these images or projections and provides general control of the system  100 . The computer system  200  possibly along with a special purpose graphics processor will typically perform tomographic reconstruction using the x-ray projections of the samples in the sample assembly  114 . 
     The x-ray source  102 , in one example, is a polychromatic x-ray source. Laboratory x-ray sources are often used because of their ubiquity and relatively low cost. Nonetheless, synchrotron sources or accelerator-based sources are other alternatives. 
     Common laboratory x-ray sources include an x-ray tube, in which electrons are accelerated in a vacuum by an electric field and shot into a target piece of metal, with x-rays being emitted as the electrons decelerate in the metal. Typically, such sources produce a continuous spectrum of background x-rays (i.e. bremsstrahlung radiation) combined with sharp peaks in intensity at certain energies that derive from the characteristic lines of the target, depending on the type of metal target used. 
     In one example, the x-ray source  102  is a rotating anode type or micro focused source, with a Tungsten target. Targets that include Molybdenum, Gold, Platinum, Silver or Copper also can be employed. A transmissive configuration of the x-ray source  102  can be used in which the electron beam strikes the thin target  103  from its backside. The x-rays emitted from the other side of the target  103  are then used as the beam  104 . Reflection targets are another option. 
     The x-ray beam  104  generated by source  102  has an energy spectrum that is controlled typically by the operating parameters of the source. In the case of a laboratory source, important parameters include the material of the target and the acceleration voltage (kVp). The energy spectrum is also dictated by any conditioning filters that suppress unwanted energies or wavelengths of radiation. For example, undesired wavelengths present in the beam can be eliminated or attenuated using, for instance, an energy filter (designed to select a desired x-ray wavelength range /bandwidth). 
     When the sample assembly  114  is exposed to the x-ray beam  104 , the x-ray photons transmitted through the sample form an attenuated x-ray beam  106  that is received by the spatially resolved detector system  118  in a projection configuration. In some other examples, an objective lens such as a zone plate lens is used to form an image onto the detector system  118  of the x-ray imaging system  100 . In alternative embodiments the detector system is a flat panel detector. 
     In the most common configuration of the detector system  118 , a magnified projection image of the sample  114  is formed on the detector system  118  with a geometrical magnification that is equal to the inverse ratio of the source-to-sample distance and the source-to-detector distance. Generally, the geometrical magnification provided by the x-ray stage is between 2× and 100×, or more. In this case, the resolution of the x-ray image is limited by the focus spot size or virtual size of the x-ray source system  102 . 
     To achieve high resolution, an embodiment of the x-ray CT system  100  further utilizes a very high resolution detector  124 - 1  of the detector system  118  in conjunction with positioning the sample  114  close to the x-ray source system  102 . In one implementation of the high-resolution detector  124 - 1 , a scintillator is used in conjunction with a microscope objective to provide additional magnification in a range between  2 x and  100 x, or more. 
     Other possible detectors can be included as part of the detector system  118  in the illustrated x-ray CT system  100 . For example, the detector system  118  can include a lower resolution detector  124 - 2 . This could be a flat panel detector or a detector with a lower magnification microscope objective, in examples. Configurations of one, two, or even more detectors  124  of the detector system  118  are possible. 
     Preferably, two or more detectors  124 - 1 ,  124 - 2  are mounted on a turret  122  of the detector system  118 , so that they can be alternately rotated into the path of the attenuated beam  106  from the sample  114 . 
     When multiple samples need to be handled in an automated fashion, an automation application  207  is employed. Based on operator defined parameters, the automation application running on the CPU  205  controls the sample handling via the controller  210 . It instructs the positioning and rotation stage  110  via its control interface  130  to move the sample assembly  114  in and out of the beam path during x-ray source system  102  calibration and sample analysis and also how the sample is positioned in the beam along the x, y, and z axes. 
     Once positioned, the automation application  207  via the controller  210  instructs the positioning and rotation stage  110  to move the sample assembly  114  in the y-axis direction to bring one of the samples S 1 -S 5  into the beam. The automation application then instructs the positioning and rotation stage  110  to rotate the sample assembly  114  relative to the beam  104  to perform the CT scan of one of the samples, such as sample S 1 . Then, once processed, the automation application  207  instructs the positioning and rotation stage  110  to move the sample assembly  114  in the y-axis direction to bring the next of the samples S 1 -S 5  into the beam such as sample S 2 . The automation application then instructs the positioning and rotation stage  110  to rotate the sample assembly  114  relative to the beam  104  to perform the CT scan of sample S 2 . 
     This process is repeated until all of the samples S 1 , S 2 , S 3 , S 4 , and S 5  contained in the outer tube  12  have been scanned. 
     Once scanned, the automation application  207  via the controller  210  further controls a sample loader that removes the sample assembly  114  from the sample holder  112  and inserts a new sample assembly. 
     Performing particle analysis using 3D x-ray microscopy automation is a significant challenge. Multiple size fractions need to be analyzed per sample and multiple samples per system in order to get a statistically representative description of particle behavior. The use of the automated sample loader can help alleviate this problem by automatically mounting a sequence of samples onto the sample stage. The use of the sample assembly allows for multiple samples to be loaded together. 
     In one example, the computer system  200  includes an image processor  202  that analyzes the x-ray projections and possibly performs the calculations necessary for tomographic reconstructions created from the x-ray projections. A display device  240 , connected to the computer system  200 , displays information from the x-ray CT system  100 . An input device  250  such as a touch screen, keyboard, and/or computer mouse enables interaction between the operator, the computer system  200 , and the display device  240 . 
     A user interface application  208  executes on an operation system  206  that controls access to a central processing unit CPU  205  of the computer system  200 . In one example, the operator defines/selects CT scan or calibration parameters via the user interface  208 . These include x-ray acceleration voltage settings, and settings for defining the x-ray energy spectrum of the scan and exposure time on the x-ray source system  102 . The operator also typically selects other settings such as the number of x-ray projection images to create for each sample S 1 -S 5  in the sample holder  114 , and the angles to rotate the rotation stage  110  for rotating the sample holder  114  for an x-ray CT scan in the x-ray beam  104 , along with the positioning of the sample in the beam along the x, y, and z axes. 
     The computer system  200 , with the assistance of its image processor  202 , accepts the image or projection information from the detector system  118  associated with each rotation angle for each of the samples S 1 -S 5 . The image processor  220  creates a separate projection image for each rotation angle for each of the samples S 1 -S 5 , and combines the projection images using CT reconstruction algorithms  209  to create 3D tomographic reconstructed volume information for each of the samples S 1 -S 5 . 
     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.