X-ray fluorescence analyzer and method for performing X-ray fluorescence analysis

Abstract

An X-ray fluorescence analyzer, comprising an X-ray tube (402) for emitting incident X-rays (206) in the direction of a first optical axis (204). A slurry processing unit (201) is configured to maintain a constant distance between a slurry sample (202) and the X-ray tube. A first crystal diffractometer (601) is positioned relative to the slurry processing unit (201) in a first direction and is configured to separate a predetermined first wavelength range from fluorescent X-rays (207) propagating in the first direction. It is configured to direct the fluorescent X-rays in the separated predetermined first wavelength range to a first radiation detector (602, 505). The input power rating of the X-ray tube (402) is at least 400 watts. The first crystal diffractometer (601) comprises a pyrolytic graphite crystal (603). The optical path between the X-ray tube (402) and the slurry processing unit (201) is direct, without a diffractometer in between.

Description

Technical Field

[0001] The present invention relates to the technical field of X-ray fluorescence analysis. In particular, the present invention relates to the task of detecting relatively small amounts of fluorescence radiation in the presence of significant background radiation. Background Art

[0002] X-ray fluorescence analysis can be used to detect the presence of an element of interest in a matrix of other elements and to measure its concentration. For example, in the mining industry it is important to know whether a mineral or metal of interest is present in a sample and in what quantity. To be applicable in industrial processes, the X-ray fluorescence analysis method should be reasonably accurate even at relatively short exposure times and be implemented with a robust and mechanically reliable measuring device.

[0003] One specific application of X-ray fluorescence analysis in the mining industry is the analysis of elements of interest in slurries. By definition, a slurry is a water-based suspension of fine, solid particles of crushed and ground ore, in which the dry weight of the solid particles is less than 90% of the total mass of the sample, typically 20%-80%. The fact that the sample is in the form of a slurry imposes special requirements on sample handling. For example, it is advantageous to maintain the flow of the sample as turbulent, so that the composition of the sample remains uniformly mixed and the fractions do not separate from each other. At the same time, the measurement geometry should be kept as constant as possible, so as not to cause undesirable geometry-based changes in the measurement results.

[0004] The concentration of the elements of interest in the slurry is usually very low. For example, copper, zinc, lead and molybdenum need to be measured at concentrations such as 0.01% or lower, while the concentration of gold to be measured may only be about a few ppm, such as 1ppm-5ppm. Such low concentrations make measurement difficult because the intensity of the fluorescent radiation from the elements of interest is very low, which inevitably increases the impact of statistical errors. When this intensity is low compared to the intensity of other radiation involved (such as fluorescent radiation from other elements of no interest), overlap with adjacent peaks will cause problems. The measurement time cannot be set to an arbitrary length because the slurry arrives as a continuous stream from the refining process and is an important online indicator of what is happening in the process. X-ray fluorescence measurements should be fast enough to detect trend changes in the slurry composition so that the measurement results can be used to control the refining process in real time. Summary of the invention

[0005] One object of the invention is to provide an apparatus for performing accurate and reliable X-ray fluorescence analysis of small concentrations of elements in slurries under harsh industrial conditions. Another object of the invention is to ensure that sufficiently accurate measurement results are obtained even in relatively short measurement times. Yet another object of the invention is to make the apparatus easily adaptable to the measurement of any element of interest in a sample.

[0006] The above and other objects are achieved by using an X-ray tube having an input power rating of at least 400 Watts; providing a direct optical path between the X-ray tube and a slurry processing unit; and using pyrolytic graphite crystals to collect fluorescent radiation from the irradiated sample.

[0007] According to a first aspect, an X-ray fluorescence analyzer is provided. The X-ray fluorescence analyzer includes an X-ray tube and a slurry processing unit, the X-ray tube is used to emit incident X-rays in the direction of a first optical axis, and the slurry processing unit is configured to maintain a constant distance between a slurry sample and the X-ray tube in the direction of the first optical axis. The X-ray fluorescence analyzer includes a first crystal diffractometer positioned in a first direction relative to the slurry processing unit. The first crystal diffractometer is configured to separate a predetermined first wavelength range from fluorescent X-rays propagating in the first direction, and is configured to guide the fluorescent X-rays in the separated predetermined first wavelength range to a first radiation detector. The input power rating of the X-ray tube is at least 400 watts, the first crystal diffractometer includes a pyrolytic graphite crystal, and the optical path between the X-ray tube and the slurry processing unit is direct, and there is no diffractometer between the X-ray tube and the slurry processing unit.

[0008] In a possible implementation of the first aspect, the slurry processing unit is a sample chamber, and a sample window is provided in the wall of the sample chamber for allowing X-rays to pass through while keeping the slurry sample in the sample chamber. The advantages are: simple sample processing and constant measurement geometry.

[0009] In a possible implementation of the first aspect, the X-ray tube comprises an anode for generating the incident X-rays, and the slurry processing unit is configured to maintain a shortest straight-line distance between the slurry sample and the anode of less than 50 mm, preferably less than 40 mm, and more preferably less than 30 mm. This has the advantage that a large proportion of the initial incident radiation can be utilized.

[0010] In a possible implementation of the first aspect, the X-ray tube is an end window type X-ray tube, which has the advantage that a short distance between the X-ray tube and the sample can be achieved while leaving enough space for the detection channel.

[0011] In a possible implementation of the first aspect, the input power rating of the X-ray tube is at least 1 kW, preferably at least 2 kW, and more preferably at least 4 kW. This has the advantage that a relatively large amount of fluorescent radiation can be generated.

[0012] In a possible implementation of the first aspect, the diffraction surface of the pyrolytic graphite crystal is one of the following: a simply connected surface curved in one direction; a simply connected surface curved in two directions; a non-simply connected rotationally symmetric surface. The advantage is that the most advantageous form of crystal can be selected for each application.

[0013] In a possible implementation of the first aspect, the first crystal diffractometer comprises a first slit in a first optical path between the slurry processing unit and the pyrolytic graphite crystal, and a second optical path between the pyrolytic graphite crystal and the first radiation detector. This has the advantage that a desired proportion of fluorescent radiation can be selected.

[0014] In a possible implementation of the first aspect, the diffraction surface of the pyrolytic graphite crystal is curved in only one direction, with a radius of curvature in a plane defined by the first and second optical paths, and the first slit is a linear slit oriented perpendicular to the plane. The advantage is that it is relatively simple to manufacture a crystal diffractometer.

[0015] In a possible implementation of the first aspect, the slurry processing unit is configured to maintain a flat surface of the slurry sample on a side facing the X-ray tube, and the first optical axis is perpendicular to the flat surface. This has the advantage that multiple measurement channels can be symmetrically placed around the X-ray tube.

[0016] In a possible implementation of the first aspect, the slurry processing unit is configured to maintain a flat surface of the slurry sample on a side facing the X-ray tube, and the optical axis is at an inclined angle to the flat surface. This has the advantage that the closest distance between the X-ray tube and the sample can be made relatively short while providing sufficient space for at least a plurality of detection channels.

[0017] In a possible implementation of the first aspect, the first crystal diffractometer is positioned at a rotation angle around the first optical axis at which the flat surface of the sample covers a maximum portion of the field of view of the first crystal diffractometer, and the second crystal diffractometer is positioned at another rotation angle around the first optical axis. The advantage is that the fluorescence radiation can be collected to the first crystal diffractometer from as large a spatial angle as possible.

[0018] In a possible implementation of the first aspect, in addition to the first crystal diffractometer, the X-ray fluorescence analyzer further includes a plurality of other crystal diffractometers, each of the first crystal diffractometer and the other crystal diffractometers being positioned at a corresponding rotation angle around the first optical axis, and each of the crystal diffractometers being configured to separate a predetermined wavelength range from the fluorescent X-rays propagating to a corresponding direction, and being configured to direct the fluorescent X-rays within the corresponding separated predetermined first wavelength range to a corresponding radiation detector. This has the advantage that a large number of elements can be analyzed from a sample without changing the physical configuration of the device.

[0019] In a possible implementation of the first aspect, the plurality of other crystal diffractometers include a second crystal diffractometer, the second crystal diffractometer includes a second crystal and is configured to direct the fluorescent X-rays in the corresponding separated second predetermined wavelength range to the corresponding second radiation detector; the second crystal includes a material different from pyrolytic graphite; and the first and second crystal diffractometers are configured to direct the characteristic fluorescent radiation of the same element to their corresponding radiation detectors. The advantage is that the measurement can be made more reliable and easier to adapt to many situations.

[0020] In a possible implementation of the first aspect, the second crystal is one of the following: silicon dioxide crystal, lithium fluoride crystal, ammonium dihydrogen phosphate crystal, potassium hydrogen phthalate crystal. The advantage is that sharp wavelength dispersive diffraction can be obtained by using the second crystal.

[0021] In a possible implementation manner of the first aspect, the second radiation detector is a gas-filled proportional counter, which has the advantage of being able to achieve relatively good detection efficiency at a relatively low manufacturing cost.

[0022] In a possible implementation of the first aspect, the element is gold. This has the advantage that even relatively valuable elements with very low concentrations can be detected.

[0023] In a possible implementation of the first aspect, at a reference energy of 5.9 keV, the energy resolution of the first radiation detector is better than 300 eV. The advantage is that the detector can provide accurate energy dispersion detection in a relatively wide wavelength range passed by the pyrolytic graphite crystal.

[0024] In a possible implementation of the first aspect, the X-ray fluorescence analyzer comprises: an analyzer body; a front wall of the analyzer body; an opening in the front wall; and a holder for removably holding the slurry processing unit against the outside of the front wall and aligned with the opening in the front wall. The advantage is that the slurry processing unit is easy to remove for maintenance.

[0025] In a possible implementation of the first aspect, the X-ray tube and the first crystal diffractometer are both inside the analyzer body, on the same side of the front wall. The advantage is that the structure is solid and well protected from accidental irradiating of anything.

[0026] In a possible implementation of the first aspect, the X-ray fluorescence analyzer comprises a filter plate in the optical path between the X-ray tube and the slurry processing unit. This has the advantage that the spectrum of the incident radiation can be tuned in a suitable manner.

[0027] In a possible implementation of the first aspect, the filter plate is located closer to the X-ray tube than to the slurry processing unit. This has the advantage that the filter plate will not unnecessarily obstruct the field of view of the detection channel.

[0028] In a possible implementation of the first aspect, the X-ray fluorescence analyzer comprises a calibration plate and an actuator, wherein the actuator is configured to controllably move the calibration plate between at least two positions, wherein the first position is not in the path of the incident X-rays, and the second position is in the path of the incident X-rays and in the field of view of the first crystal diffractometer. The advantage is that the calibration can be easily automated.

[0029] In a possible implementation of the first aspect, the first radiation detector is a solid-state semiconductor detector, preferably one of the following: a PIN diode detector, a silicon drift detector, a germanium detector, a germanium drift detector. The advantage is that the first radiation detector can combine precise and reliable operation with compact size and a sturdy overall appearance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the present invention and constitute a part of this specification. The accompanying drawings illustrate embodiments of the present invention and together with the description help explain the principles of the present invention. In the drawings:

[0031] Figure 1 Demonstrate the principles of X-ray fluorescence analysis in industrial processes,

[0032] Figure 2 showing details of an example of an X-ray fluorescence analyzer,

[0033] Figure 3 An example of using a calibrator plate is shown,

[0034] Figure 4 An example of an X-ray fluorescence analyzer is shown,

[0035] Figure 5 shows some structural details of an example of an X-ray fluorescence analyzer,

[0036] Figure 6 An example of a crystal diffractometer is shown,

[0037] Figure 7 shows some geometrical aspects of a crystal diffractometer,

[0038] Figure 8 shows some shapes of diffractor crystals,

[0039] Fig. 9 shows an example of a radiation propagation geometry,

[0040] Fig.10 Another example of a radiation propagation geometry is shown,

[0041] Fig.11 An example of a radiation spectrum is shown.

[0042] Fig.12 Another example of a radiation spectrum is shown,

[0043] Fig.13 Another example of a radiation spectrum is shown,

[0044] Fig.14 Another example of a radiation spectrum is shown,

[0045] Fig.15 Multiple detection channels are shown,

[0046] Fig.16 shows an example of a radiation spectra,

[0047] Fig.17 An example of a slurry processing unit is shown,

[0048] Fig.18 shows an X-ray tube with its optical axis perpendicular to the sample surface,

[0049] Fig.19 An X-ray tube is shown with its optical axis at an oblique angle relative to the sample surface.

[0050] Fig. 20 An example of placing multiple detection channels is shown,

[0051] Fig.21 An example of placing multiple detection channels is shown,

[0052] Fig. 22 shows the measured detection accuracy of an example device,

[0053] Fig.23 shows the measured detection accuracy of an example device,

[0054] Fig.24 shows the measured detection accuracy of an example device, and

[0055] Fig.25 The measured detection accuracy of one example device is shown. DETAILED DESCRIPTION

[0056] Figure 1 An example showing the principle of using an X-ray fluorescence analyser in an industrial process. For an industrial process it is common that the sample to be analysed may come as a more or less continuous stream of sample material and so there is a sample handling unit or system which brings the sample in for analysis and takes it away after analysis. Figure 1 In the schematic illustration of , a sample 101 arrives as a sample material flow on a conveyor 102, which here constitutes a sample handling system. An X-ray source 103 generates a beam 104 of incident X-rays, which hits a portion of the sample 101 within the field of view of the beam 104. Fluorescent X-rays 105 are emitted in all directions, and some of them are collected to Figure 1 The detection system in the plant includes a first slit 106, a wavelength-dispersive diffractometer crystal 107, a second slit 108, and a radiation detector 109. The plant may include a control computer system 110 that may control control subsystems 111 and 112 of the conveyor 102 and the X-ray fluorescence analyzer 113, respectively.

[0057] The generation of fluorescent X-rays is essentially a random process, so the more such photons that can be collected, the more reliable any analysis based on the received fluorescent X-ray photons will be. One known way to increase the statistical reliability of X-ray fluorescence analysis is to extend the duration that the sample remains illuminated by the incident radiation. If the sample is stationary, this means simply waiting longer before changing the sample. However, the nature of industrial processes may require that the sample arrives as a constantly moving stream. Even so, the concept of longer measurement times exists in a way, because if the composition of the sample stream remains essentially constant, then accumulating the fluorescent X-ray photons detected from a moving sample over X minutes is essentially the same as keeping a portion of the sample material stationary for X minutes in the analysis.

[0058] However, when analyzing a sample stream that is constantly moving, there are limits to how long the averaging time can be, since the composition of the sample stream does change, and these changes may be significant and should therefore be noted. If the sample arrives in the form of a slurry, there are other factors that complicate the situation, such as the need for the flow of the slurry to remain turbulent to prevent separation of the solid and liquid phases. It is not uncommon for a slurry sample to flow through a slurry processing unit at a rate of approximately 20 liters per minute. It is an object of the present invention to be able to obtain reasonably good detection results by using an averaging time of approximately a few minutes, such as 2 minutes or such as 3 to 5 minutes.

[0059] Therefore, in the following, improvements to X-ray fluorescence analysis are considered through factors such as measurement geometry, incident radiation power, choice of diffractometer crystal material, choice of detector type, use of multiple detection channels, and advanced utilization of the detection results.

[0060] Figure 2 is a schematic cross-sectional view of certain parts of an X-ray fluorescence analyzer. The X-ray fluorescence analyzer comprises an X-ray tube for emitting incident X-rays 206 in the direction of a first optical axis 204. Figure 2The radiation window 203 of the X-ray tube is seen in the figure. In order to process the slurry sample 202, the X-ray fluorescence analyzer includes a slurry processing unit 201, which in this case includes a sample chamber 208 or a sample cell equipped with an inlet connection and an outlet connection. The exact way in which the sample chamber 208 and its inlet connection and outlet connection are formed to ensure turbulence of the sample 202 in the chamber is irrelevant to this particular description. As an example, the principles explained in the international patent application published as WO2017140938 can be followed. In any case, the slurry processing unit is configured to maintain a constant distance between the slurry sample 202 and the X-ray tube. For example, a constant distance in the direction of the first optical axis 204 can be considered.

[0061] Keeping the distance constant has the effect that the measurement geometry does not change, at least not with regard to the distance and viewing angle which have a significant influence on the proportion of the incident X-rays 206 that will hit the sample 202. Thus, the device may comprise means for varying the distance, for example by varying the distance at which the X-ray tube is mounted. In other words, it is not mandatory that the distance will always remain constant. It is advantageous, merely for the purpose of directly processing the detection results, that the mechanical construction of the X-ray fluorescence analyzer allows maintaining the distance constant whenever necessary during the measurement.

[0062] Figure 3 It is shown how the slurry processing unit 201 comprises a sample window 301 in the wall of the sample chamber 208 for allowing X-rays to pass through while keeping the slurry sample in said sample chamber 208. The sample window 301 is an opening covered by a window foil 302, which is made of a material that is as transparent as possible to X-rays while having sufficient mechanical strength to withstand the pressure of the flowing slurry and the mechanical wear caused by the flowing slurry. In this way, the slurry processing unit is configured to maintain a flat surface of the slurry sample 202 on the side facing the X-ray tube. Figure 2 and Figure 3 In the geometry shown, the first optical axis 204 is perpendicular to the flat surface.

[0063] exist Figure 2 and Figure 3 303 and the opening in the front wall 303. A further window foil 304 covers the opening in the front wall 303. Just like the window foil 302 of the sample window 301 in the sample cavity 208, the further window foil 304 is made of a material that is as transparent to X-rays as possible. The purpose of the further window foil 304 is to protect the interior of the X-ray fluorescence analyzer device from dust, moisture and other contaminants that may be present in large quantities around it in industrial processes.

[0064] Figure 2 It shows how incident X-rays 206 hitting the sample 202 generate fluorescent X-rays 207. These fluorescent rays are initially pointed in all directions, but of interest are those fluorescent X-rays 207 that exit the sample cavity 208 through the sample window 301 and can be collected into one or more detection channels. The location, geometry and properties of such detection channels will be described in more detail later.

[0065] Figure 2 and Figure 3 Another feature shown in the is a filter plate 205 in the optical path between the X-ray tube and the slurry processing unit. Such a filter plate is an optional feature. The filter plate acts as a high pass filter, particularly by attenuating the lowest energy portion of the X-rays initially generated in the X-ray tube. The material and thickness of the filter plate 205 (if used) can be selected so that it passes those X-rays that are energetic enough to produce fluorescence in one or more elements of interest in the sample 202. It is particularly useful to use a high pass type filter, rather than, for example, a primary diffractometer that constitutes a band pass filter, because the high pass filter will pass a wide range of higher energy incident X-rays, which can then be used to produce fluorescent X-rays in multiple elements of interest simultaneously.

[0066] If a filter plate 205 is used, it is advantageous to place it closer to the X-ray tube than to the slurry processing unit. The filter plate 205 can even be attached to the X-ray tube so that the filter plate is very close to the radiation window 203 of the X-ray tube. If the filter plate 205 is additionally dimensioned in the lateral direction so that it is only slightly larger than the radiation window 203, or not larger than the radiation window at all, it can be ensured that the filter plate 205 does not unnecessarily cover any field of view that could otherwise be used for the detection channel. The thickness of the filter plate 205 can be in the order of millimeters or even less, so that using a filter plate does not increase the overall distance between the X-ray tube and the sample to any significant extent.

[0067] Figure 2 and Figure 3 Another feature shown in the X-ray fluorescence analyzer is a calibrator plate 305 which can be controllably and selectively brought into its position in the path of the incident X-rays 206 and in the field of view of the detection channel for receiving the fluorescent X-rays 207. The calibrator plate 305 has a very accurately known composition, so it can be used to calibrate the detection channel from time to time. If the calibration process should be automated, the X-ray fluorescence analyzer can be equipped with an actuator configured to controllably move the calibrator plate 305 between at least two positions, one of which is Figure 3 , and the other position is a position that is not on the path of the incident X-ray 206.

[0068] Figure 4 An example of an X-ray fluorescence analyzer according to an embodiment of the present invention is shown. The X-ray fluorescence analyzer includes an analyzer body 401, which serves as a basic support and protection structure. The front wall 303 of the analyzer body is Figure 4 As previously referenced Figure 2 and Figure 3 As illustrated, there is an opening in the front wall 303 for the passage of incident X-rays generated by the X-ray tube 402. A holder 403 is provided for holding the slurry processing unit 201 against the outside of the front wall 303 and aligned with the opening in the front wall 303.

[0069] In an advantageous embodiment, the retainer 403 can be configured to removably retain the pulp processing unit 201 against the front wall. The retainer 403 may include, for example, a hinge that allows the pulp processing unit 201 to be turned to the side, or a bayonet mount that allows the pulp processing unit 201 to be quickly disengaged from the front wall 303 to expose the above-mentioned reference Figure 2 and Figure 3 This allows relatively straightforward inspection and repair of those components that are critical to the propagation of both incident and fluorescent X-rays. Solid particles in the slurry may cause significant wear on the inside of the window foil 302 of the sample window 301 (see Figure 3 ), it is therefore advantageous to equip the sample window 301 with a mechanism that allows the window foil 302 to be replaced when necessary.

[0070] exist Figure 4 A portion of the X-ray fluorescence analyzer marked by a dashed rectangle 404 is shown in FIG. Figure 5 402 from the direction of the optical axis of the X-ray tube 402. This illustration shows an example of how the actuator 501 can be arranged to controllably move the calibrator plate 305 between two positions. Figure 5 In the first position shown, the collimator plate 305 is not in the path of incident X-rays from the radiation window 203 of the X-ray tube. In the second position, the collimator plate 305 will be substantially aligned with the radiation window 203 of the X-ray tube. Figure 5 The radiation window 203 in is concentric.

[0071] Figure 4 and Figure 5 It also shows how one or more detection channels 502 may be provided. The structure and operation of the detection channels will be described in more detail later in this document. Figure 4 and Figure 5The positioning principle is shown, according to which each detection channel is positioned at a corresponding rotation angle around the optical axis of the X-ray tube 402. When the optical axis of the X-ray tube 402 is perpendicular to the flat surface of the sample (which is defined by the sample window as part of the slurry processing unit 201), this way of placing the detection channels allows to arrange a completely equal field of view for all detection channels.

[0072] Figure 4 Other features shown are the provision of electronic boxes 405 , 406 and 407 for each detection channel and X-ray tube 402 inside the analyzer body 401 , and a cooling water circulation 408 for the X-ray tube 402 .

[0073] Figure 6 is a schematic illustration of certain parts of the so-called detection channel mentioned above. Figure 6 The main features of the detection channel of are a crystal diffractometer 601 and a radiation detector 602. As its name indicates, the crystal diffractometer 601 includes a crystal 603, which may be referred to as a diffractometer crystal or simply a crystal. Crystal 603 is a wavelength dispersive component of the crystal diffractometer 601. It may be provided in the slurry processing unit ( Figure 6 A first slit 604 is provided on a first optical path 605 between the crystal 603 (not shown) and the crystal 603, and a second slit 606 can be provided on a second optical path 607 between the crystal 603 and the radiation detector 602. Since the diffraction properties of the crystal 603 to the X-rays are highly dependent on the wavelength of the X-rays, this arrangement can be used to separate a specific wavelength range from the portion of the fluorescent X-rays that were originally emitted in the direction of the specific crystal diffractometer. Reference numeral 608 shows a housing enclosing the crystal diffractometer 601, which provides structural support for all components of the crystal diffractometer.

[0074] Figure 7 An example of a crystal diffractometer is shown in an axonometric projection. The crystal diffractometer is considered relative to the slurry processing unit ( Figure 7 The first slit 604 and the second slit 606 are formed between the corresponding limiting members, and the second optical path 607 represents the direction directed to the radiation detector ( Figure 7 The crystal diffractometer is enclosed in a housing 608 which is defined by a first flat surface 701 and a second flat surface 702 which is parallel to the first flat surface 701.

[0075] The mechanical structure described here is advantageous because the flat surfaces 701 and 702 provide a support to which the internal components of the crystal diffractometer can be attached in a relatively simple manner.

[0076] The diffraction of X-rays in crystals is governed by Bragg's law, which relates the diffraction angle to the distance between the mesh planes. Conventional crystal diffractometers have used crystals such as silicon dioxide, lithium fluoride, ammonium dihydrogen phosphate or potassium hydrogen phthalate, because sufficiently large single crystals of these materials can be relatively easily manufactured in the desired shape with the required accuracy. However, it has been found that while the wavelength selectivity of such conventional crystals is relatively good, the efficiency of diffraction of incoming X-rays is relatively poor.

[0077] Pyrolytic graphite is an alternative material for producing crystals for crystal diffractometers. Pyrolytic graphite is a general term referring to a material made from an organic compound containing a planar structure such as a benzene ring, by subjecting the compound to high temperatures so that essentially only the carbon atoms in the structure remain. The initial planar molecular structure gives pyrolytic graphite a highly ordered microstructure, so it is often referred to as HOPG (Highly Oriented Pyrolytic Graphite) or HAPG, where HAPG refers to the slightly different method of synthesizing the material. Pyrolytic graphite is not usually single crystalline in the sense of the more conventional crystalline materials mentioned above, but is polycrystalline. Nevertheless, in order to maintain consistency with established terminology in the art, it is practical to refer to diffractometer elements made from pyrolytic graphite as "crystals". In the following description, the term "HOPG crystal" will be used.

[0078] HOPG crystals have been found to be significantly more efficient as diffractors of fluorescent X-rays than conventional diffractometer crystal materials. In other words, a much higher proportion of the X-rays that hit a HOPG crystal are actually diffracted than with conventional crystalline materials. However, the polycrystalline nature of pyrolytic graphite means that not all of the reticular planes are precisely oriented like single-crystalline silicon dioxide. This in turn means that the wavelength selectivity of a HOPG crystal in a crystal diffractometer is not very precise: the fluorescent X-rays diffracted into a particular direction represent a range of wavelengths around the nominal wavelength that is diffracted into that direction according to Bragg's law, and this range is much wider than that of X-rays diffracted by conventional crystalline materials.

[0079] However, the less precise wavelength selectivity of the HOPG crystal is not a serious disadvantage because it can be balanced with other factors in the design of the X-ray fluorescence analyzer. One possible approach is to use a solid-state semiconductor detector as the radiation detector 602, directing the fluorescent X-rays in the separated wavelength range from the HOPG crystal to the radiation detector. The radiation detector 602 can be, for example, a PIN diode detector, a silicon drift detector, a germanium detector, or a germanium drift detector. In contrast to, for example, a gas-filled proportional counter, the energy resolution of a solid-state semiconductor detector can be more precise. The energy resolution of an X-ray detector is usually expressed at a reference energy of 5.9 keV. At the reference energy of 5.9 keV, the above-mentioned type of solid-state semiconductor detector can have an energy resolution better than 300 eV.

[0080] Combining the use of a HOPG crystal in a crystal diffractometer 601 with the use of a solid-state semiconductor detector as a radiation detector 602 can result in an advantageous situation, wherein the crystal diffractometer 601 is configured to separate a predetermined first wavelength range from the fluorescent X-rays 207 propagating in the direction of the crystal diffractometer 601 (reference slurry processing unit 201), and is configured to direct the separated fluorescent X-rays in the predetermined first wavelength range to the radiation detector 602, which is a solid-state semiconductor detector. The good energy resolution of the solid-state semiconductor detector is then used to produce a measurement result indicating the energy spectrum of the fluorescent X-rays in the separated predetermined first wavelength range. Based on the energy spectrum, and other measurements can be used as support, the amount of fluorescent X-rays from the element of interest can be determined with relatively good accuracy.

[0081] In the design of X-ray fluorescence analyzers, the geometric form of the diffraction surface of the HOPG crystal is another factor that needs to be considered. Figure 8 Some examples of geometric forms are shown. It may be noted here that, to be precise, a "crystal" is only a thin layer of crystalline (e.g. single crystal in the case of silicon dioxide, or e.g. polycrystalline in the case of HOPG) material constituting the actual diffraction surface. A crystal diffractometer comprises a substrate to which the crystalline material is attached. Examples of substrate materials are, for example, glass and aluminum, but the substrate material may also be iron or any other material which itself is not prone to causing unwanted interfering fluorescent radiation. The crystalline material may be attached to a suitably formed surface of the substrate by, for example, van der Waals forces. Alternatively, the crystalline material may be grown directly on a suitably formed surface of the substrate, or some other suitable attachment method, such as glue, may be used.

[0082] The substrate and the crystalline material together form three-dimensional solids, examples of which are shown in Figure 8In keeping with established usage in the art, these entities are referred to herein as crystals, although this terminology, as explained above, is slightly inaccurate. The term "diffraction surface" refers to the external, exposed surface of a crystalline material at which diffraction of X-rays occurs; strictly speaking, diffraction of X-rays occurs at reticular planes within the crystalline material close to the surface (here referred to as the diffraction surface).

[0083] Figure 8 The common feature of crystal 603, crystal 802 and crystal 804 in FIG. 1 is that the three-dimensional geometric structure of the entity consisting of the HOPG crystal and the substrate is a three-dimensional geometric structure of a prism, one side of the prism being cut off by a curved diffraction surface. In the upper-line illustration of the three crystals, the imaginary form of the prism is shown by dashed lines.

[0084] Figure 8 The lower-line illustration of the same crystal in FIG601 shows how the diffractive surface is curved differently in all three cases. In crystal 603, diffractive surface 801 is curved in only one direction (the longitudinal direction). In other words, if an imaginary horizontal line is drawn across diffractive surface 801 at an arbitrary position, such as Figure 8 The dashed line shown will always be straight. A particular advantage of this crystal is that it is relatively easy to manufacture. Figure 6 and Figure 7 By comparison, it can be seen that the radius of curvature of the diffractive surface 801 lies in the plane defined by the first optical path 605 and the second optical path 606. This plane is also parallel to the straight surfaces 701 and 702.

[0085] In crystal 802, diffractive surface 803 is curved in two directions (longitudinal and transverse) to form part of a toroidal surface. This means that if a transverse arc is drawn across diffractive surface 803 at any position, e.g. Figure 8 The two dashed arcs shown, each of these transverse arcs will be identical to each other. Although this geometry may be slightly more complex to manufacture to the required accuracy than the geometry of surface 801 on the left, it involves the advantage that it enables more accurate focusing of the diffracted X-rays.

[0086] In crystal 804, diffractive surface 805 is curved in two directions (longitudinal and transverse), but in a different way than the intermediate surface 803. Diffractive surface 805 forms part of a rotationally symmetric surface, whose axis of rotation 806 lies in the plane defined by the optical paths of the incoming and diffracted X-rays. This means that if a transverse arc is drawn across diffractive surface 805, e.g. Figure 8The dotted arc in the figure will have a different radius of curvature depending on the longitudinal position at which it is drawn. Figure 8 As can be seen in FIG. 8 , the dashed arc in the middle is not as significantly curved as the arcuate edges seen at the ends of the crystal 804. This is because the dashed arc is further away from the rotation axis 806 than the arcuate edges at the ends of the crystal.

[0087] Mathematically, a rotationally symmetric surface is formed when a continuous curve is rotated about an axis of rotation. The form of the continuous curve defines how far each point of the surface will be from the axis of rotation, and what properties the surface may have. Figure 8 An example of a curve of the diffractive surface 805 in is a segment of a logarithmic spiral. Although such a surface is more complicated to manufacture than those described above as surfaces 801 and 803, a rotationally symmetric surface made with a segment of a logarithmic spiral involves the inherent advantage that it provides very precise focusing of the diffracted X-rays.

[0088] Figure 8 The common feature of all diffraction surfaces 801, 803 and 805 in is that they are simply connected surfaces in a topological sense. A simply connected surface is a path-connected surface (i.e., any two points on the surface can be connected by a path that completely belongs to the surface), and in addition, any annular path can be continuously contracted to a point, so that all intermediate forms of the contracted ring also completely belong to the surface.

[0089] The intuitive description of a simply connected surface is that it has no holes. Therefore, a hole can be drilled through Figure 8 A small hole in any of the diffractive surfaces 801, 803, or 805 in the crystal does not change their properties as diffractors, and not simply by reducing the surface area that is drilled away. For this reason, it is defined here that the requirement that a surface be simply connected in a topological sense is to be interpreted as being related to the general form of the surface: under such an interpretation, a small hole in the surface does not mean that it will not be simply connected. Another definition of how the simply connected requirement should be interpreted is as follows: If a crystal is like Figure 8 If a surface "lies on its side" as in the example above (i.e., the principal radii of curvature defining the longitudinal curvature between the ends of the crystal are in the horizontal plane; thus diffractive surfaces are usually oriented vertically), then any imaginary horizontal line will pierce the diffractive surface at most one point. If a surface meets at least one of these intuitive descriptions, then it is a simply connected surface.

[0090] exist Figure 8On the right in FIG, crystal 807 is shown as a comparative example. The diffraction surface 808 of crystal 807 is curved in two directions (longitudinal and transverse) to form a complete rotationally symmetric surface, whose axis of rotation 809 may be in the plane defined by the optical axes of the incoming and diffracted X-rays. The rotation of the curve about the axis of rotation 809 defines the form of the diffraction surface 808, which may be, for example, a segment of a logarithmic spiral. Obviously, the diffraction surface 808 is not simply connected in a topological sense, since a closed curve drilled around the surface cannot be contracted to a point. Such crystals are relatively complex to manufacture, but they can be used with suitable shielding ( Figure 8 Used with a crystal (not shown) that blocks the propagation of direct, non-diffracted X-rays, the crystal collects fluorescent radiation from a larger spatial angle than those crystals having a single connected surface such as 801, 803 or 805.

[0091] The geometry of the diffractive surface and the resulting optical properties may have an impact on how the rest of the crystal diffractometer should be designed. It was explained above how the crystal diffractometer 601 may include a first slit 604 on a first optical path 605 between the slurry processing unit 201 and the (pyrolytic graphite) crystal, and how there is a second optical path 607 between the (pyrolytic graphite) crystal and the radiation detector 602. If the diffractive surface 801 of the (pyrolytic graphite) crystal 603 is curved in only one direction, with a radius of curvature in a plane defined by the first optical path 605 and the second optical path 607, it is advantageous to make the first slit 604 a linear slit oriented perpendicular to the plane, such as Figure 7 As shown. If the diffractive surface 803 of the (pyrolytic graphite) crystal 802 is curved in two directions to form part of an annular surface, it is advantageous to make the first slit a curved slit with a radius of curvature oriented perpendicular to the first optical path. If the diffractive surface 805 of the (pyrolytic graphite) crystal 804 is curved in two directions to form part of a rotationally symmetric surface, the rotation axis 806 of which is in the plane defined by the first and second optical paths, it is advantageous to make the first slit point-shaped.

[0092] Similar considerations apply if a second slit 606 is used on the second optical path 607. However, it should be noted that a second slit is not always necessary: ​​its use is relevant to attenuate background and scattered radiation, especially for diffractometer crystals with a high wavelength selectivity. Considering that the wavelength selectivity of HOPG is not that high, the additional advantage gained by using a second slit is relatively small.

[0093] If a second slit is used in the second optical path 607 between the (pyrolytic graphite) crystal 603, 802, 804 and the first radiation detector, the geometry of the crystal diffractometer may follow the principles of, for example, Johann geometry or Johnson geometry. These are respectively Fig. 9 and Fig.10 In Fig. 9 In , the center point 902 of the diffraction surface, the first slit 604 and the second slit 606 are located on a Rowland circle with a radius of R. The radius of curvature of the diffraction surface in the plane defined by the first and second optical paths is 2R, and the radius of curvature of the mesh plane 901 in the crystal is 2R. This means that the first crystal diffractometer has a Johann geometry. Fig.10 , the center point 1002 of the diffraction surface, the first slit 604 and the second slit 606 are similarly located on a Rowland circle with a radius R. However, here the radius of curvature of the diffraction surface in the plane defined by the first and second optical paths is R, and the radius of curvature of the mesh plane 1001 in the crystal is 2R, so that the first crystal diffractometer has a Johnson geometry.

[0094] In order to maintain the compact size of the crystal diffractometer, it is advantageous if the magnitude of R can be kept relatively small. As an example, R may be at most 40 cm.

[0095] Figures 11 to 14 is a schematic illustration of a fluorescence X-ray spectrum in certain cases. The spectrum is usually expressed as counts detected at each photon energy. In practice, the detector that produces the counts has a certain energy resolution that defines how close the energies of two photons can be to each other, allowing the detector to produce two different types of output signals. Signal processing is used to sort the received X-ray photons into energy bins of finite width and give counts per bin. The more precise the detector resolution, the narrower the energy bins can be made (in terms of energy units).

[0096] exist Fig.11 In , the graph 1101 is smooth without any visible peaks or spectral holes. Such a spectrum is rarely obtained in practice, but it shows the case where only background and randomly scattered radiation are received without any characteristic peaks of the element of interest. Fig.12, graph 1201 is otherwise identical, but there is a characteristic peak 1202 for the element of interest. The problem is that the concentration of the element of interest in the sample being measured is so small that the height of characteristic peak 1202 is low relative to the general level of the spectrum in the same energy range. Therefore, even though a relatively large number of photons are observed in this energy range, relatively few of them are actually fluorescent photons from the element of interest.

[0097] The energy of a photon is inversely proportional to its wavelength, so when the wavelength selectivity of the above diffractive crystals has been considered, the energy selectivity can also be considered. Fig.13 Schematic diagram of what a radiation detector of a crystal diffractometer equipped with a HOPG crystal can receive. The HOPG crystal will direct a relatively wide range of energy 1301 of fluorescent X-rays to the radiation detector, which is a direct result of the relatively moderate wavelength selectivity of the HOPG crystal. However, at the same time, the diffraction efficiency of the HOPG crystal is relatively good. Therefore, the radiation detector will receive radiation falling on Fig.13 A considerable proportion of the photons are within the two shaded regions in FIG. 1302 , where the photons belonging to the first shaded region 1302 are background and scattered photons, while the photons belonging to the second shaded region 1303 are actual fluorescent photons from the element of interest.

[0098] Fig.14 Schematic illustration of what a radiation detector of a crystal diffractometer equipped with a silica (or other conventional) crystal might receive under the same circumstances. Conventional crystals will direct a relatively narrow range of energies 1401 of fluorescent X-rays to their radiation detectors, which is a direct result of the relatively good wavelength selectivity of conventional crystals. However, at the same time, the diffraction efficiency of conventional crystals is lower than that of HOPG crystals. As a result, the radiation detector will receive only a limited proportion of the photons that actually originate from the element of interest in the sample (see Fig.13 1303). Fig.14 The small peak 1402 in represents the fluorescent X-rays that will actually be detected in this case.

[0099] One factor to be considered in the design of an X-ray fluorescence analyzer is the possibility of using detection channels with different configurations. Here, "different configurations" mainly refer to the choice of diffractometer crystals and the choice of radiation detectors.

[0100] Fig.15 Schematic diagram showing how an industrial X-ray fluorescence analyzer for analyzing a slurry sample may include multiple detection channels. Fig.15 In the figure, the lines are shown as straight lines because the representation is schematic. In practice, they can be, for example, Figure 4 and Figure 5The rotationally symmetrical arrangement shown is positioned around the X-ray tube, each with a field of view of the slurry processing unit directed towards the X-ray fluorescence analyzer.

[0101] The X-ray fluorescence analyzer includes a first crystal diffractometer 1501, which is positioned along a first direction relative to the slurry processing unit, and the first crystal diffractometer 1501 includes a first crystal. A first radiation detector 1505 is configured to detect fluorescent X-rays diffracted by the first crystal 1502 at a first energy resolution. The X-ray fluorescence analyzer includes a second crystal diffractometer 1511, which is positioned along the first direction relative to the slurry processing unit, and the second crystal diffractometer includes a second crystal 1512. A second radiation detector 1515 is configured to detect fluorescent X-rays diffracted by the second crystal 1512 as a second energy resolution.

[0102] As a first assumption, it can be assumed that the first crystal 1502 is a pyrolytic graphite (HOPG) crystal, and the second crystal 1512 is a material other than pyrolytic graphite, such as silicon dioxide, lithium fluoride, ammonium dihydrogen phosphate, or potassium hydrogen phthalate. In addition, as a first assumption, it can be assumed that the first and second crystal diffractometers are configured to direct the characteristic fluorescence radiation of the same element to their corresponding radiation detectors. That is, the two detection channels are equipped differently, but the purpose is to detect the presence and concentration of the same element in the slurry sample.

[0103] Therefore, configuring a crystal diffractometer to direct the characteristic fluorescence radiation of a particular element to its radiation detector is usually accomplished by: 1) selecting a crystal with a specific distance between its reticular planes; 2) selecting the curvature of the crystal and the reticular planes; and 3) selecting the angles and distance values ​​of the crystal and one or more slits so that only X-rays having a specific wavelength range that includes the desired characteristic peak of the element of interest will reach the detector. An element of interest may have several characteristic peaks, so saying that two detection channels are configured to measure the characteristic fluorescence radiation of the same element does not necessarily mean that they will be configured to measure the same characteristic peak, although this is not excluded.

[0104] If two detection channels are configured to measure the same characteristic peak, the measurement results they produce can be similar to Fig.13 (for channels with HOPG crystals) and Fig.14 The task of finding the actual concentration of the element of interest can be described in the form of a method as described below.

[0105] The purpose of the method is to perform X-ray fluorescence analysis and includes irradiating a slurry sample with incident X-rays and receiving fluorescent X-rays from the irradiated sample. Due to the measurement geometry, a first part of the fluorescent X-rays will be directed to a first detection channel, while a second part of the fluorescent X-rays will be directed to a second detection channel. The method includes separating a first predetermined wavelength range 1301 and a second predetermined wavelength range 1401 from the corresponding first and second parts of the received fluorescent X-rays with a corresponding first crystal diffractometer 1501 and a second crystal diffractometer 1511. Both the first wavelength range 1301 and the second wavelength range 1401 include characteristic fluorescence radiation of the same element. In addition, the first wavelength range 1301 is at least twice as wide as the second wavelength range 1401.

[0106] The method includes detecting fluorescent X-rays within the first and second separated wavelength ranges with respective first radiation detectors 1505 and second radiation detectors 1515. At a reference energy of 5.9 keV, the energy resolution of the first radiation detector 1505 is better than 300 eV. Thus, the method includes generating respective first and second detection results. The method includes calculating the concentration of the element in the sample based on at least one of the first and second detection results.

[0107] The "at least one" here emphasizes the fact that not all detection results are best treated in an equal manner. A lot depends on the sample. In some samples, the concentration of the element of interest may be relatively large, resulting in a relatively large number of fluorescent photons being detected even in the second radiation detector 1515 despite the moderate diffraction efficiency of the second crystal 1512. In some other cases, the concentration of the element of interest may be so small that only a very small and faint peak is visible in the second wavelength range 1401. In some cases, the first wavelength range 1301 may appear relatively clean and free from any interfering radiation, while some other samples may contain a large amount of some other elements whose characteristic peaks are so close that they are visible or even dominant in the first wavelength range 1301, but not in the second wavelength range 1401.

[0108] Typically, the calculation may include calculating the combined intensity of background radiation and fluorescent X-rays from elements other than the element using at least one of the first detection result and the second detection result. The method may then include subtracting the calculated combined intensity of background radiation and fluorescent X-rays from elements other than the element of interest in the sample from the total intensity detected within the wavelength range containing the characteristic peak of fluorescent X-rays of the element to be measured in the sample. The method may then include providing the result of the subtraction as the calculated intensity of the characteristic fluorescent X-ray peak.

[0109] The calculation may include analyzing whether the effect of the characteristic peak from another element on the first detection result is greater than a predetermined threshold value based on the first and second detection results. If the analysis shows that the effect of the characteristic peak from the other element on the first detection result is greater than the predetermined threshold value, the method may include calculating the concentration of the element in the sample based on the second detection result. On the other hand, if the analysis shows that the effect of the characteristic peak from the other element on the first detection result is not greater than the predetermined threshold value, the method may include calculating the concentration of the element in the sample based on the first detection result.

[0110] Another possibility is to use calibration samples to form a specific model for each measurement channel of each sample line. The measurement channel for the actual measurement of this sample line is then selected depending on which of the channels gives the most accurate calibration.

[0111] The element of interest may be gold, both because it is valuable and because there are reasonably efficient methods for extracting it from slurry streams even where its concentration is very low. There are other elements whose interfering signatures may or may not be present and may appear very close to one of the signatures of gold. If such interfering elements are present in significant amounts in the sample, the detection channel with the HOPG crystal may give relatively imprecise and unreliable results, at least if used alone.

[0112] There can be intermediate forms between these two extremes, where the contribution of the first and second detection results is considered in various ways. For example, the decision about which calculation method to select can be made using an artificial intelligence algorithm that compares the first and second detection results with previously obtained comparable results and with some evaluation data about how various available calculation methods perform with said comparable results.

[0113] Fig.16 Schematically shows a fluorescence X-ray spectrum including two clear peaks 1601 and 1602. In this case, the calculation method selected may depend on whether peaks 1601 and 1602 are both characteristic peaks of the same element of interest, or whether one of them is a characteristic peak of some interfering element. The smaller peak closer to the energy axis indicates that a detection channel equipped with a conventional (e.g., silicon dioxide) crystal will produce an estimated detection result for these two peaks.

[0114] One interesting case is the case where both peaks 1601 and 1602 are peaks of an element of interest. Of particular interest is whether one of them (here: peak 1601) is stronger, for which the detection channel equipped with SiO2 is configured for its measurement. In this case, the best features of both channels can begin to be used: The precise wavelength selectivity of the silica crystal can be used to separate a strictly defined wavelength range 1401 comprising only the desired characteristic peak, so that the relatively large intensity of this peak still gives a sufficient number of counts in the corresponding detector within a relatively short time. At the same time, the good diffraction efficiency of the HOPG crystal can be used to separate a wider wavelength range 1301 comprising another, lower characteristic peak. When the overall performance of the two detection channels is known from calibration measurements, the concentration of the element of interest can be calculated from the detection results given by the two detectors.

[0115] In many cases where the characteristic fluorescence radiation includes a K peak or an L peak of an element having 30≤Z≤92, where Z is the atomic number of the element, a method of the type described above may be applicable. The flexible adaptability of the method is well suited to measurements of samples including one or more elements of interest in a matrix having a major elemental composition of Z≤8, where Z is the atomic number. This is the case, for example, with water-based slurries.

[0116] The principles discussed above regarding the use of two detection channels can be generalized to involve the use of three or more detection channels. The form factor of the detection channels as described above, i.e., the form factor in which each crystal diffractometer 601 is enclosed in a housing defined by a first flat surface 701 and a second flat surface 702 parallel to the first flat surface 701, enables multiple detection channels to be distributed as a "cassette" in a layout that is, for example, rotationally symmetrical around an X-ray tube. The detection results from detection channels configured to detect characteristic fluorescence radiation of the same element can be combined in various ways as described above. If the detection channel is configured to measure the characteristic fluorescence radiation of two or more elements of interest, a large number of detection channels allow the concentration of two or more elements of interest in the sample to be calculated simultaneously. It is also possible to cross-correlate the detection results from channels configured to detect different elements. For example, if an element has two characteristic peaks, one of which is measured with a dedicated first detection channel, and the other is close to the characteristic peak of another element of interest, the detection result from the first channel can be used to correct the detection result from the channel configured to measure the characteristic peak of another element.

[0117] One factor to consider in the design of an industrial X-ray fluorescence analyzer for analyzing slurry samples is the power of the X-ray tube, and the geometry and size of the area between the X-ray tube and the slurry processing unit.

[0118] Fig.17 The possibility of using the so-called transmission geometry is shown. The radiation window 203 of the X-ray tube is Fig.17 204, and the incident X-rays are emitted in the direction of the optical axis 204 through the primary filter plate 205. The slurry processing unit 201 includes a chamber 1701 with an output slit 1702, from which the sample 202 flows out in a curtain-like manner and falls downward under the influence of gravity. The incident X-rays generate fluorescent X-rays in the relatively thin falling slurry. Reference numeral 1703 refers to the fluorescent X-rays directed obliquely backwards, and can be used in a manner very similar to that of the previous reference numeral 1704. Figure 2 , Figure 3 , Figure 4 and Figure 5 Describes the geometry of the detection channel placement ( Fig.17 Reference numeral 1704 refers to fluorescent X-rays directed to other directions, in particular, to the direction on the other side of the sample flow. These can be detected by a detection channel ( Fig.17 This can be a particularly advantageous way to place the detection channels, as they can achieve a better field of view and therefore better spatial efficiency in collecting fluorescent X-rays. It may also be helpful to place the X-ray tube very close to the sample. However, it must be noted that appropriate radiation shielding geometric precautions must be taken to prevent any incident X-rays from entering the detection channels.

[0119] Fig.18 18 is a partial cross section of the output portion of the X-ray tube 402. The X-ray tube comprises an anode 1801 for generating incident X-rays. The incident X-rays will be emitted in the direction of the optical axis 204 towards the sample 202, where only the sample is schematically shown without the slurry processing unit for reasons of clarity of the figure. However, it is assumed that the slurry processing unit is configured to maintain a flat surface 1802 of the slurry sample 202 on the side facing the X-ray tube 402. As previously described, this can be achieved, for example, by providing a sample window with a window foil made of a material transparent to X-rays. The sample window can be provided in the wall of the sample chamber for allowing X-rays to pass through while the slurry sample is held in the sample chamber.

[0120] Fig.18 Other parts of the X-ray tube schematically shown in FIG. 1 are a cooling water circulation 1803 , an annular cathode 1804 for emitting accelerated electrons, and a radiation window 203 .

[0121] When the goal is to produce so much fluorescent radiation that even very small concentrations of elements of interest can be detected, it is advantageous if as many photons of incident radiation as possible (of sufficient energy) can hit the sample 202. One way to achieve this is to have a very powerful X-ray tube. According to one embodiment, the input power rating of the X-ray tube 402 is at least 400 watts. Even more powerful X-ray tubes can be used: according to other embodiments, the input power rating of the X-ray tube 402 can be at least 1 kilowatt, or at least 2 kilowatts, or even at least 4 kilowatts. Even if only a small portion of the power declared as the input power rating of the X-ray tube will ultimately appear in the form of incident X-rays generated, the input power rating is still an important indicator of the ability of the X-ray tube to produce a high flux of incident X-rays.

[0122] The use of X-ray tubes with higher power ratings than before means that radiation shielding associated with previously known lower power X-ray sources must be reconsidered. According to one embodiment, thicker radiation shielding panels and denser radiation shielding materials may be used to ensure that ionizing radiation does not leak into areas where it could be hazardous.

[0123] Another way to ensure that a very high flux of incident X-rays hits the sample 202 is to make the distance between the anode 1801 and the sample 202 as small as possible. The slurry processing unit can be configured to maintain a minimum linear distance d between the anode 1801 and the sample 202, such that d is shorter than 50 mm. In another embodiment, d can be shorter than 40 mm. In another embodiment, d can be shorter than 30 mm.

[0124] However, it must be noted that generally, the closer the anode 1801 of the X-ray tube 402 is to the sample 202, the larger the spatial angle around the sample 202 is blocked by the structure of the X-ray tube. This is an important factor to consider because the structure of the X-ray tube 402 may block the field of view of the detection channel. One way to alleviate this problem is to use a so-called end window type X-ray tube, rather than a side window type X-ray tube. Fig.18 and Fig.19 It can be considered that the use of an end window type X-ray tube is shown. In such an X-ray tube, the radiation window 203 is usually located at one end of the generally tubular structure, which leaves a relatively large free space around the tubular structure for the detection channel to be placed. Another possibility is to use a side window type X-ray tube and place the detection channel on one or both sides of the X-ray tube.

[0125] In all the figures described so far, the optical path between the X-ray tube 402 and the sample 202 is also direct, which means that there is no diffractometer between them. This is another way to ensure that the maximum number of incident X-ray photons can hit the sample. Firstly, setting up a diffractometer between the X-ray tube and the sample will inevitably mean a longer distance between the anode 1801 and the sample 202, because some space needs to be reserved for the diffractometer. Secondly, the nature of a diffractometer is to separate only a certain wavelength range from the initial radiation spectrum, which inevitably means that fewer incident X-ray photons hit the sample. Other advantageous consequences of not using any so-called primary diffractometer between the X-ray tube 402 and the sample 202 are that (multiple) incident X-rays are provided simultaneously to excite the characteristic peaks of multiple elements in the sample, and there are fewer structural parts that may block the field of view of the detection channel.

[0126] exist Fig.18 In the embodiment of FIG. 1 , the optical axis 204 of the X-ray tube 402 is perpendicular to the flat surface 1802 of the sample 202. Although this arrangement provides excellent rotational symmetry for the detection channel placed around the X-ray tube 402, it is not the only possibility. Fig.19 An alternative embodiment is shown in which the optical axis 204 of the X-ray tube 402 is at an oblique angle to the flat surface. Such an arrangement can help to make the shortest linear distance d between the anode 1801 and the sample 202 even shorter while leaving a sufficiently free field of view for the detection channels on at least some sides of the X-ray tube 402. Fig. 20 and Fig.21 This principle is further elaborated.

[0127] Fig. 20 An X-ray tube 402 and five detection channels are shown as seen from the direction of the sample. The radiation window 203 of the X-ray tube 402 is visible in the middle of the figure. The entrance window of each detection channel for receiving fluorescent radiation is located in the proximal end face of the corresponding crystal diffractometer; the entrance window 2001 is shown as an example. In order to allow the generated fluorescent radiation to enter the detection channel in the largest possible proportion, it is advantageous to place these entrance windows as close to the sample as possible, and also so that the entrance window sees the sample surface at the largest possible spatial angle. Each of the multiple crystal diffractometers is positioned at a corresponding rotation angle around the optical axis of the X-ray tube 402. Each of the crystal diffractometers is configured to separate a predetermined wavelength range from the fluorescent X-rays propagating to the corresponding direction, and is configured to guide the fluorescent X-rays within the corresponding separated predetermined first wavelength range to the corresponding radiation detector.

[0128] Fig.21 The X-ray tube 402 and two detection channels are shown as seen from the side. Fig.21This is schematically shown in: This shows the area where the slurry processing unit is configured to maintain a flat surface of the slurry sample on the side facing the X-ray tube 402. Therefore, this is the area that should be within the field of view of the X-ray tube 402 in order for the incident X-rays to hit the sample. This also shows the area that should cover as large a spatial angle as possible in the field of view of the detection channel in order to collect as many fluorescent X-rays as possible.

[0129] The optical axis 204 of the X-ray tube 402 is at an oblique angle to the flat surface. The first crystal diffractometer 1501 is positioned at that rotation angle about the optical axis 204, at which the flat surface of the sample covers the largest part of the field of view of the first crystal diffractometer 1501. Assuming that no other structures block any part of the available field of view, in practice this means that the first crystal diffractometer 1501 is located opposite the X-ray tube, i.e. in the direction into which an imaginary beam along the optical axis 204 would be reflected if the sample surface were a mirror.

[0130] The second crystal diffractometer 1511 is positioned at another rotation angle around the optical axis 204. Fig.21 In the embodiment, the second crystal diffractometer 1511 can be positioned at what is described as the worst possible rotation angle because its field of view of the sample surface is limited by the edge of the X-ray tube 402 near the sample window 301. If the other rotation angle differs from the rotation angle at which the first crystal diffractometer 1501 is positioned by less than 180 degrees, the second crystal diffractometer 1511 can be positioned more like Fig. 20 In this case, the flat surface of the sample at the sample window 301 will cover the Fig.21 A portion of the field of view of the second crystal diffractometer 1511 between the two extremes is shown.

[0131] According to one embodiment, Fig. 20 and Fig.21 The first crystal diffractometer 1501, which is placed at an optimal rotation angle (in terms of field of view), is a crystal diffractometer in which the diffractometer crystal is a HOPG crystal and the radiation detector is a solid-state semiconductor detector. Given the good diffraction efficiency of the HOPG crystal, placing the first crystal diffractometer in this way helps to ensure that the maximum number of fluorescent X-ray photons will eventually reach the detector. If there is some a priori knowledge about the assumed concentration levels of various elements in the sample to be measured, it is advantageous to place the crystal diffractometer to an optimal rotation angle that is configured to separate and direct the characteristic fluorescent radiation of the element of interest that is expected to have the smallest concentration to its corresponding detector.

[0132] One factor to consider in the design of an industrial X-ray fluorescence analyzer for analyzing slurry samples is the choice of radiation detector in those channels having diffractometer crystals of materials other than pyrolytic graphite. The relatively good wavelength selectivity of conventional diffractometer crystal materials such as silicon dioxide understandably makes it less necessary to have precise energy resolution in the radiation detector as with HOPG crystals. A gas-filled proportional counter can provide fairly satisfactory detection results in detection channels having diffractometer crystals other than HOPG at advantageously lower manufacturing costs than solid-state semiconductor detectors.

[0133] However, the foregoing should not be understood as an objection to selecting solid-state semiconductor detectors also for detection channels having diffractometer crystals other than HOPG. Likewise, it is not mandatory to use solid-state semiconductor detectors in detection channels equipped with HOPG crystals if the energy resolution of another type of radiation detector is found to be sufficient.

[0134] Figure 22 to Figure 25 A calibration measurement is shown, where the vertical axis represents the concentration measured with one detection channel of the device being tested, which is an industrial X-ray fluorescence analyzer for analyzing slurry samples according to an embodiment. The horizontal axis represents the concentration in the same sample, but measured for a long time using laboratory-grade equipment in order to obtain results that are as accurate and reliable as possible. In order to make the laboratory measurements comparable to industrial-type measurements, the slurry samples are dried and homogenized for the laboratory measurements, and the water removal is compensated by calculation. If this calibration measurement shows that the points are settled along a straight line, two different devices give highly matched results, which means that the device being tested is very accurate. Deviations from the straight line show that the device being tested produces inaccurate results.

[0135] The scale is arbitrary, but Fig. 22 and Fig.23 The scales in are the same, and Fig.24 and Fig.25 The element of interest in all measurements is gold. Fig. 22 and Fig.23 represents the measurement of samples where the concentration of interfering elements is less than 300 ppm, while Fig.24 and Fig.25 The concentration of the measured interfering elements varies between 0% and 2%. Interfering elements are elements having a characteristic fluorescence peak close to at least one characteristic fluorescence peak of the element of interest.

[0136] Fig. 22 and Fig.24 Represents the case where measurement with the device under test is performed using a detection channel having a silicon dioxide crystal in a crystal diffractometer and a gas-filled proportional counter as a radiation detector. Fig.23 and Fig.25 This represents the case where measurement with a device under test is performed using a detection channel having a HOPG crystal in a crystal diffractometer and a solid-state semiconductor detector as a radiation detector.

[0137] Fig. 22 and Fig.23 The comparison between the two shows that when the concentration of interfering elements is small, the detection channel with HOPG crystal and solid-state semiconductor detector gives more accurate detection results than the detection channel with silicon dioxide crystal and gas-filled proportional counter. The average error between the concentration measured by the HOPG channel of the tested device and the concentration measured in the laboratory is + / -0.24ppm, while the comparable average error with silicon dioxide crystal and gas-filled proportional counter (measured) is + / -0.56ppm.

[0138] Fig.24 and Fig.25 The comparison between the two shows that when the concentration of interfering elements is significant, the detection channel with HOPG crystal and solid-state semiconductor detector gives less accurate detection results than the detection channel with silica crystal and gas-filled proportional counter. The average error between the concentration measured by the HOPG channel of the tested device and the concentration measured in the laboratory is + / -1.62ppm, while the comparable average error with silica crystal and gas-filled proportional counter (measured) is + / -0.42ppm.

[0139] There are many ways to use Figure 22 to Figure 25 Results shown. For example, an industrial X-ray fluorescence analyzer for analyzing a slurry sample may be equipped with a first, second, and third detection channel, wherein both the first and second detection channels are equipped with a crystal diffractometer, which is configured to separate and direct the characteristic fluorescence X-rays of the same element (such as gold) to its corresponding detector. The first detection channel may be a detection channel having a HOPG crystal and a solid-state semiconductor detector, and the second detection channel may be a detection channel having a silicon dioxide crystal and a gas-filled proportional counter. The third detection channel may be equipped with a crystal diffractometer, which is configured to separate and direct the fluorescence X-rays of the interfering elements to their corresponding detector characteristic fluorescence X-rays. The detection results of all three detection channels may then be analyzed. If the detection result generated by the third detection channel indicates that there is a significant concentration of interfering elements in the sample, the calculation of the concentration of gold will focus more on (or even exclusively use) the detection result of the second detection channel. Accordingly, if the detection result generated by the third detection channel indicates that there is only a very small (insignificant) concentration of interfering elements in the sample, the calculation of the concentration of gold will focus more on (or even exclusively use) the detection result of the first detection channel.

[0140] A number of advantageous features of industrial X-ray fluorescence analyzers for analyzing slurry samples have been described above. Ultimately, they all serve a common purpose, namely to reliably measure even very small concentrations of elements of interest in various slurries at a reasonable cost under the harsh conditions that an industrial environment may be subject to (short measuring times; extreme temperatures; frequent presence of moisture, dust and dirt; long maintenance intervals, etc.). The advantageous features can be combined with one another in a variety of ways, so that the most advantageous combination may depend on the specific case and its specific boundary conditions.

[0141] It is obvious to a person skilled in the art that, with the advancement of technology, the basic idea of ​​the invention can be implemented in various ways. Therefore, the present invention and its embodiments are not limited to the above examples, on the contrary, they can be varied within the scope of the claims. As an example, even if gold has been frequently mentioned above as a typical element of interest, the same principle also applies to the measurement of other elements of interest. Examples of such other elements of interest are, for example, copper, silver, platinum group metals and uranium.

Claims

1. An X-ray fluorescence analyzer, comprising: - an X-ray tube (402) for emitting incident X-rays (206) in the direction of a first optical axis (204), - a slurry processing unit (201) configured to maintain a constant distance between a sample (202) of slurry and the X-ray tube, - a first crystal diffractometer (601), positioned relative to the slurry processing unit (201) along a first direction, the first crystal diffractometer (601) being configured to separate a predetermined first wavelength range from the fluorescent X-rays (207) propagating in the first direction, and being configured to direct the fluorescent X-rays in the separated predetermined first wavelength range to a first radiation detector (602, 1505), Features: - the X-ray tube (402) has an input power rating of at least 400 Watts, - the first crystal diffractometer (601) comprises a pyrolytic graphite crystal (603), - the optical path between the X-ray tube (402) and the slurry processing unit (201) is direct, without a diffractometer in between, and - At a reference energy of 5.9 keV, the energy resolution of the first radiation detector (602, 1505) is better than 300 eV.

2. The X-ray fluorescence analyzer according to claim 1, wherein: The slurry processing unit comprises a sample chamber (208) having a sample window (301) in a wall of the sample chamber (208), the sample window being used to allow X-rays to pass through while retaining the sample (202) of slurry in the sample chamber (208).

3. The X-ray fluorescence analyzer according to any one of claims 1 or 2, wherein - the X-ray tube (402) comprises an anode (1801) for generating the incident X-rays (206), and - the slurry processing unit (201) is configured to maintain a shortest linear distance between the sample (202) of slurry and the anode (1801) shorter than 50 mm.

4. The X-ray fluorescence analyzer according to claim 3, wherein: The X-ray tube (402) is an end-window type X-ray tube.

5. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: The X-ray tube (402) has an input power rating of at least 1 kilowatt.

6. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: The diffraction surface of the pyrolytic graphite crystal (603) is one of the following: a simply connected surface curved in one direction; a simply connected surface curved in two directions; or a non-simply connected rotationally symmetric surface.

7. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: The first crystal diffractometer comprises: - a first slit (604) located on a first optical path (605) between the slurry processing unit (201) and the pyrolytic graphite crystals (603, 802, 804), and - a second optical path (607) between the pyrolytic graphite crystal (603, 802, 804) and the first radiation detector (602, 1505).

8. The X-ray fluorescence analyzer according to claim 7, wherein: - the diffractive surface (801) of the pyrolytic graphite crystal (603) is curved in only one direction, with a radius of curvature lying in a plane defined by the first optical path (605) and the second optical path (606), and - said first slit (604) is a linear slit oriented perpendicularly to said plane.

9. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: - the slurry processing unit (201) is configured to maintain a flat surface of the sample (202) of slurry on a side facing the X-ray tube (402), and - said first optical axis (204) is perpendicular to said flat surface.

10. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: - the slurry processing unit (201) is configured to maintain a flat surface of the sample (202) of slurry on a side facing the X-ray tube (402), and - The first optical axis (204) is at an inclined angle to the flat surface.

11. The X-ray fluorescence analyzer according to claim 10, wherein: The first crystal diffractometer (601) is positioned at a rotation angle around the first optical axis (204) at which the flat surface of the sample (202) covers a maximum portion of the field of view of the first crystal diffractometer (601).

12. The X-ray fluorescence analyzer according to claim 1 or 2 further includes a plurality of other crystal diffractometers besides the first crystal diffractometer, each of the first crystal diffractometer and the other crystal diffractometers being positioned at a corresponding rotation angle around the first optical axis (204), and each of the crystal diffractometers being configured to separate a predetermined wavelength range from the fluorescent X-rays (207) propagating to a corresponding direction, and being configured to direct the fluorescent X-rays within the corresponding separated predetermined first wavelength range to a corresponding radiation detector.

13. The X-ray fluorescence analyzer according to claim 12, wherein: - the plurality of other crystal diffractometers include a second crystal diffractometer (1511), the second crystal diffractometer including a second crystal (1512) configured to direct fluorescent X-rays within the respective separated second predetermined wavelength ranges to respective second radiation detectors, - the second crystal (1512) comprises a material different from pyrolytic graphite, and - said first crystal diffractometer and said second crystal diffractometer are configured to direct characteristic fluorescence radiation of the same element to their respective radiation detectors.

14. The X-ray fluorescence analyzer according to claim 13, wherein: The second crystal (1512) is one of the following: silicon dioxide crystal, lithium fluoride crystal, ammonium dihydrogen phosphate crystal, potassium hydrogen phthalate crystal.

15. The X-ray fluorescence analyzer according to claim 13, wherein: The second radiation detector (1515) is a gas-filled proportional counter.

16. The X-ray fluorescence analyzer according to claim 13, wherein: The element is gold.

17. The X-ray fluorescence analyzer according to claim 1 or 2, comprising: -Analyzer body (401), - the front wall (303) of the analyzer body (401), - an opening in the front wall (303), and - a holder (403) for removably holding the pulp processing unit (201) against the outside of the front wall (303) and aligned with the opening in the front wall (303).

18. The X-ray fluorescence analyzer according to claim 17, wherein: The X-ray tube (402) and the first crystal diffractometer (601) are both located inside the analyzer body, on the same side of the front wall (303).

19. The X-ray fluorescence analyzer according to claim 1 or 2, comprising a filter plate (205) located on the optical path between the X-ray tube (402) and the slurry processing unit (201).

20. The X-ray fluorescence analyzer according to claim 19, wherein: The filter plate (205) is positioned so that the distance to the X-ray tube (402) is smaller than the distance to the slurry processing unit (201).

21. An X-ray fluorescence analyzer according to claim 1 or 2, comprising a calibrator plate (305) and an actuator (501), wherein the actuator is configured to enable the calibrator plate (305) to move controllably between at least two positions, wherein a first position is not in the path of the incident X-ray (206), and a second position is in the path of the incident X-ray (206) and in the field of view of the first crystal diffractometer (601).

22. The X-ray fluorescence analyzer according to claim 1 or 2, wherein: The first radiation detector (602) is a solid-state semiconductor detector.

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