EA042286B1 - X-RAY FLUORESCENCE ANALYZER SYSTEM AND METHOD FOR PERFORMING FLUORESCENCE ANALYSIS OF AN ELEMENT OF INTEREST IN PULP - Google Patents

Description

Technical field

The invention relates to the field of X-ray fluorescence analysis. In particular, the invention relates to the task of detecting relatively small amounts of characteristic fluorescent radiation in a pulp sample from a given element of interest from Z to 60 inclusive.

Prior Art

X-ray fluorescence analysis can be used to detect the presence of elements of interest in a matrix of other elements and measure their concentration. For example, in the mining industry it is important to know if a mineral or metal of interest is present in a sample and in what quantities. The method of X-ray fluorescence analysis, in order to be used in an industrial process, must be sufficiently accurate even with a relatively short exposure time, and it could be used with noise-resistant and mechanically reliable measuring devices.

A particular application of X-ray fluorescence analysis in the mining industry is the analysis of elements of interest in cuttings. By definition, slurry is an aqueous suspension of fine solids of crushed and ground ore in which the solids dry weight is less than 90%, typically 20-80% of the total mass of the sample. The fact that the sample is in the form of a slurry places special demands on the handling of the sample. For example, it is preferable to keep the sample flow turbulent so that its composition remains evenly mixed and fractions do not separate from each other. At the same time, the measurement geometry must remain as constant as possible so as not to cause undesirable geometric changes in the measurement results.

The concentrations of the elements of interest in the pulp are often very low.

For example, copper, zinc, lead, and molybdenum need to be measured at concentrations such as 0.01% or less, and gold concentrations that can be measured can be as low as a few parts per million, such as 1 to 5 ppm. The concentration of silver and some other elements of interest with their atomic number Z between the concentrations of niobium and neodymium inclusive can be of the same order of magnitude. This low concentration makes measurements difficult because the intensity of the fluorescent emission from the element of interest is very low, which inevitably increases the influence of statistical errors. When the intensity is low compared to that of other emissions present, such as fluorescent emissions from other uninteresting elements, overlap with adjacent peaks and continuous background radiation causes problems. The measurement time cannot be arbitrarily long since the slurry comes as a continuous stream from the cleaning process and is an important current indicator of what is going on in the process. The X-ray fluorescence measurement must be fast enough to detect trends in pulp composition so that the measurement results can be used to control the cleaning process in real time.

One known document US 2014/0037053 A1 describes an X-ray fluorescence analyzer with cylindrically symmetrical barrel-shaped crystal diffractors located between the X-ray source and the sample and between the sample and the detector.

Another well-known document US 2012/0294418 A1 describes a device containing a wavelength-swept selector for use in X-ray diffraction or fluorescence analysis.

The essence of the invention

The aim of the invention is to provide a device for performing accurate and reliable X-ray fluorescence analysis of low concentrations of a given element of interest with Z of 41 and 60 inclusive in pulp under difficult industrial conditions. Another object of the invention is to ensure that sufficiently accurate measurement results are obtained even with a relatively short measurement time. Yet another object of the invention is to easily adapt the device to measure any given element of interest in a specified range in a sample.

The above and other objectives are achieved by using a pyrolytic graphite crystal to collect fluorescent radiation from an irradiated sample and using a detector whose energy resolution is relatively accurate to detect the collected fluorescent radiation.

According to a first aspect, an X-ray fluorescence analyzer system is provided. The X-ray fluorescence analyzer system contains an X-ray tube for emitting incident X-ray radiation in the direction of the first optical axis, a pulp processing unit configured to maintain a constant distance between the pulp sample and the specified X-ray tube, and the first crystal diffractor located in the first direction from the specified pulp processing unit . Said first crystal diffractor is configured to isolate a predetermined first wavelength range from fluorescent X-ray radiation that propagates in the specified first direction, and is configured to direct fluorescent X-ray radiation in the selected predetermined first wavelength range to the first radiation detector. The first crystalline diffractor is a pyrolytic graphite crystal. Said predetermined first wavelength range includes the characteristic fluorescent emission of a predetermined element of interest with its atomic number Z from 41 to 60 inclusive. The energy resolution of said first radiation detector is better than 600 eV at the energy of said characteristic fluorescent radiation.

In one possible implementation of the first aspect, the X-ray fluorescence analyzer system comprises a processor configured to receive and process the output signals generated by said first radiation detector, wherein said processor is configured to calculate a background radiation fraction using at least a first fraction of said output signals, characteristic of the detected x-ray radiation, the wavelength of which is in the specified first wavelength range, but different from the wavelength of the specified characteristic fluorescent radiation of the specified element of interest.

In one possible implementation of the first aspect, the processor is configured to calculate the specified fraction of the background radiation using at least the specified first fraction of the specified output signals characteristic of the detected X-ray radiation, the wavelength of which is in the specified first wavelength range, but shorter than the wavelength said characteristic fluorescent emission of said element of interest, and a second fraction of said output signals indicative of detected X-rays whose wavelength is in said first wavelength range but longer than the wavelength of said characteristic fluorescent emission of said element of interest.

In one possible implementation of the first aspect, the processor is configured to calculate a detected amount of said characteristic fluorescent radiation from said element of interest by subtracting said calculated background radiation fraction from output signals at said characteristic fluorescent wavelengths.

In one possible implementation of the first aspect, said energy resolution of the first radiation detector is better than 300 eV at the energy of said characteristic fluorescent radiation, and the first radiation detector is a solid state semiconductor detector, preferably one of the following detectors: a PIN diode detector, a silicon drift detector, germanium detector, germanium drift detector, cadmium telluride detector.

In one possible implementation of the first aspect, the nominal input power of said x-ray tube is at least 1 kilowatt, preferably at least 2 kilowatts, and more preferably at least 4 kilowatts.

In one possible implementation of the first aspect, the x-ray fluorescence analyzer system comprises a base filter material in the form of a layer crossing said first optical axis between said x-ray tube and said pulp processing unit.

In one possible implementation of the first aspect, the transmission of said base filter material layer is greater than 5% for photons with energies greater than 15 keV.

In one possible implementation of the first aspect, the x-ray tube comprises an anode for generating said incident x-ray radiation, and said pulp processing unit is configured to maintain the shortest linear distance, which is less than 50 mm, preferably less than 40 mm, and more preferably less than 30 mm, between said sample pulp and the specified anode.

In one possible implementation of the first aspect, the diffractive surface of said pyrolytic graphite crystal is one of the following surfaces: a singly bonded surface that is curved in one direction; a simply connected surface, curvilinear in two directions; axisymmetric non-simply connected surface.

In one possible implementation of the first aspect, the pulp processing unit is configured to maintain a flat surface of said pulp sample on the side facing said x-ray tube, said first optical axis being perpendicular to said flat surface.

In one possible implementation of the first aspect, the pulp processing unit is configured to support a flat surface of said pulp sample on the side facing said x-ray tube, said first optical axis being at an oblique angle to said flat surface.

In one possible implementation of the first aspect, the X-ray fluorescence analyzer system, in addition to said first crystal diffractor, comprises several other crystal diffractors, each of said first and other crystal diffractors being located at a respective angle of rotation around said first optical axis, and configured to isolate a given range wavelengths from fluorescent x-rays that propagate in the corresponding direction, and with the possibility of directing fluorescent x-rays in the corresponding selected predetermined first dia

- 2 042286 wavelength range to the appropriate radiation detector.

In one possible implementation of the first aspect, said several other crystal diffractors comprise a second crystal diffractor comprising a second crystal configured to direct fluorescent x-rays in a respective dedicated second predetermined wavelength range to a respective second radiation detector, said second crystal being made of a material other than from pyrolytic graphite.

In one possible implementation of the first aspect, said second crystal is one of the following crystals: a silicon dioxide crystal, a lithium fluoride crystal, an ammonium dihydrogen phosphate crystal, a potassium hydrogen phthalate crystal; and said second radiation detector is a gas-filled proportional counter.

In one possible implementation of the first aspect, the X-ray fluorescence analyzer system comprises a housing, a front wall of said housing in which an opening is made, and a holder for removably holding said pulp processing unit on the outer side of said front wall and aligned with said opening in said front wall.

In one possible implementation of the first aspect, the x-ray tube and the first crystal diffractor are inside said analyzer housing on one side of said front wall.

In one possible implementation of the first aspect, the X-ray fluorescence analyzer system comprises a calibration plate and an actuator capable of controlled movement of said calibration plate between at least two positions, the first of which is not in the path of the incident X-ray, and the second position is in the path of the incident X-ray. radiation and in the field of view of the first crystal diffractor.

In one possible implementation of the first aspect, the specified element of interest is silver.

According to a second aspect, a method is provided for performing X-ray fluorescence analysis of a given element of interest in a pulp, said given element of interest having an atomic number Z of 41 to 60 inclusive. The method includes emitting incident X-ray radiation in the direction of the first optical axis to the sample of said pulp and using the first crystal diffractor with a pyrolytic graphite crystal to separate the specified first wavelength range from the fluorescent X-ray radiation that the specified incident X-ray radiation generates in the specified pulp sample, and the specified specified the first wavelength range contains the characteristic fluorescent emission of said predetermined element of interest. The method also includes directing fluorescent X-ray radiation in the selected predetermined first wavelength range to the first radiation detector, the energy resolution of which is better than 600 eV at the energy of said characteristic fluorescent radiation. The method also includes using the outputs of said first radiation detector to calculate a background radiation fraction in said first wavelength range and calculating a detected amount of said characteristic fluorescent radiation of a given element of interest by subtracting said estimated background radiation fraction from the wavelength outputs of said characteristic fluorescent radiation. .

Brief description of the figures

The accompanying drawings, which are included to provide a further understanding of the invention and form part of this specification, illustrate embodiments of the invention and, together with the description, help to explain the principles of the invention.

On the figures:

fig. 1 illustrates the principle of X-ray fluorescence analysis in an industrial process;

fig. 2 shows in detail an example of an X-ray fluorescence analyzer system;

fig. 3 illustrates an example of the use of a calibration plate;

fig. 4 shows an example of an X-ray fluorescence analyzer system;

fig. 5 shows some structural details of an example X-ray fluorescence analyzer system;

fig. 6 shows an example of a crystal diffractor;

fig. 7 depicts some geometric aspects of a crystal diffractor;

fig. 8 shows some shapes of diffractor crystals;

fig. 9 shows an example of radiation propagation geometry;

fig. 10 shows another example of radiation propagation geometry;

fig. 11 shows an example of an emission spectrum;

fig. 12 shows another example of an emission spectrum;

fig. 13 shows another example of an emission spectrum;

fig. 14 shows another example of an emission spectrum;

fig. 15 shows another example of an emission spectrum;

- 3 042286 fig. 16 shows detection channels;

fig. 17 shows examples of emission spectra;

fig. 18 illustrates an example of the method;

fig. 19 shows an example of a pulp handling unit;

fig. 20 depicts an X-ray tube whose optical axis is perpendicular to the surface of the sample;

fig. 21 depicts an x-ray tube whose optical axis is located at an oblique angle to the surface of the sample;

fig. 22 shows an example of the placement of detection channels;

fig. 23 shows an arrangement example of a plurality of detection channels;

fig. 24 illustrates the measured detection accuracy of an exemplary device;

fig. 25 illustrates the measured detection accuracy of an exemplary device;

fig. 26 illustrates the measured detection accuracy of an exemplary device; and fig. 27 illustrates the measured detection accuracy of an exemplary device.

Detailed description

Fig. 1 illustrates an example of the principle of using an X-ray fluorescence analyzer in an industrial process. It is typical for industrial processes that the sample to be analyzed may come as a more or less continuous flow of material, so that there is a sample handling unit or system that transfers the sample for analysis and collects it after analysis. In the schematic illustration in Fig. 1, sample 101 enters as a material stream onto conveyor 102, which in this case is the sample handling system. An x-ray source 103 generates an incident x-ray beam 104 that hits the part of the sample 101 that is within the field of view of the beam 104. Fluorescent x-rays 105 are emitted in all directions and part of it is collected in the detection system, which in FIG. 1 includes a first slit 106, a wavelength dispersive diffraction crystal 107, a second slit 108, and a radiation detector 109. The installation may include a computer control system 110 that can control the control subsystems 111 and 112 of the conveyor 102 and the X-ray fluorescence analyzer 113, respectively.

The generation of fluorescent X-rays is inherently a random process, so any analysis that is performed on the basis of received fluorescent X-ray photons is generally more reliable the more such photons can be collected. A known way to increase the statistical reliability of X-ray fluorescence analysis is to increase the time during which the sample remains illuminated by the incident radiation. If the sample is immobile, this means simply waiting a longer time before changing the sample. However, due to the nature of the industrial process, it may be necessary for the sample to arrive as a constantly moving stream. Even then, the concept of a longer measurement time is somewhat present, because if the composition of the sample stream remains essentially constant, then the accumulation of the number of detected fluorescent X-ray photons from the moving sample stream for X minutes is essentially the same as holding a portion of the material the sample is immobile when analyzed for X minutes.

However, there are limitations on the longest averaging time when analyzing a constantly moving sample stream because the composition of the sample stream does change and these changes can be important and therefore should be noticed. In addition, if the sample is a slurry, there are other factors that make the situation more difficult, such as the requirement that the slurry flow remain turbulent to prevent solid-liquid separation. It is not uncommon for a pulp sample to flow through the pulp handling unit at a rate of about 20 l/min. The object of the invention is to obtain sufficiently good detection results using an averaging time on the order of minutes, for example 2 minutes or 3 to 5 minutes.

The improvements in X-ray fluorescence analysis due to factors such as measurement geometry, incident power, choice of diffractive crystal materials, choice of detector types, use of multiple detection channels, and improved utilization of detection results are discussed below.

Fig. 2 is a schematic cross-sectional view of some parts of an X-ray fluorescence analyzer system. The X-ray fluorescence analyzer system includes an X-ray tube for emitting incident X-rays 206 in the direction of the first optical axis 204. A window 203 for transmitting X-ray tube radiation is seen in FIG. 2. To handle a pulp sample 202, the X-ray fluorescence analyzer system includes a pulp processing unit 201, which in this case includes a chamber 208 or sample cell equipped with inlet and outlet connections. The precise manner in which sample chamber 208 is formed and its inlet and outlet connections to provide turbulent flow of sample 202 within the chamber is not relevant to this specific description. For example, the principles set forth in the international patent application published as WO 2017/140938 can be followed. In any case, the pulp processing unit is configured to maintain a constant distance between the pulp sample 202 and the x-ray tube. The constant distance can be considered, for example, in the direction of the first optical axis 204.

Keeping the distance constant results in the measurement geometry not changing, at least not in terms of distance and angle of view, which have an important influence on how much of the incident X-ray 206 hits the sample 202. Thus, the device may include means for changing the distance, for example, by changing the distance at which the x-ray tube is installed. In other words, it is not necessary that the specified distance always remain the same. Simply for purposes of direct processing of detection results, it is advantageous for the mechanical configuration of the X-ray fluorescence analyzer system to be able to maintain said distance constant during the measurement, when necessary.

Fig. 3 shows that the pulp handling unit 201 in the wall of the sample chamber 208 comprises a sample window 301 to allow X-rays to pass while retaining the pulp sample 202 in the chamber 208. The window 301 is an opening covered by a foil 302 made from a material that maximally transparent to X-rays, but at the same time mechanically strong enough to withstand the pressure and mechanical wear caused by the flowing liquid slurry. Thus, the pulp processing unit is configured to maintain a flat surface of the pulp sample 202 on the side facing the x-ray tube. In the geometry shown in Fig. 2 and 3, the first optical axis 204 is perpendicular to said flat surface.

Also in FIG. 2 and 3, the front wall 303 of the analyzer housing and the opening in said front wall 303 are shown. Another foil 304 covers said opening in the front wall 303. Just like the foil 302 of the window 301 in the chamber 208, the other foil 304 is made of a material that as transparent as possible to x-rays. The purpose of the other 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 in the industrial process environment.

In FIG. 2 shows how incident x-rays 206 striking sample 202 produce fluorescent x-rays 207. This is initially omnidirectional, but what is of interest is the fluorescent x-rays 207 that exit chamber 208 through sample window 301 and can be collected into one or more detection channels. The location, geometry, and properties of such detection channels are described in more detail below.

Another feature shown in Fig. 2 and 3 is the implementation of the main filter material in the form of a layer or plate 205 installed across the specified optical soy 204 between the x-ray tube 402 and the pulp processing unit 201. A filter bed or filter plate of this type is an additional feature. It works as a high-pass filter, attenuating in particular the lowest energy portion of the X-rays that were originally generated in the X-ray tube. The material and thickness of the filter plate 205, if used, can be chosen such that the plate transmits that X-ray that has sufficient energy to generate fluorescence in the element(s) of interest in the sample 202. It is especially useful to use a high-pass filter instead of, for example, the main diffractor, which is a band pass filter, since the high pass filter will pass a wide spectrum of higher energy incident X-rays, which is then available to simultaneously generate fluorescent X-rays in a number of elements of interest. The transmission of the base filter material layer 205 is preferably greater than 5% for photons with energies greater than 15 keV.

If a filter plate 205 is used, it is preferable to place it closer to the x-ray tube than to the pulp processing unit. The filter plate 205 may even be attached to the x-ray tube so that it is very close to the window 203 for transmitting the radiation of the x-ray tube. If the filter plate 205 has additional dimensions in the transverse direction such that it is only slightly larger than or even no larger than the radiation window 203, it can be ensured that the filter plate 205 will not unnecessarily obstruct any field of view that otherwise it would be available for detection channels. The thickness of the filter plate 205 may be on the order of a millimeter or even less so that the use of the plate does not increase the overall distance between the X-ray tube and the sample to any great extent. The radiation attenuating characteristics of metals and other suitable materials for the filter plate 205 are well known, so choosing the combination of material and thickness to achieve the desired transmission is straightforward.

Another feature shown in Fig. 2 and 3 is a calibration plate 305 that can be controlled and selectively placed in a position in which it is in the path of the incident X-rays 206 and within the field of view of the detection channels that are used to receive the fluorescent X-rays 207. The calibration plate 305 has a very well known composition and can be given a precise position in the structures that define the measurement geometry, so it can be used to periodically calibrate detection channels. If the calibration process is to be automated, the X-ray fluorescence analyzer system may be equipped with an actuator that is configured to move the calibration plate 305 in a controlled manner between at least two positions, one of which is the position shown in FIG. 3 and the other at a position that is not in the path of the incident x-rays 206.

Fig. 4 illustrates an example of an X-ray fluorescence analyzer system made in accordance with one embodiment of the invention. It contains a housing 401 which functions as the main supporting and protective structure. The front wall 303 of the analyzer housing is visible on the left in FIG. 4. As explained above with reference to FIG. 2 and 3, an opening is provided in the front wall 303 for the passage of the incident X-ray radiation generated by the X-ray tube 402. A holder 403 is provided to hold the pulp processing unit 201 on the outside of the front wall 303 aligned with said opening in the front wall 303.

In a preferred embodiment, the holder 403 may be configured to hold the pulp processing unit 201 on the front wall in a removable manner. The holder 403 may include, for example, hinges that allow the pulp handling unit 201 to be rotated sideways and/or a bayonet mount that allows the pulp handling unit 201 to be quickly detached from the front wall 303 so that the window foil described above with reference to FIG. 2 and 3 is open. This makes it relatively easy to inspect and maintain those parts that are critical to the propagation of both incident and fluorescent X-rays. Particulate matter in the slurry can cause significant wear on the interior of the foil 302 of the sample window 301 (see FIG. 3), so it is advisable to equip the window 301 with a mechanism to allow the foil 302 to be replaced when needed.

The part of the X-ray fluorescence analyzer system marked in FIG. 4 with a dashed box 404 is shown from the optical axis direction of the x-ray tube 402 shown in FIG. 5. This illustration shows an example of how an actuator 501 can be configured to move the calibration plate 305 in a controlled manner between these two positions. In the first position shown in Fig. 5, the calibration plate 305 is not in the path of the incident X-rays that exit the X-ray tube window 203. In the second position, the gauge plate 305 will be substantially concentric with the window 203 shown in FIG. 5.

In FIG. 4 and 5 also show how one or more detection channels 502 can be performed. The design and operation of the detection channel will be described in more detail later in this description. Fig. 4 and 5 illustrate the positioning principle in which each of the detection channels is positioned at a respective angle of rotation about the optical axis of the x-ray tube 402. pulp), this way of placing the detection channels allows you to organize virtually the same field of view for all detection channels.

Other features shown in FIG. 4 are blocks 405, 406 and 407 with electronics inside the analyzer housing 401 for each of the detection channels and x-ray tube 402, as well as circulating 408 cooling water for x-ray tube 402.

In FIG. 6 schematically shows some parts of what is referred to above as a detection channel. The main characteristics of the detection channel in Fig. 6 are a crystal diffractor 601 and a radiation detector 602. As the name implies, the crystal diffractor 601 contains a crystal 603, which may be referred to as a diffractive crystal, or simply a crystal for short. Crystal 603 is a wavelength dispersive diffractor element 601. A first slit 604 may be located in the first optical path 605 between the pulp processing unit (not shown in FIG. 6) and the crystal 603, and a second slit 606 may be located in the second optical path 607 between the crystal 603 and the radiation detector 602. Since the diffraction properties crystal 603 for X-rays are highly dependent on the wavelength of the X-rays, such an arrangement can be used to isolate a certain range of wavelengths from that part of the fluorescent X-rays that was originally emitted in the direction in which this particular crystal diffractor is located. Reference numeral 608 designates a shroud that encloses the crystal diffractor 601, providing structural support and protection for all of its components.

In FIG. 7 shows an example of a crystal diffractor in axonometric projection. It is assumed that the crystal diffractor is located in the first direction from the pulp processing unit (not shown in Fig. 7), so that the first optical path 605 represents the nominal direction of that part of the fluorescent x-rays that enters this crystal diffractor. The first 604 and second 606 slits are formed between the respective parts of the limiter, and the second optical path 607 represents the nominal direction of the diffracted fluorescent X-rays, which is directed to the radiation detector (not shown in Fig. 7).

The crystal diffractor is enclosed in a housing 608 defined by a first flat surface 701 and a second flat surface 702 which is parallel to the first flat surface 701.

The mechanical design described here is advantageous because the flat surfaces 701 and 702 provide a support to which the internal parts of the crystal diffractor can be attached with relative ease.

X-ray diffraction in a crystal is governed by Bragg's law, which relates the diffraction angle to the distance between the reticular planes. Conventional crystalline diffractors use crystals such as silicon dioxide, lithium fluoride, ammonium dihydrogen phosphate, or potassium hydrogen phthalate, since sufficiently large single crystal pieces of these materials can be relatively easily produced with the required accuracy in the desired shapes. However, it has been found that although the wavelength selectivity of such conventional crystals is relatively high, the efficiency with which the incoming X-rays are diffracted is relatively low.

Pyrolytic graphite is an alternative material for making a crystal for a crystal diffractor. Pyrolytic graphite is a general term that refers to materials made from organic compounds containing planar structures such as benzene rings by exposing them to high temperatures, leaving essentially only carbon atoms in the structure. The original planar molecular structures cause pyrolytic graphite to exhibit a highly colored microscopic structure, for which reason it is often referred to as HOPG (Highly Oriented Pyrolytic Graphite) or HAPG, the latter referring to a slightly different way of synthesizing the material. Pyrolytic graphite is often not single-crystal in the same sense as the more traditional crystalline materials mentioned above, but is polycrystalline. However, for consistency with common terminology in the art, in practice, a diffractive element made of pyrolytic graphite is referred to as a crystal. In the following description, the term HOPG crystal is used.

It has been found that the efficiency of the HOPG crystal as a fluorescent X-ray diffractor is significantly higher than conventional diffractive crystal materials. In other words, much more of the X-rays that hit the 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 oriented in exactly the same way as, for example, in single-crystal silicon dioxide. This, in turn, means that the wavelength selectivity of a HOPG crystal in a crystal diffractor is not very accurate: fluorescent X-rays that are diffracted in a certain direction are a range of wavelengths near the nominal wavelength, which, according to Bragg's law, will be diffracted in this direction, and this range is much wider in HOPG crystals than in X-rays diffracted on conventional crystalline materials.

However, the less accurate wavelength selectivity of the HOPG crystal is not a serious disadvantage, as it can be compensated for by other factors in the development of an X-ray fluorescence analyzer system. One possible approach is to use a solid state semiconductor detector as the radiation detector 602, to which fluorescent X-rays in the selected wavelength range are directed from the HOPG crystal. The radiation detector 602 may be, for example, a PIN diode detector, a silicon drift detector, a germanium detector, a germanium drift detector, or a cadmium tellurium detector. Unlike, for example, gas-filled proportional counters, the energy resolution of solid-state semiconductor detectors can be made more accurate. The energy resolution of an X-ray detector is usually expressed at a reference energy of 5.9 keV. A solid state semiconductor detector of the above type may have an energy resolution of better than 600 eV and preferably better than 300 eV, with said reference energy of 5.9 keV. Another way to express the energy resolution of an X-ray detector is to refer to the energy of the characteristic fluorescent emission of the element of interest. Also at these energies, a solid state semiconductor detector of the above type can have an energy resolution of better than 600 eV, and preferably better than 300 eV.

By combining the use of a HOPG crystal in the crystal diffractor 601 with the use of a solid state semiconductor detector as the radiation detector 602, an advantageous situation can be achieved in which the crystal diffractor 601 is configured to extract a predetermined first wavelength range from the fluorescent X-ray radiation 207 propagating in the direction in which it is located a crystal diffractor 601 (with reference to the pulp processing unit 201), and is configured to direct fluorescent X-rays in a selected predetermined first wavelength range to a radiation detector 602, that is, a solid state semiconductor detector. The good energy resolution of the solid state semiconductor detector is then used to obtain a measurement result that gives the energy spectrum of the fluorescent x-rays in the selected predetermined first wavelength range. Based on the indicated energy spectrum, and possibly using other measurements as confirmation, the amount of fluorescent x-rays from the element of interest can be determined with relatively good accuracy.

The geometric shape of the diffractive surface of the HOPG crystal is another factor to consider when designing an X-ray fluorescence analyzer system. Fig. 8 illustrates some examples of geometric shapes. It can be noted here that, more precisely, a crystal is just a thin layer of crystalline (single-crystalline, as, for example, in the case of silicon dioxide, or polycrystalline, as, for example, in the case of HOPG) material, which forms a real diffractive surface. The crystalline diffractor contains a substrate to which the crystalline material is attached. Examples of substrate materials are, for example, glass and aluminum, but the substrate material can also be iron or any other similar material that is not too prone to cause unwanted interfering fluorescent radiation by itself. The crystalline material can be attached to the properly formed surface of the substrate, for example by means of van der Waals forces. Alternatively, the crystalline material may be grown directly on a properly formed substrate surface, or some other suitable attachment method such as adhesive may be used.

Together, the substrate and the crystalline material constitute a three-dimensional object, with examples of these objects shown in FIG. 8. To maintain consistency with conventional terminology in this technical field, in the present description, these objects are referred to as crystals, despite the small accuracy of this term, as explained above. The term diffractive surface refers to the outer exposed surface of a crystalline material on which X-rays are diffracted; strictly speaking, X-ray diffraction occurs in reticular planes within the crystalline material near the surface, which is referred to herein as the diffractive surface.

A feature common to die 603, die 802, and die 804 shown in FIG. 8 lies in the fact that the three-dimensional geometric shape of an object consisting of a HOPG crystal and a substrate is a prism, one side face of which is cut off to form a curved diffractive surface. The imaginary shape of the prism in the top row of images of these three crystals is shown by dotted lines.

The bottom row of images of the same crystals in Fig. 8 shows how the nature of the curvilinearity of the diffractive surface differs in all three cases. In the crystal 603, the diffractive surface 801 is curved in only one direction (longitudinal direction). In other words, if an imaginary transverse line like the dotted line shown in FIG. 8, pass through the diffractive surface 801 anywhere, it will always be straight. A particular advantage of such a crystal is that it is relatively easy to manufacture. Compared to FIG. 6 and 7 that the radius of curvature of the diffractive surface 801 lies in the plane defined by the first 605 and second 606 optical paths. This plane is also parallel to flat surfaces 701 and 702.

In the crystal 802, the diffractive surface 803 is curved in two directions (longitudinal and transverse), forming part of the toroidal surface. This means that if a transverse arc is drawn anywhere through the diffractive surface 803, like the two dotted arcs shown, for example, in FIG. 8, then the curvature of all these transverse arcs will be identical. While this geometry may be somewhat more difficult to manufacture to the required accuracy than the surface 801 shown at left, it has the advantage that it focuses the diffracted x-rays more accurately.

In the crystal 804, the diffractive surface 805 is curved in two directions (longitudinal and transverse), but differently from the surface 803 shown in the middle. The diffractive surface 805 forms part of an axisymmetric surface whose axis of rotation 806 is in a plane defined by the optical paths of the incoming and diffracted x-rays. The radius of the axisymmetric surface varies depending on the distance along the rotation axis 806 . This means that if a transverse arc is drawn through the diffractive surface 805, such as the dotted arc shown in FIG. 8, then the radius of curvature of such a transverse arc will be different depending on the longitudinal position in which it is drawn. In FIG. 8, it can be seen that the dotted arc in the middle is not as noticeably curvilinear as the arcuate edges seen at the ends of the die 804. This is because the dotted arc is farther away from the axis of rotation 806 than the arcuate edges at the ends of the crystal. In other words, the axisymmetric surface radius is larger in the middle of the crystal 804 than at its ends, making the axisymmetric surface look like a shuttle or an ellipsoid.

From a mathematical point of view, an axisymmetric surface is formed when a continuous curve rotates around the axis of rotation. The shape of the specified continuous curve determines how far from the axis of rotation each surface point is and what properties it can have. One example of a curve that can be used to form diffractive surface 805 in FIG. 8 is a portion of a logarithmic spiral. Although this type of surface is more difficult to fabricate than the surfaces shown above as surfaces 801 and 803, an axisymmetric surface made from a logarithmic helix section has the inherent advantage of providing very precise focusing of diffracted x-rays.

A feature that is common to all diffractive surfaces 801, 803, and 805 depicted in FIG. 8 is that in the topological sense all these surfaces are simply connected surfaces. A simply connected surface is a linearly connected surface (i.e. any two points on the surface can be connected by a trajectory that belongs entirely to the specified surface) and, in addition, any loop-shaped contour can be continuously compressed to a point, so that also all intermediate the shapes of the compressed loop completely belong to the specified surface.

An intuitive description of a simply connected surface is that it has no holes. As such, through any of the diffractive surfaces 801, 803, or 805 shown in FIG. 8, it is possible to drill a small hole without changing their properties as diffractors, no more than the amount by which the surface area is reduced by the drilled hole. For this reason, this specification defines that the requirement for a simply connected surface in a topological sense should be interpreted as referring to the overall shape of the surface: in this interpretation, a small hole in the surface does not mean that it will not be simply connected. Another definition of how to interpret the requirement of simply connectedness is as follows: if the crystal is lying on its side, as shown in Fig. 8 (i.e. the principal radius of curvature, which defines the longitudinal curvature between the ends of the crystal, is in the horizontal plane; so the diffractive surface is usually oriented vertically), any imaginary horizontal line will intersect the diffractive surface at at most one point. A surface is simply connected if it matches at least one of these intuitive descriptions.

On the right in FIG. 8, crystal 807 is shown as a comparative example. The diffractive surface 808 of the crystal 807 is curved in two directions (longitudinal and transverse), forming a complete axisymmetric surface, the rotation axis 809 of which may be in the plane defined by the optical axes of the incoming and diffracted x-rays. The curve whose rotation about the rotation axis 809 defines the shape of the diffractive surface 808 may, for example, be a section of a logarithmic spiral. It is obvious that the diffractive surface 808 is simply connected in a topological sense, since no closed curve that goes around the hole of the surface can be compressed to a point, while maintaining a contracting curve shape inside the diffractive surface 808. Crystals of this type are relatively difficult to manufacture, but they can be used in conjunction with suitable shields (not shown in Figure 8) that block the propagation of direct, undiffracted X-rays to collect fluorescent radiation from a larger solid angle than those with a single bond surface such as 801, 803 or 805.

The geometric shape and resulting optical properties of the diffractive surface can influence how other parts of the crystal diffractor should be made. It has been explained above that the crystal diffractor 601 may have a first slit 604 in the first optical path 605 between the pulp processing unit 201 and the (pyrolytic graphite) crystal, and that there is a second optical path 607 between the (pyrolytic graphite) crystal and the radiation detector 602. If the diffractive surface 801 of said crystal 603 (pyrolytic graphite) is curved in only one direction with a radius of curvature in a plane defined by said first 605 and second 607 optical paths, then it is preferable to make said first slit 604 a linear slit oriented perpendicular to said plane, as shown in fig. 7.

If the diffractive surface 803 of said crystal 802 (pyrolytic graphite) is curved in two directions, forming part of a toroidal surface, it is preferable to make said first slit a curved slit with a radius of curvature oriented perpendicular to said first optical path. If the diffractive surface 805 of said crystal 804 (pyrolytic graphite) is curved in two directions, forming part of an axisymmetric surface whose axis of rotation 806 is in the plane defined by said first and second optical paths, then it is preferable to make said first slit in the form of a pinhole.

If the second slot 606 is used in the second optical path 607, then similar considerations can be applied. However, it should be noted that the second slit is not always necessary: its use is associated with the attenuation of the background and scattered radiation, especially with diffractive crystals, which have a high wavelength selectivity. Considering that the wavelength selectivity of HOPG is not so high, the additional advantage obtained with the second slit is relatively small.

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, then the geometry of the crystal diffractor may follow, for example, the principle of Johann's geometry or Johanson's geometry. This is shown respectively in FIG. 9 and 10. In FIG. 9, the center point 902 of said diffractive surface, and the first slit 604 and the second slit 606 are located on a Rowland circle whose radius is R. The radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is 2R, and the radius of curvature of the reticular planes 901 in the specified crystal is equal to 2R. This means that the first crystal diffractor has a Johann geometry. In FIG. 10, the central point 1002 of said diffractive surface, and the first slit 604 and the second slit 606 are similarly located on a Rowland circle whose radius is R. However, here, the radius of curvature of said diffractive surface in the plane defined by said first and second optical paths is R, and the radius of curvature of the reticular planes 1001 in said crystal is 2R, so that the first crystal diffractor has a Johanson geometry.

In order to maintain the compact size of the crystal diffractor, it is preferable that the value of R remain relatively small. For example, R can have a value of no more than 40 centimeters.

Fig. 11-14 are schematic illustrations of fluorescent x-ray spectra in some cases. Spectra are usually expressed as the number of counts recorded at each photon energy. In practice, the sampling detector has a certain energy resolution, which determines how close the energies of two photons can be to each other so that the detector can generate two different types of output signals. Signal processing is used to classify the received X-ray photons into energy cells of finite width, and the number of detected counts is output per energy cell. The more accurate the resolution of the detector, the narrower (in energy units) the energy intervals can be.

In FIG. 11 plot 1101 is smooth without any visible peaks or spectral holes. Such a spectrum is rarely obtained in practice, but it illustrates the situation when only background and randomly scattered radiation is received, without any characteristic peaks of the elements of interest. In FIG. 12, plot 1201 is otherwise the same, but there is a characteristic peak 1202 of the element of interest. The problem is that the concentration of the element of interest in the measured sample is so low that the height of the characteristic peak 1202 is small compared to the overall level of the spectrum in the same energy range. Thus, even if a relatively large number of photons are observed in this energy range, only a relatively small number of them are actually fluorescent photons from the element of interest.

The energy of a photon is inversely proportional to its wavelength, so when the wavelength selectivity of various diffractive crystals was considered above, the energy selectivity could also be taken into account. In FIG. 13 schematically shows what a crystal diffractor radiation detector equipped with a HOPG crystal can receive. The energy range 1301 of the fluorescent X-rays that the HOPG crystal will direct to said radiation detector is relatively wide, 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. Thus, the radiation detector will receive a significant fraction of the photons that fall in the two shaded areas in FIG. 13. The drawing is schematic in the sense that it assumes a diffraction efficiency of 100%, which is not possible in practice, but the representation chosen is good for graphical clarity. Of the photons in the energy range 1301, 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 the actual fluorescent photons from the element of interest.

In FIG. 14 schematically shows what a crystal diffractor radiation detector equipped with a silicon dioxide crystal (or other conventional crystal) could obtain in the same situation. The energy range 1401 of the fluorescent X-rays that a conventional crystal directs to its radiation detector is relatively narrow, which is a direct result of the conventional crystal's relatively good wavelength selectivity. However, at the same time, the diffraction efficiency of a conventional crystal is lower than that of a HOPG crystal. Thus, the radiation detector will only receive a limited portion of the photons that actually come from the element of interest in the sample (see shaded area 1303 in FIG. 13). Small peak 1402 in FIG. 14 denotes this fluorescent X-ray, which in this case will actually be detected.

It should be noted that although the small peak 1402 is located relatively precisely at the wavelength of interest (ie, the characteristic fluorescent emission of the element of interest), in the original spectrum shown in FIG. 12, it is still on top of a practically continuous background, the level of which depends, for example, on the amount of scattering in the sample. In this regard, slurries present a particular challenge as samples because the amount of scatter in a slurry sample can vary greatly depending on the solids content. When a conventional X-ray tube with an accelerating voltage of 50 kV or so is used as the incident X-ray source, the scattered X-ray energy usually overlaps with the energies of the characteristic fluorescent emission of elements with atomic number Z between 41 and 60. Thus, from the small peak 1402 depicted in fig. 14, it can be difficult to tell how much of the emission is background and how much is the actual characteristic fluorescent emission from the element of interest.

In FIG. 15 shows comparisons of the two plots, with the top plot 1501 assuming to be continuous even though some of its highest peaks are outside the range shown. The top graph 1501 illustrates the spectrum of all the fluorescent x-rays that the detector would receive in a certain first direction from the sample, without any crystal diffractor or other type of wavelength dispersion device interposed. The advantage of making such a measurement would be that (also) all the characteristic fluorescent radiation of a given element of interest emitted in that direction would be received by the detector without any loss caused by the diffractor. A detector with good energy resolution could be used to isolate, from a wide range of received wavelengths, only those energies that were relevant to the element of interest. However, the detector can detect (and the subsequent analyzer can analyze) only a certain maximum number of photons per unit time. If all of the photons included in the spectrum represented by plot 1501 are detected, then much of the detection capability and processing power will be wasted on completely uninteresting portions of the spectrum. At the same time, a high overall intensity of the incident X-ray radiation can lead to a higher level of radiation damage to the detector and, as a result, a shorter lifetime.

The lower graph 1502 represents the spectrum of x-rays that the detector can receive through the crystal diffractor. This particular crystal diffractor contains a HOPG crystal and is thus capable of separating a given first wavelength range 1301 from fluorescent x-rays that propagate in said first direction. This first wavelength range 1301 includes, among other things, the characteristic fluorescent emission of a given element of interest with its atomic number Z between 41 and 60 inclusive. A comparison of graphs 1501 and 1502 shows that the total number of photons that now need to be detected and processed is much less than if all the photons represented by the top graph 1501 had to be taken into account. However, in a given first wavelength range (in in particular, on its right side, i.e. at longer wavelength) the good diffraction efficiency of the HOPG crystal means that not too many photons are lost: plot 1502 is not much lower than plot 1501. In the case of plot 1502, the line intensity of the element of interest may actually be further increased, for example, by increasing the power of the x-ray tube. This is possible because, unlike plot 1501, the overall intensity is no longer limited by the counting capability of the detector.

Partial enlargement on the right in Fig. 15 shows the determined subband of the first wavelength band 1301. Parts of the detected spectrum are shown that correspond to three adjacent regions of interest 1511, 1512 and 1513 of the detector. The energy resolution of the radiation detector is good - better than 600 eV at the energy of the characteristic fluorescent emission of the specified element of interest, or even better than 300 eV. This means that the photon counts in regions of interest 1511, 1512 and 1513 can be used to separately determine the number of background photons 1514 at slightly shorter wavelengths and the number of background photons 1515 at slightly longer wavelengths than the wavelength of the characteristic fluorescent emission of the specified representative. element interest.

The processor of the X-ray fluorescence analyzer system may be configured to receive and process the output signals generated by the above detector. In particular, the processor may be configured to calculate the proportion of background radiation 1516 using a particular proportion of specified output signals that are within the first wavelength range 1301 but not the same wavelength (average region of interest 1512) of the characteristic fluorescent radiation of interest. element. This specific proportion may indicate the number of background photons 1514 at wavelengths that are slightly shorter than the wavelength of the characteristic fluorescent emission of the specified element of interest and/or the number of background photons 1515 at wavelengths that are slightly greater than the wavelength of the characteristic fluorescent emission of the specified element of interest. .

One way to do this is through linear interpolation. The processor may count photons in the left region of interest 1511 and count photons in the right region.

- 11 042286 area of interest 1513 and calculate their average value. This average value will then be used as a calculation of the number of background photons 1516 in the average region of interest 1512. The processor may then calculate the detected amount of the specified characteristic fluorescent emission of the specified element of interest by subtracting from the output signals at wavelengths of the specified characteristic fluorescence emission (region of interest 1512) of the specified calculated background radiation fraction.

One of the factors to consider when designing an X-ray fluorescence analyzer system is the possibility of using differently equipped detection channels. Here, the term differently equipped means, first of all, the choice of a diffractive crystal and the choice of a radiation detector.

In FIG. 16 schematically shows how a commercial X-ray fluorescence analyzer system for analyzing pulp samples can contain a large number of detection channels. The detection channels are shown in Fig. 16 in a straight line because the image is schematic. In practice, they can be arranged, for example, axisymmetrically around the X-ray tube, as shown in FIG. 4 and 5, each with a field of view directed towards the pulp processing unit of the X-ray fluorescence analyzer system.

The X-ray fluorescence analyzer system shown in FIG. 16 includes a first crystal diffractor 1601 located in a first direction from said pulp processing unit, said first crystal diffractor 1601 comprising a first crystal. The first radiation detector 1605 is configured to detect fluorescent x-rays diffracted by said first crystal 1602 with a first energy resolution. The X-ray fluorescence analyzer system comprises a second crystal diffractor 1611 located in the second direction from said pulp processing unit, said second crystal diffractor comprising a second crystal 1612. energy resolution.

As a first assumption, it can be assumed that the first crystal 1602 is a pyrolytic graphite (HOPG) crystal, and that the second crystal 1612 is made of a material other than pyrolytic graphite, such as silicon dioxide, lithium fluoride, ammonium dihydrogen phosphate, or potassium hydrogen phthalate. Also, as a first assumption, it can be assumed that the first and second crystal diffractors are configured to direct the characteristic fluorescent radiation of the same element to their respective radiation detectors. In other words, the two detection channels are equipped differently, but both of them are aimed at detecting the presence of the same element in the pulp sample and determining its concentration.

Thus, tuning a crystal diffractor to direct the characteristic fluorescent radiation of a particular element to its radiation detector is usually done by 1) choosing a crystal with a certain distance between its reticular planes, 2) choosing the curvature of the crystal and the reticular planes, and 3) choosing values for the angle and distance of the crystal and slit(s) such that only a specific wavelength range of X-rays reaches the detector, said specific wavelength range including the required characteristic peak of the element of interest. An element of interest may have multiple characteristic peaks, so stating that two detection channels are capable of measuring the characteristic fluorescence emission of the same element does not necessarily mean that they will be set to measure the same characteristic peak, although this is not excluded.

If these two detection channels are configured to measure the same characteristic peak, then the measurement results they produce may resemble those shown in FIG. 13 (for the HOPG channel) and in FIG. 14 (for a channel with a different crystal).

Fig. 17 schematically illustrates a fluorescent X-ray spectrum that contains two distinct peaks 1701 and 1702. In such a case, the calculation method chosen may depend on whether both peaks 1701 and 1702 are characteristic peaks of the same element of interest, or whether one of them is the characteristic peak of some interfering element. Smaller peaks closer to the energy axis represent the expected detection result that a detection channel equipped with a conventional crystal (eg, silicon dioxide) could obtain from these two peaks.

An interesting case is that both peaks 1701 and 1702 are peaks of the element of interest. It is of particular interest if one of them (in this document: peak 1701) is more intense, for the measurement of which a detection channel equipped with SiO ₂ is provided. In such a case, the best characteristics of both channels can be used: the precise wavelength selectivity of the silica crystal can be used to separate a well-defined wavelength range 1401 that includes only the required characteristic peak, so that the relatively high intensity of this peak still gives a sufficient amount of counts in the corresponding detector in a relatively short time. At the same time, the good diffraction efficiency of the HOPG crystal can be used to highlight a wider wavelength range 1301 that includes a different, lower characteristic peak. The concentration of the element of interest can be calculated from the detection results provided by the two detectors when the overall characteristics of the two detection channels are known from calibration measurements.

A method of the type described above may be applicable in many cases where the characteristic fluorescent emission includes the K or L peak of an element with 41<Z<60, where Z is the atomic number of said element. The adaptability of the method is well suited for measuring samples that contain one or more elements of interest in a matrix consisting primarily of elements with Z<8, where Z is the atomic number. These are, for example, water-based pulps.

The principles discussed above regarding the use of two detection channels can be generalized to apply to the use of three or more detection channels. The form factor of the detection channel as described above, i.e., one in which each crystal diffractor 601 is enclosed by a first flat surface 701 and a second flat surface 702 that is parallel to said first flat surface 701, allows multiple detection channels to be distributed in the form cassettes, for example, in an axisymmetric manner around the x-ray tube. Detection results from detection channels configured to detect the characteristic fluorescent emission of the same element can be combined in various ways as described above. A large number of detection channels makes it possible to simultaneously calculate the concentrations of two or more elements of interest in a sample, if the detection channels are configured to measure the characteristic fluorescent emission of such two or more elements of interest. It is also possible to cross-correlate the detection results of channels configured to detect different elements. For example, if one element has two characteristic peaks, one of which is measured using a dedicated first detection channel and the other approaches the characteristic peak of another element of interest, the detection results from the first channel can be used to correct the detection results from the channel that is performed with the ability to measure the characteristic peak of another element.

The task of determining the actual concentration of an element of interest can be described as a method, for example, as follows with reference to FIG. 18.

The method is directed to performing X-ray fluorescence analysis of a given element of interest in the pulp, said given element of interest having an atomic number Z between 41 and 60 inclusive. The method includes emitting incident X-ray radiation in the direction of the first optical axis towards the sample of said pulp, so that fluorescent X-ray radiation is generated. Due to the geometry of the measurement, the first part of the fluorescent X-rays is directed to the first detection channel. The method includes using a first crystal diffractor with a pyrolytic graphite crystal in said first detection channel to isolate a given first wavelength range from fluorescent X-ray radiation, wherein said given first wavelength range contains the characteristic fluorescent radiation of said given given element of interest.

The method includes directing fluorescent X-ray radiation in the selected predetermined first wavelength range to the first radiation detector, the energy resolution of which is better than 600 eV at the energy of the specified characteristic fluorescent radiation. The detector provides output signals indicating the detected photons and their energies. The method includes using the output signals of the said first radiation detector to calculate the fraction of background radiation in the said first wavelength range and calculating the detected amount of the said characteristic fluorescent radiation of the given element of interest by subtracting the said calculated fraction of background radiation from the output signals at wavelengths of the said characteristic fluorescent radiation.

In FIG. 18, the output signals 1801 are subdivided into mid range signals 1802 and marginal range signals 1803. These definitions assume that, as in FIG. 14, 15 and 17, the wavelength (and therefore energy) of the characteristic fluorescent emission of the element of interest is somewhere in the middle of the range, so that the amount of background radiation can be examined from both sides of it. The border band signals 1803 are used to calculate the background radiation level 1804, for example, by linear interpolation or higher order interpolation. Another possibility is to use one or more energy intervals on only one side of this area of interest, in which the characteristic fluorescent emission of the element of interest is located, for extrapolation. The background radiation level 1804 is a best estimate of how many samples in the main region of interest 1802 are actually background, so the calculation in step 1805 is essentially a subtraction resulting in signals of interest 1806.

- 13 042286

In general, the calculation may include calculating the total intensity of the background radiation and fluorescent X-ray radiation from an element other than the specified element, using at least one of the detection results in other energy ranges than the region of interest where the characteristic fluorescence emission of the element of interest is located. . The method may then include subtracting from the total intensity detected in the wavelength range containing the specified characteristic peak of the fluorescent X-ray emission of the element to be measured in the specified sample, the calculated total intensity of the background radiation and fluorescent X-ray emission from other elements, excluding the specified element of interest in the specified sample. The method may then include presenting the result of said subtraction as a calculated intensity of said characteristic X-ray fluorescent peak.

One of the factors to consider when designing a commercial X-ray fluorescence analyzer system for analyzing pulp samples is the power of the X-ray tube and the geometry and dimensions of the area between the X-ray tube and the pulp processing unit.

Fig. 19 illustrates the possibility of using the so-called transmission geometry. A window 203 for transmitting X-ray tube radiation is seen on the right in FIG. 19, the incident x-rays are emitted in the direction of the optical axis 204 through the main filter plate 205. The pulp processing unit 201 includes a chamber 1901 with an exit slit 1902 from which the sample 202 flows out as a curtain and falls under the action of gravity. Incident X-rays generate fluorescent X-rays in a relatively thin curtain of falling pulp. Reference number 1903 indicates fluorescent x-rays that are directed at an oblique angle backwards and that can be detected using detection channels (not shown in FIG. 19) arranged in the same way as in the geometries described previously with reference to FIG. 2, 3, 4, and 5. Position number 1904 indicates fluorescent x-rays that are directed in other directions, especially in directions that are on the other side of the sample flow. They can be detected using detection channels (not shown in Fig. 19) located on that side. This can be a particularly advantageous way of arranging the detection channels since they can have a better field of view and therefore a better spatial collection efficiency of the fluorescent x-rays. It can also cause the X-ray tube to get very close to the sample. However, it should be noted that proper geometric radiation protection measures must be taken to prevent any incident X-rays from entering the detection channels.

Fig. 20 is a partial cross-sectional view of the exit portion of an x-ray tube 402. The x-ray tube includes an anode 2001 for generating incident x-rays. Incident x-rays are emitted in the direction of the optical axis 204 to the sample 202, which is shown here only schematically without the pulp processing unit for clarity. However, it is contemplated that the pulp handling unit is configured to maintain a flat surface 2002 of the pulp sample 202 on the side facing the x-ray tube 402. As explained above, this can be accomplished, for example, by providing a sample window with a foil of a material that is transparent. for x-rays. A sample window may be provided in the wall of the chamber so that X-rays can pass through while the pulp sample is kept within the sample chamber.

The remaining parts of the X-ray tube, shown schematically in FIG. 20 are a cooling water circuit 2003, an annular cathode 2004 for emitting accelerated electrons, and a window 203 for transmitting radiation.

When the goal is to produce such a large fluorescent emission that even very small concentrations of elements of interest can be detected, it is preferable that as many photons (of sufficient energy) of the incident radiation as possible can enter the sample 202. One way to achieve this is using a very powerful x-ray tube. In accordance with one implementation, the nominal input power 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 nominal input power of 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 fraction of the power claimed as the rated input power of the x-ray tube ends up as random x-rays generated, the rated input power is nevertheless an important indicator of the x-ray tube's ability to produce an intense incident x-ray beam.

The use of x-ray tubes with higher power than before means that radiation shielding needs to be re-evaluated compared to known lower power x-ray sources. According to one embodiment, thicker radiation shielding plates and denser radiation shielding materials can be used to ensure that ionizing radiation does not penetrate areas where it could be hazardous.

- 14 042286

Another way to ensure that a very intense incident X-ray beam hits the sample 202 is to make the distance between the anode 2001 and the sample 202 as small as possible. The pulp processing unit may be configured to maintain the shortest linear distance d between the anode 2001 and the sample 202 such that d is less than 50 mm. In yet another embodiment, d may be less than 40 mm. In yet another embodiment, d may be less than 30 mm.

However, it should be noted that, as a general rule, the closer the anode 2001 of the X-ray tube 402 approaches the sample 202, the greater the spatial angle around the sample 202 is blocked by the X-ray tube structures. This is an important factor to consider because X-ray tube 402 designs can block the field of view of the detection channels. One way to solve this problem is to use an X-ray tube with a so-called end window rather than an X-ray tube with a side window. Fig. 20 and 21 can be seen as illustrating the use of an end window X-ray tube. In this type of X-ray tube, the radiation window 203 is usually located at one end of the overall tubular structure, which leaves a relatively large amount of free space around said tubular structure for accommodating detection channels. Another possibility would be to use an X-ray tube with a side window and place the detection channels on one or both sides of the X-ray tube.

In all of the drawings described above, the optical path between X-ray tube 402 and sample 202 is also straight, which means that there are no diffractors between them. This is another way to ensure that the maximum number of incident X-ray photons can enter the sample. First, the presence of a diffractor between them would inevitably mean a greater distance between the anode 2001 and the sample 202, because some space must be reserved for the diffractor. Secondly, the very nature of the diffractor is to separate only a certain range of wavelengths from the original radiation spectrum, which necessarily means fewer incident X-ray photons hitting the sample. Other beneficial consequences of not using any so-called main diffractor between the x-ray tube 402 and the sample 202 are that incident x-rays are simultaneously delivered to excite characteristic peaks of a number of elements in the sample, and that fewer features can block the field of view of the detection channels.

In FIG. 20, the optical axis 204 of the x-ray tube 402 is perpendicular to the flat surface 2002 of the sample 202. While this arrangement provides excellent rotational symmetry for the detection channels located around the x-ray tube 402, this is not the only possibility. In FIG. 21 shows an alternative embodiment in which the optical axis 204 of the x-ray tube 402 is at an oblique angle to said flat surface. This arrangement can help to make the shortest linear distance d between anode 2001 and sample 202 even shorter, while still leaving a sufficiently free field of view for detection channels on at least some sides of X-ray tube 402. This principle is discussed in more detail below with reference to FIG. 22 and 23.

In FIG. 22 shows the x-ray tube 402 and five detection channels as viewed from the sample side. The radiation window 203 of the x-ray tube 402 is visible in the middle of the drawing. The entrance window of each detection channel for receiving fluorescent radiation is located at the proximal end of the corresponding crystal diffractor; the input window 2201 is shown as an example. In order for the largest possible part of the generated fluorescent radiation to enter the detection channel, it is advisable to place these entrance windows as close as possible to the sample, and also so that the entrance window is visible on the sample surface at the largest spatial angle possible. Each of said plurality of crystal diffractors is positioned at a respective angle of rotation about the optical axis of the x-ray tube 402. Each of said crystal diffractors can be configured to extract a predetermined range of wavelengths from fluorescent x-rays that propagate in a respective direction, and configured to direct the fluorescent x-ray radiation in the corresponding selected predetermined first wavelength range to the corresponding radiation detector.

In FIG. 23 is a side view showing the x-ray tube 402 and two detection channels. An exemplary window 301 is shown schematically in FIG. 23: this illustrates the area where the pulp handling unit can maintain a flat surface of the pulp sample on the side facing the x-ray tube 402. Thus, this area is the area that must be within the field of view of the x-ray tube 402 for the incident x-rays to reach for a test. This also illustrates the area that should cover as large a spatial angle as possible in the field of view of the detection channels in order to collect as much fluorescent X-rays as possible.

The optical axis 204 of the x-ray tube 402 is located at an oblique angle to the specified flat surface. The first crystal diffractor 1601 is located at that angle of rotation around the specified optical axis 204, at which the specified flat surface of the specified sample covers

- 15 042286 the largest part of the field of view of the first crystal diffractor 1601. Assuming that no other designs block any part of the available field of view, in practice this means that the first crystal diffractor 1601 is located opposite the X-ray tube, that is, in that direction, in which would reflect an imaginary light beam along the optical axis 204 if the surface of the sample was a mirror.

The second crystal diffractor 1611 is positioned at a different angle of rotation around said optical axis 204. In FIG. 23, the second crystal diffractor 1611 is positioned at what could be described as the worst possible angle of rotation because its view of the sample surface is limited to that edge of the x-ray tube 402 that is closest to the sample window 301. If said other rotation angle is less than 180 degrees different from the angle at which the first crystal diffractor 1601 is located, then the second crystal diffractor 1611 may be positioned rather as one of several other crystal diffractors in FIG. 22. In such a case, the flat surface of the sample in the sample window 301 will cover the part of the field of view of the second crystal diffractor 1611 that is between the two extreme points shown in FIG. 23.

According to one embodiment, the first crystal diffractor 1601, which is positioned at the optimum angle of rotation (in terms of field of view) in FIG. 22 and 23 is a crystal in which the diffraction crystal is a HOPG crystal and the radiation detector is a solid state semiconductor detector. Considering the good diffraction efficiency of the HOPG crystal, this placement of the first crystal diffractor helps to ensure that the maximum amount of X-ray fluorescent photons actually reaches the detector. If there is some prior knowledge of the expected levels of concentrations of various elements in the samples to be measured, then it may be advantageous to install this crystal diffractor with the most optimal angle of rotation, which is designed to highlight and direct to the appropriate detector the characteristic fluorescent radiation of that element of interest, the concentration of which is expected to be the smallest.

One factor to consider when designing a commercial X-ray fluorescence analyzer system for analyzing pulp samples is the choice of radiation detectors in those channels that have diffractive crystals made from materials other than pyrolytic graphite. The wavelength selectivity of conventional diffractive crystalline materials such as silicon dioxide is relatively good, which can be interpreted to mean that there is not as much need for precise energy resolution in the radiation detector as if a HOPG crystal were used. A gas-filled proportional counter can provide quite satisfactory detection results in a detection channel that uses a crystal other than HOPG as the diffraction crystal at a significantly lower manufacturing cost than a solid state semiconductor detector.

However, nothing said above should be construed against the selection of a solid state semiconductor detector also for detection channels which have other than HOPG crystals as diffraction crystal. Similarly, the use of a solid state semiconductor detector in a detection channel equipped with a HOPG crystal is not a requirement if the energy resolution of another type of radiation detector is sufficient.

Fig. 24-27 illustrate calibration measurements, in which the vertical axis represents the concentrations measured with a single detection channel of the device under test, which was an industrial X-ray fluorescence analyzer system for analyzing pulp samples in accordance with one embodiment. The horizontal axis represents the concentrations in the same samples but measured over long periods with laboratory equipment in order to obtain the most accurate and reliable results possible. For laboratory measurements, pulp samples were dried and homogenized, with the amount of water removed being compensated by calculation to make the laboratory measurements comparable to industrial type measurements. If this type of calibration measurement shows that the points are along a straight line, then two different devices give very similar results, which means that the device under test is very accurate. Deviations from a straight line indicate that the device under test is not giving accurate results.

The scales are arbitrary, but the scales in FIG. 24 and 25 are the same, and the scales in FIG. 26 and 27 are the same. In these measurements, the element of interest was gold, but the results are also sufficiently representative to measure the characteristic fluorescent X-ray emission from elements of interest with atomic number Z between 41 and 60 inclusive. Fig. 24 and 25 depict measurements of samples in which the concentration of the interfering element was below 300 ppm, while in the measurements presented in FIG. 26 and 27, the concentration varied from 0 to 2%. An interfering element is an element that has a characteristic fluorescence peak close to at least one characteristic fluorescence peak of the element of interest.

- 16 042286

Fig. 24 and 26 are cases in which measurement with the device under test was performed using a detection channel that had a silicon dioxide crystal in the crystal diffractor and a gas-filled proportional counter as a radiation detector. Fig. 25 and 27 are cases in which the measurement with the device under test was performed using a detection channel that had a HOPG crystal in a crystal diffractor and a solid state semiconductor detector as a radiation detector.

Comparison of FIG. 24 and 25 shows that when the interfering element concentration is low, 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 concentrations measured with the HOPG channel of the device under test and the concentrations measured in the laboratory was ±0.24 ppm, while the comparable average error with a silica crystal and a gas-filled proportional counter was ±0.56 ppm

Comparison of FIG. 26 and 27 shows that when the interfering element concentration is significant, the detection channel with HOPG crystal and solid state semiconductor detector gives less accurate detection results than the detection channel with silicon dioxide crystal and gas-filled proportional counter. The average error between the concentrations measured with the HOPG channel of the DUT and the concentrations measured in the laboratory was ±1.62 ppm, while the comparable average error with a silica crystal and a gas-filled proportional counter was ±0.42 ppm

The results shown in FIG. 24-27 can be used in many ways. For example, an industrial X-ray fluorescence analyzer system for analyzing pulp samples may be equipped with first, second, and third detection channels, of which the first and second detection channels are equipped with crystal diffractors configured to separate and direct to their respective detectors the characteristic fluorescent X-rays of the same element, such as silver. The first detection channel may be a channel with a HOPG crystal and a solid state semiconductor detector, and the second detection channel may be a channel with a silicon dioxide crystal and a gas-filled proportional counter. The third detection channel may be equipped with a crystal diffractor capable of separating and directing the characteristic fluorescent x-rays from the interfering element to a suitable detector. Then, the detection results of all three detection channels can be analyzed. If the detection results obtained using the third detection channel indicate that there is a significant concentration of the interfering element in the sample, then the calculation of the silver concentration will more emphasize (or even exclusively use) the detection results of the second detection channel. Accordingly, if the detection results obtained by the third detection channel indicate that there is only a negligible concentration of the interfering element in the sample, then the calculation of the silver concentration will further enhance (or even exclusively use) the detection results of the first detection channel.

The many advantages of a commercial X-ray fluorescence analyzer system for pulp sample analysis have been described above. After all, they all serve a common goal, which is to make reliable measurements of even very low concentrations of the elements of interest in various types of slurries, at a reasonable cost and under the harsh conditions that can occur in an industrial environment: short measurement times, extreme temperatures, frequent occurrence of moisture, dust and dirt, long service intervals, and the like. Advantageous characteristics can be combined with each other in a variety of ways, so that the most advantageous combination may depend on the particular case and its particular boundary conditions.

For a person skilled in the art it is obvious that with the development of technology the main idea of the invention can be implemented in various ways. Thus, the invention and its embodiments are not limited to the examples described above, instead they may vary within the scope of the claims. For example, even though silver has often been mentioned above as a typical element of interest, the same principles apply to measurements of other elements of interest. Examples of such other elements of interest are, for example, niobium, palladium, cadmium and neodymium.

Claims (19)

CLAIM 1. An X-ray fluorescence analyzer system comprising an X-ray tube (402) for emitting incident X-ray radiation (206) in the direction of the first optical axis (204), a pulp processing unit (201) configured to maintain a constant distance between the pulp sample (202) and specified x-ray tube, - 17 042286 the first crystal diffractor (601) located in the first direction from said pulp processing unit (201), wherein the first crystal diffractor (601) is configured to isolate a given first wavelength range from fluorescent x-ray radiation (207), which is said incident X-ray radiation is generated in the specified pulp sample and which propagates in the specified first direction, and with the possibility of directing fluorescent X-ray radiation in the specified selected predetermined first wavelength range to the first radiation detector (602, 1605), the first crystalline diffractor (601) contains a crystal ( 603) of pyrolytic graphite, characterized in that said predetermined first wavelength range contains the characteristic fluorescent emission of a predetermined element of interest with its atomic number Z between 41 and 60 inclusive, the energy resolution of the first radiation detector (602, 1605) is better than m 600 eV at the energy of the specified characteristic fluorescent radiation, and the system contains a processor configured to receive and process the output signals generated by the specified first radiation detector, while the specified processor is configured to calculate the fraction of background radiation using at least the first fraction said output signals indicative of detected x-rays whose wavelength is in said first wavelength range but different from the wavelength of said characteristic fluorescent light of said element of interest. 2. The system of claim 1, wherein said processor is configured to calculate said background radiation fraction using at least said first fraction of said output signals indicative of detected x-ray radiation whose wavelength is within said first wavelength range. waves, but less than the wavelength of the specified characteristic fluorescent radiation of the specified element of interest, and the second fraction of the specified output signals, characteristic of the detected X-ray radiation, the wavelength of which is within the specified first wavelength range, but greater than the wavelength of the specified characteristic fluorescent emission of said element of interest. 3. The system of claim 1 or 2, wherein said processor is configured to calculate a detected amount of said characteristic fluorescent emission of the element of interest by subtracting said calculated background radiation fraction from output signals at said characteristic fluorescent emission wavelengths. 4. A system according to any one of the preceding claims, wherein said first radiation detector (602, 1605) energy resolution is better than 300 eV at said characteristic fluorescent radiation energy, said first radiation detector (602, 1605) being a solid state semiconductor detector, preferably a detector selected from a PIN diode detector, a silicon drift detector, a germanium detector, a germanium drift detector, a cadmium telluride detector. 5. A system according to any one of the preceding claims, wherein the nominal input power of the X-ray tube (402) is at least 1 kW, preferably at least 2 kW, and more preferably at least 4 kW. 6. The system according to claim 5, containing the main filter material in the form of a layer (205) located across the specified first optical axis (204) between the x-ray tube (402) and the pulp processing unit (201). 7. The system according to claim 6, wherein the transmission of said base filter material layer (205) is greater than 5% for photons with energies greater than 15 keV. 8. The system according to any of the preceding claims, characterized in that the x-ray tube (402) contains an anode (2001) for generating said incident x-ray radiation (206), and the pulp processing unit (201) is configured to maintain between said sample (202) pulp and the specified anode (2001) of the shortest linear distance, which is less than 50 mm, preferably less than 40 mm and more preferably less than 30 mm. 9. A system according to any one of the preceding claims, wherein the diffractive surface of said pyrolytic graphite crystal (603) is one of the following surfaces: single bond surface, unidirectionally curved, single bonded surface, bidirectionally curved, axisymmetric non-singly bonded surface. 10. The system according to any of the preceding claims, wherein the pulp processing unit (201) is configured to maintain a flat surface of said pulp sample (202) on the side facing said x-ray tube (402) and said first optical axis (204) is perpendicular specified flat surface. 11. The system according to any one of claims 1 to 9, in which the pulp processing unit (201) is configured to maintain a flat surface of said pulp sample (202) on the side facing the indicated - 18 042286 zana x-ray tube (402), and the specified first optical axis (204) is located at an oblique angle to the specified flat surface. 12. A system according to any of the preceding claims, comprising, in addition to said first crystal diffractor, other crystal diffractors, each of said first and other crystal diffractors being positioned at a respective angle of rotation about said first optical axis (204) and configured to highlight a predetermined wavelength range of fluorescent x-rays (207), which propagates in the corresponding direction, and with the possibility of directing fluorescent x-rays in the corresponding selected predetermined first wavelength range to the corresponding radiation detector. 13. The system of claim 12 wherein said other crystal diffractors comprise a second crystal diffractor (1611) comprising a second crystal (1612) configured to direct fluorescent x-rays in a respective dedicated second predetermined wavelength range to a respective second radiation detector, wherein said second crystal (1612) is made of a material other than pyrolytic graphite. 14. The system of claim 13, wherein the second crystal (1612) is one of the following crystals: a silicon dioxide crystal, a lithium fluoride crystal, an ammonium dihydrogen phosphate crystal, a potassium hydrogen phthalate crystal, wherein the second radiation detector (1615) is a gas-filled proportional counter . 15. System according to any one of the preceding paragraphs, containing the body (401) of the analyzer, the front wall (303) of the specified body (401), the opening in the specified front wall (303) and the holder (403) for removable holding of the specified unit (201) pulp processing on the outer side of the specified front wall (303) aligned with the specified hole in the front wall (303). 16. The system of claim 15, wherein both the x-ray tube (402) and the first crystal diffractor (601) are inside said analyzer housing on one side of said front wall (303). 17. System according to any one of the preceding claims, comprising a calibration plate (305) and an actuator (501) configured to move said calibration plate (305) in a controlled manner between at least two positions, of which the first position is not in the path of the incident X-ray radiation (206), and the second position is in the path of the incident X-ray radiation (206) and in the field of view of the first crystal diffractor (601). 18. The system of any one of the preceding claims, wherein said predetermined element of interest is silver. 19. A method for performing X-ray fluorescence analysis of a given element of interest in a pulp using an X-ray fluorescence analyzer system according to any one of the preceding claims, wherein said specified element of interest has an atomic number Z between 41 and 60 inclusive, the method comprising emitting incident X-ray radiation ( 206) in the direction of the first optical axis (204) towards the sample (202) of said pulp, using the first crystal diffractor (601) with a crystal (603) of pyrolytic graphite to isolate a predetermined first wavelength range from the fluorescent X-ray radiation (207), which is incident X-ray radiation (206) generates in said pulp sample, wherein said predetermined first wavelength range contains the characteristic fluorescent radiation of said predetermined element of interest, the direction of the fluorescent x-ray radiation in the selected predetermined the first wavelength range to the first radiation detector (602, 1605), the energy resolution of which is better than 600 eV at the energy of the specified characteristic fluorescent radiation, using the output signals of the specified first radiation detector (602, 1605) to calculate the fraction of background radiation in the specified first wavelength range waves, and calculating a detected amount of said characteristic fluorescent emission of a given element of interest by subtracting said calculated background radiation fraction from output signals at wavelengths of said characteristic fluorescent emission.