Energy-dispersive X-ray diffraction analyser comprising a substantially X-ray transparent member having an improved reflection geometry

An on-line energy dispersive X-ray diffraction (EDXRD) analyser for mineralogical analysis of material in a process stream or a sample is disclosed. The analyser includes a collimated X-ray source to produce a diverging beam of polychromatic X-rays, and an energy resolving X-ray detector, and a substantially X-ray transparent member having the form of a solid of revolution which is circularly symmetric about a central axis between the collimated X-ray source and the energy resolving X-ray detector, an outer surface of the X-ray transparent member positionable adjacent the material to be analysed. A primary beam collimator is disposed adjacent to or within the substantially X-ray transparent member to substantially prevent direct transmission of polychromatic X-rays emitted from the source to the detector. The analyser is configured such that the diverging beam of polychromatic X-rays are directed towards the substantially X-ray transparent member, and where the energy resolving X-ray detector collects a portion of the beam of X-rays diffracted by the material and outputs a signal containing energy information of the collected, diffracted X-rays.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Australian Patent Application No. 2018903962, filed 19 Oct. 2018, the entire contents of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to an on-line energy dispersive X-ray diffraction (EDXRD) analyser. The analyser is particularly targeted towards mineralogical analysis of mineral slurries and dry powdered samples. The invention has application in the field of on-stream analysis of mineralogy for minerals processing, mining and exploration.

BACKGROUND

Bragg's law states that X-rays can be diffracted by regular arrays of atoms in crystals provided that the X-ray energy, E, and the diffraction angle θ satisfy the relationship:

E=h⁢c2⁢d⁢sin⁢θ(1)
where h is Planck's constant, c is the speed of light and d is the spacing between planes of atoms in the crystal. If the X-ray energy is measured in kiloelectron volts (keV) and the crystal spacing in Angstroms (Å), then equation 1 can be rewritten to express the crystal d-spacing in terms of the X-ray energy and diffraction angle:

Energy-dispersive X-ray diffraction analysers can provide information about the composition of a material by measuring the rate at which X-rays of different energies are diffracted through a given angle. From equation (2), it follows that the resolution of the analyser—or the ability to distinguish diffraction occurring from different crystals with similar crystal-plane or so-called d-spacing values—depends directly on the resolution with which the X-ray energy and diffraction angle can be determined.

To maintain good resolution for the measurement of d-spacing, an effective EDXRD analyser design must ensure that only X-rays diffracted through a narrow range of angles are accepted by the detector, and that the detector is capable of measuring X-ray energy with good resolution.

Conventional EDXRD analysers realise this design using one of the following configurations (i) reflection geometries that use parallel ‘pencil’ or ‘ribbon’ X-ray beams, (ii) transmission geometries that use parallel ‘pencil’ or ‘ribbon’ X-ray beams, (iii) transmission geometries that use conical X-ray beams or (iv) transmission geometries that use a combination of pencil, ribbon and conical beams.

FIG.1illustrates a conventional EDXRD transmission analyser that has a type (i), ribbon beam geometry.

X-rays from the focal-spot of an X-ray tube, assumed to be a line-source oriented perpendicularly to the plane of the page, pass through a slit-shaped primary beam collimator to form an approximately parallel beam. The beam passes through a sample, where a fraction of the incident X-rays are diffracted. A portion of the diffracted X-rays emerge in the direction of a slit-shaped aperture in the detector collimator and are counted by the detector. The apertures in the primary beam and detector collimators must be of finite width to accept some fraction of X-rays emitted by the source and diffracted by the sample, which leads to divergence of both the incident and diffracted beams. For clarity, this divergence is shown greatly exaggerated inFIG.1.

The divergence in the incident and diffracted beams means that the analyser measures diffraction through a range of angles Δθ=|θ1−θ2|, rather than through an ideal single angle θ. The magnitude of Δθ is determined directly by the opening widths of the primary beam and detector collimator slits and the dimensions of the X-ray focal spot. In particular, there is an approximately linear relationship between the collimator opening widths and AO. This angular spread has the effect of broadening the diffraction peaks in the profiles of the measured sample and reducing instrument resolution. At the same time, the X-ray throughput of the analyser also increases approximately linearly with the collimator opening width.

Modern, semiconductor detectors are capable of measuring individual X-rays in the energy range of 10-50 keV with a resolution ΔE/E of better than 1-2%. In practice therefore, the width of the collimator openings is the primary factor in determining the d-spacing, resolution of the analyser.

Poor resolution is undesirable as it results in a greater degree of overlap between closely spaced diffraction peaks. Wide collimator openings however provide high X-ray throughput to the detector and therefore greater count-rates and reduced measurement times. In the conventional ribbon-beam EDXRD instrument design, the decrease in resolution and increase in X-ray throughput are both linear with increased collimator width. This means that achieving good d-spacing resolution necessarily means accepting a low X-ray throughput.

Analogous arguments apply to the other conventional EDXRD designs listed above.

It would be highly desirable to find an improved EDXRD analyser design that allows for high X-ray throughput and good d-spacing resolution to be achieved simultaneously.

SUMMARY

In one aspect of the present disclosure, an on-line energy dispersive X-ray diffraction (EDXRD) analyser for mineralogical analysis of material in a process stream or a sample is provided, the EDXRD analyser comprising:a collimated X-ray source to produce a diverging beam of polychromatic X-rays;an energy resolving X-ray detector;a substantially X-ray transparent member having the form of a solid of revolution which is circularly symmetric about a central axis between the collimated X-ray source and the energy resolving X-ray detector, an outer surface of the X-ray transparent member positionable adjacent the material to be analysed; anda primary beam collimator disposed adjacent to or within the substantially X-ray transparent member and configured to substantially prevent direct transmission of polychromatic X-rays emitted from the source to the detector;where the analyser is configured such that the diverging beam of polychromatic X-rays are directed towards the substantially X-ray transparent member, and where the energy resolving X-ray detector collects a portion of the diffracted beam of X-rays scattered by the material and outputs a signal containing energy information of the collected, diffracted X-rays.

In some embodiments, the on-line EDXRD analyser further comprises a detector collimator comprising an aperture which further defines the diffracted beam of X-rays scattered by the material. The detector collimator may be situated in close proximity to, or attached to, the X-ray detector.

In some embodiments, the collimated X-ray source is a sealed X-ray tube which is configured to operate at voltages between 15-150 kV. Preferably the sealed X-ray tube is configured to operate at voltages between 15-100 kV or 15-50 kV.

In some embodiments, the sealed X-ray tube is a low-power X-ray tube, operable at an electron beam power of less than approximately 300 W. Low power X-ray sources have the advantage that they require no active cooling or can utilise more energy efficient active cooling such as air cooling instead of water cooling.

In some embodiments, the sealed X-ray tube features a focal spot size in the range of tens of microns to a few hundred microns.

In some embodiments the substantially X-ray transparent member may be configured in the form of a cylinder. In other embodiments, the substantially X-ray transparent member may be configured such that its radius varies along its length. Depending on the material from which the substantially X-ray transparent member is formed, it may be substantially solid or it may comprise a thin shell.

In some embodiments the primary beam collimator may be rigidly held within the inner passage of the transparent member.

The on-line EDXRD analyser may further comprise a first hollow tube connecting the X-ray source and a front end of the substantially X-ray transparent member to facilitate the passage of X-rays between the collimated X-ray source and the substantially X-ray transparent member; and a second hollow tube connecting a second end of the substantially X-ray transparent member and the energy-resolving X-ray detector, to facilitate the passage of the diffracted beam of X-rays scattered by the material between the X-ray transparent member and X-ray detector. The walls of each of the first and second hollow tubes may be substantially opaque to X-rays.

In some embodiments, an X-ray window may extend across an end of the first hollow tube proximate to the front end of the substantially X-ray transparent member. Additionally or alternatively, an X-ray window may extend across an end of the second hollow tube proximate to the second end of the substantially X-ray transparent member.

In some embodiments the primary beam collimator may be rigidly held within the inner passage of the X-ray transparent member. Further, the connection of the respective hollow tubes to the X-ray transparent member may be rigid such that the combination of the primary beam collimator, X-ray transparent member and respective hollow tubes form a probe. In some embodiments, other features such as the X-ray windows, and X-ray beam divergence and convergence collimators as discussed further below, may be comprised in the probe, e.g. by being rigidly connected with the primary beam collimator, X-ray transparent member and hollow tubes. The probe may be encased in a protective X-ray transparent sleeve.

In some embodiments, the energy resolving X-ray detector is a silicon detector such as a silicon drift detector (SDD) or Si-PiN diode detector. In other embodiments, the detector may be another high-resolution semiconductor, such as a CdTe detector. Detectors with greater X-ray stopping power may be advantageously used when the X-ray source is operated at voltages above 50 kV.

In some embodiments the collimated X-ray source may comprise a source collimator in close proximity to, or attached to the X-ray source. In other embodiments the source collimator is an inherent part of the X-ray source. In some embodiments, the source collimator may have a cylindrical-shaped aperture, having a diameter to substantially reduce background scatter. The detector collimator may also have a cylindrical-shaped aperture. In other embodiments, the source collimator may have a conical-shaped aperture. In such embodiments the detector collimator may also have a conical-shaped aperture.

In some embodiments, an X-ray beam divergence collimator is positioned proximate the front end of the substantially X-ray transparent member. The beam divergence collimator may be annular, having a central circular opening that has approximately the same diameter as the outer surface of the substantially X-ray transparent member at the front end of the substantially X-ray transparent member. The beam divergence collimator may ensure that X-rays may only enter the material of the process stream or sample by first travelling through the substantially X-ray transparent member. Additionally or alternatively, an X-ray beam convergence collimator is positioned proximate the second end of the substantially X-ray transparent member. The beam convergence collimator may be annular, having a central circular opening that has approximately the same diameter as the outer surface of the substantially X-ray transparent member at the second end of the substantially X-ray transparent member. The beam convergence collimator may ensure that diffracted X-rays may only reach the detector after passing out of the substantially X-ray transparent member.

The primary beam collimator is preferably substantially circularly symmetric about the central axis between the source of X-rays and the energy resolving X-ray detector. Accordingly, together with the collimation of the X-ray source, the primary beam collimator serves to define a cone-shaped beam of X-rays diverging from the source and incident on the outer surface of the tubular member. Further, together with the detector collimator, the primary beam collimator serves to define a cone-shaped beam of diffracted X-rays converging from the outer surface of the tubular member onto the detector.

The primary beam collimator may comprises a machined plug of material whose outer surface is circularly symmetric with respect to the central axis. In some embodiments, the primary beam collimator may have a central circular shaped aperture, which is blocked with a removable plug. Measurement of a direct beam of X-rays from the source passing through this central aperture to the detector can be advantageously used to ensure correct alignment of the components of the analyser.

In some embodiments the EDXRD analyser may further comprise a source translation stage upon which is mounted the collimated X-ray source and a detector translation stage upon which is mounted the detector and the detector collimator.

In any of the embodiments, the, or each, translation stage may comprise one or more micrometer-driven positioning devices to enable fine adjustment of the source collimator and detector collimator at least in a direction normal to a central axis between the X-ray source and the energy resolving X-ray detector, preferably in at least 2 axes and more preferable in 3D translation.

In some embodiments, the EDXRD analyser may further comprise a signal processor (for examples,161inFIG.2A;1601inFIG.7A) to process signals from the detector(s) so as to determine the presence and concentration of different minerals species in the process stream, based on the presence and intensity of diffracted X-rays corresponding to particular d-spacing values, and/or to determine the spacings of atomic planes in crystals in the material, and/or the proportions of different mineral species present in the material.

DETAILED DESCRIPTION

Referring now to the drawings in which like numerals represent like elements throughout several views,FIG.2schematically illustrates a practical arrangement for installation of an on-line energy dispersive X-ray diffraction analyser10. Whilst the configuration of the analyser10in the following description is described in relation to the analysis of a mineral slurry, it should be appreciated that the configuration of the analyser is suitable for the analysis of dry powders, thus the sample in certain embodiments may be a discrete sample of material. It will be appreciated by those skilled in the art that on-line analysers measure the material of interest directly thereby enabling measurement of process stream without the need to remove a sample of the material.

The analyser10comprises a sealed X-ray tube12. The X-ray tube12may be a low power device (e.g., beam power up to˜50 watts, and in some instances below 10 watts) which is configured to operate between 20-50 kV. However, in some embodiments, the X-ray tube12may be a device having a higher power (e.g., beam power up to˜500 watts and preferably below 300 watts) which is configured to operate between 20-100 kV. Regardless, such X-ray tubes may have a lower X-ray power than various X-ray sources typically used in EDXRD analysers, which may be operated at powers up to thousands of watts. The use of lower power sources is made possible by the efficiency gained through the new beam geometry of the analyser10. Such X-ray sources have the advantage that they require no active cooling or can utilise more energy efficient active cooling such as air cooling instead of water cooling.

A source collimator14is provided which comprises a machined metal plate. In this example the source collimator14is immediately adjacent to and movably attached to the X-ray source12, moveable by means of the source positioning means28which will be described later in the description. In this example, the aperture of the source collimator14is illustrated as being cylindrical in shape. The analyser10further comprises an energy-resolving X-ray detector16which is a high-resolution semiconductor detector. A detector collimator18is provided which is comprised of a machined metal plate with a central aperture movably attached to the detector16. The aperture of the detector collimator is also shown to be cylindrical in shape. In another example (FIG.2A), a signal processor161may be provided to process signals from the detector16.

The analyser10further comprises a substantially X-ray transparent member20, also referred to herein as a tubular member. Tubular member20is in the form of a volume of revolution which is circularly symmetric about the central axis22between the X-ray source12and the detector16. In this example, the tubular member is shown as being cylindrical. The tubular member20may be manufactured from carbon-fibre, a polymer or polymer foam material having a low atomic number to render the tubular member substantially transparent to the passage of X-rays. For example, the tubular member may be made of low-density rigid polyurethane foam with an outer surface machined to high tolerance. The surface of the tubular member20thus acts as a window through which the X-rays pass and irradiate the sample material36present immediately adjacent to the tubular member's surface. At least some of the diffracted rays are then collected by the detector16.

A primary beam collimator24is positioned between the X-ray source12and energy-resolving X-ray detector16to prevent X-rays from the source from reaching the detector16directly. In the example shown, the primary beam collimator24comprises a single machined piece of metal, passing through the centre of the tubular member20. The primary beam collimator24is circularly symmetric, and its axis corresponds to the axis connecting the X-ray source12and detector16.

Hollow metal tubes26are positioned between the X-ray source12and the front end of the tubular member20, and between the second (rear) end of the tubular member20and the X-ray detector16. These tubes26serve two purposes. Firstly, they define a region through which X-rays may travel with minimum attenuation. In the example where the analyser10is used to measure diffraction from minerals in a process stream, the hollow tubes26allow the tubular member20to be situated inside the process stream36, and allow passage of X-rays through a region that would be otherwise filled with the process stream material. Secondly, the hollow tubes26may prevent X-rays from the source entering the process stream material, except through the outer surface of the tubular member20, and may prevent scattered X-rays from the process stream material from reaching the detector16, except through the outer surface of the tubular member20.

The tubular member20, together with the primary beam collimator24and hollow tubes26may be fixed together to form a rigid unit, termed the EDXRD probe. The EDXRD probe may be further encased in a thin plastic tube32for the purposes of providing a water-tight seal and to protect the outer surface of the tubular member from wear or damage by the process stream material. The EDXRD probe may then be mounted in for instance a launder tank arrangement which accommodates a wide range of flow rates of a mineral slurry. Alternatively, the probe may be directly insert into a mineral process stream.

In this example the collimated X-ray source12and detector16arrangements are mounted to the exterior of the launder tank. Source positioning means28in the form of a translation stage is provided to mount the X-ray tube12and bring it and the source collimator14into correct alignment with the collimator24and detector16. Detector positioning means30in the form of a translation stage is provided to mount the detector16and detector collimator18and bring each into correct alignment with the collimator24and the X-ray source12.

Source positioning means28and detector positioning means30each provide tranverse motion in at least two axes and ideally 3-dimensional translation. This is important because the X-ray focus spot position in the X-ray tube12can vary significantly from tube to tube, making realignment important each time the X-ray tube12is serviced or replaced. Similarly, it is desired that the detector16be aligned as close to the central axis22in order to obtain optimal resolution.

The analyser10configured in accordance with the invention significantly reduces the spread in diffraction angle Δθ on the collimator opening angles. As a result, the trade-off between count-rate and resolution is significantly improved which allows high resolution spectra to be rapidly collected.

With reference toFIG.3, X-rays are emitted from the source12and diffract at the surface of the sample material, where the sample material36contacts the thin plastic tube32overlying the tubular member20. For simplicity, the source12is considered to be a point source. One X-ray38is shown to interact at the near edge of the tubular member20and diffracts at the angle θ1. Another X-ray40interacts at the centre line of the tubular member20and diffracts at the angle θ2. The length of the tubular member is L. The angular resolution is approximately Δθ/θ=(θ1−θ2)/θ.

Since the X-ray source12is preferably operated at a voltage of up to 50 kV or up to 100 kV and produces intense X-rays between energies of approximately 10 and 40 keV, the central diffraction angle θ is ideally chosen so that the energies of the diffraction lines of key mineral phases of interest fall in this energy range. For minerals with d-spacing values in the range of 1-10 Å, the relevant range of diffraction angles is 3°-15°.

FIG.4plots values of the resolution Δθ/θ, expressed as percentage, for tubular member lengths L up to 50 mm and diffraction angles in the range θ=[3°-15° ]. The aperture in the detector collimator in this example has a diameter of 0.5 mm.

Conventional EDXRD analysers operated in transmission geometry have the attractive property that relatively thick samples (up to 10-20 mm) may be analysed. This means that large volumes of material can be measured compared to conventional reflection geometry XRD instruments such as the Bragg-Brentano geometry used in a typical laboratory XRD system. This is important in the measurement of process streams, which may be highly inhomogeneous. The ability of the invention in suit to preserve excellent resolution whilst measuring samples of lengths of 50 mm or more is highly advantageous. The volume of material measured is much greater than other reflection geometry instruments including transmission geometry analysers. The volume measured may be hundreds of times greater using the present invention.

The simplified case inFIG.3assumes that the X-ray interacts at the surface of the sample material where the sample material contacts the thin plastic tube32overlaying the tubular member20. Whilst this is a reasonable approximation, the incident X-ray beam does penetrate some distance into the sample and this distance contributes an additional amount to the angular spread AO. Given that the densities of typical mineral process stream slurries range from 1.3-1.5 g/cm3, the mean-free path, λ, of 10-40 keV X-ray photons ranges from a small fraction of a millimetre to approximately 1 cm. Therefore the depth that the photon penetrates into the sample in the direction normal to the sample surface, given by λ sin θ, is generally significantly less than 1 mm. This small penetration depth makes only a minor contribution to the angular resolution Δθ/θ.

With reference toFIG.5, the resolution of the analyser10can be improved by allowing the radius of outer surface of the tubular member20to vary along its length. In particular, the shape of the tubular member20may be chosen such that the diffraction angle θ is constant regardless of where an X-ray interacts along the length of the surface of the tubular member20. Specifically, with reference to the inscribed angle theorem that states that the angle inscribed in a circle by a chord is constant, and equal to one half of the angle subtended by the chord at the centre of the circle, the outer surface of the tubular member20is ideally formed by rotating an arc of a circle about the axis connecting the X-ray source and detector. The radius R of the circular arc is chosen to obtain the desired diffraction angle θ:

R=D2⁢sin⁢2⁢θ
where D is the distance from the source to the detector. The displacement, h, of the centre of the circle from the axis connecting the source and detector is given by

This choice for the outer surface of the tubular member20maximises the angular resolution of the EDXRD analyser10, which is then limited only by the finite size of the X-ray source12, the aperture in the detector collimator18and X-ray penetration into the sample material36.

Typical focal spot sizes for X-ray sources applicable to the invention range from tens of microns to a few hundred microns. The aperture in the detector collimator may be freely chosen, with larger apertures resulting in increased X-ray throughput, but decreased instrument resolution. Typical aperture sizes are in the range of a few hundred microns to a few millimetres. The effect on resolution of the X-ray penetration into the sample varies with sample composition and density, X-ray energy and the diffraction angle, but as discussed previously is generally small.

FIG.6compares the X-ray throughput/d-spacing resolution trade-off for a reflection geometry design in accordance with the current specification and the ‘cone-cone’ geometry of U.S. Pat. No. 8,311,183. The results inFIG.6are calculated using a detailed computer model that tracks X-ray scattering and diffraction through a 3-dimensional representation of the two instrument designs.

For both designs, the source/detector distance is held fixed at 32 cm and the diameter of the X-ray source spot is fixed at 0.5 mm. The collimator openings and sample dimensions are independently varied. One hundred variations were simulated for each design, and for each variation the resulting count rate and resolution for a quartz diffraction line (d-spacing of 3.34 Å) were calculated.FIG.6plots the ‘Pareto-optimal’ results for each of the two designs: that is, the family of designs that represent the best trade-off in X-ray throughput and resolution. Resolution is plotted on an inverted scale, so that the ‘best’ designs fall towards the top-right hand corner of the plot.

It can be clearly seen that the new reflection geometry design of the current specification provides a substantial advantage over the cone-cone geometry of U.S. Pat. No. 8,311,183, particularly at higher resolutions. For resolutions better than 10%, the new design affords almost an order of magnitude increase in X-ray throughput.

FIG.7schematically illustrates a practical arrangement for installation of an on-line energy dispersive X-ray diffraction analyser100according to another embodiment of the present disclosure. The analyser100is configured to be used in a similar manner to the analyser10described above with reference toFIGS.2to6. The analyser100includes various structural features that are similar or identical to features of the analyser10, but the analyser100also differs in a number of respects, including through inclusion of an X-ray beam convergence collimator, an X-ray beam divergence collimator and X-ray windows.

In more detail, the analyser100comprises a sealed X-ray tube120, source collimator140and source positioning means280that can be similar or identical in structure and function to the X-ray tube12, source collimator14and source positioning means28as described above. The analyser100also comprises an energy-resolving X-ray detector160, detector collimator180and detector positioning means300that can be similar or identical in structure and function to the X-ray detector16, detector collimator18and detector positioning means30as described above. In another example (FIG.7A), a signal processor1601may be provided to process signals from the detector160.

The analyser100is used to analyse a slurry sample360contained within a launder tank380.

The analyser100again comprises a substantially X-ray transparent member200, which is in the form of a volume of revolution which is circularly symmetric about the central axis220between the X-ray source120and the detector160. The surface of the transparent member200acts as a window through which the X-rays pass and irradiate the sample material360present immediately adjacent to the transparent member's surface within the tank380.

In this embodiment, in accordance with the arrangement shown inFIG.5and its accompanying description, the radius of outer surface of the transparent member200varies along its length such that the diffraction angle θ is constant regardless of where an X-ray interacts along the length of the surface of the transparent member200. The outer surface of the transparent member200in this embodiment is a curved, convex surface, providing the transparent member200with a bulbous shape that is widest approximately at the centre of the transparent member200between the front end and second (rear) end of the transparent member200.

A primary beam collimator240is positioned between the X-ray source120and energy-resolving X-ray detector160to prevent X-rays from the source from reaching the detector160directly. The primary beam collimator240is circularly symmetric, and its axis corresponds to the axis connecting the X-ray source12and detector160. The primary beam collimator240is made of a high atomic number material to block transmission of a direct beam of X-rays.

A hollow metal tube260is positioned between the X-ray source120and a front end of the transparent member and a further hollow metal tube260is positioned between a second (rear) end of the transparent member200and the X-ray detector160, allowing passage of X-rays through a region inside the tubes260that would be otherwise filled with the sample material360, and preventing X-rays from the source entering the sample material360, except through the outer surface of the transparent member200.

In this embodiment, X-ray windows270are provided that extend across the open end of each tube260closest to the transparent member200and primary beam collimator240. The x-ray windows270provide a low density medium to both seal the launder tank380adjacent the open ends of each tube260and transport X-rays to and from the transparent member200. The X-ray windows may be made of a polymer material, such as polyether ether ketone (PEEK).

Mounted to the outside surface of the X-ray windows270are annular shaped x-ray beam collimators265,275including a beam divergence collimator265and a beam convergence collimator275. The beam divergence collimator265is located proximate the front end of the transparent member200. The beam divergence collimator265has a central circular opening, through which X-rays can pass, that has approximately the same diameter as the front end of the transparent member200. The function of the beam divergence collimator265is to ensure that X-rays may only enter the sample360by first travelling through the transparent member200. The beam convergence collimator275is located proximate the second, rear end of the transparent member200. The beam convergence collimator275has a central circular opening, through which X-rays can pass, that has approximately the same diameter as the second, rear end of the transparent member200. The function of the beam convergence collimator275is to ensure diffracted X-rays may only reach the detector160after passing out of the transparent member200.

In this embodiment, the transparent member200, together with the primary beam collimator240, hollow tubes260, X-ray windows270and beam divergence and convergence collimators265,275may be fixed together to form a rigid unit in the form of an alternative EDXRD probe. In use, the EDXRD probe may be inserted in and/or removed from a launder tank380as shown inFIG.7as a single part, which launder tank380may accommodate a wide range of flow rates of a mineral slurry. Alternatively, the EDXRD probe may be directly inserted in and/or removed from a mineral process stream as a single part.

The advantages of using a curved surface for the transparent member200are further evident from the plot ofFIG.8, which shows the geometric resolution Δθ/θ as a function of different lengths of the transparent member200. As can be understood by comparison withFIG.4, much higher resolution (low Δθ/θ value) is obtained not only for higher diffraction angles but also for longer transparent members. In general, key advantages are therefore the preservation of the diffraction angle along the length of the tubular member and far superior d-spacing resolution. Much longer tubular member lengths can therefore be used whilst maintaining excellent resolution (the plot ofFIG.8shows resolution values for lengths up to 200 mm).

In the above example, whilst the aperture of the source collimator14,140and detector collimator18,180are each described as being cylindrical in shape in a further example they could each respectively be conical in shape, shaped to better conform with the profile of the X-ray beam emitted by the source, or converging on the detector respectively.

In the above example, the primary beam collimator24,240is shown as being formed as a single piece. In another example, the primary beam collimator may comprise two separate machined pieces, fixed to the flat surfaces of the tubular member respectively facing the X-ray source12,120and X-ray detector16,160.

Further, whilst the analyser10,100is described as being mounted in a launder tank, with the collimated source and collimated detector components being mounted on respective outer sides of the tank, a single-sided design is also envisaged. In the single-sided design, the detector16,160, detector collimator18,180and detector mounting30,300are contained in a sealed chamber fixed to the end of the EDXRD probe. Power and data cables running to the detector16,160may pass back through the EDXRD probe, or through a separate conduit running parallel to the EDXRD probe. With the single-sided design, the complete assembly comprising EDXRD probe and attached detector chamber may be mounted on one wall of a large vessel or pipe, such that the probe and chamber are immersed in the process stream material.

In accordance with this embodiment of the invention, superior diffraction peak resolution is able to be obtained for a given count-rate at the detector. Resultantly, mineral samples are able to be analysed with relatively better accuracy, since less peak overlap is obtained between adjacent diffraction peaks. Furthermore, low power X-ray sources are able to be used due to the greater efficiency of the system which reduces the cost and mechanical complexity of the analyser compared to existing analysers. Moreover, measurement times are reduced.