X-ray fluorescence analysis method and device

Abstract

The invention relates to a method for the X-ray fluorescence analysis of an object to be analysed, which method comprises: - focusing an X-ray measurement beam (10) on or in the object to be analysed, the X-rays being suitable for exciting an emission of X-rays by the object to be analysed; - two-dimensionally scanning the measurement beam (10) over the object to be analysed at a plurality of measurement points on the object to be analysed; - two-dimensionally detecting, using X-ray fluorescence spectrometry means (3), the X-rays emitted by the object along a two-dimensional detection axis (13), at the plurality of measurement points; - identifying at least one measurement point of interest from among the plurality of measurement points; and - confocally detecting, using X-ray fluorescence spectrometry means (4), the X-rays emitted by the object at the at least one measurement point of interest in a measurement volume and along a confocal detection axis (12), the focusing means (5, 6) being configured to generate the measurement volume. The invention further relates to a portable device used by the method, the measurement volume being offset outwards relative to a periphery of the device.

Description

X-ray fluorescence analysis method and apparatus

[0001] The present invention relates to a method for analyzing an object to be analyzed using X-ray fluorescence. The invention also relates to an X-ray fluorescence analysis device used in such a method.

[0002] The field of invention is, without limitation, that of the analysis of heritage objects and in particular painted works. State of the art

[0003] Non-destructive microanalysis of ancient cultural heritage objects is essential for identifying the nature of the materials composing them, studying their provenance, manufacturing techniques, or investigating alteration phenomena in museums and heritage sites.

[0004] Non-destructive X-ray-based analysis and imaging techniques exist. X-ray fluorescence spectrometry analyses are highly sensitive and can detect chemical elements in very low concentrations. These analyses are generally performed using two-dimensional scanning, allowing for laterally resolved imaging.

[0005] However, it is often difficult to know, for example, in which paint layer the detected chemical element is located. Being able to pinpoint the chemical elements and specify their correlations is important for interpreting chemical maps, as well as for identifying artistic techniques, retouching, overpainting, or other factors.

[0006] To do this, it is often necessary to take micro-samples to locate the paint layers. Generally, sampling is prohibited or very restricted on museum paintings.

[0007] Information on the stratigraphy of the pictorial layers can also be obtained non-invasively from independent measurements by confocal X-ray microfluorescence, for which a micro-volume of measurement is moved into the layers of interest.

[0008] However, these systems are generally stationary. The objects to be analyzed, and in particular paintings of art, must therefore be moved and transported to laboratories or near facilities such as synchrotrons.

[0009] Furthermore, by performing lateral and depth analyses separately, the exact positions of the analyses can be lost, and superimposing measurement results is not always possible due to the heterogeneity of the objects studied. In addition, the objects are exposed to ionizing radiation repeatedly, and the analysis time is consequently prolonged.

[0010] One aim of the present invention is to overcome at least one of these drawbacks.

[0011] One aim of the invention is to provide a method and device for analysis that enables laterally and depth-resolved X-ray fluorescence spectrometry analyses to be performed in a correlated or combined manner.

[0012] Another objective of the present invention is to provide a method and device for analysis that enables laterally and deep-resolved X-ray fluorescence spectrometry analyses to be performed in a non-invasive manner.

[0013] Another objective of the present invention is to provide a method and device for analysis that allows for laterally and depth-resolved X-ray fluorescence spectrometry analyses to be performed in situ, without moving or manipulating the object to be analyzed.

[0014] At least one of these goals is achieved with an X-ray fluorescence analysis method for an object to be analyzed, implemented in situ by means of a portable X-ray fluorescence analysis device, the method comprising the following steps: focusing an X-ray beam, called the measurement beam, by focusing means onto or into the object to be analyzed, the X-rays being adapted to excite X-ray emission by the object to be analyzed; two-dimensional scanning of the measurement beam over the object to be analyzed at a plurality of measurement points on the object to be analyzed; two-dimensional detection, by means of two-dimensional X-ray fluorescence spectrometry, of the X-rays emitted by the object along a first detection axis, called the two-dimensional detection axis, at the plurality of measurement points; identification of at least one measurement point of interest among the plurality of measurement points; and confocal detection, by means of confocal X-ray fluorescence spectrometry.X-rays emitted by the object at at least one measurement point of interest within a measurement volume and along a second detection axis, called the confocal detection axis, the focusing means being configured to generate the measurement volume,

[0015] the measurement volume being offset outwards relative to a periphery of the device, and the device being adapted for transport.

[0016] The method according to the invention allows for the analysis of an object using X-ray fluorescence and combining elemental imaging and depth analysis. The object can be a painting, for example, a historical painting in a museum or in a cave, particularly a prehistoric one, or another work of art. The method according to the invention notably provides high resolution for analyzing paint layers in depth, at one or more areas of interest predetermined through the two-dimensional detection step.

[0017] The method according to the invention makes it possible both to characterize the entire object, to efficiently identify important areas, and to obtain high-quality data for these areas, while maintaining a reasonable analysis time. This criterion is crucial in the context of time-limited analytical campaigns, which are common in heritage studies.

[0018] The method combines confocal X-ray fluorescence spectrometry (CXRF) and two-dimensional fluorescence spectrometry (MA-XRF or 2D XRF), techniques which are implemented separately in the state of the art. By performing them together, using a portable X-ray fluorescence analysis device, the position of the depth analyses relative to the two-dimensional analysis is preserved, even for highly heterogeneous objects.

[0019] The measurements or analyses are carried out in situ using a portable analytical device, eliminating the need to move the object, such as a painting, to a laboratory or other facility, which could damage it. The method according to the invention thus saves time and minimizes the exposure of the artwork to radiation during analysis.

[0020] Of course, measurements can also be taken in the laboratory, when the artwork or other object to be analyzed can be brought to the laboratory.

[0021] The method according to the invention thus allows for a complete analysis of an object by X-ray fluorescence. Thanks to the coupling of CXRF and MA-XRF techniques, the method according to the invention allows for a more complete and detailed selection of the area to be analyzed and more precise control of the measurement volume. In particular, the measurements make it possible to determine, qualitatively and semi-quantitatively, the layer-by-layer chemical composition of painted works. For these works, a better understanding of complex stratigraphies can be obtained by combining the two measurement techniques.

[0022] It should be noted that the term "measurement point" indicates a location or place where the measurement is carried out, the measurement point being able to have a more or less extensive dimension depending on the degree of focus of the measurement beam.

[0023] According to one embodiment, the two-dimensional detection step is carried out for a set of measurement points covering substantially the entire surface of the object to be analyzed, the process further comprising a step of establishing a two-dimensional map from detected signals.

[0024] This could be, for example, a chemical mapping of a painted work or any other structure exhibiting a dispersion of chemical elements.

[0025] According to one embodiment, the method according to the invention may further include the following steps, for each measurement point of interest: displacement of the confocal measurement volume in the direction of the depth of the object to be analyzed, and reiteration of the confocal detection step at several depths of the object to be analyzed.

[0026] For a plurality of measurement points of interest, the measurement beam is thus scanned three-dimensionally on and in the object to be analyzed.

[0027] Advantageously, the confocal measurement volume displacement and confocal detection step reiteration steps can be performed for a plurality of juxtaposed measurement points of interest.

[0028] Confocal measurements at different depths and for juxtaposed measurement points of interest, i.e., close together, allow the establishment of a three-dimensional map from detected signals, at least over a small area.

[0029] This could be, for example, a 3D chemical map of a painted work or any other structure exhibiting a dispersion of chemical elements.

[0030] According to an advantageous embodiment, the method according to the invention further includes a step of adjusting the focus of the measuring volume.

[0031] The adjustment step is preferably carried out automatically.

[0032] The adjustment step thus allows the focus of the measurement volume to be adjusted in order to perform the confocal detection step.

[0033] Thus, confocal detections, or measurements, are reproducible, especially when the device has been transported between measurements.

[0034] According to another aspect of the same invention, a portable X-ray fluorescence analysis device for an object to be analyzed is proposed, the device comprising: means for generating X-rays configured to produce an X-ray beam, called the measurement beam, the X-rays being adapted to excite X-ray emission from the object to be analyzed; focusing means configured to focus the X-ray beam on or in the object to be analyzed and to generate a confocal measurement volume; means for two-dimensional X-ray fluorescence spectrometry, comprising a first X-ray detector, called the two-dimensional detector, configured to detect the X-rays emitted by the object along a first detection axis, called the two-dimensional detection axis, at a plurality of measurement points; means for confocal X-ray fluorescence spectrometry, comprising a second X-ray detector, called the confocal detector.the confocal detector being configured to detect the X-rays emitted by the object at at least one measurement point of interest among the plurality of measurement points in the confocal measurement volume and along a second detection axis, called the confocal detection axis,

[0035] the measurement volume being offset outwards relative to a periphery of the device, and the device being adapted for transport,

[0036] the device being configured to implement the analysis method according to the invention.

[0037] The term "portable device" refers to the fact that the analytical device according to the invention can be carried by one or more people, by hand, from one place to another. The device can be carried in one or more suitable containers, such as cases designed to hold this type of equipment, without the need for a transport aid such as a trolley or wheels.

[0038] The device according to the present invention combines confocal X-ray fluorescence spectrometry (CXRF) and two-dimensional X-ray fluorescence spectrometry (MA-XRF or 2D-XRF). It enables comprehensive analysis and three-dimensional elemental imaging of objects, particularly heritage objects and especially painted works, with a higher resolution than that obtained with a prior art device.

[0039] The device according to the invention allows for combined, successive CXRF and MA-XRF measurements, enabling a more complete and detailed selection of the area under study. The device also saves time and minimizes the exposure of artworks to radiation during analysis.

[0040] Of course, the device according to the invention also allows MA-XRF and CXRF measurements to be carried out separately and independently of each other.

[0041] A single analytical device is required to perform combined or independent analyses.

[0042] Advantageously, the X-ray generation means, the X-ray detectors and the focusing means are arranged together to form a portable measuring head.

[0043] Because the measurement volume is offset outwards from the periphery of the device, the device can be brought closer to the object to be analyzed without risk of damaging it.

[0044] Preferably, the means for generating X-rays may include an X-ray tube.

[0045] X-ray tubes offer the advantage of a wide energy range and stable performance over long measurement periods, while also allowing for intensity control. They are easy to use and versatile.

[0046] According to one embodiment, the device according to the invention may further include means for moving the confocal measurement volume in the direction of the depth of the object to be analyzed.

[0047] Means of displacement along the depth direction can also be implemented to correct the position of the measuring head during two-dimensional measurements or scans, when it gets too close to or too far from the surface of the object during the analysis.

[0048] In addition, in the case of non-planar objects, automatic distance correction ensures the safety of the object as well as the reliability of the recorded signal.

[0049] According to an advantageous embodiment, the device according to the invention further includes means for adjusting the focus of the measurement volume.

[0050] The means of adjusting the focus are preferably means of automatic alignment.

[0051] Depending on the embodiment, X-ray detectors can each include one of the following: a gas proportional counter, a scintillation detector, a solid state detector.

[0052] Preferably, the confocal detector and the two-dimensional detector are of the same type.

[0053] In this case, the detectors can be easily interchanged. Detector control and signal processing are also simplified. Furthermore, one detector can be used to replace another in case of failure.

[0054] Even more preferentially, the confocal detector and the two-dimensional detector are both silicon drift detectors (SDD).

[0055] According to some embodiments, the measurement beam can be incident on the surface of the object at an angle between 30° and 150°.

[0056] Preferably, the measurement beam is incident on the surface of the object at an angle of 45° or 90°.

[0057] The confocal detection axis can be oriented relative to the surface of the object at an angle between 30° and 150°.

[0058] The angle between the measurement beam and the confocal detection axis can be between 30° and 90°.

[0059] The two-dimensional detection axis can be oriented relative to the surface of the object at an angle between 1° and 179°.

[0060] According to some embodiments, the energy of the X-ray beam incident on the object to be analyzed, i.e., the measurement beam, is between 1 and 40 keV, and preferably between 1 and 20 keV.

[0061] The analytical method and apparatus according to the invention are particularly well-suited for use in heritage science. They can also be applied in other fields outside of cultural heritage, such as the study of materials of pharmaceutical interest, in the recycling industry (e.g., rare or precious metals), the automotive industry, and the semiconductor industry. Through the combination of confocal X-ray fluorescence spectrometry and two-dimensional X-ray fluorescence spectrometry, the chemical distribution of different constituents in various materials or structures can be characterized comprehensively and in a completely non-invasive manner. Description of the figures and methods of implementation

[0062] Other advantages and features will become apparent from the detailed description of non-limiting examples and the accompanying drawings in which: a schematic representation of a measuring head of an X-ray fluorescence analysis device according to an embodiment of the invention; a demonstration of an arrangement of a measuring beam and a detection axis implemented in a device and an analysis method according to the present invention.

[0063] It is understood that the embodiments described below are by no means exhaustive. In particular, all the variants and embodiments described are combinable with each other provided there are no technical obstacles to such combination.

[0064] In the figures, elements common to several figures can retain the same reference.

[0065] Lamontre presents an example of a measurement head for a device used in X-ray fluorescence analysis of an object. The device can be implemented in an X-ray fluorescence analysis process.

[0066] The measurement head of the analysis device 1, shown in the figure, includes an X-ray tube 2 and a first and second X-ray detector 3, 4.

[0067] X-ray tube 2 is configured to deliver an X-ray beam. The X-ray beam, called the measurement beam, is used to excite an X-ray emission in the object to be analyzed, by exciting electrons within a small sampling area in the object.

[0068] The two X-ray detectors 3, 4 are configured to detect the X-rays emitted by the object.

[0069] The first detector 3, called a two-dimensional detector, is a detector used for detection in two-dimensional mode, that is, for detection along two axes in a plane perpendicular to the measurement beam.

[0070] The first detector 3 is oriented to detect the X-rays emitted by the object along a first detection axis, called the two-dimensional detection axis.

[0071] The second detector 4, called the confocal detector, is used for confocal detection. The confocal detector 3 is configured to detect X-rays emitted by the object being analyzed within a measurement volume, as described below.

[0072] The second detector 4 is oriented to detect the X-rays emitted by the object along a second detection axis, called the confocal detection axis.

[0073] According to one embodiment, the two detectors 3, 4 are of the same type.

[0074] These are preferably silicon drift detectors (SDD).

[0075] Detectors can also be proportional gas meters, scintillation detectors, or solid-state detectors.

[0076] Proportional or gas proportional meters use a chamber filled with gas, typically high-purity argon, xenon, neon, or krypton, with a central anode wire surrounded by a cathode. Incoming X-rays ionize the gas molecules, leading to the generation of electron-ion pairs, primarily through the photoelectric effect. The amplitude of the ionization signal is proportional to the energy of the incident X-rays.

[0077] Scintillation detectors offer significantly higher detection efficiency for high-energy photons than proportional counters. They utilize a scintillating material that emits light when exposed to incident X-rays. Coupled to photomultiplier tubes, photodiodes, or charge-coupled devices (CCDs), the emitted light is detected, converting the optical signal into an electrical signal.

[0078] Solid-state detectors, more specifically semiconductor detectors, are the most widely used detectors in X-ray spectroscopy, particularly when energy resolution is critical. They include, in addition to silicon drift detectors (SDDs), lithium-silicon (Si(Li)) drift detectors, high-purity germanium (HPGe) detectors, and silicon positive-intrinsic-negative (Si-PIN) detectors. They convert incident X-rays into electrical signals by generating electron-hole pairs in the detector's semiconductor material. The number of electron-hole pairs generated is proportional to the energy of the incident X-rays. Semiconductor detectors, especially SDDs, offer excellent energy resolution, fast response times, and compact size.

[0079] Device 1 also includes focusing means for focusing the X-ray beam onto or into the object to be analyzed and for focusing the X-rays emitted by the object onto at least one of the detectors.

[0080] In the embodiment shown in the figure, the X-ray tube 2 and the confocal detector 4 are each equipped with a focusing polycapillary optic 5, 6. The polycapillary optic 5 of the X-ray tube 2 focuses the measurement beam onto or into the object to be analyzed. The polycapillary optic 6 of the confocal detector 4 focuses the X-rays emitted by the object into a measurement volume onto the sensitive surface of the detector.

[0081] For example, the X-ray tube can be equipped with a mini-lens approximately 100 mm long and with a focal length of approximately 5-6 mm. The confocal detector can be equipped with a half-mini-lens approximately 50 mm long and with a focal length of approximately 5-6 mm.

[0082] The two polycapillary optics 5 and 6 thus have a common action in creating the confocal measurement volume. The measurement volume is defined by the intersection of the foci of the two focusing optics.

[0083] The incident X-ray beam penetrates, for example, a few tens to hundreds of µm into the object to be analyzed. The field of view of the emitted radiation seen by the confocal detector is then limited by its focusing optics.

[0084] Polycapillary optics use arrays of small, hollow glass tubes (capillaries) that collect, guide, and focus X-rays through numerous total internal reflections. These capillaries are typically aligned parallel to each other, and X-rays incident on the inlet surface undergo multiple internal reflections, emerging from the outlet surface as a collimated or focused beam.

[0085] Alternatively, focusing means may also include one or more focusing lenses, slits or pinholes.

[0086] X-ray lenses may include collimators, Fresnel zonal plates, or compound refractive lenses.

[0087] The measurement volume, or micro-volume, allows the analysis of the deep layers of a multilayered object by performing depth-resolved scans. For example, the dimensions of the micro-volume can vary from 1 µm 3 (for high-energy X-rays and with polycapillary optics) at 60 x 60 x 60 µm 3 (for low-energy X-rays).

[0088] Lamontre schematically shows the orientation of the measurement beam as well as two detection axes relative to a plane of the object to be analyzed, according to an embodiment of the invention.

[0089] The measuring beam 10 is incident on the surface 11 of the object at an angle of 45°.

[0090] The measuring beam 10 can also be incident on the surface 11 of the object at another angle between 30° and 150°.

[0091] As shown in the figure, a first detection axis 13, called the two-dimensional detection axis, is oriented with respect to the surface 11 of the object at an angle of 45°. A second detection axis 12, called the confocal detection axis, is oriented with respect to the surface 11 of the object at an angle of 45°.

[0092] In the example, the angle between the measuring beam 11 and the detection axis 12 is 90°.

[0093] According to some embodiments, the confocal detection axis can be oriented with respect to the surface 11 of the object at an angle between 30° and 150°.

[0094] According to some embodiments, the two-dimensional detection axis can be oriented with respect to the surface 11 of the object at an angle between 1° and 179°.

[0095] The angle between the measurement beam 10 and the confocal detection axis can be between 30° and 90°.

[0096] In the case of confocal detection, to minimize the measurement volume, a 90° angle between the measurement beam axis and the confocal detection axis is sought, as illustrated in the figure. Therefore, when the measurement beam is incident, for example, at 30°, 45°, or 60° to the object surface, the detection axis is oriented at 60°, 45°, or 30° accordingly. Most often, the 45° angle is chosen.

[0097] An angle of incidence that is not perpendicular to the object's surface results in a slightly larger excitation area than a perpendicular angle of incidence. However, the resulting measurement volume is smaller.

[0098] All the components described (detectors, X-ray tube, focusing optics) are mounted together to form a measurement head.

[0099] The components of the measuring head can, for example, be housed in a casing or mounted on a support. The entire measuring head can be mounted on a stable mechanical structure, such as a tripod, to be positioned in front of an object to be analyzed. The measuring head can also be mounted on a rigid frame on legs, adjustable in height and tilt.

[0100] As an example, the measuring head can weigh approximately 10 to 12 kg.

[0101] By using ultralight detectors and / or a less powerful X-ray tube, the weight of the measuring head can be between 5 and 8 kg.

[0102] The device according to the invention also includes means for moving the measuring head along the three dimensions x, y, z of space.

[0103] The means of moving the measuring head may include, for example, a combination of translation platforms or plates.

[0104] These platforms are preferably equipped with linear motors, for example, one motor per spatial direction (x, y, z). Linear motors provide smooth and highly precise platform movements, with sub-micrometer steps. Encoders and controllers can be integrated.

[0105] The translation platforms can also be equipped with piezoelectric actuators.

[0106] To perform two-dimensional measurements on the surface of the object being analyzed, the measurement beam must be moved across the object along the x and y axes within the object's plane. To perform these 2D measurements, the device, and in particular the measurement head, is moved in front of the object being analyzed using the movement mechanisms.

[0107] To perform three-dimensional measurements on the surface of the object being analyzed and in its depth, not only must the measurement beam be moved across the object along the x and y axes in the object's plane, but the measurement volume must also be moved along the z-axis, which is substantially perpendicular to the object's surface. The measurement volume can thus penetrate a few micrometers or hundreds of micrometers below the object's surface.

[0108] To move the measurement volume along the z-axis, the measurement head is moved closer to or further from the object along the z-axis, substantially perpendicular to the surface of the object, using the means for moving the measurement head.

[0109] Advantageously, the device according to the invention includes means for adjusting the measurement volume to a desired measurement point.

[0110] The adjustment means allow the focus of the measurement volume to be adjusted by moving the focusing means in front of the confocal detector. The focus can be optimized, that is, the measurement volume is minimized, by using a standard.

[0111] For example, the means for adjusting the measurement volume may include a motor, in particular a micro-precision motor, for moving and adjusting the focusing optics in front of the confocal detector. Preferably, the micro-precision motor allows the focusing optics of the detector to be moved along the three axes x, y, z.

[0112] Preferably, the adjustment means are automatic adjustment means, to automatically adjust the focus of the measuring volume.

[0113] Thanks to the automatic adjustment of the confocal volume, confocal measurements are reproducible, especially when the device has been transported between measurements.

[0114] Typically, the energy of the X-ray beam incident on the object to be analyzed, i.e., the measurement beam, is between 1 and 40 keV. Preferably, the energy is between 1 and 20 keV.

[0115] The energy range of the device is notably limited by the nature and / or material of the focusing means used.

[0116] For example, due to factors such as internal reflections and the critical acceptance angle in capillaries, polycapillary optics filter out energies above a certain value. However, polycapillary optics can analyze energies below this value and allow for good distribution of light intensity across the detector surface.

[0117] The device according to the invention further includes a control and processing module, configured to control the means of movement, the acquisition of measurement signals, the processing of measurements and images.

[0118] This control module includes at least one computer, a central processing unit or computing unit, a microprocessor (preferably dedicated), and suitable software.

[0119] Using dedicated software, measurement parameters are controlled and modifiable, and the acquired data can be viewed and recorded with all their metadata.

[0120] According to one embodiment, the device according to the present invention includes security means to protect persons and works to be analyzed.

[0121] These safety measures may include, for example, clear and visible signage on or around the device, indicating the level of danger associated with X-rays, an emergency stop system, for example accessible on the software or with a push button, cameras to visualize the relative position of the measuring head, and / or a laser and / or ultrasonic distance control system.

[0122] Advantageously, the device according to the invention is designed to be worn or transported. In particular, the measuring head is portable. It can thus be positioned directly in front of the object to be analyzed, especially painted works that cannot be moved. The other components of the device according to the invention are also portable.

[0123] Furthermore, in the device according to the invention, the confocal measurement volume is offset outwards from a periphery of the device. This means that the measurement volume can be positioned as close as possible to the object being analyzed, without any risk of other elements of the measurement head coming into contact with the object's surface. It is also possible to move the measurement volume within the depth of the object being analyzed without damaging it, thus enabling non-invasive measurements.

[0124] The device according to the invention can be transported, and in particular carried, for in situ analysis missions, using a set of containers.

[0125] The containers can be, for example, suitcases, preferably padded ones.

[0126] For example, it is possible to pack the components of the measuring head (detectors, X-ray tube, focusing optics) in a suitcase or a backpack, and to pack the other components of the device (motors for the means of movement or alignment, translation tables, etc.) in a second suitcase or a second backpack.

[0127] As an example, the other components of the device may weigh, for example, approximately 15 kg to 20 kg.

[0128] Of course, the device according to the invention can also be implemented in a laboratory.

[0129] The device according to the invention, for example as described with reference to Figures 1 and 2, can be implemented in an X-ray fluorescence analysis process of an object to be analyzed.

[0130] The analysis method according to the invention includes a step of focusing an X-ray beam, referred to as the measurement beam, onto or into the object to be analyzed. The X-rays may, for example, be produced from an X-ray tube and are adapted to excite X-ray emission by fluorescence from the object to be analyzed.

[0131] The measurement beam is scanned, in the plane of the object, over the object to be analyzed at a plurality of measurement points.

[0132] At each measurement point, a detection step is performed to detect an X-ray fluorescence signal using a primary X-ray detector. A signal is detected at a plurality of measurement points. The signals are detected along a measurement axis known as two-dimensional detection.

[0133] This detection step is called two-dimensional detection.

[0134] According to one embodiment, the two-dimensional detection step can be carried out for a set of measurement points covering substantially the entire surface of the object to be analyzed.

[0135] Thus, an X-ray fluorescence spectrum is obtained for each measurement point on the object's surface. The relative intensity of the fluorescence peaks corresponding to chemical elements in the spectra varies according to their position on the surface. By plotting the surface area under the characteristic peaks of the elements as a function of their position on the object's surface, two-dimensional chemical profiles of the object are obtained. It is then possible to create a two-dimensional elemental map from the signals detected at each measurement point.

[0136] The method according to the invention includes a step of identifying at least one measurement point of interest from among the plurality of measurement points, based on the signals detected in the preceding step. By way of example, a measurement point of interest may be identified as a point where the X-ray fluorescence spectrum exhibits an X-ray fluorescence line corresponding to a chemical element characteristic of a pigment of interest, or a point exhibiting compositional differences compared to a neighboring point.

[0137] Once the measurement point(s) of interest have been identified, a confocal detection step is performed to detect an X-ray fluorescence signal at each point of interest using a second X-ray detector in confocal mode. Confocal detection is carried out within a measurement volume and along a confocal detection axis. As described previously, the measurement volume is created by the focusing means, specifically the focusing optics of the confocal detector and the X-ray tube.

[0138] The measuring head is positioned manually by an operator at the chosen measurement point(s).

[0139] According to one embodiment, the method according to the invention further includes a step of adjusting the focus of the measurement volume.

[0140] The adjustment step is preferably carried out automatically.

[0141] The adjustment step thus allows the focus of the measurement volume to be adjusted in order to perform the confocal detection step.

[0142] This adjustment step is carried out in particular before the start of confocal measurements.

[0143] Thus, confocal measurements are reproducible, especially when the device has been transported between measurements.

[0144] According to one embodiment, the method according to the invention may further include, for at least one of the identified measurement points of interest, the displacement of the confocal measurement volume in the direction of the depth of the object to be analyzed, and the repetition of the confocal detection step at several depths of the object to be analyzed.

[0145] For example, after selecting a location on the artwork to be analyzed during the two-dimensional detection stage, a depth-resolved scan can be performed by moving the artwork away from the measuring head along the z-axis. This movement can be achieved in increments of 10 µm, for instance. It is also possible to perform increments of 1 µm or 5 µm, for example. The resolution of the increments depends on the size of the focused measurement beam spot, and therefore on the focusing optics, as well as the stability of the device. Naturally, the smaller the measurement increment and the longer the chosen acquisition time per point, the longer the analysis time for the depth scan.

[0146] Thus, the micro-volume of measurement scans the element distributions throughout the entire artwork. An X-ray fluorescence spectrum is obtained for each depth position. The relative intensity of the element fluorescence lines, or peaks, in the spectra varies with depth. By plotting the area of ​​the characteristic peaks of the elements as a function of depth position, depth scan profiles are obtained.

[0147] The spatial resolution obtained is on the order of a micrometer.

[0148] When the confocal measurement volume displacement and confocal detection step reiterations are performed for a plurality of juxtaposed or adjacent measurement points of interest, a three-dimensional map from the detected signals can be created. This map is generated for a small area of ​​the object being analyzed due to the large number of signals to be detected and processed.

[0149] Mapping can also be performed first before identifying points of interest where C-XRF analysis could reveal the material's stratigraphy. These points of interest are chosen based on information directly obtained by MA-XRF, then located by the device and acquired in a supervised manner. If a layer is particularly interesting and requires detailed characterization, a long acquisition can be performed at a specific depth using a confocal profile.

[0150] Systematic recording of the measuring head's position allows for 3D spatialization of the information and the retrieval of details down to the micrometer scale. Furthermore, data visualization and processing tools can be integrated into the control software, enabling real-time analysis of the acquired signals. This ensures the relevance of the analyses performed as the process progresses.

[0151] The MA-XRF and CXRF coupling provides detailed knowledge of the object by exploiting the complementary information from the two acquisition modes and at the same time promotes the efficiency of the analysis campaign.

[0152] All the data is finally gathered and indexed in a single file, allowing for efficient data archiving and processing.

[0153] Of course, the analysis device according to the invention can be implemented to perform only confocal measurements or only two-dimensional measurements. In particular, confocal measurements can be carried out without having previously performed two-dimensional measurements.

[0154] For example, it is possible to perform quick, low-resolution scans to get an overview of the object being analyzed, and then select areas of interest for longer analysis at higher resolution. This applies regardless of the mode used, CXRF or MA-XRF.

[0155] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

Claims

A method for analyzing an object to be analyzed by X-ray fluorescence, implemented in situ using a portable X-ray fluorescence analysis device, the method comprising the following steps: focusing an X-ray beam, referred to as the measurement beam (10), by focusing means (5, 6), onto or into the object to be analyzed, the X-rays being adapted to excite X-ray emission by the object to be analyzed; two-dimensional scanning of the measurement beam (10) over the object to be analyzed at a plurality of measurement points on the object to be analyzed; two-dimensional detection, by means (3) of two-dimensional X-ray fluorescence spectrometry, of the X-rays emitted by the object along a first detection axis (13), referred to as the two-dimensional detection axis, at the plurality of measurement points; identification of at least one measurement point of interest among the plurality of measurement points; and confocal detection, by means (4) of confocal X-ray fluorescence spectrometry.X-rays emitted by the object at at least one measurement point of interest within a measurement volume and along a second detection axis (12), called the confocal detection axis, the focusing means (5, 6) being configured to generate the measurement volume, the measurement volume being offset outwards from a periphery of the device, and the device being adapted for transport. Method according to claim 1, characterized in that the two-dimensional detection step is carried out for a set of measurement points covering substantially the entire surface (11) of the object to be analyzed, the method further comprising a step of establishing a two-dimensional chemical map from detected signals. Method according to claim 1 or 2, characterized in that it further comprises the following steps, for each measurement point of interest: displacement of the confocal measurement volume in the direction of the depth of the object to be analyzed, and reiteration of the confocal detection step at several depths of the object to be analyzed. Method according to the preceding claim, wherein the steps of shifting the confocal measurement volume and of repeating the confocal detection step are carried out for a plurality of juxtaposed measurement points of interest. A method according to any one of the preceding claims, further comprising a step of adjusting, preferably automatically, the measurement volume. A portable X-ray fluorescence analysis device for an object to be analyzed, comprising: means (2) for generating X-rays configured to produce an X-ray beam, called the measurement beam (10), the X-rays being adapted to excite X-ray emission by the object to be analyzed; focusing means (5, 6) configured to focus the X-ray beam onto or into the object to be analyzed and to generate a confocal measurement volume; means for two-dimensional X-ray fluorescence spectrometry, comprising a first X-ray detector (3), called the two-dimensional detector, configured to detect the X-rays emitted by the object along a first detection axis (13), called the two-dimensional detection axis, at a plurality of measurement points; means for confocal X-ray fluorescence spectrometry, comprising a second X-ray detector (4), called the confocal detector.the confocal detector (4) being configured to detect the X-rays emitted by the object at at least one measurement point of interest among the plurality of measurement points in a measurement volume and along a second detection axis (12), referred to as the confocal detection axis, the measurement volume being offset outwards relative to a periphery of the device, and the device being adapted for transport, the device being configured to implement the analysis method according to any one of claims 1 to 5. Device according to the preceding claim, further comprising means for moving the confocal measurement volume in the direction of the depth of the object to be analyzed. Device according to claim 6 or 7, further comprising adjustment means, preferably automatic, configured to adjust the focus of the measuring volume. Device according to any one of its claims 6 to 8, characterized in that the X-ray detectors (3, 4) each comprise one of: a gas proportional counter, a scintillation detector, a solid state detector. Device according to any one of claims 6 to 9, characterized in that the X-ray detectors (3, 4) each comprise a silicon drift detector, SDD. Device according to any one of claims 6 to 10, characterized in that the measuring beam (10) is incident on the surface (11) of the object at an angle between 30° and 150°, preferably the measuring beam (10) being incident on the surface (11) of the object at an angle of 45° or 90°. Device according to any one of claims 6 to 11, characterized in that the confocal detection axis (12) is oriented with respect to the surface (11) of the object at an angle between 30° and 150°. Device according to any one of claims 6 to 12, characterized in that the angle between the measuring beam (10) and the confocal detection axis (12) is between 30° and 90°. Device according to any one of claims 6 to 13, characterized in that the two-dimensional detection axis (13) is oriented with respect to the surface (11) of the object at an angle between 1° and 179°. Device according to any one of claims 6 to 14, characterized in that the energy of the X-ray beam incident on the object to be analyzed is between 1 and 40 keV, preferably between 1 and 20 keV.

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