Neutron source with heavy water moderation and its application to thermal neutron imaging

Abstract

The invention particularly relates to a device for generating thermal neutrons for thermal neutron imaging, comprising: A neutron generator (2); Neutron moderator (4), A thermal neutron reflector (6) at the exit from the moderator and The present invention relates to a device comprising:

Description

[Technical field]

[0001] The present invention relates to a thermal neutron source, particularly for thermal neutron imaging applications. The present invention also relates to a thermal neutron imaging system and a thermal neutron imaging method. [Background technology]

[0002] Neutron imaging is known, but it involves the use of large facilities such as particle accelerators.

[0003] Portable neutron sources are known and comprise a neutron generator and a moderator 4, the moderator 4 typically being made of HDPE.

[0004] Existing portable neutron sources do not provide sufficient thermal neutron flux to perform thermal neutron imaging. Typically, neutron sources provide a low intensity (1 s -1 The neutron flux required by neutron imaging (number of neutrons produced per second (s -1 ) and 1 surface unit (s -1 cm -2 The number of neutrons produced during the reaction is not evaluated. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, for both intensity and resolution issues, high thermal neutron flux / s / cm 2 There is a need for new thermal neutron sources or generators for thermal neutron imaging that produce

[0006] According to another aspect, the present invention relates to imaging techniques for imaging composite materials, e.g., materials that include both carbon and ceramic materials, and more generally, materials that are not typically distinguished by known imaging techniques such as X-ray imaging.

[0007] There is also a need for new imaging processes that provide sufficient contrast between different materials, especially materials that have similar X-ray attenuation coefficients and cannot be distinguished by conventional imaging techniques, especially X-ray imaging. There is no device or method that can provide an image of an object or device that contains hydrogen or a hydrogen-containing compound, such as water, contained or embedded in an environment made of ceramic or metal, such as an automobile engine or an aircraft engine. There is no device or method for imaging lubricating oil inside a piece made of ceramic or metal, for example, to detect whether a seal or gasket is sufficiently tight or watertight and / or to detect a leak. Conventional investigation techniques of a part or object or a material that contains such a seal or gasket include opening or removing said part or object or piece. It would be very useful to have a device or method for imaging such a part or object or piece without the need to open or remove it. [Means for solving the problem]

[0008] The present invention relates first to a neutron generator for thermal neutron imaging, the neutron generator comprising: A neutron generator; A neutron moderator; A neutron reflector at the exit from the moderator Equipped with.

[0009] The generator essentially produces fast neutrons, the moderator slows them down and thus produces thermal neutrons, and the neutron reflector is for reflecting the neutrons towards the beam axis of the device such that said neutrons leave the moderator in a direction that is not aligned with said beam axis or that does not propagate towards the target or sample material being investigated.

[0010] Both the moderator and the reflector may be made of the same material and combined in the same piece.

[0011] In one embodiment, the moderator and / or the reflector may include or be made of HDPE.

[0012] In a more preferred embodiment, the moderator and / or the reflector may comprise or be made of heavy water.

[0013] The moderator may, for example, be comprised between 20mm or 25mm and 70mm or 80mm in thickness. Moderators made of heavy water are typically thinner than moderators made of HDPE, for example, heavy water moderators may be comprised between about 40mm or 30mm and 50mm in thickness, while HDPE moderators may be comprised between about 60mm or 50mm and 70mm in thickness.

[0014] Preferably, the reflector has a thickness of 2 cm to 10 cm.

[0015] The neutron generator according to the invention may further comprise at least one shield for shielding the area around the generator, or at least part of said area, from gamma radiation and / or X-rays.

[0016] The neutron generator according to the invention may comprise an X-ray filter located at the outlet from said neutron reflector, which may for example have a thickness of 2 mm to 10 mm and may be made of lead or bismuth.

[0017] Preferably, the neutron generator according to the present invention has an output neutron flux of thermal neutrons of 10 6 s -1 cm -2 ~10 9 s -1 cm -2 or 10 7 s -1 cm -2 ~10 8 s -1 cm -2 Such a neutron flux range allows for fairly short exposure times, especially if a detector with a microchannel plate is implemented.

[0018] The present invention also provides a thermal neutron imaging system, comprising: A neutron generator according to the invention as disclosed above and / or in the present application, and a detector of thermal neutrons, preferably comprising a microchannel plate (MCP), which is preferred as it is particularly efficient in this imaging application.

[0019] An imaging system according to the present invention may further comprise a camera for capturing an image formed by the detector.

[0020] The invention also relates to an imaging process for imaging a sample of material comprising implementing a thermal neutron imaging system according to the invention.

[0021] The invention also relates to an imaging process for imaging a sample of a material, the imaging process comprising: Positioning said sample between a neutron generator according to the invention as disclosed above and / or in the present application and a detector, for example of the type comprising a microchannel plate; For example, if the output neutron flux is 10 6 s -1 cm -2 ~10 9 s -1 cm -2 generating thermal neutrons, detecting a neutron flux of thermal neutrons traveling through the sample with a neutron detector; forming an image of the sample using imaging means based on signals provided by the detector; Includes.

[0022] In the imaging process according to the invention, the sample may comprise a mixture or combination of materials having different thermal neutron attenuation coefficients. For example, the sample may comprise a mixture or combination of steel and / or iron with at least one of boron, lithium, carbon, plastic, gold, cobalt, Teflon, aluminum. Other combinations of materials are disclosed in the present application.

[0023] The invention is particularly suitable for imaging different combinations of materials, in particular any piece made of ceramic or metal and a fluid, for example water or oil or lubricant or any liquid, in said piece. The fluid can be or contain hydrogen or hydrogen-containing substances (for example PTFE, or organic materials, or oil, or grease, or lubricant, etc.). The piece made of ceramic or metal can be used to investigate ions in said material, for example At least a portion of a tube, or an engine, such as an automobile engine or an aircraft engine, or any other part of a vehicle, for example an aircraft wing or aircraft fuselage, or an aerospace device or vehicle; At least a portion of the turbine; Alternatively, it may be an energy storage material, for example at least part of a battery. [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 shows a neutron generating device according to the present invention. [Diagram 2] FIG. 2 shows a neutron generating device according to the invention comprising a combined moderator and reflector according to an embodiment of the invention. [Diagram 3] FIG. 1 shows a curve giving the relative thermal neutron flux as a function of reflector thickness versus the neutron flux for HDPE moderator (no reflector). [Figure 4] FIG. 1 shows the relative thermal neutron flux obtained with different materials used for both the moderator and the reflector. [Diagram 5] FIG. 1 shows an imaging system comprising a neutron generator according to the invention, a detector and imaging means. [Figure 6A] FIG. 2 illustrates a CPU cooling device. [Figure 6B] FIG. 1 shows a thermal neutron image of a CPU cooling device. [Figure 7] FIG. 1 shows a thermal neutron image of the pen. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] An example of a thermal neutron source or generator 1 according to the invention for an imaging device is shown in FIG.

[0026] The thermal neutron source or generator 1 comprises a neutron generator 2 for generating neutrons, the majority of which are fast neutrons, which are then thermalized by a moderator 4 .

[0027] More precisely, the neutron generator 2 comprises an ion generator, e.g. a microwave generator, for producing ions from a heavy water source or a deuterium-tritium source. The generator further comprises an acceleration part for accelerating the ions towards a target 22, e.g. made of titanium or a titanium alloy. Such a generator produces a neutron beam from a nuclear fusion reaction, rather than from nuclear fission, which is the reaction that occurs in a nuclear reactor.

[0028] The present invention is for carrying out imaging, and the beam of thermal neutrons (having an energy below 1 eV, for example about 25 meV) generated by the neutron source 1 is preferably 10 6 s -1 cm -2 or 10 7 s -1 cm -2 ~10 8 s -1 cm -2 or 10 9 s -1 cm -2to collect as many thermal neutrons as possible. At the exit of the moderator a reflector 6 is located, by which thermal neutrons that are neither moving towards the detector nor along the direction D (beam axis) can be scattered or reflected, as the case may be, in the direction D towards the detector. Some high energy neutrons can also escape the target without being thermalized and can be thermalized by the reflector 6, but the essential effect of the reflector is on the thermal neutrons.

[0029] The moderator and reflector may be made of the same material, for example HDPE or heavy water.

[0030] The reflector 6 can for example have the shape of a ring and is provided with a central hole 61 aligned with the exit 41 from the moderator. The reflector 6 has an extension along the beam axis D of the neutrons towards the sample comprised between 2 cm or 3 cm and 10 cm or 15 cm depending on the material.

[0031] Neutrons are generated from the target 22 and then moderated by the moderator 4, thereby generating essentially thermal neutrons. The thermal neutrons escape from the moderator and enter the reflector 6. The thermal neutron flux travels in the direction of the beam axis D and therefore does not interact with the reflector, but the portion of the thermal neutrons that do not travel in direction D are reflected or scattered by the reflector 6 and then travel in direction D. As will be explained below in relation to FIG. 3, the increase in neutron flux due to the reflector 6 can be significant.

[0032] The generator may be housed in a shield 8, 8', for example made of high density polyethylene (HDPE) possibly containing a few percent, for example 5%, of boron. At least a part of the reflector 6 may be positioned in an opening 81 made in at least a part of the shield 8 and / or in an opening 83 made in a part of the moderator.

[0033] It is possible to add a further shield 10 to stop gamma radiation, which may be made of lead. The shield 10 includes holes 101 aligned with the holes 61 in the reflector.

[0034] A pinhole 12 may be positioned downstream from the reflector, for example between the reflector outlet and the further shield 10. The pinhole 12 is aligned with the hole 61 in the reflector. The diameter of the pinhole 12 is for example comprised between 1 cm and 5 cm. The pinhole is preferably made in one material extending over the front face 63 of the reflector (see for example the extension 12' of the pinhole in FIG. 1), so that no neutrons escape from said front face 63, and thus neutrons moving towards the sample material to be investigated either travel through the pinhole hole along the beam axis D or travel through the pinhole hole along a direction close to the beam axis D. The pinhole 12 can absorb thermal neutrons that are not directed towards the sample or neutrons that are directed towards the sample but do not escape from the reflector through the hole 61 outlet. The pinhole 12 may for example be made of boron.

[0035] To stop the X-rays a filter 14 may be used, which may be made of bismuth or lead. The filter 14 may be a few mm thick and may be located at the exit of the device in contact with a further shield 10.

[0036] In figure 1 the reflector 6 and the moderator 4 are different pieces. In another embodiment of a neutron source 1' according to the invention, shown in figure 2, the reflector 6 is combined with the moderator 4, both being made of the same material.

[0037] As already explained above, the extension of the reflector along the beam axis D of the neutrons towards the sample is a few cm, comprised between 2 cm or 3 cm and 10 cm or 15 cm.

[0038] Figure 3 shows the relative thermal neutron flux (s ) obtained by simulation and measured at the detector entrance according to the reflector thickness for various configurations (moderator and reflector both made of HDPE, moderator and reflector both made of heavy water, moderator made of HDPE and reflector made of heavy water). -1 cm -2 The curves giving the neutron flux (units) are shown. The neutron flux is relative to the neutron flux obtained with HDPE moderator and without reflector. These curves show that there is an optimum range for the reflector length l (measured along the beam axis of the generator) where the reflector 6 contributes significantly to the neutron flux and is comprised between 3 cm or 5 cm and 7 cm or 10 cm. Above 10 cm or 15 cm, the efficiency of the reflector decreases. The different curves have a similar general shape, but the combination of moderator and reflector, both made of heavy water, usually has a shorter optimum range than the combination of HDPE moderator and HDPE reflector (optimum thickness range is 2 cm to 8 cm). As can be seen from these curves, the reflector improves the output neutron flux by at least 30% to 70%, while the heavy water reflector brings a higher improvement, for example 40% to 80%. The combinations of moderator and reflector, both made of heavy water, are particularly efficient.

[0039] The present invention is particularly well suited for non-destructive imaging of composite parts, including, for example, combinations of metals with boron or lithium or plastics. For example, stainless steel and iron (Fe) have thermal neutron attenuation coefficients of about 1 cm. -1 and the damping coefficient is For boron, it is about 99 cm -1 and For plastic (polyethylene, PE) 6 to 7 cm -1 and About 6.3cm for gold -1 and For cobalt, about 3.9 cm -1 and For copper (Cu), it is about 1 cm -1 It is.

[0040] The thermal neutron attenuation coefficients of these and other materials are given in table I below.

[0041] [Table 1]

[0042] Carbon fiber has a thermal neutron attenuation coefficient of about 0.5 cm -1 Teflon, SiC, Al 2 O 3 The coefficient is about 0.4 cm -1 and hydrogen or hydrogen-containing substances embedded in any of these materials can be seen on thermal neutron images.

[0043] Aluminum (Al) has a very low thermal neutron attenuation coefficient of about 0.1 cm -1 , which is much smaller than the thermal neutron attenuation coefficient of steel or iron or Cu or carbon fiber, or plastic, or boron, or Co, or Au, or Li, allowing thermal neutron imaging to contrast Al with any of these materials to a large extent.

[0044] The above table shows that materials containing at least one of Li, B, Cd and Gd may be particularly interesting materials for thermal neutron imaging. Li and Cd are found, for example, in batteries and are therefore relevant for research into sustainable technologies. Gd can be dissolved and used as a contrast agent to highlight defects in ceramic materials, and in another application, Gd can be mixed or mixed into an adhesive to highlight the contrast between the adhesive and other materials. The assembly quality of two parts, for example two metal parts, bonded with said adhesive can be inspected by neutron imaging according to the invention, especially when Gd is added to the adhesive.

[0045] As already explained, the present invention is particularly adapted to imaging or visualising materials or compounds such as fluids or liquids, such as oil or lubricants or water, in ceramic or metal parts, for example in engines or valves, or parts of an aircraft or vehicle (car, truck) or machine, or in airbags, or plastics (PE) or organic materials, or materials containing hydrogen or hydrogen-containing substances, such as rubber.

[0046] The present invention also relates to a method for producing a method for manufacturing a semiconductor device comprising the steps of: Residues after the production of parts, for example by casting, such as turbine blades, for example organic or ceramic materials, For example, it is adapted to image or visualize the presence or location of one or more rubber rings within a piece or component, such as an airbag or a metal or ceramic piece.

[0047] More generally, the invention also relates to a method for producing a neutron attenuation coefficient of 0.5 cm -1 Less than or equal to 0.2cm -1 In materials with a thermal neutron attenuation coefficient of less than 1 cm, such as aluminum or semiconductor materials, especially silicon (Si), -1 The imaging or visualizing device is adapted to image or visualize samples that contain at least one material having a higher Cr content than 100%, for example water or PE or Co or Au, or B, or Ni, or Fe.

[0048] Figure 4 shows the thermal neutron flux obtained by simulation for the different materials used for the moderator 4 (heavy water (curve I), polyethylene (curve II) and light water (curve III)) as a function of the moderator thickness (measured along the D axis). It is clear that the smaller the moderator thickness (2-6 cm, the optimal range is 5 cm-7 cm for HDPE and 6 cm-8 cm for light water), the higher the efficiency of heavy water.

[0049] The detector for the imaging device according to the invention is most preferably a microchannel plate (MCP) detector. MCP detectors make it possible to image samples with both good resolution and reasonable exposure times (for example 1 hour to 5 minutes depending on the thermal neutron flux). MCPs are disclosed for example in FR 2925218. MCPs have in particular a very high detection efficiency and are thereby very well adapted to the lower neutron flux compared to nuclear reactors, which is generated by the generator according to the invention.

[0050] FIG. 5 shows a neutron generator according to the present invention, and a microchannel plate (MCP) detector 20 which may be combined with a camera 30 and possibly a lens 40 .

[0051] A sample 50 is represented diagrammatically between the neutron generator and the detector 20. A beam 52 of thermal neutrons is generated by a neutron source and propagates along a beam axis D to the sample 50.

[0052] The distance L between the pinhole 12 or the exit of the thermal neutron source 1, 1' and the entrance face of the detector can be, for example, 0.5 m to 2 m or 3 m. The resolution of the system is limited by the ratio of this distance L over the diameter D of the pinhole, for example comprised between 20 and 500, for example comprised between 100 and 200. For the same distance L, a smaller diameter D improves the resolution, but the neutron source is neutron flux limited compared to a nuclear reactor, and therefore a smaller diameter D limits the neutron flux. When a nuclear reactor is implemented to perform thermal neutron imaging, the ratio L / D can be around 1000, since a very high intensity or neutron flux is generated by the reactor.

[0053] The incident neutron flux to the detector is proportional to (1 / L), and the longer the distance L, the smaller the incident neutron flux. Therefore, in order to have sufficient neutron flux on the incident surface of the detector, the distance L should not be too long.

[0054] As mentioned above, a ratio L / D comprised between 20 and 200 represents a compromise that favours the invention.

[0055] FIG. 6A shows a CPU cooling block 70, and FIG. 6B shows a thermal neutron image of the same block with water 72 and air bubbles 74 visible in the figure (thermal neutron flux is about 10 7 s -1 cm -2 The cooling block is made of aluminum and is particularly transparent to neutrons, as opposed to the internal cooling fluid, which blocks or stops the neutrons.

[0056] Figure 7 shows a thermal neutron image of a pen made of a metal that is highly transparent to neutrons and allows the presence of ink inside the pen to be visualized. This shows the feasibility of imaging fluids or liquids such as water or lubricating oils inside metal pieces, for example tubes or ducts in an engine.

[0057] The present invention particularly relates to Imaging of inserts, e.g. made of plastic or ceramic, in metal parts; or detection of gaps or inclusions in materials; or detection of water penetration in materials, such as metal pieces, or soil, or porous materials; Or for example, detecting corrosion of metal pieces, especially aluminum pieces, within aircraft parts, such as aircraft wings or aircraft fuselages, or parts of aerospace devices or vehicles; Or detection of ceramic residues in channels made in metal pieces, for example in turbine blades, or in aluminum pieces, for example in aircraft parts, for example aircraft wings or aircraft fuselages, or parts of aerospace devices or vehicles; or testing the porosity or internal structure of parts or pieces made by additive manufacturing; or locating ions or ion transport within an energy storage material, e.g., within a battery or within or around an electrode; or to identify the movement or location of fluids in porous materials, e.g. soil or stone (archaeology); or identification of two-phase liquid in a tube, e.g., a thermal tube; or carbon or CO in the material 2 Identification of isolation or bioisolation; is well adapted to.

[0058] When imaging gaps or cracks in any material, or ceramic residues or materials, or porosity, a contrast agent, for example Gd dissolved in a liquid, can be used to highlight the differences between different parts of a piece or sample. [Explanation of symbols]

[0059] 1, 1' Thermal neutron source or generator 2. Neutron Generator 4 Moderator 6 reflector 8, 8' Shield 10. Shield 12 Pinhole 12' extension 14 Filters 20 Microchannel plate (MCP) detector, neutron detector 22 Target 30 Camera, imaging means 40 Lenses 41 Exit 50 Samples 52 Beam 61 center hole 63 Front 70 CPU Cooling Block 72 water 74 Bubbles 81 Aperture 83 Aperture 101 holes

Claims

1. 1. A device for generating thermal neutrons for thermal neutron imaging, comprising: A neutron generator (2) for generating fast neutrons; A neutron moderator (4) for generating thermal neutrons from fast neutrons; a thermal neutron reflector (6) at the exit from the moderator; A device comprising:

2. The neutron generator of claim 1 , wherein the moderator comprises heavy water.

3. The neutron generator according to claim 1 or 2, wherein the moderator has a thickness of between 20 mm and 80 mm.

4. The neutron generator of claim 1 , wherein the reflector comprises heavy water.

5. The neutron generator of claim 4, wherein the reflector has a thickness of between 2 cm and 10 cm.

6. The neutron generator of claim 1 , wherein the moderator and the reflector are both made of the same material.

7. 7. The neutron generator of claim 6, wherein the moderator and the reflector are both made of or include HDPE.

8. 10. The neutron generator of claim 1, wherein said moderator and said reflector are both made of or include heavy water.

9. A neutron generator according to any one of claims 1 to 8, further comprising at least one shield (8, 8', 10).

10. 10. The neutron generator of any one of claims 1 to 9, further comprising an X-ray filter (14) at the outlet from the moderator (4).

11. The neutron generator of claim 10, wherein the filter (14) is between 2 mm and 10 mm thick measured along the axis of propagation (D) of the thermal neutrons and is made of lead or bismuth.

12. A neutron generator according to any one of claims 1 to 11, further comprising a pinhole (12) outlet having a diameter between 0.5 cm and 7 cm.

13. 10 ６ s －１ cm －２ ~10 ９ s －１ cm －２ 13. The neutron generator according to claim 1, having an output thermal neutron flux of

14. 10 ７ s －１ cm －２ ~10 ８ s －１ cm －２ 13. The neutron generator according to claim 1, having an output thermal neutron flux of

15. A neutron generator according to any one of claims 1 to 14; and a detector (20) for thermal neutrons.

16. The imaging system of claim 15 , wherein the detector comprises a microchannel plate (MCP).

17. 17. The imaging system of claim 15 or 16, further comprising a camera (30) for capturing an image formed by the detector.

18. 1. An imaging process for imaging a sample (50) of material, comprising: Positioning the sample (50) between a neutron generator according to any one of claims 1 to 14 and a detector (20); 10 ６ s －１ cm －２ ~10 ９ s －１ cm －２ generating a beam of thermal neutrons having a neutron flux of detecting a flux of thermal neutrons traveling through the sample with the neutron detector (20); forming an image of said sample using imaging means (30); an imaging process comprising:

19. The imaging process of claim 18, wherein the sample (50) comprises a mixture or combination of materials having different thermal neutron attenuation coefficients.

20. 20. The imaging process of claim 19, wherein the sample comprises a mixture or combination of steel and / or iron with at least one of boron, lithium, carbon, plastic, gold, cobalt, Teflon, aluminum.

21. 20. The imaging process of claim 18 or 19, wherein the sample comprises at least a part of an engine containing a fluid such as water or a lubricating oil or hydrogen or a hydrogen-containing substance made of or embedded or contained in a piece comprising a ceramic material and / or a metal, such as steel or iron.

22. 22. The imaging process of claim 21 , wherein the piece made of or comprising a ceramic material and / or metal is at least part of an engine, for example an aircraft engine or an automobile engine, or an aircraft wing or aircraft fuselage, or at least part of an aerospace device or vehicle.

23. 20. The imaging process of claim 18 or 19, wherein the sample comprises at least one of Li and Cd in a battery.

24. The sample containing at least one of Li, B, Cd, and Gd in the material has a thermal neutron attenuation coefficient of 50 cm －１ Less than or equal to 30 cm －１ Less than or equal to 10 cm －１ 20. The imaging process of claim 18 or 19, wherein the imaging

25. The sample has a thermal neutron attenuation coefficient of 0.5 cm －１ Less than or equal to 0.2 cm －１ In materials with thermal neutron attenuation coefficients of less than 1 cm, for example aluminum or semiconductor materials, －１ 20. The imaging process of claim 18 or 19, comprising at least a material having a higher

26. 26. The imaging process according to any one of claims 18 to 25, wherein the ratio of the distance L between the exit of the neutron source and the entrance of the detector to the diameter D of the neutron source exit is comprised between 10 and 500.

27. 26. The imaging process according to any one of claims 18 to 25, wherein the ratio of the distance L between the exit of the neutron source and the entrance of the detector to the diameter D of the neutron source exit is comprised between 20 and 200.

28. 28. The imaging process of any one of claims 18 to 27, wherein the sample contains at least one gap or crack or ceramic residue or material or porosity, and the imaging comprises injecting a contrast agent, for example Gd dissolved in a liquid, into the material of the sample.

Images