Reentrant cones for moderator chambers of neutron imaging systems.

Abstract

A neutron imaging system including a central neutron source configured to generate source neutrons, the central neutron source comprising a beam target, a moderator chamber surrounding at least a portion of the beam target, the moderator chamber housing the moderator, and a reentrant cone extending into the moderator chamber. The reentrant cone includes an entrance surface facing the beam target. The entrance surface surrounds and isolates the cone chamber from the moderator. Further, the entrance surface is shaped such that source neutrons generated at the beam target impinge on the entrance surface, and the neutron flux varies by 10% or less along the entrance surface.

Description

[Technical field]

[0001] The present disclosure relates generally to the field of neutron imaging systems (e.g., radiography and tomography systems) and methods that provide high quality, high throughput 2D and 3D rapid or thermal neutron images. Such systems and methods are useful for commercial-scale imaging of industrial components. [Background technology]

[0002] Neutron radiography and tomography are proven techniques for non-destructive testing and quality control of components manufactured in aerospace, energy, automotive, defense, and other sectors. Similar to x-rays, when neutrons pass through an object, they provide information about the internal structure of that object. Neutrons pass easily through many high density materials and can provide detailed information about interior materials, including many low density materials. This property is important for several components that require non-destructive evaluation, including jet engine turbine blades, munitions, aircraft and spacecraft components, and composite materials. Historically, commercial neutron radiography used nuclear reactors as neutron sources. Nuclear reactors are expensive, difficult to calibrate, and are becoming increasingly more difficult to access, making this powerful inspection technique impractical for many commercial applications.

[0003] Therefore, a need exists for improved neutron imaging methods and systems. Summary of the Invention [Means for solving the problem]

[0004] According to a first aspect of the present disclosure, a neutron imaging system includes a central neutron source configured to generate source neutrons, the central neutron source including a beam target, a moderator chamber surrounding at least a portion of the beam target, the moderator chamber housing the moderator, and a reentrant cone extending into the moderator chamber. The reentrant cone includes an entrance surface facing the beam target. The entrance surface surrounds and isolates the cone chamber from the moderator. Furthermore, the entrance surface is shaped such that source neutrons generated at the beam target impinge on the entrance surface, and the neutron flux varies by 10% or less along the entrance surface.

[0005] The second side includes the neutron imaging system of the first side, and the entrance surface of the reentrant cone has a spherical concave curvature.

[0006] The third side includes a neutron imaging system on the first side or the second side, and the distance from the entrance surface of the reentrant cone to the center point of the beam target varies by less than 10% along the entrance surface.

[0007] The fourth side includes a neutron imaging system on the first side or the third side, and the entrance surface of the reentrant cone is flat.

[0008] A fifth aspect includes the neutron imaging system of any of the previous aspects, further comprising a neutron collimator extending outwardly from the moderator chamber, the neutron collimator coupled to the reentrant cone such that a neutron path extends from an entrance surface of the reentrant cone into the neutron collimator.

[0009] The sixth side includes the neutron imaging system of the fifth side, where the inner surface of the neutron collimator is lined with a neutron absorbing material configured to absorb a portion of the source neutrons such that the neutron collimator produces a thermal neutron imaging beam line.

[0010] A seventh aspect includes the neutron imaging system of any of the previous aspects, further comprising a neutron imaging detector, the neutron imaging detector comprising a detector medium and an imaging plane.

[0011] An eighth aspect includes the neutron imaging system of the seventh aspect, wherein the detector medium comprises a film, a scintillating conversion mechanism, or a digital neutron imaging detector.

[0012] A ninth aspect includes the neutron imaging system of any of the previous aspects, wherein the central neutron source comprises a particle accelerator for generating neutrons from the beam target.

[0013] A tenth aspect includes the neutron imaging system of any of the preceding aspects, wherein the reentrant cone is one of a plurality of reentrant cones extending into the moderator chamber in a radial array around the beam target, and an entrance surface of each reentrant cone of the plurality of reentrant cones faces the beam target.

[0014] An eleventh aspect includes the neutron imaging system of any of the previous aspects, wherein the moderator comprises heavy water, and the cone chamber of the reentrant cone is fluidly isolated from the moderator chamber.

[0015] According to a twelfth aspect of the present disclosure, a method includes generating source neutrons at a beam target of a central neutron source of a neutron imaging system, the neutron imaging system further comprising a moderator chamber surrounding at least a portion of the beam target, the moderator chamber housing a moderator; and receiving the source neutrons using a reentrant cone extending into the moderator chamber, the reentrant cone comprising a cone chamber and an entrance surface facing the beam target, the cone chamber being surrounded by the entrance surface and isolating the cone chamber from the moderator, the entrance surface of the reentrant cone being received using the reentrant cone, the source neutrons being configured to impinge on the entrance surface, and the neutron flux varying by less than 10% along the entrance surface.

[0016] A thirteenth aspect includes the method of the twelfth aspect, wherein the neutron imaging system further comprises a neutron imaging detector and a neutron collimator, the neutron imaging detector comprising a detector medium and an imaging plane, the neutron collimator extending outwardly from the moderator chamber, and the neutron collimator coupled to the reentrant cone such that a neutron path extends from an entrance surface of the reentrant cone, into the neutron collimator and onto the neutron imaging detector.

[0017] A fourteenth aspect includes the method of the thirteenth aspect, further including generating a thermal neutron imaging beam line comprising source neutrons within the neutron collimator, and collecting a neutron image of an object positioned at an imaging plane of a neutron imaging detector from a portion of the thermal neutron imaging beam line that passes through the object.

[0018] A fifteenth aspect includes the method of the fourteenth aspect, wherein the object is an airplane part, an airplane engine, a munitions article, a product utilizing energetic materials, a fuse, a rocket, a chemically activated device, a spacecraft part, a wind turbine component, or an aerospace part.

[0019] A sixteenth aspect includes the method of the fourteenth or fifteenth aspect, wherein an inner surface of the neutron collimator is lined with a neutron absorbing material configured to absorb a portion of the source neutrons such that the neutron collimator produces a thermal neutron imaging beam line.

[0020] A seventeenth aspect includes the method of any of the twelfth to sixteenth aspects, wherein the central neutron source comprises a particle accelerator for generating neutrons from the beam target.

[0021] According to an eighteenth aspect of the present disclosure, a neutron imaging system includes a central neutron source configured to generate source neutrons, the central neutron source comprising a particle accelerator and a beam target, the beam target configured to generate and propagate source neutrons in a beam direction along the beam plane in response to collision with a beam accelerated by the particle accelerator, a moderator chamber surrounding at least a portion of the beam target, the moderator chamber housing a moderator, and a reentrant cone extending into the moderator chamber from a chamber opening in a chamber wall of the moderator chamber, the reentrant cone having an entrance surface facing the beam target, the entrance surface surrounding the cone chamber and isolating the cone chamber from the moderator, the chamber opening being offset from the beam plane, and the entrance surface being non-parallel to the chamber wall.

[0022] The nineteenth side includes the neutron imaging system of the eighteenth side, the entrance surface having a first surface region at a location along the entrance surface closest to the beam plane and a second surface region at a location along the entrance surface furthest from the beam plane, the first surface region being closer to the chamber wall than the second surface region.

[0023] The twelfth side includes a neutron imaging system of the eighteenth side or the nineteenth side, wherein the entrance surface is shaped such that source neutrons generated at the beam target impinge on the entrance surface, the neutron flux has a 50% or greater reduction in variability along the entrance surface compared to the variability of neutron flux along a reference region located on a reference plane that intersects the front edge of the entrance surface and is parallel to the chamber wall, and the reference region is sized to match the chamber opening.

[0024] These and additional features provided by the embodiments described herein will be more fully understood in light of the following detailed description taken in conjunction with the drawings. [Brief description of the drawings]

[0025] The embodiments described in the drawings are illustrative and exemplary in nature and are not intended to limit the subject matter defined by the claims. The following detailed description of the illustrative embodiments can be understood when read in conjunction with the following drawings, in which like structure is indicated with like reference numerals and in which:

[0026] [Figure 1] FIG. 1 diagrammatically depicts a neutron imaging system with a reentrant cone according to one or more embodiments shown and described herein.

[0027] [Diagram 2] FIG. 2 diagrammatically depicts a neutron imaging system with another reentrant cone according to one or more embodiments shown and described herein.

[0028] [Diagram 3] FIG. 3 diagrammatically depicts a neutron imaging system with yet another reentrant cone according to one or more embodiments shown and described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Detailed Description Generally, with reference to the figures, embodiments of the present disclosure are directed to a neutron imaging system configured to generate high-resolution, high-throughput, fast or thermal neutron images and provide viable commercial-scale thermal and fast neutron radiography. Neutron radiography and tomography are proven techniques for non-destructive testing of components manufactured in aerospace, energy, automotive, defense, and other sectors. Like x-rays, when neutrons pass through an object, they provide information about the internal structure of the object. However, x-rays interact weakly with low atomic number elements (e.g., hydrogen) and strongly with high atomic number elements (e.g., many metals). As a result, their ability to provide information about low-density materials is poor, especially when in the presence of higher density materials. Neutrons do not suffer from this limitation. Neutrons pass easily through high-density metals and provide detailed information about internal materials, including low-density materials. Neutrons can therefore be used for non-destructive evaluation of many components that are not amenable to X-ray or other non-destructive evaluation modalities, such as engine turbine blades, munitions, spacecraft components, and composite materials such as certain aerospace components and wind turbine blades.

[0030] Currently, neutron radiography and tomography are underutilized due to the lack of accessible high flux neutron sources with suitable spectral characteristics. The disclosed neutron imaging system includes an accelerator-based neutron source that can be used instead of a nuclear reactor or a large nuclear spallation reaction source. One challenge of accelerator-based neutron sources is that they provide source neutrons that are several orders of magnitude lower than a nuclear reactor. Thus, when using an accelerator-based neutron source, the neutron detection medium is positioned closer to the neutron source than when using a nuclear reactor source. In fact, in a nuclear reactor or a large nuclear spallation reaction source, the detection medium is typically several meters away from the neutron source, and it may be possible to provide space therein to install filters to mitigate undesirable types of radiation, mainly stray gamma and fast neutrons, but this would partially blur the image upon acquisition. It is difficult to install such filters in an accelerator-based neutron source.

[0031] Embodiments of the present disclosure are directed to a reentrant cone positioned within a moderator chamber of a neutron imaging system, which operates to maximize the reception of desired thermal neutron radiation while mitigating this undesired radiation. The reentrant cone of the present disclosure extends into the moderator chamber (e.g., a heavy water tank) and facilitates sampling of a higher thermal neutron population closer to the target while maintaining a large volume of heavy water within the moderator chamber. Increasing the volume of heavy water increases the moderation of radiation that does not enter the reentrant cone (i.e., is not used as part of the imaging process). The reentrant cone includes an entrance surface that is shaped to maximize the neutron flux uniformity of source neutrons generated by the neutron source. For example, the reentrant cone can be shaped to match a nominal constant flux surface within the heavy water, increasing the neutron uniformity entering the reentrant cone and then impinging on the neutron detector, leading to higher quality and higher resolution neutron images. An embodiment of a neutron imaging system will now be described and, wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0032] 1-3, a neutron imaging system 100 is diagrammatically depicted. The neutron imaging system 100 includes a central neutron source 120, which comprises a particle accelerator 121 and a beam target 122. The central neutron source 120 is configured to generate source neutrons at the beam target 122. For example, the particle accelerator 121 accelerates a beam, such as an ion beam, in a beam direction 10 along a beam plane 15. The source neutrons generated by the central neutron source 120 extend radially outward (in the neutron propagation direction 11) from the beam target 122 in a ring-shaped pattern, as shown by the neutron flux lines 12, 12', 12'' in FIG. 1-3. Using the coordinate system of FIG. 1-3, the beam plane 15 is an XY plane parallel to the beam direction 10. It is contemplated that the embodiments described herein may utilize several different central neutron sources 120. For example, the central neutron source 120 may generate source neutrons by a deuterium-deuterium (DD) fusion reaction, a deuterium-tritium (DT) fusion reaction, or any other source neutrons using a particle accelerator, such as particle accelerator 121, to generate the reaction.

[0033] 1-3, the neutron imaging system 100 further comprises a moderator chamber 110 that houses a moderator 105, such as heavy water or graphite, a reentrant cone 130 that extends into the moderator chamber 110, a neutron collimator 140 that is coupled to the reentrant cone 130 at a chamber opening 114 in a chamber wall 112 of the moderator chamber 110, and a neutron imaging detector 150. The reentrant cone 130 and the neutron collimator 140 provide a particle path for some of the source neutrons exiting the moderator chamber 110 to reach the neutron imaging detector 150 and image the object.

[0034] The moderator chamber 110 includes one or more chamber walls, such as chamber wall 112, which includes a chamber opening 114 from which the reentrant cone 130 extends into the moderator chamber 110. In operation, the moderator 105 attenuates the source neutrons such that the neutron flux is reduced as the source neutrons travel away from the beam target 122 in the neutron propagation direction 11. For example, the neutron flux of the source neutrons in neutron flux line 12 exceeds the neutron flux in neutron flux line 12', which exceeds the neutron flux in neutron flux line 12''. The moderator 105 surrounds at least a portion of the beam target 122. The moderator 105 reduces the amount of gamma radiation that reaches the neutron imaging detector 150 and reduces the amount of radiation that reaches the one or more chamber walls.

[0035] 1-3, the reentrant cone 130 extends into the moderator chamber 110 from a chamber opening 114 in the chamber wall 112. The reentrant cone 130 provides a region that is isolated from the moderator 105 (e.g., fluidically isolated from the heavy water) such that the neutron flux of source neutrons traveling within the reentrant cone 130 decays at a reduced rate compared to source neutrons propagating through the moderator 105. The reentrant cone 130 comprises an inlet surface 132, 132' that surrounds and isolates the cone chamber 138 from the moderator chamber 110. For example, when the moderator 105 comprises heavy water, the cone chamber 138 is fluidically isolated from the moderator chamber 110.

[0036] The cone chamber 138 may comprise a chamber having a hollow chamber, a solid chamber (e.g., filled with a moderating material), or portions that are hollow and filled. For example, the hollowed portion of the cone chamber 138 facilitates the transfer of thermal neutrons towards the neutron collimator 140, and the filled portion sustains the moderation of the radiation generated by the central neutron source 120. The hollow portion of the reentrant cone 130 may store air or other gas and allow for a relatively uniform optical path length for thermal neutrons to enter the neutron collimator 140. The filled portion of the reentrant cone 130 may be made of materials such as, for example, water, high density polyethylene (HDPE), and graphite. Further, one or more reentrant cones 130 enable a larger moderator chamber 110 to provide increased radiation shielding without a corresponding reduction of the neutron beam at the neutron imaging detector 150. The reentrant cone 130 may have a tapered shape that is cylindrical or rectangular. As depicted in FIGS. 1-3, the taper is such that the cross-sectional shape of the reentrant cone 130 increases as the reentrant cone 130 approaches the beam target 122.

[0037] Still referring to FIGS. 1-3, the chamber opening 114 of the chamber wall 112 is offset from the beam plane 15 (e.g., in the -Z direction of the coordinate system shown in FIGS. 1-3). For example, the chamber opening 114 comprises a center point 115 that is offset from the beam plane 15 by a distance D OFF offset, offsetting the reentrant cone 130 from the beam plane 15. Without intending to be limited by theory, the thermal neutron population of the source neutrons is more significantly uniform throughout the moderator chamber compared to the fast neutron and gamma population of the source neutrons. Offsetting the reentrant cone 130 from the beam plane 15 (e.g., in the -Z direction as shown in FIGS. 1-3) results in a reentrant cone 130 that aims at the region of approximately the highest thermal flux but not at the regions of the highest fast neutron and gamma fluxes.

[0038] Thus, offsetting the chamber opening 114 and reentrant cone 130 from the beam plane 15 reduces the gamma flux (e.g., 2.2 MeV hydrogen-trapping gamma) and other high energy radiation, such as neutrons, relative to thermal neutrons, that enters the neutron collimator 140 and reaches the neutron imaging detector 150, improving the resulting image quality. Furthermore, the offset of the beam plane 15 from the chamber opening 114 and reentrant cone 130 is large enough to obstruct a direct line of sight from the beam target 122 to the chamber opening 114, and therefore from the beam target 122 to the imaging plane of the neutron imaging detector 150.

[0039] 2 and 3, the entrance surface 132' of the reentrant cones 130, which faces the beam target 122, is shaped to increase the uniformity of the neutron flux entering each reentrant cone 130, as compared to the uniformity of the neutron flux entering the entrance surface 132 of FIG. 1, which is parallel to the chamber wall 112 of the moderator chamber 110, for example. In fact, the entrance surface 132' may be shaped to correspond to the neutron flux line 12, 12', 12''. The shape of the entrance surface 132' may be configured to match the neutron flux distribution of the source neutrons generated at the beam target 122. Increasing the uniformity of the neutron flux incidence across the reentrant cones 130 increases the uniformity of the neutron flux across the field of view of an image captured using the neutron imaging detector 150, leading to a more consistent exposure across the image and resulting in a higher quality neutron image. The inlet surface 132' may be curved as depicted in FIG. 2, flat as depicted in FIG. 3, or variable. With a curved shape, the inlet surface 132' may have a concave or convex curvature. As an example, the inlet surface 132 comprises a spherical concave curvature. Furthermore, embodiments in which the flux lines assume a variable shape and the inlet surface 132 comprises a correspondingly variable shape are also contemplated. This variable shape may be determined by Monte Carlo simulation.

[0040] In operation, the reentrant cone 130 increases the neutron flux received by the neutron imaging detector 150 compared to simply having a hole (e.g., the chamber opening 114) in the chamber wall 112 because the entrance surfaces 132, 132' are closer to the beam target 122 than the chamber opening 114 and have a surface area larger than the area of ​​the chamber opening 114. The smaller size of the chamber opening 114 will increase the neutron flux uniformity compared to the entrance surface 132 of FIG. 1, but the smaller size of the chamber opening 114 will reduce the total neutron flux reaching the neutron imaging detector 150. In contrast, the reentrant cone 130 having the entrance surface 132' of Figures 2 and 3 increases the neutron flux incident on the film plane of the neutron imaging detector 150 due to the surface area and positioning of the entrance surface 132' while maintaining sufficient uniformity across the captured image due to the increased neutron flux uniformity promoted by the shape and orientation of the entrance surface 132'.

[0041] 2 and 3, the entrance surface 132' comprises a first surface region 134 at a location along the entrance surface 132' closest to the beam plane 15, and a second surface region 136 at a location along the entrance surface 132' furthest from the beam plane 15. The first surface region 134 is closer to the chamber wall 112 than the second surface region 136. This orients the entrance surface 132' towards the beam target 122. Still referring to FIGS. 2 and 3, the entrance surface 132' is non-parallel to the chamber wall 112 (from which the reentrant cone 130 extends into the moderator chamber 110).

[0042] 2 and 3 further depict a reference plane 131 that intersects a front edge of entrance surface 132′ (the front edge corresponding to second surface region 136) and is parallel to chamber wall 112. Entrance surface 132′ is shaped such that source neutrons generated at the beam target impinge on entrance surface 132′, and the neutron flux has a 25% or greater reduction in variability along entrance surface 132′ compared to the variability of neutron flux along a reference region located on reference plane 131, the reference region being a portion of 132′ that is sized to match chamber opening 114. For example, the reduction in variability may be 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, 70% or more, 80% or more, 90% or more, 95% or more, 99% or more, or a value within a range having any two of these values ​​as endpoints.

[0043] In some embodiments, the distance from the entrance surface 132' of the reentrant cone 130 to the beam target center point 125 of the beam target 122 varies along the entrance surface 132 by 20% or less, e.g., 18% or less, 15% or less, 12% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, 0.5% or less, 0.1% or less, or the like. In some embodiments, the entrance surface 132' is shaped such that source neutrons generated at the beam target 122 impinge on the entrance surface 132, and the neutron flux varies along the entrance surface 132 by a value of 20% or less, e.g., 18% or less, 15% or less, 12% or less, 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, 1.5% or less, 1% or less, 0.5% or less, 0.1% or less, or within a range having any two of these values ​​as endpoints.

[0044] 1-3, the reentrant cone 130 provides a path for source neutrons to exit the moderator chamber 110 and enter the neutron collimator 140. The neutron collimator 140 provides a particle path for some of the source neutrons exiting the moderator chamber 110 to reach the neutron imaging detector 150. The neutron collimator 140 extends outwardly from the moderator chamber 110. The neutron collimator 140 is coupled to the reentrant cone 130 and the chamber opening 114. Thus, the neutron path extends from the entrance surface 132, 132' of the reentrant cone 130 into the neutron collimator 140. An inner surface 145 of the neutron collimator 140 is lined with a neutron absorbing material configured to absorb a portion of the source neutrons and generate a thermal neutron imaging beam line 20, for example, from the thermal neutrons of the source neutrons. The thermal neutron imaging beam rays 20 impinge on a neutron imaging detector 150 to image the object. In some embodiments, the neutron absorbing material positioned along the inner surface 145 of the one or more neutron collimators 140 is selected from the group consisting of cadmium, boron and boron-containing compounds, lithium and lithium-containing compounds, gadolinium, and composites containing any of these materials.

[0045] Still referring to FIGS. 1-3 , the neutron imaging detector 150 comprises a detector medium and an imaging plane. The detector medium may comprise a film (e.g., radiographic film), a scintillating conversion mechanism, a storage phosphor, a direct conversion screen, an amorphous silicon flat panel, a microchannel plate, a digital detector array, and / or an indirect conversion screen. In some embodiments, the neutron imaging detector 150 is a non-planar neutron detector that conforms to the contours of the object to be imaged and minimizes blurring effects from the thermal neutron imaging beam line 20 that is non-parallel to the object. In such cases, the non-planar detector may comprise a film or digital medium, such as a scintillating material, coupled to light transmission, conversion, multiplication, and / or detector elements, such as fiber optic guides and photomultiplier tubes. Although not depicted, in some embodiments, the neutron imaging system 100 may further comprise neutron focusing and / or reflecting elements, which are configured to increase the neutron flux at the imaging plane of the neutron imaging detector 150 and increase image resolution.

[0046] Imaging operations using the neutron imaging system 100 include generating source neutrons at the beam target 122 and receiving the source neutrons with the reentrant cone 130 such that the source neutrons enter the neutron collimator 140, generating a thermal neutron imaging beam line 20 within the neutron collimator 140, and collecting a neutron image of an object positioned at an imaging plane of the neutron imaging detector 150 from a portion of the thermal neutron imaging beam line 20 that passes through the object, thereby generating a neutron image. In some embodiments, the object is an airplane part (e.g., a wing), an airplane engine, a munitions item, a product that utilizes energetic materials, a fuse, a rocket, a chemically activated device, a spacecraft part, a wind turbine component, (e.g., a composite part), or an aerospace part.

[0047] The neutron imaging techniques described herein may be combined with other non-destructive evaluation techniques, including x-ray radiography and tomography, to create a fused image data set that provides more information than a stand-alone neutron or x-ray image. Other non-destructive evaluation techniques that provide 2D and 3D information about components that can be fused with a neutron image include ultrasound, magnetic resonance, magnetic penetrant inspection, thermography, x-ray fluorescence, and small angle neutron scattering, among others. In such cases, image registration software may be used to correlate the data from two or more non-destructive evaluation techniques and create a fused image data set.

[0048] 1-3, a single reentrant cone 130 and a single neutron collimator 140 are depicted for ease of understanding of the concepts described herein, however, it should be understood that embodiments comprising multiple reentrant cones extending into the moderator chamber, for example in a radial array around the beam target 122, are also contemplated. In such an embodiment, each of the multiple reentrant cones may comprise an entrance surface 132' as described herein that is oriented to the beam target, and each may be coupled to a corresponding neutron collimator. Furthermore, the multiple reentrant cones may extend into the moderator chamber 110 in a radial array along a common plane, for example a common XY plane that passes through a center point 115 of the chamber opening 114, that is offset from the beam plane 15, for example, offset along the Z-axis as depicted in FIG. 1-3.

[0049] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications may be made without departing from the spirit and scope of the claimed subject matter. Moreover, although various aspects of the claimed subject matter have been described herein, such aspects need not be utilized in combination. It is therefore intended that the appended claims cover all such changes and modifications that are within the scope of the claimed subject matter.

[0050] As used herein, the terms "approximately," "about," "substantially," and similar terms are intended to have broad meanings in keeping with common and accepted usage by those of ordinary skill in the art to which the subject matter of the present disclosure pertains. It should be understood by those of ordinary skill in the art reviewing this disclosure that these terms are intended to enable the description of certain features described and claimed without limiting the scope of these features to the precise numerical values ​​or idealized geometric forms provided. Thus, these terms should be interpreted to indicate that insubstantial or insignificant modifications or alterations of the subject matter described and claimed are considered to be within the scope of the present disclosure as recited in the appended claims.

[0051] The term "coupled" and variations thereof, as used herein, means the joining of two members to one another, directly or indirectly. Such a joining may be fixed (e.g., permanent or fixed) or movable (e.g., removable or releasable). Such a joining may be achieved by the two members being directly joined to one another, by the two members being joined to one another using separate intervening members that are joined to one another and optional additional intermediate members, or by the two members being joined to one another using an intervening member that is integrally formed as a single unitary body with one of the two members. When "coupled" or variations thereof are modified by an additional term (e.g., directly coupled), the general definition of "coupled" provided above is modified by the plain language meaning of the additional term (e.g., "directly coupled" means the joining of two members without any separate intervening members), resulting in a definition narrower than the general definition of "coupled" provided above. Such coupling may be mechanical, electrical, or fluid.

[0052] References herein to the location of elements (e.g., "top," "bottom," "upper," "lower") are used merely to describe the orientation of the various elements in the figures. It should be noted that the orientation of the various elements may differ according to other exemplary embodiments, and such variations are intended to be encompassed by the present disclosure.

[0053] Although the figures and description may illustrate a specific order of method steps, the order of such steps may differ from that depicted and described unless otherwise specified above. Also, two or more steps may be performed in parallel or partially in parallel unless otherwise specified above. Such variations may depend, for example, on software and hardware system choices and designer choices. All such variations are within the scope of this disclosure. Similarly, software implementations of the described methods may be performed using standard programming techniques involving rule-based logic and other logic to perform the various connection, processing, comparison, and decision steps.

Claims

1. A neutron imaging system, A central neutron source configured to generate source neutrons, wherein the central neutron source comprises a beam target, A moderator chamber surrounding at least a portion of the beam target, wherein the moderator chamber comprises a moderator chamber housing a moderator, A re-entering cone extending within the moderator chamber and Equipped with, The re-entry cone has an entrance surface facing the beam target, The inlet surface surrounds the cone chamber and isolates the cone chamber from the moderator. A neutron imaging system wherein the entrance surface is shaped so that source neutrons generated in the beam target collide with the entrance surface, and the neutron flux fluctuates by 10% or less along the entrance surface.

2. The neutron imaging system according to claim 1, wherein the inlet surface of the re-entrant cone has a spherical concave curvature.

3. The neutron imaging system according to claim 1, wherein the distance from the entrance surface of the re-entry cone to the center point of the beam target varies by less than 10% along the entrance surface.

4. The neutron imaging system according to claim 1, further comprising a neutron collimator extending outward from the moderator chamber, wherein the neutron collimator is coupled to the reentrant cone such that the neutron path extends from the inlet surface of the reentrant cone into the neutron collimator.

5. The neutron imaging system according to claim 4, wherein the inner surface of the neutron collimator is lined with a neutron-absorbing material configured to absorb a portion of the source neutrons so that the neutron collimator generates a thermal neutron imaging beam.

6. The neutron imaging system according to claim 1, further comprising a neutron imaging detector, wherein the neutron imaging detector comprises a detector medium and an imaging plane.

7. The neutron imaging system according to claim 1, wherein the central neutron source comprises a particle accelerator for generating neutrons from the beam target.

8. The neutron imaging system according to claim 1, wherein the reentrant cone is one of a plurality of reentrant cones extending into the moderator chamber in a radial array around the beam target, and the entrance surface of each of the plurality of reentrant cones faces the beam target.

9. The neutron imaging system according to claim 1, wherein the moderator comprises heavy water, and the cone chamber of the re-entrant cone is fluidly isolated from the moderator chamber.

10. It is a method, The method involves generating source neutrons in the beam target of the central neutron source of a neutron imaging system, wherein the neutron imaging system further comprises a moderator chamber surrounding at least a portion of the beam target, and the moderator chamber houses a moderator. The method involves receiving source neutrons using a reentrant cone extending within the moderator chamber, wherein the reentrant cone comprises a cone chamber and an entrance surface facing the beam target. Includes, The cone chamber is surrounded by the inlet surface, isolating the cone chamber from the moderator. The method wherein the inlet surface of the reentrant cone is configured such that source neutrons received using the reentrant cone collide with the inlet surface, and the neutron flux fluctuates by less than 10% along the inlet surface.

11. The neutron imaging system further comprises a neutron imaging detector and a neutron collimator. The neutron imaging detector comprises a detector medium and an imaging plane. The neutron collimator extends outward from the moderator chamber, The method according to claim 10, wherein the neutron collimator is coupled to the reentrant cone such that the neutron path extends from the inlet surface of the reentrant cone into the neutron collimator and onto the neutron imaging detector.

12. Within the neutron collimator, a thermal neutron imaging beam containing source neutrons is generated, The neutron image of an object positioned on the imaging plane of the neutron imaging detector is collected from a portion of the thermal neutron imaging beam passing through the object. The method according to claim 11, further comprising:

13. A neutron imaging system, A central neutron source configured to generate source neutrons, wherein the central neutron source comprises a particle accelerator and a beam target, the beam target being configured to generate source neutrons in response to collisions with a beam accelerated by the particle accelerator and propagating in the beam direction along the beam plane, A moderator chamber surrounding at least a portion of the beam target, wherein the moderator chamber houses a moderator and Within the moderator chamber, a re-entrant cone extending from the chamber opening of the chamber wall of the moderator chamber and Equipped with, The re-entry cone has an entrance surface facing the beam target, The inlet surface surrounds the cone chamber and isolates the cone chamber from the moderator. The chamber opening is offset from the beam plane, A neutron imaging system in which the inlet surface is non-parallel to the chamber wall.

14. The inlet surface comprises a first surface region along the inlet surface closest to the beam plane and a second surface region along the inlet surface furthest from the beam plane. The neutron imaging system according to claim 13, wherein the first surface region is closer to the chamber wall than the second surface region.

15. The neutron imaging system according to claim 13, wherein the inlet surface is shaped so that source neutrons generated in the beam target collide with the inlet surface, the neutron flux has a reduction of 50% or more in variability along the inlet surface compared to the variability along a reference region located on a reference plane intersecting the front edge of the inlet surface and parallel to the chamber wall, and the reference region is sized to match the chamber opening.

Images