Dual scintillator system for neutron and electromagnetic imaging.

Abstract

1. An imaging system including: an imaging detector, an object region, and a scintillator stack positioned along an imaging path between the imaging detector and the object region, the scintillator stack having a first scintillator and a second scintillator, the first scintillator being positioned along the imaging path upstream of the second scintillator and configured to convert first ionizing radiation into first photons having a first wavelength, and the second scintillator being configured to convert second ionizing radiation into second photons having a second wavelength, the second scintillator having a higher transmittance at the second wavelength than the first scintillator.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Application No. 63 / 412,128, filed September 30, 2022, which is incorporated herein by reference in its entirety.

[0002] (Technical field) The present disclosure relates generally to the field of neutron, X-ray, and gamma-ray imaging systems (eg, radiography and tomography systems) and methods. [Background technology]

[0003] (background) Neutron radiography and tomography are proven techniques for nondestructive testing and quality control of components manufactured in aerospace, energy, automotive, defense, and other sectors. Like X-rays and gamma rays, neutrons pass through an object, providing information about its internal structure. 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 requiring nondestructive evaluation, including jet engine turbine blades, munitions, aircraft and spacecraft components, and composite materials. Neutrons, X-rays, and gamma rays can also be used to determine the material properties of objects located in cargo containers and other visually obstructed locations.

[0004] Cargo containers (e.g., multi-transport modality containers used to transport goods via ships, trains, or trucks, such as intermodal containers, also known as shipping containers, sea cans, or conex boxes) can present security risks because a variety of unwanted materials can be placed within such containers, and significant challenges exist at ports or other border entry points associated with determining the exact contents of incoming containers. One of the major challenges relates to the large number of such containers that arrive daily at busy ports and the need to scan them quickly so as not to unduly interrupt the flow of goods at such ports. While the detection of special nuclear materials (SNM) (i.e., fissile materials) merits particular attention, other unwanted materials may include explosives, drugs, and other contraband. Traditionally, commercial neutron radiography has used nuclear reactors as neutron sources. Nuclear reactors are expensive, difficult to modulate, and increasingly difficult to access, making this powerful inspection technique impractical for many commercial applications.

[0005] Therefore, a need exists for improved x-ray, gamma-ray, and neutron imaging methods and systems for both imaging and material identification purposes. Summary of the Invention [Means for solving the problem]

[0006] (summary) According to a first aspect of the present disclosure, an imaging system includes an imaging detector, an object region, and a scintillator stack positioned along an imaging path between the imaging detector and the object region, the scintillator stack having a first scintillator and a second scintillator, the first scintillator being positioned along the imaging path upstream of the second scintillator and configured to convert first ionizing radiation into first photons having a first wavelength, and the second scintillator being configured to convert second ionizing radiation into second photons having a second wavelength, the second scintillator having a higher transmittance at the second wavelength than the first scintillator.

[0007] A second aspect includes the imaging system of the first aspect, wherein the first ionizing radiation comprises X-rays, gamma rays, or a combination of X-rays and gamma rays, and the second ionizing radiation comprises neutrons.

[0008] A third aspect includes the imaging system of the second aspect, wherein the neutrons include thermal neutrons or fast neutrons.

[0009] A fourth aspect includes the imaging system of the first aspect, wherein the first ionizing radiation includes neutrons and the second ionizing radiation includes X-rays, gamma rays, or a combination of X-rays and gamma rays.

[0010] A fifth aspect includes the imaging system of the fourth aspect, wherein the neutrons include thermal neutrons or fast neutrons.

[0011] A sixth aspect includes the imaging system of any of the preceding aspects, wherein the second scintillator has a transmittance at the second wavelength that is at least 10% greater than the transmittance of the first scintillator at the second wavelength.

[0012] A seventh aspect includes the imaging system of any of the preceding aspects, wherein the first scintillator has a transmittance of 25% or less at the second wavelength and the second scintillator has a transmittance of 75% or more at the second wavelength.

[0013] An eighth aspect includes the imaging system of any of the preceding aspects, wherein the first scintillator has a transmittance of 15% or less at the second wavelength, and the second scintillator has a transmittance of 90% or more at the second wavelength.

[0014] A ninth aspect includes the imaging system of any of the preceding aspects, wherein the first wavelength and the second wavelength differ by at least 10 nm.

[0015] A tenth aspect includes the imaging system of any of the preceding aspects, wherein the first wavelength is in the range of 520 nm to 565 nm, and the second wavelength is in the range of 435 nm to 500 nm.

[0016] An eleventh aspect includes the imaging system of any of the preceding aspects, further including a radiation source configured to direct both the first ionizing radiation and the second ionizing radiation into the imaging passageway.

[0017] A twelfth aspect includes the imaging system of any of the preceding aspects, further including a first radiation source configured to direct first ionizing radiation into the imaging passageway, and a second radiation source configured to direct second ionizing radiation into the imaging passageway.

[0018] A thirteenth aspect includes the imaging system of any of the preceding aspects, wherein the first scintillator is in direct contact with the second scintillator.

[0019] A fourteenth aspect includes the imaging system of any of the first to thirteenth aspects, wherein the first scintillator includes a gadolinium oxide scintillator doped with terbium or europium.

[0020] A fifteenth aspect includes the imaging system of any of the first to thirteenth aspects, wherein the first scintillator includes a zinc sulfide scintillator doped with copper.

[0021] A sixteenth aspect includes the imaging system of any of the first to thirteenth aspects, wherein the first scintillator includes a cesium iodide scintillator doped with thallium.

[0022] A seventeenth aspect includes the imaging system of any of the first to thirteenth aspects, wherein the second scintillator comprises a polymer.

[0023] An eighteenth aspect includes the imaging system of the seventeenth aspect, wherein the second scintillator comprises polyvinyl toluene.

[0024] A nineteenth aspect includes the imaging system of any of the preceding aspects, wherein the second scintillator is thicker than the first scintillator.

[0025] A twentieth aspect includes the imaging system of the nineteenth aspect, wherein the thickness ratio of the second scintillator to the first scintillator is 20:1 or greater.

[0026] A twenty-first aspect includes the imaging system of any of the preceding aspects, further including an optical filter positioned along the imaging path between the scintillator stack and the imaging detector.

[0027] A twenty-second aspect includes the imaging system of the twenty-first aspect, wherein the optical filter is configured to selectively block the first photons or the second photons.

[0028] A twenty-third aspect includes the imaging system of the twenty-first aspect, wherein the imaging detector is a first imaging detector, and the imaging system further includes a second imaging detector, and wherein the optical filter comprises a dichroic mirror, and the dichroic mirror is configured to allow transmission of first photons through the dichroic mirror toward the first imaging detector and to reflect second photons toward the second imaging detector.

[0029] A twenty-fourth aspect includes the imaging system of any of the preceding aspects, wherein the imaging detector comprises a color camera having two or more sets of detector sensor pixels, each set of detector sensor pixels being sensitive to a different wavelength range.

[0030] A twenty-fifth aspect includes the imaging system of the twenty-fourth aspect, wherein a first set of detector sensor pixels are sensitive to a first wavelength range, the first wavelength being within the first wavelength range, and a second set of detector sensor pixels are sensitive to a second wavelength range, the second wavelength being within the second wavelength range.

[0031] A twenty-sixth aspect includes the imaging system of any of the preceding aspects, further including a lens positioned along the imaging path between the scintillator stack and the imaging detector.

[0032] According to a twenty-seventh aspect of the present disclosure, a method includes directing first ionizing radiation through an object region onto a scintillator stack including a first scintillator and a second scintillator. The first scintillator is positioned upstream of the second scintillator, and a target object is positioned within the object region. The method further includes converting the first ionizing radiation in the first scintillator into first photons having a first wavelength, the first photons propagating from the first scintillator through the second scintillator toward an imaging detector, directing second ionizing radiation through the object region onto the scintillator stack, and converting the second ionizing radiation in the second scintillator into second photons having a second wavelength, the second photons propagating from the second scintillator toward the imaging detector, the second scintillator having a higher transmittance at the second wavelength than the first scintillator.

[0033] A twenty-eighth aspect includes the method of the twenty-seventh aspect, wherein the first ionizing radiation comprises X-rays, gamma rays, or a combination of X-rays and gamma rays, and the second ionizing radiation comprises neutrons.

[0034] A twenty-ninth aspect includes the method of the twenty-eighth aspect, wherein the neutrons include thermal neutrons or fast neutrons.

[0035] A thirtieth aspect includes the method of the twenty-seventh aspect, wherein the first ionizing radiation comprises neutrons and the second ionizing radiation comprises X-rays, gamma rays, or a combination of X-rays and gamma rays.

[0036] A thirty-first aspect includes the method of the thirty-first aspect, wherein the neutrons are thermal neutrons or fast neutrons.

[0037] A thirty-second aspect includes the method of any of aspects twenty-seven to thirty-first, wherein the second scintillator has a transmittance at the second wavelength that is at least 10% greater than the transmittance of the first scintillator at the second wavelength.

[0038] A thirty-third aspect includes a method of any of aspects twenty-seven to thirty-second, further including generating, using an imaging detector, one or more images of the target object based on the first photons and the second photons.

[0039] A thirty-fourth aspect includes the method of the thirty-third aspect, wherein the one or more images of the target object comprise a first image based on the first photons and a second image based on the second photons.

[0040] A thirty-fifth aspect includes the method of any of the twenty-seventh to thirty-fourth aspects, wherein the first wavelength and the second wavelength differ by at least 10 nm.

[0041] A thirty-sixth aspect includes a method of any of aspects twenty-seventh through thirty-fifth, further including determining a first attenuation coefficient of the target object based on the first photons and a second attenuation coefficient of the target object based on the second photons.

[0042] A thirty-seventh aspect includes the method of the thirty-sixth aspect, further including comparing the first attenuation coefficient and the second attenuation coefficient to determine one or more material properties of the target object.

[0043] A thirty-eighth aspect includes the method of the thirty-seventh aspect, wherein the target object comprises a cargo item positioned within the cargo container, and the method further includes determining a classification of the cargo item based on one or more material properties.

[0044] A thirty-ninth aspect includes the method of the thirty-eighth aspect, wherein classification of the cargo items provides input for a quality control process, an illegal substance identification process, or a hazardous material identification process.

[0045] A fortieth aspect includes the method of any of the thirty-seventh to thirty-ninth aspects, wherein at least one of the one or more material properties is an approximate effective atomic number of the target object.

[0046] A forty-first aspect includes the method of any of the twenty-seventh through fortieth aspects, wherein the first scintillator includes a doped gadolinium oxide scintillator and the second scintillator comprises a polymer.

[0047] A forty-second aspect includes the method of the forty-first aspect, wherein the doped gadolinium oxide scintillator is doped with terbium or europium, and the second scintillator comprises polyvinyltoluene.

[0048] 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 explanation of the drawings]

[0049] The embodiments set forth 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 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:

[0050] [Figure 1] FIG. 1 diagrammatically depicts one exemplary embodiment of an imaging system comprising a radiation source, an object region, a scintillator stack, and an imaging detector according to one or more embodiments shown and described herein.

[0051] [Figure 2] FIG. 2 diagrammatically depicts another exemplary embodiment of an imaging system comprising a radiation source, an object region, a scintillator stack, and an imaging detector according to one or more embodiments shown and described herein. DETAILED DESCRIPTION OF THE INVENTION

[0052] (Detailed explanation) Generally, with reference to the figures, embodiments of the present disclosure are directed to an imaging system configured to generate images of a target object and / or determine its material properties using multiple types of ionizing radiation. For example, the imaging system may use a single radiation source and scintillator stack to generate both X-ray and neutron images of the target object, providing an agile and versatile imaging and testing system, particularly compared to current non-destructive imaging systems. Like X-rays, neutrons provide information about the internal structure of an object as they pass through it. However, X-rays interact weakly with low atomic number elements (e.g., hydrogen) and strongly with high atomic number elements (e.g., many metals). Neutrons do not suffer from this limitation and can easily pass through high-density metals, providing detailed information about internal materials, including low-density materials. Therefore, combining both X-ray and neutron radiography can provide a more complete image of the target object and provide robust material information about the target object. For example, the imaging systems described herein may be used for non-destructive testing of manufactured components for quality control or safety (detection of unwanted / foreign objects / materials within an object) in aerospace, energy, automotive, defense, and other sectors, as well as inspection of cargo for contraband and inspection of packages for illicit / hazardous substances, and any other context where non-destructive identification or imaging is desired, especially with respect to objects that cannot be visually inspected. Whenever embodiments of an imaging system are described and considered possible herein, the same reference numbers will be used throughout the drawings to refer to the same or similar parts.

[0053] 1 and 2, an imaging system 100 is diagrammatically depicted. The imaging system 100 comprises a radiation source 120, an imaging detector 160, and an imaging path 102 extending from the radiation source 120 to the imaging detector 160. The imaging path 102 is a path along which ionizing radiation and / or photons propagate. The imaging system 100 further comprises a scintillator stack 130 comprising a first scintillator 131 and a second scintillator 132. The scintillator stack 130 is positioned along the imaging path 102 between the radiation source 120 and the imaging detector 160. The radiation source 120 is configured to output ionizing radiation, such as x-rays, gamma rays, and neutrons, which may include thermal neutrons, epithermal neutrons, fast neutrons, or a combination thereof.

[0054] In operation, ionizing radiation travels from radiation source 120 through object region 110, which is located along imaging path 102. A target object 112 may be positioned within object region 110. Target object 112 is an object of interest for imaging and / or analysis, such as material property analysis. At least a portion of the ionizing radiation traverses object region 110 (e.g., the portion not blocked, reflected, absorbed, or otherwise obstructed by target object 112) and reaches scintillator stack 130. As described in more detail below, scintillator stack 130 converts the ionizing radiation into photons, which then propagate from scintillator stack 130 to imaging detector 160. Imaging detector 160 captures the photons output by scintillator stack 130 to generate one or more images of target object 112 and / or determine one or more material properties of target object 112.

[0055] 1 and 2 , the first scintillator 131 is positioned upstream of the second scintillator 132 along the imaging path 102. As used herein, “upstream” and “downstream” refer to the relative positions of two locations or components along the imaging path 102 with respect to the radiation source 120. For example, a first component is upstream from a second component if the first component is closer to the imaging path 102 than the second component along the path traversed by the ionizing radiation and / or photons. Because the first scintillator 131 is positioned upstream of the second scintillator 132 along the imaging path 102, ionizing radiation output by the radiation source 120 that reaches the second scintillator 132 first passes through the first scintillator 131. The first scintillator 131 comprises an input surface 133 and an output surface 135. Input surface 133 faces upstream along imaging path 102 and receives ionizing radiation. Output surface 135 faces downstream along imaging path 102 and outputs first photons. Second scintillator 132 comprises input surface 134 and output surface 136. Input surface 134 of second scintillator 132 faces output surface 135 of first scintillator 131 and receives ionizing radiation. Output surface 136 faces downstream along imaging path 102 and outputs second photons. In some embodiments, as depicted in FIGS. 1 and 2 , first scintillator 131 may be in direct contact with second scintillator 132. This direct contact may increase the clarity of the resulting image generated by imaging detector 160. Alternatively, the first scintillator 131 may be spaced apart from the second scintillator 132, and in some embodiments, one or more intervening optical components, such as a lens, collimator, or the like, may be positioned between the first scintillator 131 and the second scintillator 132.

[0056] The first scintillator 131 is configured to convert the first ionizing radiation into first photons having a first wavelength, and the second scintillator 132 is configured to convert the second ionizing radiation into second photons having a second wavelength. The first ionizing radiation and the second ionizing radiation comprise types of radiation having different energy levels. In some embodiments, the first ionizing radiation (e.g., the radiation converted into the first photons in the first scintillator 131) comprises X-rays, gamma rays, or a combination of X-rays and gamma rays, and the second ionizing radiation (e.g., the radiation converted into the second photons in the second scintillator 132) comprises neutrons, such as fast neutrons, epithermal neutrons, or thermal neutrons. In other embodiments, the first ionizing radiation (e.g., the radiation converted to the first photons in the first scintillator 131) includes neutrons, e.g., fast neutrons, epithermal neutrons, or thermal neutrons, and the second ionizing radiation (e.g., the radiation converted to the second photons in the second scintillator 132) includes X-rays, gamma rays, or a combination of X-rays and gamma rays. Thus, the scintillator stack 130 facilitates radiography using a combination of different types of ionizing radiation, such as X-rays and neutron radiation, to provide a more complete image of the target object 112 and provide robust material information about the target object 112. Also, without intending to be limited by theory, it should be understood that the first scintillator 131 and the second scintillator 132 both have a sensitivity to both the first ionizing radiation and the second ionizing radiation, but each is more sensitive to one of the first and second ionizing radiations than the other.

[0057] The first scintillator 131 is more opaque to photons comprising the second wavelength than the second scintillator 132. In other words, the second scintillator 132 comprises a higher transmittance at the second wavelength than the first scintillator 131. As used herein, "transmittance percentage" refers to the percentage of the initial intensity of a particular wavelength or wavelength range (e.g., the portion of light that is not attenuated, reflected, absorbed, or otherwise blocked by the material) that passes through a material. Thus, because the first scintillator 131 is positioned upstream of the second scintillator 132, the first scintillator 131 does not block the second photons generated in the second scintillator 132, allowing both the first and second photons to reach the imaging detector 160, facilitating both X-ray / gamma-ray and neutron imaging of the target object 112.

[0058] In practice, the second scintillator 132 includes a transmittance at the second wavelength that is at least 5% greater than the transmittance of the first scintillator, for example, at least 10% greater, at least 15% greater, at least 20% greater, at least 25% greater, at least 30% greater, at least 35% greater, at least 40% greater, at least 45% greater, at least 50% greater, at least 55% greater, at least 60% greater, at least 65% greater, at least 70% greater, at least 75% greater, at least 85% greater, at least 90% greater, or a transmittance difference within a range having any two of these values ​​as endpoints. For example, in some embodiments, the first scintillator 131 includes a transmittance at the second wavelength of 25% or less, e.g., 15% or less, and the second scintillator includes a transmittance at the second wavelength of 75% or more, e.g., 90% or more. While it is desirable for the second scintillator 132 to have a high transmittance at the second wavelength to minimize attenuation of the second photons, the methods described herein are still possible with a low transmittance at the second wavelength. In such situations, post-processing steps of the resulting image and other material information determined using the imaging detector 160 may be performed to clarify, enhance, or otherwise adjust the results. Also, in some embodiments, scintillation of the first ionizing radiation into the first photons occurs within first scintillator 131 closer to output surface 135 than to input surface 133 of first scintillator 131, minimizing attenuation of the first photons within first scintillator 131, which may also have some opacity to the first wavelength. For example, in some embodiments, first scintillator 131 includes a support portion connected to a film portion, input surface 133 is a surface of the support portion, and output surface 135 is a surface of the film portion, and scintillation of the first ionizing radiation into the first photons occurs in the film portion.

[0059] In some embodiments, the first scintillator 131 comprises a doped gadolinium oxide scintillator, which may be doped with terbium, europium, praseodymium, calcium, cerium, strontium, or fluorine. In some embodiments, the first scintillator 131 comprises a doped zinc sulfide scintillator, which may be doped with copper. Other dopants that may be used in doped zinc sulfide scintillators include antimony, magnesium, and manganese. In some embodiments, the first scintillator 131 comprises a doped cesium iodide scintillator, which may be doped with thallium or sodium. In some embodiments, the second scintillator 132 comprises a polymer such as polyvinyl toluene (PVT) or a liquid scintillator (which may be sealed within a container and form the surface of the scintillator). Without intending to be limited by theory, doped zinc sulfide scintillators have a relatively low thermal neutron cross section and are therefore substantially unreactive with thermal neutrons. In embodiments in which the second scintillator 132 generates thermal neutrons along with the second photons, as occurs when using a polymer scintillator, any of these thermal neutrons that travel upstream back to and reach the doped zinc sulfide scintillator (e.g., the first scintillator 131) will minimally react with the doped zinc sulfide scintillator, minimizing unwanted noise in the imaging system 100, particularly compared to scintillators with higher thermal neutron cross sections.

[0060] 1 and 2, second scintillator 132 can be thicker than first scintillator 131. For example, the thickness ratio of the second scintillator to the first scintillator can be 5:1 or more, 10:1 or more, 15:1 or more, 20:1 or more, 25:1 or more, 30:1 or more, 35:1 or more, 40:1 or more, 50:1 or more, 60:1 or more, 75:1 or more, or a range having any two of these values ​​as endpoints. In other embodiments, first scintillator 131 is thicker than second scintillator 132. For example, the thickness ratio of the first scintillator to the second scintillator can be 5:1 or greater, 10:1 or greater, 15:1 or greater, 20:1 or greater, 25:1 or greater, 30:1 or greater, 35:1 or greater, 40:1 or greater, 50:1 or greater, 60:1 or greater, 75:1 or greater, or a range having any two of these values ​​as endpoints. When the first scintillator 131 and the second scintillator 132 are of different thicknesses, the first and second photons have different brightness and sharpness, further providing a distinctive visual feature between the resulting images of the target object 112 generated by the first and second photons, i.e., a distinctive feature in addition to different wavelengths. In practice, and not intending to be limited by theory, a thicker scintillator will produce a resultant image that is brighter than the resultant image produced by a thinner scintillator, while a thinner scintillator will produce a resultant image that is sharper than the resultant image produced by a thicker scintillator. Thus, the relative sizing of first scintillator 131 and second scintillator 132 can be adjusted to produce a desired contrast in brightness and sharpness in the resultant image of target object 112.It should be understood that although it may be desirable to use scintillators with different thicknesses, still other embodiments are envisioned in which first scintillator 131 and second scintillator 132 have equal thicknesses. Indeed, in each of these embodiments, the benefit of scintillator stack 130 is the total amount of first and second photons produced, which may help to generate an image of target object 112 with increased overall brightness compared to, for example, an image generated using a single scintillator system.

[0061] In some embodiments, the first wavelength (i.e., the wavelength of the first photon) may differ from the second wavelength (i.e., the wavelength of the second photon) by at least 10 nm, e.g., at least 15 nm, at least 25 nm, at least 50 nm, at least 75 nm, at least 100 nm, at least 125 nm, at least 150 nm, at least 200 nm, or by a wavelength value within a range having any two of these values ​​as endpoints. In some embodiments, the first wavelength is longer than the second wavelength; in other embodiments, the first wavelength is shorter than the second wavelength. In some embodiments, the first wavelength is in the range of 520 nm to 565 nm, and the second wavelength is in the range of 435 nm to 500 nm. It should be understood that the first and second wavelengths may include any wavelength within the visible light spectrum.

[0062] 1 and 2, radiation source 120 may comprise a single source generator configured to direct both the first ionizing radiation and the second ionizing radiation into imaging passageway 102. In other embodiments, radiation source 120 is the first radiation source and imaging system 100 comprises at least one additional radiation source. In such embodiments, the first radiation source is configured to direct the first ionizing radiation (e.g., x-rays, gamma rays, or a combination thereof) and the second radiation source is configured to direct the second ionizing radiation (e.g., neutrons).

[0063] 1 and 2 , imaging system 100 may further include an optical filter 150 positioned between imaging detectors 160. Optical filter 150 may include a filter wheel, an optical bandpass filter, a spectrometer, or any known or yet to be developed optical filter configured to selectively block first and / or second photons. In operation, optical filter 150 may first selectively block the second photons such that imaging detector 160 receives only the first photons and generates an image and / or determines material properties of target object 112 based on the portion of the first ionizing radiation not blocked by target object 112. Optical filter 150 may then be modified to selectively block the first photons such that imaging detector 160 receives only the second photons and generates an image and / or determines material properties of target object 112 based on the portion of the second ionizing radiation not blocked by target object 112.

[0064] Referring now to FIG. 2 , in some embodiments, the imaging detector is a first imaging detector 160a, and the imaging system further includes a second imaging detector 160b. In FIG. 2 , the optical filter 150 is a dichroic mirror 152. The dichroic mirror 152 is configured to allow transmission of one or more ranges of wavelengths therethrough and reflect one or more other ranges of wavelengths. For example, in some embodiments, a first photon passes through the dichroic mirror 152 and a second photon is reflected by the dichroic mirror 152, while in other embodiments, the first photon is reflected by the dichroic mirror 152 and the second photon passes through the dichroic mirror 152. Also shown in FIG. 2 , the dichroic mirror 152 splits the imaging path 102 into a first path arm 104 and a second path arm 106. The first path arm 104 extends from the dichroic mirror 152 to a first imaging detector 160a, and the second path arm 106 extends from the dichroic mirror 152 to a second imaging detector 160b.

[0065] In some embodiments, imaging detector 160 comprises a color camera having two or more sets of detector sensor pixels, each set of detector sensor pixels sensitive to a different wavelength range. For example, the two or more sets of detector sensor pixels may include a first set of detector sensor pixels and a second set of detector sensor pixels. The first set of detector sensor pixels is sensitive to a first wavelength range that encompasses the wavelength of the first photon (i.e., the first wavelength). That is, the first wavelength is within the first wavelength range. The second set of detector sensor pixels is sensitive to a second wavelength range that encompasses the wavelength of the second photon (i.e., the second wavelength). That is, the second wavelength is within the second wavelength range. In this embodiment, optical filter 150 may be removed because imaging detector 160 itself discriminates between the first photon and the second photon. In practice, in embodiments that include optical filter 150, imaging detector 160 may comprise a monochrome camera in which all pixels are equally sensitive to a wide range of wavelengths. However, it should be understood that a color camera may be used as the imaging detector 160 in any of the embodiments of the imaging system 100 described herein.

[0066] 1 and 2 , the imaging system may further include one or more lenses 140 and one or more mirrors positioned along the imaging path 102 between the scintillator stack 130 and the imaging detector 160. The one or more lenses 140 and the one or more mirrors may focus, direct, collimate, or otherwise modify the first and second photons to facilitate imaging and analysis at the imaging detector 160. FIG. 2 depicts one example arrangement of lenses in which an objective lens 142 is positioned between the scintillator stack 130 and the dichroic mirror 152, a first lens barrel 144 is positioned along the first path arm 104 of the imaging path 102 between the dichroic mirror 152 and the first imaging detector 160 a, and a second lens barrel 146 is positioned along the second path arm 106 of the imaging path 102 between the dichroic mirror 152 and the second imaging detector 160 b. Although not depicted, in some embodiments, imaging system 100 may further include neutron focusing and / or reflecting elements positioned along imaging path 102 between radiation source 120 and scintillator stack 130.

[0067] Still referring to Figures 1 and 2, the operation of imaging system 100 will now be described. Imaging system 100 may be used to image and / or determine one or more material properties of target object 112 in a variety of contexts. For example, imaging system 100 may be used to generate images of the target object based on different ionizing radiations, i.e., generating X-ray and / or gamma ray images of the target object and neutron images of the target object. Imaging system 100 may also be used to determine one or more material properties of the target object using different types of ionizing radiation. For example, imaging system 100 may be used to determine X-ray, neutron, and gamma ray attenuation coefficients of target object 112, which may be used to identify the target object 112.

[0068] One method of operating imaging system 100 includes directing first ionizing radiation from radiation source 120 through object region 110 onto scintillator stack 130. First scintillator 131 of scintillator stack 130 converts the first ionizing radiation into first photons having a first wavelength. Once converted, the first photons propagate from first scintillator 131 through a second scintillator toward imaging detector 160. The method also includes directing second ionizing radiation from radiation source 120 through object region 110 onto scintillator stack 130. Second scintillator 132 of scintillator stack 130 converts the second ionizing radiation into second photons having a second wavelength. Once converted, the second photons propagate from first scintillator 131 through the second scintillator toward imaging detector 160.

[0069] When imaging system 100 is used for imaging, the method then includes generating, using imaging detector 160 (and one or more computing components communicatively coupled to imaging detector 160), one or more images of target object 112 based on the first photons and the second photons. For example, the method may include generating a first image (i.e., one of an X-ray / gamma-ray image or a neutron image) of target object 112 based on the first photons, and generating a second image (i.e., the other of an X-ray / gamma-ray image or a neutron image) of target object 112 based on the second photons.

[0070] When the imaging system 100 is used for material property analysis, the method then includes using the imaging detector 160 (and one or more computing components communicatively coupled to the imaging detector 160) to determine a first attenuation coefficient of the target object 112 based on the first photons and a second attenuation coefficient of the target object 112 based on the second photons. The first attenuation coefficient includes one of an X-ray / gamma-ray attenuation coefficient or a neutron attenuation coefficient, and the second attenuation coefficient includes the other of an X-ray / gamma-ray attenuation coefficient or a neutron attenuation coefficient. The first and second attenuation coefficients may be compared to determine one or more material properties of the target object 112, such as an approximate effective atomic number of the target object 112, which allows the imaging system 100 and / or a user of the imaging system 100 to identify the target object 112. For example, the target object 112 may include a cargo item positioned within a cargo container, and the imaging system 100 may be used to determine the classification of the cargo item based on one or more material properties. Classification of cargo items may provide input for quality control processes, illegal substance identification processes, or hazardous material identification processes. Indeed, some specific applications of imaging system 100 include inspection of cargo for contraband, inspection of packages for illegal / hazardous substances, inspection of objects for quality control or safety (detection of unwanted / foreign objects / materials within the object), and any other context in which a non-destructive identification or imaging process is desired, especially with respect to obscured materials that cannot be visually inspected.

[0071] While particular embodiments have been illustrated and described herein, it should be understood that various other changes and modifications can be made without departing from the spirit and scope of the claimed subject matter. Also, 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.

[0072] As used herein, the terms "approximately," "about," "substantially," and similar terms are intended to have a broad meaning consistent with common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It will 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 those features to the precise numerical values ​​or idealized geometric forms provided. These terms should thus be interpreted as indicating that insubstantial or insignificant modifications or variations of the subject matter described and claimed are considered to be within the scope of the present disclosure as recited in the appended claims.

[0073] The term "coupled" and variations thereof, as used herein, refer to the direct or indirect joining of two members to one another. Such a joining may be fixed (e.g., permanent or fixed) or movable (e.g., removable or releasable). Such a joining may be achieved using two members directly joined to one another, two members joined to one another using a separate intervening member and optional additional intermediate members joined to one another, or two members joined to one another using an intervening member that is integrally formed with one of the two members as a single, unitary body. 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 fluidic.

[0074] References herein to the location of elements (e.g., "top," "bottom," "above," "below") are merely used to describe the orientation of various elements within the figures. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and that such variations are intended to be encompassed by the present disclosure.

[0075] While the figures and descriptions 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 with partial parallelism unless otherwise specified above. Such variations may depend, for example, on the software and hardware systems selected and designer choice. 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 and other logic to perform the various connecting, processing, comparing, and determining steps.

Claims

1. 1. An imaging system, comprising: an imaging detector; an object region; a scintillator stack positioned along an imaging path between the imaging detector and the object region, the scintillator stack comprising a first scintillator and a second scintillator; Equipped with the first scintillator is positioned upstream of the second scintillator along the imaging path and configured to convert first ionizing radiation into first photons having a first wavelength; the second scintillator is configured to convert second ionizing radiation into second photons having a second wavelength and has a higher transmittance at the second wavelength than the first scintillator.

2. The imaging system of claim 1 , wherein the first ionizing radiation comprises x-rays, gamma rays, or a combination of x-rays and gamma rays, and the second ionizing radiation comprises neutrons.

3. The imaging system of claim 1 , wherein the first ionizing radiation comprises neutrons and the second ionizing radiation comprises x-rays, gamma rays, or a combination of x-rays and gamma rays.

4. The imaging system of claim 1 , wherein the second scintillator has a transmittance at the second wavelength that is at least 10% greater than the transmittance of the first scintillator at the second wavelength.

5. 2. The imaging system of claim 1, wherein the first scintillator has a transmittance of 15% or less at the second wavelength and the second scintillator has a transmittance of 90% or more at the second wavelength.

6. The imaging system of claim 1 , wherein the first wavelength and the second wavelength differ by at least 10 nm.

7. The imaging system of claim 1 , wherein the first scintillator is in direct contact with the second scintillator.

8. 10. The imaging system of claim 1, wherein the second scintillator is thicker than the first scintillator, and the thickness ratio of the second scintillator to the first scintillator is 20:1 or greater.

9. 10. The imaging system of claim 1, further comprising an optical filter positioned along the imaging path between the scintillator stack and the imaging detector, the optical filter configured to selectively block the first photons or the second photons.

10. the imaging detector is a first imaging detector, and the imaging system further comprises a second imaging detector; 10. The imaging system of claim 9, wherein the optical filter comprises a dichroic mirror configured to allow transmission of the first photons through the dichroic mirror toward the first imaging detector and to reflect the second photons toward the second imaging detector.

11. the imaging detector comprises a color camera having two or more sets of detector sensor pixels, each set of detector sensor pixels sensitive to a different wavelength range; a first set of detector sensor pixels sensitive to a first wavelength range, the first wavelength being within the first wavelength range; 10. The imaging system of claim 1, wherein a second set of detector sensor pixels is sensitive to a second wavelength range, the second wavelength being within the second wavelength range.

12. The imaging system of claim 1 , wherein the first scintillator comprises a copper-doped zinc sulfide scintillator.

13. 1. A method comprising: directing first ionizing radiation through an object region onto a scintillator stack comprising a first scintillator and a second scintillator, the first scintillator being positioned upstream of the second scintillator, and a target object being positioned within the object region; converting the first ionizing radiation into first photons having a first wavelength in the first scintillator, the first photons propagating from the first scintillator through the second scintillator toward an imaging detector; directing second ionizing radiation through the object region onto the scintillator stack; converting the second ionizing radiation into second photons having a second wavelength in the second scintillator, the second photons propagating from the second scintillator toward the imaging detector, the second scintillator having a higher transmittance at the second wavelength than the first scintillator; A method comprising:

14. 14. The method of claim 13, wherein the first ionizing radiation comprises x-rays, gamma rays, or a combination of x-rays and gamma rays, and the second ionizing radiation comprises neutrons.

15. 14. The method of claim 13, wherein the first ionizing radiation comprises neutrons and the second ionizing radiation comprises x-rays, gamma rays, or a combination of x-rays and gamma rays.

16. 14. The method of claim 13, wherein the second scintillator has a transmittance at the second wavelength that is at least 10% greater than the transmittance of the first scintillator at the second wavelength.

17. 14. The method of claim 13, further comprising generating, using the imaging detector, one or more images of the target object based on the first photons and the second photons, wherein the one or more images of the target object comprise a first image based on the first photons and a second image based on the second photons.

18. 14. The method of claim 13, wherein the first wavelength and the second wavelength differ by at least 10 nm.

19. determining a first attenuation coefficient of the target object based on the first photons and a second attenuation coefficient of the target object based on the second photons; comparing the first attenuation coefficient and the second attenuation coefficient to determine one or more material properties of the target object; 14. The method of claim 13, further comprising:

20. 20. The method of claim 19, wherein at least one of the one or more material properties is an approximate effective atomic number of the target object.

Images