HK1203632B - X-ray inspection using wavelength-shifting fiber-coupled scintillation detectors - Google Patents

Description

X-ray inspection using wavelength-shifting fiber-coupled scintillation detectors

Cross Reference to Related Applications

This application claims priority to two U.S. provisional patent applications serial nos. 61/598,521 and 61/598,576 filed on day 14, 2/2012, and to 61/607,066 filed on day 6, 3/2012, which are incorporated herein by reference in their entirety.

Technical Field

The present invention relates to fiber-coupled scintillation detectors and to methods of making them, and to x-ray inspection systems and methods for efficiently detecting x-rays using fiber-coupled scintillation detectors.

Background

Fiber-coupled scintillation detectors of radiation and particles have been used for over 30 years. In some cases, the scintillator is pixelated, comprising discrete scintillator elements, while in other cases other means (e.g., orthogonal cross-coupled fibers) are employed to provide spatial resolution. U.S. patent nos. 6,078,052 (to DiFilippo) and 7,326,9933 (to Katagiri et al) provide examples of fiber coupled scintillation detectors, the contents of both of which are incorporated herein by reference. The detectors described by DiFilippo and Katagiri et al employ Wavelength Shifting Fibers (WSFs) so that light re-emitted by the core of the fiber can be conducted with low attenuation to a photodetector disposed at a convenient location, which is typically remote from the scintillator itself. Spatial resolution is of particular value in applications such as neutron imaging. Spatial resolution is also of paramount importance in the application of Fermi Large Area Space telescopes (formerly known as GLAST), in which a High Efficiency segmented scintillation detector employs a WSF reader for detecting High energy cosmic rays, as in High Efficiency plastic scintillator detector with wavelength-shifting fiber readout of the GLAST Large Area Telescope,Nucl.Instr.Meth.Phys.Res.Avol.538, pp.372-81(2007), the contents of which are incorporated herein by reference.

Since all known fiber coupled scintillator detectors have calculated the pulses resulting from the independent interaction of particles (photons or bulk particles) with the scintillator in the context of fiber coupled scintillator detectors that have been employed to date, the energy deposited by incident particles can be determined based on the cumulative flux of light re-emitted by the scintillator.

However, the detection requirements of x-ray backscatter inspection systems are quite different from those set forth by existing fiber-coupled luminescence detectors. Backscatter x-ray inspection systems have been in use for over 25 years for detecting organic matter concealed within the interior of luggage, containers, vehicles, and individuals. Since large amounts of organic matter preferentially scatter x-rays (by Compton scattering) rather than absorbing them, these substances appear as brighter objects in backscatter imaging. The sensitivity requirement far exceeds spatial resolution as long as the incident x-rays are scattered in all directions, and in most scattering applications detector spatial resolution is not a concern, since resolution is controlled by the incident beam rather than by detection.

The particular detection requirements of large area and high sensitivity caused by x-ray scattering systems are particularly difficult to meet in the case of a "conventional" scintillation detector 100 of the type shown in the side cross-section of fig. 1A and in the cross-section in front of fig. 1B. An example of such a detector is described in U.S. patent No. 5,302,817 to Yokota, the contents of which are incorporated herein by reference. Typically, a scintillation screen 103 is used as a substrate in an opaque box 102, where incident x-ray radiation 101 is converted to scintillation light, usually having UV, visible, or longer wavelengths, which is part of the Electromagnetic (EM) spectrum. A photomultiplier tube (PMT)105 of the large photocathode region is connected to receive the scintillating light via an aperture 108. There is a problem here: the scintillation light component emitted within the screen will be emitted by the screen into the enclosed space. The remaining scintillation light is lost in the screen material. The scintillation screen 103 is designed to maximize the component of the emitted light, which is equivalent to ensuring that the interface between the screen 103 and the medium (typically air) filling the detector space has a large transmission coefficient T. However, in such conventional backscatter detectors depicted in fig. 1A and 1B, the scintillation screen 103 should also function as a good reflector because the scintillating light, once emitted into the space of the box 102, typically requires multiple reflections until it reaches the photodetector 105. Therefore, the reflection coefficient R of the screen surface should also be large, but since the sum of T and R is limited to a uniform number, both T and R cannot be maximized at the same time, and a compromise must be made. As a result, the light collection efficiency of conventional backscatter detectors is inherently low, only a few percent of the scintillation produced by the light collected into the photodetector.

For imaging detectors, the photon statistical noise is calculated as the photons absorbed by the detector and used to generate the image. All photons that pass through the detector without being absorbed, or even those that are absorbed without generating image information, will be wasted and do not contribute to reducing noise in the image. Since photons are not subdivided, they represent the fundamental quantum level of the system. It is common practice to compute the statistical noise from the smallest number of sub-quantities used to render an image at any position along the imaging chain. The smallest number of dots along the imaging chain that are used to render an image is called the "quantum well". The noise level at the quantum well determines the noise limit of the imaging system. Without increasing the number of information carriers (i.e. quanta) at the quantum well, the system noise limit is not improved. Poor light collection can create secondary quantum wells, that is, it will limit the component of incident x-rays that cause PMT current. Furthermore, it will increase imaging noise. Light collection efficiency can be improved by increasing the sensitive area of the photon detector, however, the way to obtain efficiency is expensive.

Referring now to FIG. 2, a prior art x-ray scintillation detector is illustratedThe structure of a flicker screen is generally adopted. A layer of composite scintillator 202 is sandwiched between a substrate sheet 204 for structural support and a thin transparent protective film 206 composed of, for example, a polymer. The composite scintillator typically includes micron-sized inorganic crystals in an organic matrix or resin. The crystal is the actual scintillation material. Barium fluoride chloride (BaFCl, or "BFC") or gadolinium oxysulfide (Gd) doped with rare earth elements₂O₂S, or "Gadox") is a convenient choice for these. The stopping power (stopping power) for the screen is determined by the thickness of the composite scintillation layer 202, which is typically measured in milligrams of scintillator crystal per unit area. Since inorganic scintillators (e.g., BFC or Gadox) are limited by higher self-absorption, the composite scintillator layer must be kept fairly thin in order to extract more of the component of the scintillating light. This limits the effective stopping force of the screen and makes it applicable only for detecting x-rays with energies up to about 100 keV.

Thus, it would be advantageous to obtain a scintillation detector for x-ray scatter detection applications that provides more efficient extraction, collection, and detection of scintillation light.

As briefly discussed above at the beginning, Wavelength Shifting Fibers (WSFs) have long been used for scintillation detection. The wavelength-shifting optical fiber includes a relatively high refractive index core surrounded by one or more lower refractive index cladding layers. The core comprises a wavelength-shifting material, also called dye (dye). The scintillation light entering the fiber is absorbed by the dye, which then emits light of a longer wavelength. The light of this longer wavelength is emitted isotropically into the fiber material. The total internal reflection captures these light components and directs them over a long distance with relatively low loss. This is possible, as explained with reference to fig. 3, because the absorption 304 and emission 302 wavelength ranges of the dye do not overlap effectively, so that the wavelength-shifted light cannot be re-absorbed. The captured component is determined by the index of refraction coefficient at the surface of the fiber. An additional advantage of the WSF is that the wavelength shift can bring the scintillation light 306 into the sensitive wavelength range of a photodetector (PMT, silicon photomultiplier (SiPM), or multi-pixel photon counter (MPPC), or other device).

Various fabrication techniques have been used to produce scintillator structures, including, for example, die casting, injection molding (e.g., by Yoshimura et al in Plastic cement manufactured by the injection-molding technique,Nucl.Instr.Meth.Phys.Res.Avol.406, pp.435-41(1998), and molding (as described in U.S. patent No. 7,067,079 to Bross et al), both of which are incorporated herein by reference.

Disclosure of Invention

In accordance with various embodiments of the present invention, systems and methods are provided that employ fiber-coupled scintillation detectors to address problems in backscatter and transmission x-ray examinations.

For ease of labeling, the wavelength-shifting fiber-coupled scintillation detector may be referred to herein as a "Sc-WSF" detector.

In a first embodiment of the invention, a penetrating radiation detector is provided having a non-pixilated space of scintillation media for converting energy of incident penetrating radiation into scintillation light. The detector has a plurality of optical waveguides that are substantially collimated to be parallel to each other over a scintillation light absorbing region that is continuous with a non-pixilated space of the scintillation medium. The optical waveguide directs light from the scintillating light to a photodetector for detecting photons directed by the waveguide and for generating a detector signal.

In other embodiments of the present invention, the detector may also have an integration circuit for integrating the detector signal during a specified time.

In an alternative embodiment of the invention, a detector of penetrating radiation is provided having a space of scintillation medium for converting energy of incident penetrating radiation into scintillation light and a plurality of optical waveguides substantially collimated to be parallel to each other over a scintillation light absorbing region continuous with the space of scintillation medium. The optical waveguide directs light from the scintillating light to a photodetector to generate a detector signal. Finally, an integration circuit is used to integrate the detector signal over a specified time period.

In a further embodiment of the invention, the optical waveguide in the aforementioned detector may be adapted to wavelength shift the scintillating light, and, more particularly, may be a wavelength shifting optical fiber. The scintillation media may include a lanthanide-doped barium mixed halide, such as barium fluorochloride. The photodetector may comprise a photomultiplier.

In a further embodiment of the present invention, the square of the thickness of any of the aforementioned detectors, divided by the detector area, may be less than 0.001. At least one of the plurality of waveguides may lack a cladding, and the scintillation medium may be characterized by: the index of refraction value is lower than the index of refraction of the characterized waveguide. The optical waveguides may be disposed on a plurality of parallel planes, each of the parallel planes including a plurality of subsets of optical waveguides.

In other embodiments of the invention, the detector may have multiple layers of scintillator medium, which layers are encountered sequentially by the incident beam, and which layers may be characterized by: different spectral sensitivities to the incident beam. Alternative scintillator layers may include Li⁶F: ZnS (Ag) in place of at least one of fiber-coupled BaFCl (Eu) and fiber-coupled BaFl (Eu). The first layer of the plurality of layers of scintillation media may be a wavelength-shifting fiber-coupled detector that is preferably sensitive to lower energy x-rays, and the last layer of the plurality of layers of scintillation media may be a scintillator of plastic.

The segments of the scintillator medium can be disposed in a plane transverse to the direction of propagation of the incident beam and can be coupled to the photodetectors via optical fibers in a unique manner.

According to another aspect of the present invention, there is provided a method for manufacturing a scintillation detector, the method comprising: a shell of scintillation material is molded around the optical waveguide, and in particular embodiments, the optical waveguide is a wavelength-shifting optical fiber.

In an alternative embodiment, a method for detecting scattered x-ray radiation comprises the steps of:

a. providing a detector characterized by a plurality of independent readout segments; and

b. summing signals from a subset of the independent readout segments, wherein the subset is at a relative signal-to-noise ratio

Selected on the basis of the ratio.

In another aspect of the invention, a method for detecting scattered x-ray radiation is provided. The method comprises the following steps:

a. providing a detector characterized by a plurality of independently read segments; and

b. summing signals from a subset of the independent readout segments, wherein the subset is known to be predominantly

The position of the irradiation beam is selected.

In accordance with another embodiment, a mobile x-ray inspection system is provided. The inspection system includes a source of x-ray radiation deployed on a conveyance having a platform and a ground-contacting member, and a fiber-coupled scintillation detector deployed outside the conveyance during an inspection operation for detecting x-rays interacting with a detected target.

The mobile x-ray inspection system may also have a fiber-coupled scintillation canopy detector that is used over the detected object during the inspection process, and the canopy detector may be slid out of the roof of the transport prior to the inspection operation. There may also be a down-swing detector for use under the vehicle platform, and a roof detector for detecting a higher space than the vehicle, and substantially transverse and substantially vertical fiber-coupled scintillator detector segments. The substantially transverse and substantially vertical light coupled scintillator detector segments can be constructed as a unitary structure.

According to another aspect of the present invention, there is provided an apparatus for detecting radiation irradiating the apparatus, the apparatus comprising:

a. a plurality of substantially parallel effective collimating vanes comprising wavelength-shifting optical fibers sensitive to radiation

Coupling a scintillation detector to generate at least a first detection signal;

b. a rear large area detector for detecting substantial parallelism among a plurality of effectively collimated leaves

Collimating the radiation passing between the leaves effectively and generating a second detection signal; and

c. a processor for receiving and processing the first and second detection signals.

In accordance with an alternative embodiment of the present invention, a top-bottom imaging inspection system is provided for inspecting an object disposed on a bottom surface. The top and bottom imaging inspection system has a source of x-rays directed substantially downward and a linear detector array disposed in a projection above the lower surface. The linear detector array may include wavelength-shifting fiber-coupled scintillation detectors.

In accordance with another aspect of the present invention, an underlying x-ray inspection system for inspecting a vehicle is provided. The x-ray inspection system has a substantially upwardly directed source of x-rays coupled to the vehicle frame, and a wavelength-shifting fiber-coupled scintillation detector disposed on the vehicle frame for detecting x-rays scattered by the vehicle and objects concealed under or within the vehicle. The frame may be adapted to be maneuvered under the vehicle by at least one of an electric motor and a manual control.

Drawings

The foregoing features of the invention will be better understood upon reading the following detailed description with reference to the drawings, in which:

fig. 1A and 1B show cross-sectional views of the side and front of a "cassette" prior art scintillation detector, respectively.

Fig. 2 is a schematic view of a prior art scintillator screen.

Fig. 3 depicts the spectral relationship between scintillation light and typical wavelength-shifting fiber absorption and emission spectra.

FIG. 4 is a schematic perspective view of an array of wavelength-shifting optical fibers sandwiched between scintillator materials in accordance with an embodiment of the present invention.

FIG. 5 is a cross-sectional schematic view of an array of wavelength-shifting optical fibers embedded in a scintillator material matrix, in accordance with an embodiment of the present invention.

FIG. 6A is a perspective view of a cylindrical scintillator molded around a WSF, in accordance with embodiments of the present invention.

FIG. 6B is a schematic depiction of a system for molding a cylindrical scintillator around a WSF, in accordance with an embodiment of the present invention.

FIG. 6C is a cross-sectional view of a stamper for simultaneously stamping a cylindrical scintillator with WSF, in accordance with an embodiment of the present invention.

FIG. 7 is a schematic cross-sectional view of a scintillation detector with multiple rows of WSFs in accordance with an embodiment of the present invention.

FIG. 8 is a top view of a wavelength-shifting fiber-coupled scintillation detector, in accordance with an embodiment of the present invention.

Fig. 9 shows a roof-top and a skirt backscatter detector loaded in accordance with an embodiment of the invention, while fig. 10 shows the same detector used during the course of an inspection operation.

FIG. 11 illustrates a tent detector and a skirt detector using a backscatter inspection system, in accordance with an embodiment of the invention.

FIG. 12 is a cross-sectional schematic view of a stacked scintillator layer for use as a high energy x-ray transmission detector, in accordance with an embodiment of the present invention.

Fig. 13A and 13B show a layered transmission detector inside a 2 inch high speed bump, while fig. 13C shows a cross section of a detector assembly inserted into the frame of the speed bump, in accordance with an embodiment of the present invention.

Fig. 14A shows a perspective view of a segmented x-ray transmission detector for measuring the distribution of detected intensity across the x-ray beam width, while fig. 14B and 14C show end cross-sections of the detector in fig. 14A and a typical beam profile, in accordance with an embodiment of the present invention.

FIG. 15 is a cross-sectional view of a scintillation detector with multiple energy resolutions according to an embodiment of the present invention.

FIG. 16 illustrates a multi-layered scintillation detector for detecting x-rays and thermal neutrons in accordance with an embodiment of the present invention.

Figure 17 shows a perspective view of a detector with an effective collimator.

Fig. 18A and 18B show perspective and cross-sectional views of a WSF detector used as an efficient collimator according to embodiments of the present invention, and fig. 18C and 18D show an arrangement according to further embodiments of the present invention with individual readers separated by opaque (light-light) x-ray absorbers to distinguish radiation impinging on each face.

Fig. 19A and 19B illustrate a plurality of detectors of a handheld scanner in open, storage and use conditions, respectively, in accordance with an embodiment of the present invention.

Fig. 20A and 20B illustrate an inverted diffuser unit that can be slid under a vehicle for inspection under the chassis, by virtue of the Sc-WSF detector, according to embodiments of the present invention.

Fig. 21A and 21B depict the use of a detector for right angle combination in conjunction with a mobile inspection system based on Sc-WSF technology and in accordance with embodiments of the present invention.

Detailed Description

In accordance with embodiments of the present invention, optically coupling the scintillator material to the optical waveguide, and more particularly, to the wavelength-shifting optical fiber, advantageously enables targets including those specific to x-ray scatter detection.

Defining:

the term "image" shall relate to any one-or multi-dimensional representation, whether tangible or otherwise perceptible, or otherwise, whereby some characteristic value (e.g., in the case of x-ray transmission imaging, the component transmission intensity through a column of inspected objects intersected by an incident beam) is associated with each of a plurality of positions (or Euclidean space vectors, typically R) corresponding to the spatial coordinates of objects in physical space²) Although not necessarily one-to-one mapped thereto. The image may comprise a digital array in computer memory or holographic media. Similarly, "imaging" means presenting a determined physical characteristic in terms of one or more images.

Spatial relational terms, such as "above," "below," "upper," "lower," and the like may be used herein to facilitate describing the relationship of one element to another as illustrated in the figures. It will be understood that such spatial relationship terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted and/or illustrated in the figures.

When an element is described as being "on," "connected to," or "coupled to" another element, it can be directly on, connected to, or coupled to the other element or, alternatively, one or more intervening elements may be present, unless otherwise specified.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. The singular forms "a", "an" and "the" are intended to include the plural forms as well.

WSF detector

Referring first to FIG. 4, in one embodiment of the invention, a layer of closed-space parallel wavelength-shifting optical fibers 400 is sandwiched between two layers of a composite scintillating screen 403. A preferred scintillator material is barium fluorochloride doped with europium (BaFCl: Eu), but other scintillators such as BaFl: Eu, or other lanthanide-doped barium mixed halides (further examples include BaBrI: Eu and BaCsI: Eu) may also be used within the scope of the invention. Since the scintillator material employed for x-ray detection usually exhibits a very strong self-absorption for the scintillation photons, embodiments according to the invention advantageously enable the use of a very large number of scintillators 403 while still efficiently coupling out the scintillation signal.

One advantage of using a composite scintillation screen in this application is that it can be manufactured by embossing a fiber-coupled scintillation detector.

The composite scintillator 403 is structurally supported by an outer plastic layer 404, or other material, that provides mechanical support. Optical contact between the fiber cladding 401 and the composite scintillator 403 is established by filling the blank with an index matching material 405 that is transparent to the scintillating light and has a suitable index of refraction. The refractive index of the filler material is selected to optimize the collection of the primary photon into the WSF and to capture the wavelength shifted photons in the fiber. The filler material 405 may be, for example, an optical grease (optical grease) or an optical epoxy (optical epoxy), but any material is within the scope of the present invention.

Upon incidence of an x-ray photon, scintillation light emitted by scintillator 403 is coupled to core 407 of the respective optical fiber via cladding 401, frequency shifted down (i.e., red shifted), and propagated to one or more photodetectors 805 (e.g., as shown in fig. 8). Light from the light core 407 is converted to a current via the photodetector 805 and the current is integrated over a time interval (typically in the range of 1-12 mus) to obtain the signal intensity of each pixel. Integration of the detector signal may be performed by an integrating circuit (not shown), such as an integrating preamplifier.

Referring now to fig. 5, a wavelength-shifting optical fiber 400 is embedded in the base material of a scintillation screen 503. Embedding the WSF in the scintillation medium produces optimal optical contact.

In yet another embodiment of the present invention, now explained with reference to fig. 6A, the composite scintillator material 603 is used as a cladding or shell surrounding the WSF 601 with the core 602. The application lends itself to the compression molding manufacturing process and enables the most efficient use of the expensive scintillator material 603. The scintillator material 603 is sealed by a protective layer 604 that also acts to reflect the scintillating light. It is within the scope of the invention that the cladding may be omitted when the scintillator has a lower index of refraction than the optical fiber, and the scintillator fiber binder has the necessary smoothness and robustness.

Referring now to the embodiment of the present invention illustrated by the system schematically depicted in FIG. 6B, a wavelength-shifting polymer optical fiber can be fabricated. A source comprising a WSF polymer melt 606, a low index cladding polymer melt 608, and a transparent polymer melt 610 of optically embedded phosphor, all under pressure, is fed to and co-molded with a co-molding die 612 within a molding zone 614. A dry gas 611, such as dry air or nitrogen, is sprayed onto the molded optical fiber to cool it. With light-reflective pigments 616 (e.g., TiO)₂) Is fed under pressure into a molding die 618 for mounting a light reflective protective jacket over the scintillator coated WSF 613. The resultant scintillator coated WSF620 is wound for storage by windings 622. FIG. 6C shows a cross-sectional view of a co-molding system for use in making a scintillator coated WSF in accordance with an embodiment of the present invention. WSF polymer melt 606 and low index cladding polymer melt 608 and optically embedded phosphor transparent polymer melt 610 are injected into a common chamberAnd the die 612 is molded. The polymer melt with light reflective pigment 616 is fed under pressure into a molding die 618. The finished fiber has a WSF core 602, a low index cladding 601, a scintillator-loaded cladding 603, and a reflective coating 604.

For all embodiments of the scintillation detector according to the invention, it is advantageous to optimize the thickness of the scintillator material with respect to the energy of the radiation to be detected. The design should ensure that enough light is collected to avoid secondary quantum wells. In particular, the embodiments of the invention described herein provide extremely thin detectors with respect to their area.

Defining: for the purposes of this specification, and in all of the appended claims, the term "thickness", when used in reference to a scintillation detector, shall mean the average extent of the detector along or parallel to the dimension of the center of the detector's field of view. The term area, as used for the detector, or equivalently the term "active area" refers to the dimension of the detector measured in a plane transverse to the center of all propagation vectors of radiation within the field of view of the detector.

Embodiments of the present invention, even those detectors with up to 8 WSF layers, have a ratio of the square of the detector thickness to the effective detector area of less than 0.001. For example, an 8-layer inspector having an area of 48 "12" has a thickness of no more than 0.5 "such that the ratio of the square of the thickness to the area of the inspector is 0.0005. This ratio of square thickness to area is typically on the order of one, or more, orders of magnitude less than a comparable ratio of backscatter detectors where scintillator light is directly detected by a photodetector.

According to a further embodiment of the present invention depicted in FIG. 7, the useful stopping force of the detector can be increased by incorporating multiple layers 701, 702 (or other optical waveguides) of WSF 400, thereby increasing the depth of scintillator material 403 along the incident radiation path.

An embodiment of a wavelength-shifting scintillator detector in accordance with the present invention is shown in FIG. 8. Wavelength shifting optical fibers 801 are embedded within the scintillator material 803, couple the light, and shift the detection frequency downward through a photomultiplier tube 805.

According to various embodiments of the foregoing description, the ends of the WSF are bundled and optically connected to at least one photodetector. Examples of suitable photodetectors include PMTs and silicon photomultipliers (SiPMs).

The advantages of the detector of the invention described therein include the efficiency of detection and the implementation of a lower geometry. This allows more freedom in designing the detection system and it enables entirely new, space-limited applications. The mechanical flexibility of the detector structure allows the shape of the detector surface to be tailored to the application, e.g., the implementation of a detector volume around which the imaging subject is to be surrounded. The lower profile also makes it relatively easy to orient and shield the detector area in a way that minimizes the detection of unwanted scattered radiation (cross talk) from nearby x-ray imaging systems.

Absorption of scintillation light over a larger area of the scintillator enables a detector with a larger width to depth aspect ratio to be obtained. In particular, detectors with relative spatial angles of 0.1sr or more are advantageous for embodiments of the present invention.

In a typical backscatter x-ray imaging system, a pencil beam of x-rays scans the imaging target in a linear motion while elongated radiation detectors are disposed on both sides of the exit aperture of the x-ray source. As the pencil beam moves, the detector area closest to the beam will generally receive the strongest signal and the detector areas further from the beam will be fewer. If the detector area is segmented into independently readable portions, the signal-to-noise ratio of the detection system can be improved by reading only the portions with good signal-to-noise ratio and ignoring the segments that add noise mostly to the total signal. The selection of the active detector segments can be based on the actually detected signal or on the known position of the pencil beam.

Advantages of scintillator production by molding

The embossing or "autocoating" process described above with reference to fig. 6A-6C is in sharp contrast to the typical method of laying down polycrystalline scintillating material (e.g., bafcl (eu)) on a flat back. The molding method to make individual wavelength-shifting fibers coated with a uniform thickness of scintillator, as taught above, produces a contoured fiber such that the limitations on the shape of the Sc-WSF detector are largely dictated by the requirement of complete trapping due to total internal reflection in the fiber. The concept of uniformly coated coupling fibers gives more freedom to design Backscatter (BX) detectors, especially for hand-held and robot-mounted detectors, where space is at a premium.

The detector may be deployed to improve the geometric efficiency of scattered x-rays

Some mobile x-ray systems, such as those described in, for example, U.S. patent nos. 5,764,683 to Swift et al and 7,099,434 to Chalmers et al, the contents of both of which are incorporated herein by reference, use a method of backscatter x-ray (BX) to inspect cars and trucks from one side. The former uses detectors deployed outside the vehicle during operation, while the latter uses detector areas that are completely contained within the enclosure (i.e., the skin of the vehicle). Both of which use large area detectors to maximize the efficiency of detecting scattered x-rays. In the case of the product according to the teachings of the Chalmers' 434 patent, the footprint of the surface backscatter detectors covers on the order of 20 square feet of the interior surface of the enclosure facing the target. Such a covert detector area is relatively inefficient in terms of geometry for collecting scattered radiation from a high or low target. The geometry of such detectors necessary for the photomultiplier to directly capture the scintillation light is inherently deep and not conducive to off-board deployment.

Defining: as used herein and in all the appended claims, the term "large area detector" refers to any single detector, or to any detector module, subtending an opening angle of at least 30 ° in each of two orthogonal transverse directions, as viewed looking at a point on an object under inspection, equivalently characterized by a spatial angle of at least pi steradians.

"conveyance" shall be any device for transporting an implement from one location to another, having the characteristic of having a platform-like load on ground engaging members such as wheels, rails, pedals, brakes, etc.

According to the embodiment of the invention, the Sc-WSF detector can realize unobtrusive placement of a large-area detector, and can be rapidly deployed at a proper position outside a vehicle, so that the detection efficiency is fully improved.

Referring now to fig. 9, a large area Sc-WSF tent detector 1101 is shown in a stowed position, placed on the roof of a backscatter inspection vehicle 1103, and showing a thinner downswing detector 1105 in the stowed position above the wheels of the backscatter inspection vehicle. In fig. 10, both the roof and skirt detectors are shown deployed with increasing solid angle (solid angle) to inspect higher and lower targets, respectively; during inspection, the tent detector is deployed above the inspection object while the skirt detector is deployed at least partially under the platform of the conveyance. In another embodiment of the present invention, illustrated with reference to FIG. 11, the sail detector 1301 may be used for lower, closer objects, such as for detecting contraband in the trunk 1303 of a car. The sail detector 1301 may be slid out of the roof of the vehicle prior to inspection operations. Fig. 11 also shows the deployment of a Sc-WSF downswing detector 1105 for effective inspection of tires, wheel walls, and enclosed vehicle interiors.

Dual and multi-energy detectors for transmission detection of scanning x-ray pencil beams

The pencil beam of scanning x-rays not only reveals internal objects by analyzing backscattered radiation, but in some applications additional information can be obtained by analyzing both Transmitted (TX) and forward scattered (FX) radiation simultaneously. The TX and FX detectors need not be segmented because the cross-sectional area of the pencil beam, together with the signal integration time, defines the pixel size. Furthermore, the TX and FX detectors need only be total energy detectors, since in most applications the throughput of TX or FX x-rays is too high for pulse counting. A scintillation screen is a conventional detector for such scanning beam applications. The Sc-WSF detector greatly expands the range of applications for current TX and FX scintillation detectors, as is clear from the following example.

TX for x-ray beams up to at least 250keV

Conventional scintillation screens made of, for example, bafcl (eu) or Gadox, have an absorption efficiency that drops by 50% at x-ray energies in excess of-80 kev. The 50% points for both layers are at about 100 keV. For discrimination, the Sc-WSF detector can be made with more than two layers of scintillators without significantly increasing the profile of the detector. A cost-efficient Sc-WSF detector with 4 layers can be used for TX with a scanning x-ray beam generated by a standard 140keV x-ray tube. A multi-layer detector such as that shown in fig. 12, e.g., a 9-layer detector, generally indicated by reference numeral 1400, may be highly efficient for detecting x-rays 1402 emitted by a standard 225keV x-ray tube (not shown), e.g., as used in x-ray inspection of vehicles passing through an entrance. A layer 1404 of scintillator material is shown, and a WSF fiber 1406 is coupled to a photodetector 1408.

Portable TX detector for up and down imagers in three-sided portal inspection

The thinner profile of the multi-layer Transmission (TX) detector results in a top-of-the-road Transmission (TX) detector being used in practice. Fig. 13A and 13B show such detectors inside a 2 inch high speed bump 1131 that is strong enough to support a fully loaded tractor trailer and does not require excavation of the ground for deployment. The source 1132 of penetrating radiation emits a fan-shaped beam 1134 that is incident on a linear detector assembly 1135 within a frame 1136 of the deceleration strip 1131 or similar protrusion above the bottom surface. Detector assembly 1135 includes segments of scintillation material 1137 separated by higher atomic number wagons 1138. As explained above, for example, with reference to fig. 4, the scintillating light is coupled to the photodetector by wavelength shifting optical fiber 1139.

Segmented TX detector for determining scanned beam intensity profile

Referring now to fig. 14A and 14B, a segmented transmission detector for measuring the scanned beam intensity profile of incident x-rays 1143 is shown, generally indicated by reference numeral 1141. When a mobile security system is deployed with a TX detector, there are significant challenges to collimating the Sc-WSF detector 1141 (to be used in transmission) with the scanning pencil beam plane. Fig. 14B shows a cross-section of a vertical Sc-WSF detector 1141 with a separate readout of WSF fiber 1145 (otherwise referred to as a "transmission detector" or "TX detector" as understood herein) that provides a means to simultaneously measure the emission intensity of each pixel and its linear distribution across the beam width to determine its position of center of gravity. The optical fibers 1145 are bundled 1147 to a single photodetector 1149, such as a PMT. The intensity distribution can be extended to obtain forward scattered intensity, which includes useful information about the scattering material, and to give a measure of the non-scattered (in-scattered) radiation, which is reported as the transmitted intensity.

The relative position of the detector plane and the scanning x-ray plane can be automatically controlled. The detector used for this concept is shown schematically in fig. 14A. A reflective surface 1148 may be provided at the end of the detector 1141 distal to the photodetector 1149.

Using a single data channel to transmit the signals, the spatial resolution in the transport direction (transverse to the fan-shaped representation of the x-ray beam) is determined by the smaller of the two dimensions: the width of the sensitive detector area or the beam size on the TX detector. (for heuristic purposes, the under-sampling case is not considered in this description). However, the spatial resolution can be improved by narrowing the sensitive detector area, as now explained with reference to fig. 14C. In accordance with embodiments of the present invention, spatial resolution in the direction of conveyance (along the detection lines) may be enhanced by employing multiple detectors in a detector array 1450 associated with multiple channels (A, B, C in FIG. 14C) and interleaving their sensitive areas. The pitch of the interlaced pattern depends on the beam width along the detector. Ideally, the pitch (i.e., the separation between the two detectors 1451 and 1454 associated with a single channel "a") must be large enough so that two detector segments of the same detection channel do not receive direct radiation from the beam at the same time. Reference numeral 1456 depicts a beam intensity curve. This requirement is not very strict for practical purposes, as some cross-talk between pixels is acceptable. The multiple composite images need to be interleaved using any method, including methods known in the art, to produce a higher resolution image. It should be noted that the improvement of spatial resolution at the detector leads to an expansion of the throughput and is therefore limited by signal-to-noise factors.

Another configuration within the scope of the present invention includes the combination of the vertical detector 1141 shown in FIG. 14A and the horizontal road detector 1135 shown in FIG. 13B to form an L-shaped detector, which is advantageous in that it is easy to install and align.

In another embodiment of the present invention, transmission detector array 1450 (regardless of geometric orientation, whether vertical, transverse, L-shaped, etc.) is segmented into a plurality of elements, such as B, C in FIG. 14C, and A. As shown, the beam curve 1456 is symmetric about B and a, making the ratio of the measured intensities unique. For any reason, if the collimation is changed, the ratio will change substantially. If the collimation deviates as the illuminating x-ray pencil beam is scanned up and down, a change in the B/A ratio will measure the deviation and lateral offset. The collected data may then be calibrated row-by-row for such offsets.

Dual and multi-energy TX detector for discriminating materials

Splitting the signals from the front and back layers of the scintillator enables the front layer to give a measure of the low energy content of each pixel whilst the back layer gives a measure of the high energy content. Placing a layer of absorbing material between the front and back scintillators is a standard way to enhance the distinction between high and low energy components and is easily achieved by Sc-WSF detectors.

The Sc-WSF detector implements a dual energy detector that includes a layer of Sc-WSF, such as BaFCl-WSF, on top of a plastic scintillator detector; BaFCl is sensitive to low energy x-rays and not sensitive to high energy x-rays, whereas plastic detectors are sensitive to high energy x-rays and very insensitive to low energy x-rays.

Alternative and potentially most efficient material discriminators can be made by using Sc-WSF with two or more separate layers, each with a separate reader. A passive extractor, such as copper of appropriate thickness, may be inserted behind the top Sc-WSF to enhance dual energy applications, as implemented using a segmented detector. Alternatively, an intermediate scintillator may be used as the active absorption layer. Measurement of three independent parameters enables measurement of the average atomic number across the material and the beam hardening range. Sc-WSF can be further extended to obtain more than three energy values per pixel, with the limit of statistical uncertainty, which increases with the number of components. The detector 1400 shown in fig. 12 is an extreme example of such a detector.

One important application of dual energy TX is in x-ray personal scanners used at airport terminals. The TX images are provided while confirming the BX valid check. Adding dual energy to TX images has heretofore been impractical, primarily because of the size limitations imposed by conventional detectors. Sc-WSF eliminates these limitations and conventions and thus significantly improves performance because multiple detectors with different energy sensitivities can be stacked, as shown in FIG. 15, where a dual (or multi) energy detector 1500 includes a Sc-WSF detector 1508 sensitive to the lower energy component of the incident x-ray 1501, positioned in front of a thick slab of plastic scintillator 1502 sensitive to the higher energy x-rays. The Sc-WSF detector 1508 includes a scintillator 1504 that is read by a two-layer WS ray 1506.

Compact radiation detector for gamma and neutron radiation

The Sc-WSF method enables a small, lightweight, inexpensive monitor 1601 for neutrons and gamma rays. BaFCl (Eu) -WSF is quite sensitive to gamma radiation but not to neutrons, while Li⁶ZnS (Ag) -WSF is not sensitive to gamma rays but is very sensitive to the detection of thermal neutrons. FIG. 16 shows a multilayer "Dagwood" type layer clip comprising one or more layers 1602BaFCl (Eu) read by a single photodetector (not shown) via optical fiber 1604, and one or more layers 1606Li read by a second independent photodetector (not shown)⁶ZnS (Ag) -WSF having an active element occupying a thickness of not more than one or two centimeters. A layer of suitable neutron moderator 1612, such as polyethylene, may be placed in Li⁶Zns (ag) -WSF on either side to enhance the efficiency of detecting neutrons. An optically reflective foil 1608, such as aluminum foil, limits scintillation to the corresponding detector area.

U.S. patent application serial No. 13/163,854 (issued to Rothschild), entitled "Detector with active detectors" and incorporated herein by reference, illustrates a backscatter Detector module 30 that increases the depth of examination by distinguishing between scattering from the near and far sound fields of an object under examination, as depicted in fig. 17. The angle of a set of active collimating blades 31 can be adjusted before the factory or can be connected to any type of motor arrangement for dynamically adjusting them, depending on the type and/or distance of the object being scanned. Scintillation light from the collimating vanes is detected by one or more photodetectors (e.g., by PMTs 32 placed at the top and bottom of the front compartment of the detector). The back compartment 36 of the detector is optically isolated from the front compartment 35 by a light deflector plate, and scintillation light from x-rays detected in the back compartment 36 is collected by a second set of one or more photodetectors (e.g., PMTs 37 mounted behind the detector). The rear compartment may be lined with, for example, a flash phosphor screen, or in other embodiments of the invention, may include a plastic or liquid scintillator.

A useful addition to a standard backscatter unit may be a "louvered" collimator made of scintillators. The slats block the radiation so that it cannot enter directly into the gaps between the slats, so that the cassette detector preferably detects deeper internal objects. An active collimator records the intercepted radiation. Light from the active collimators is detected by the PMTs, which rapidly decrease in collection efficiency as the spacing between the collimators decreases. The use of blades comprising a Sc-WSF detector instead of PMT and scintillator blades addresses the main drawbacks and enables a louvered collimator. First, the light collection is independent of the gap between the leaves. Second, the active area of a PMT or silicon photomultiplier used to collect light from an active collimator is typically much smaller than the active area of a PMT required, which makes the cost of the photodetector much lower. Third, placing the photodetector at the end of the WSF bundle is not critical to the efficiency of light collection. Fourth, the WSF signal from each slat can be processed individually, giving reasonable latitude to maximize internal information about the object under examination. Fifth, light from thin scintillator screens on each of the front and rear leaves can be collected by independent WSFs, which can significantly improve depth discrimination.

Fig. 18C and 18D depict (perspective and cross-sectional views, respectively) an effective WSF collimator 181 that is sensitive to x-rays impinging from either side of the scintillator. Scintillation light from both scintillator regions 182 is coupled to a photodetector via wave shifting optical fibers 183. Fig. 18A and 18B show (in perspective and cross-sectional views, respectively) an effective WSF collimator 185 with individual readers 187 separated by opaque x-ray absorbers 189 to distinguish radiation impinging on each face. In one embodiment, for example, each collimator 185 may include a two-layer Sc-WSF detector 182, each including an areal density of 60mg BaFCl Eu per square centimeter. The opaque x-ray absorber 189 may comprise a thin layer of tin, which also provides structural support.

Detector for a miniature backscatter inspection system

The thinness of the Sc-WSF detector offers unique potential for low weight and low power driven applications referring to FIGS. 19A and 19B, a handheld imaging system 193 is an example of such an application, the power requirements, inspection time, and image quality are all affected by the solid angle of detection, a cross-section of, for example, 10cm × 10cm (100cm × cm)²) Up to twice the weight of a 10cm cube of Sc-WSF may be made from a separate Sc-WSF 10cm × 10cm and a thickness of less than 5mm each, which in this example may be unfolded to present at least 2,000cm of detector weight²In this example by a factor of 20. The additional detection coverage may improve the performance of the handheld system by an order of magnitude.

The thin profile of the Sc-WSF detector described herein allows for a contoured detector to fit in a small space. For example, the detector may be adapted for a personal scanner defined to be snapped into a limited airport inspection space.

Fig. 19 shows an example where four detectors 191 are deployed or slid out of the handheld scanner 193 to significantly increase detection efficiency, especially for things that are more deeply hidden in the object under examination. Backscatter detector 195 straddles clamp beam of radiation 197.

Backscatter inspection of stationary vehicle undersides

Inspection of the underside of a vehicle by a portable x-ray backscatter system presents particular problems. The road clearance of the car does not exceed 8 "and can be as small as 6". A fixed inspection system, such as a portal, may place the detector on the ground, or, as explained above, may be placed on the ground using Sc-WSF. However, in many areas, under-vehicle mobile inspection systems that require security have never been developed. Inspectors rely on passive inspection tools, such as mirrors and cameras, which will miss contraband in the tank or be disguised as seemingly harmless contraband.

The Sc-WSF detector enables an x-ray backscatter system not exceeding 6 "high. Referring now to fig. 20A and 20B, sketches of a practical system are illustrated. The x-ray source includes an electromagnetic scanner 221 of electron beams across an anode. The electromagnetic scanner 221 is driven by the electronics module 223. The x-rays are calibrated by a linear array of apertures 225 that span, for example, 30 "across the bottom in one pass. A Sc-WSF detector 227 is mounted on each side of the x-ray tube to detect x-rays 236 backscattered from the vehicle 229. The power supply, pulse and image processor may be suitably mounted. The frame 234 of the inspection unit 230 on the wheel 232 may be adapted to be operated under a vehicle 229, by motor or manual control.

Mobile transport inspection using L-shaped detector array segments

In accordance with another aspect of the present invention, a mobile detection system (generally indicated by reference numeral 240) is now described with reference to fig. 21A and 21B. It is within the scope of the present invention for a source (not shown, and as illustrated herein in terms of x-rays, but not limited thereto) of transmitted penetrating radiation to be in mobile inspection unit 241, which is typically capable of being moved by its own power, but which can also be towed or otherwise transported. A beam 242 of penetrating radiation is emitted from the mobile examination unit 241, either as a scanning pencil beam or as a fan beam, or in the case of emission in the plane indicated by the representative beam 242 in fig. 21A. The object 244 being inspected, which may be a vehicle as shown (or a cargo such as being transported), traverses the beam 242 during the inspection process and passes through an integral L-shaped detection unit 245 during lateral movement, as will now be further explained. Detector unit 245 has a transverse segment 246 and a vertical segment 247 as indicated in fig. 21B.

Each of the transverse and vertical segments 246 and 247 of the L-shaped detector unit 245 may include a plurality of parallel layers 249 providing dual energy resolution or more generally multi-energy resolution of the detected x-rays so as to provide material identification, as explained above with reference to fig. 12. Furthermore, vertical detector array segment 247 may have a plurality of detector segments 248 in a direction transverse to beam 242 and substantially along the direction of relative motion between object 244 under examination and beam 242 to indicate skew or lateral offset of the detectors relative to the beam, as explained with reference to fig. 12. Furthermore, the vertical detector array segment 247 may have a plurality of detector segments 248 in a direction transverse to the beam 242 and substantially along the direction of relative motion between the object 244 under examination and the beam 242 so as to indicate tilt or measurement offset of the detector relative to the beam, as illustrated in fig. 14A-14C above. The unitary L-shaped detection unit 245 may be transmitted to a checkpoint on the mobile inspection unit 241 or a checkpoint on the trailer 250 or other companion and may be partially assembled on site at the inspection base deployment site. A supplemental collimation aid, such as a collimation laser 251, may be employed in establishing the proper positioning and orientation of detector unit 245 relative to mobile inspection unit 241 and beam 242.

The examples presented herein relate to specific combinations of method acts or system elements, which should be understood as those acts and those elements may be combined in other ways to accomplish the same goal of x-ray detection. Furthermore, the features of a single device may fulfill the requirements of several elements recited in the claims individually. The embodiments of the invention described herein are intended to be merely exemplary, and variations and modifications will be apparent to those skilled in the art. All such variations and modifications are intended to be included within the scope of the present invention as defined in all of the appended claims.

Claims (12)

1. An x-ray detector characterized by a thickness and an area, the x-ray detector comprising:

a. a first space of a first scintillator medium for converting energy of incident x-ray radiation into first scintillation light;

b. a first plurality of wavelength-shifting optical waveguides substantially collimated to be parallel to each other over a first scintillation light absorption region that is contiguous with the first space of the first scintillator medium to direct light originating from the first scintillation light and at a longer wavelength than a wavelength of the first scintillation light;

c. a second space of a second scintillator medium for converting energy of incident penetrating radiation having passed through the first space into second scintillation light;

d. a second plurality of wavelength-shifting optical waveguides substantially collimated to be parallel to each other over a second scintillation light absorption region that is contiguous with the second space of the second scintillator medium to guide light originating from the second scintillation light and at a longer wavelength than a wavelength of the second scintillation light;

e. a first photodetector for detecting photons at a first wavelength guided through the first plurality of wavelength-shifting optical waveguides and for generating a first detector signal;

f. a second photodetector for detecting photons at a second wavelength guided through the second plurality of wavelength-shifting optical waveguides and for generating a second detector signal indicative of incident x-ray flux.

2. The x-ray detector of claim 1, further comprising an integration circuit for integrating the first and second detector signals during a particular time period.

3. The x-ray detector of claim 1, wherein the scintillator medium comprises barium chlorofluoride.

4. The x-ray detector of claim 1, wherein the photodetector comprises a photomultiplier.

5. The x-ray detector of claim 1, wherein a square of the detector thickness divided by the area of the detector is less than 0.001.

6. The x-ray detector of claim 1, wherein at least one of the plurality of wavelength-shifting optical waveguides is an optical fiber lacking cladding, and the scintillator medium is characterized by a refractive index value lower than a refractive index of the optical fiber.

7. The x-ray detector of claim 1, wherein the plurality of wavelength-shifting optical waveguides are disposed on a plurality of parallel planes, each of the parallel planes comprising a subset of the plurality of wavelength-shifting optical waveguides.

8. The x-ray detector of claim 1, wherein the first and second scintillator media are characterized by different spectral sensitivities to the incident beam.

9. The x-ray detector of claim 1, wherein the alternative scintillator layer comprises Li replacing at least one of fiber-coupled bafcl (eu) and fiber-coupled bafi (eu)⁶F:ZnS(Ag)。

10. The x-ray detector of claim 1, wherein a first space in the first scintillator medium is a wavelength-shifting fiber coupled detector that is preferentially sensitive to low energy x-rays, and a second space in the second scintillator medium is a plastic scintillator.

11. The x-ray detector of claim 1, further comprising a plurality of segments of the scintillator medium disposed in a plane transverse to a direction of propagation of an incident beam.

12. The x-ray detector of claim 11, wherein the plurality of segments of scintillator medium are respectively coupled to photodetectors via optical fibers.