Rotatable muon detection device and detection method for customs

Abstract

This invention discloses a rotatable muon detection device and method for customs. The rotatable muon detection device includes a first detection unit, a second detection unit, and a rotation drive unit. The first detection unit and the second detection unit are arranged opposite to each other, forming a detection space between them that allows the object to be detected to pass through. The first detection unit and the second detection unit each include two layers of scintillator array groups, and each layer of the scintillator array group includes a detection area for receiving muons. The detection area extends along the passage direction of the object to be detected. The rotation drive unit is driven to both the first detection unit and the second detection unit, and is configured to drive the first detection unit and the second detection unit to rotate synchronously by a preset angle around the detection space in the direction of the passage direction.

Description

Technical Field

[0001] This invention relates to the field of muon detection, and more specifically to a rotatable muon detection device and method for customs. Background Technology

[0002] Currently, customs inspections of prohibited items (such as nuclear materials, explosives, and drugs) in large containers and vehicles primarily rely on X-ray and gamma-ray imaging. However, X-rays have limited penetrating power into high-density materials (such as lead and uranium) and pose a risk of ionizing radiation, making them unsuitable for rapid screening of special nuclear materials shielded by lead. Muons, naturally occurring cosmic ray particles, can penetrate thick materials, and the principle of muon scattering allows for non-destructive testing of materials with high atomic numbers.

[0003] Existing muon detection devices are mostly fixed, full-ring, or array-type structures, requiring a large number of scintillator units to cover the entire detection area, resulting in high material costs and manufacturing difficulties. Furthermore, these devices have a fixed detection angle, making it difficult to perform multi-angle, full-length continuous scanning of long, strip-shaped objects, leading to large detection blind spots and failing to meet customs' needs for rapid, accurate, and low-cost inspections. Summary of the Invention

[0004] The purpose of this invention is to provide a rotatable muon detection device and method for customs, in order to solve the problems existing in the prior art.

[0005] To address the aforementioned problems, a first aspect of the present invention provides a rotatable muon detection device for customs, the rotatable muon detection device comprising a first detection unit, a second detection unit, and a rotation drive unit;

[0006] The first detection unit and the second detection unit are arranged opposite to each other, forming a detection space between them that allows the object to be detected to pass through. The first detection unit and the second detection unit each include two layers of scintillator array groups. Each layer of the scintillator array group includes a detection area for receiving muons. The detection area extends along the passage direction of the object to be detected.

[0007] The rotary drive unit is connected to the first detection unit and the second detection unit respectively. The rotary drive unit is configured to drive the first detection unit and the second detection unit to rotate synchronously by a preset angle around the detection space in the direction of the central axis of the passage direction.

[0008] Optionally, the scintillator array group includes at least one column of scintillator arrays, and the scintillator array includes a plurality of scintillator units distributed along the central axis direction;

[0009] In each layer of the scintillator array group, the planes containing the detection areas of the scintillator units are coplanar, so that the planes containing the detection areas of the multiple layers of the scintillator array group are parallel to each other.

[0010] Alternatively, in each layer of the scintillator array group, multiple columns of the scintillator arrays are arranged sequentially along the circumference, and the planes containing the detection areas of adjacent columns of the scintillator arrays form a preset angle, so that the planes containing the detection areas of the scintillator array group are arc-shaped; in the first detection unit or the second detection unit, the opening directions of the arc-shaped detection areas of the two layers of the scintillator array groups are the same; the openings of the arc-shaped detection areas of the scintillator array groups of the first detection unit and the scintillator array groups of the second detection unit are opposite to each other.

[0011] Optionally, the rotatable muon detection device includes an inlet bracket and an outlet bracket. The inlet bracket includes a support body arranged around the perimeter and an inlet arranged in the middle for the object to be detected to enter the detection space. The outlet bracket includes a support body arranged around the perimeter and an outlet arranged in the middle for the object to be detected to leave the detection space.

[0012] The rotary drive unit includes a ring track, a first support arm, a second support arm, and a rotary drive mechanism.

[0013] The annular track includes an inlet-side annular track and an outlet-side annular track. The inlet-side annular track is disposed on the support body of the inlet bracket, and the outlet-side annular track is disposed on the support body of the outlet bracket. The axis of the annular track coincides with the central axis of the detection space.

[0014] The first support arm extends along the central axis and its two ends are respectively in sliding or rolling engagement with the inlet-side annular track and the outlet-side annular track, and the first detection unit is disposed on the first support arm; the second support arm extends along the central axis and its two ends are respectively in sliding or rolling engagement with the inlet-side annular track and the outlet-side annular track, and the second detection unit is disposed on the second support arm;

[0015] The rotary drive mechanism is configured to drive the first support arm and the second support arm to move along the annular track, thereby causing the first detection unit and the second detection unit to rotate synchronously.

[0016] Optionally,

[0017] The rotatable muon detection device further includes a translation drive unit, which drives the first detection unit and the second detection unit to move along the passage direction or in the opposite direction of the passage reaction.

[0018] The translation drive unit includes a linear guide rail, a first moving member, a second moving member, and the translation drive unit itself. The linear guide rail extends along the central axis and is disposed on the first support arm and the second support arm. One end of the first moving member is disposed on the first detection unit, and the other end is in sliding or rolling engagement with the linear guide rail on the first support arm. One end of the second moving member is disposed on the second detection unit, and the other end is in sliding or rolling engagement with the linear guide rail on the second support arm.

[0019] The translation drive unit is configured to drive the first moving member and the second moving member to move along the linear track, thereby causing the first detection unit and the second detection unit to move along the passage direction or in the opposite direction of the passage reaction.

[0020] Optionally, the rotatable muon detection device further includes a signal transmission unit, a sensor, and a processor.

[0021] The signal transmission unit is configured to have an independent readout circuit connected to each scintillator unit in the first and second detection units, for independently acquiring the output signal of the corresponding scintillator unit.

[0022] The sensor is configured to acquire rotation angle information or translation information of the first detection unit and the second detection unit in real time.

[0023] The processor is configured to determine the abnormality of the detected object based on the output signal of the scintillator unit and the rotation angle information or the translation information.

[0024] A second aspect of the present invention provides a method for inspection by customs, the method comprising the following steps:

[0025] From a single muon event, determine two incident representative points where the muon passes through the two-layer scintillator array group of the first detection unit of the rotatable muon detection device, and two exit representative points where the muon passes through the two-layer scintillator array group of the second detection unit. Record the coordinates of the two incident representative points and the two exit representative points in the local coordinate system of the rotatable muon detection device.

[0026] Obtain the rotation angle of the first detection unit and the second detection unit about the central axis of the detection space in the passage direction, and use the rotation angle to transform the coordinates in the local coordinate system to the reference coordinate system to obtain the reference coordinates;

[0027] The incident direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between the two representative points of the incident shots; the exit direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between the two representative points of the exit shots.

[0028] The scattering angle is calculated based on the incident direction and the exit direction, and the anomaly of the detected object is judged based on the scattering angle.

[0029] Optionally, "judging the anomaly of the detected object based on the scattering angle" includes:

[0030] Anomalies in the detected object are determined based on the scattering angle by employing either a fixed spatial area rotational scanning method or a combination of fixed spatial area rotational scanning and segmented scanning with translation in different spatial areas.

[0031] Optionally, the fixed spatial region rotational scanning includes:

[0032] Multiple scattering angles corresponding to muon events passing through the same spatial region on the object under multiple different rotation angles are obtained. The distribution of the comprehensive scattering feature value of the same spatial region is calculated based on the multiple scattering angles. The distribution of the comprehensive scattering feature value is compared with a preset anomaly judgment standard. When the anomaly condition is met, it is determined that there is an anomaly in the spatial region.

[0033] Optionally, the segmented scanning of different spatial regions includes:

[0034] After completing the acquisition of muon data in the current spatial region, the first detection unit and the second detection unit move a preset step length along the direction of the object being detected or in the opposite direction of the passage reaction to reach a new spatial region, and perform the fixed spatial region rotation scan in the new spatial region.

[0035] The distribution of the comprehensive scattering feature values ​​collected in each spatial region is correlated with the corresponding spatial region to reconstruct the full-length scattering feature distribution map of the detected object, and anomalies in the full-length range of the detected object are judged.

[0036] Optionally, the step "transforming the coordinates in the local coordinate system to the reference coordinate system using the rotation angle to obtain the reference coordinates" includes:

[0037] Based on the rotation angle, the rotation matrix corresponding to the rotation angle is obtained, and the coordinates in the local coordinate system are transformed using the rotation matrix to obtain the reference coordinates in the reference coordinate system.

[0038] Optionally, "judging the anomaly of the detected object based on the scattering angle" includes:

[0039] For the i-th muon event, based on the scattering angle, muon momentum, and the ratio of muon velocity to the speed of light, a momentum-scattering angle joint feature is constructed:

[0040] ,

[0041] Among them, S i p represents the combined characteristics of momentum and scattering angle. i Denotes muon momentum, β i θ represents the ratio of the muon velocity to the speed of light. i Indicates the scattering angle.

[0042] The test region of the object to be detected is divided into multiple voxels, and the comprehensive scattering index of muon events passing through the voxels is statistically analyzed:

[0043] ,

[0044] in, Indicates the overall scattering index, The number of muons passing through the voxel is represented by Si, which represents the momentum-scattering angle combined characteristic.

[0045] The comprehensive scattering index is compared with data from a preset standard database to determine whether the voxel is abnormal.

[0046] The beneficial effects of this invention are as follows:

[0047] By driving the first and second detection units to rotate synchronously around the central axis by a preset angle using a rotary drive unit, multi-angle muon collection of the same spatial region of the object being detected can be achieved, increasing the diversity of detection perspectives and effectively improving the ability to identify high atomic-order radioactive materials (such as uranium and plutonium), while reducing the size and cost of the device. Attached Figure Description

[0048] Figure 1 This is a perspective view of a rotatable muon detection device according to an embodiment of the present invention;

[0049] Figure 2 This is a perspective view of a rotatable muon detection device according to an embodiment of the present invention.

[0050] Figure 3This is a three-dimensional schematic diagram of a scintillator array group according to an embodiment of the present invention;

[0051] Figure 4 This is a schematic diagram of a scintillator array group according to another embodiment of the present invention. Detailed Implementation

[0052] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so as to better understand the purpose, features and advantages of the present invention. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of the present invention, but are only for illustrating the essential spirit of the technical solution of the present invention.

[0053] In the following description, certain specific details are set forth for the purpose of illustrating various disclosed embodiments in order to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the art will recognize that the embodiments may be practiced without one or more of these specific details. In other instances, well-known apparatuses, components, and techniques associated with this application may not have been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.

[0054] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, component, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, component, or characteristic may be combined in any manner in one or more embodiments.

[0055] In the following description, in order to clearly demonstrate the components and working method of the present invention, a number of directional terms will be used. However, terms such as "front", "back", "left", "right", "outer", "inner", "outward", "inward", "up", and "down" should be understood as convenient terms and not as limiting terms.

[0056] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that a component must be absolutely horizontal or suspended, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the component must be completely horizontal, but can be slightly tilted.

[0057] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0058] Example 1

[0059] This embodiment provides a rotatable muon detection device for customs, referring to... Figures 1 to 4 The rotatable muon detection device 1 includes a first detection unit 11, a second detection unit 12, and a rotation drive unit 14. The first detection unit 11 and the second detection unit 12 are arranged opposite to each other and form a detection space 15 between them that allows the object to be detected to pass through. The first detection unit 11 and the second detection unit 12 each include two layers of scintillator array groups 13. Each layer of scintillator array group 13 includes a detection area 132 for receiving muons. The detection area 132 extends along the passage direction of the object to be detected. The rotation drive unit 14 is connected to the first detection unit 11 and the second detection unit 12. The rotation drive unit 14 is configured to drive the first detection unit 11 and the second detection unit 12 to rotate synchronously around the detection space 15 in the direction of the central axis of the passage direction by a preset angle.

[0060] This design, through a rotary drive unit that synchronously rotates the first and second detection units around the central axis by a preset angle, enables multi-angle muon collection of the same spatial region of the object being detected. This increases the diversity of detection perspectives and effectively improves the identification capability of high-atomic-order radioactive materials (such as uranium and plutonium), while simultaneously reducing the size and cost of the device. For example, it enhances the identification of the scattering characteristics of high-atomic-order radioactive materials, thereby improving the accuracy of detecting special nuclear materials during customs inspections.

[0061] In one embodiment of the present invention, the rotatable muon detection device 1 includes an inlet support 16 and an outlet support 17. The inlet support 16 includes a support body 161 arranged around the perimeter and an inlet 162 arranged in the middle for the object to be detected to enter the detection space 15. The outlet support 17 includes a support body 171 arranged around the perimeter and an outlet 172 arranged in the middle for the object to be detected to leave the detection space 15. The rotation drive unit 14 includes an annular track 141, a first support arm 142, a second support arm 143, and a rotation drive mechanism (not shown in the figure). The annular track 141 includes an inlet-side annular track 1411 and an outlet-side annular track (not shown in the figure). The inlet-side annular track 1411 is arranged on the support body 161 of the inlet support 16, and the outlet-side annular track is arranged on the support body 171 of the outlet support 17. The axis of the annular track 141 coincides with the central axis of the detection space 15. A first support arm 142 extends along the central axis, and its two ends are in sliding or rolling engagement with the inlet-side annular track 1411 and the outlet-side annular track, respectively. A first detection unit 11 is disposed on the first support arm 142. A second support arm 143 extends along the central axis, and its two ends are in sliding or rolling engagement with the inlet-side annular track 1411 and the outlet-side annular track, respectively. A second detection unit 12 is disposed on the second support arm 143. A rotary drive mechanism is configured to drive the first support arm 142 and the second support arm 143 to move along the annular track 141, thereby causing the first detection unit 11 and the second detection unit 12 to rotate synchronously.

[0062] Through this design, the rigid synchronous rotation of the two detection units (the first detection unit and the second detection unit) is achieved by using the entrance-side circular track and the exit-side circular track, as well as the first support arm and the second support arm extending along the central axis. This ensures that the two detection units are always aligned with the same spatial area, avoids data misalignment caused by rotational deviation, improves the consistency of multi-angle scattering angle calculation, and thus enhances the positioning accuracy of abnormal areas.

[0063] Specifically, the first support arm 142 and the second support arm 143 have the same structure. The following description uses the first support arm 142 as an example; the structure of the second support arm 143 can be referenced to that of the first support arm 142. Figure 1 There can be four first support arms 142, with each scintillator array group 13 correspondingly positioned between two first support arms 142. Alternatively, there can be two first support arms, with the two scintillator array groups in the first detection unit positioned as a whole between the two first support arms.

[0064] Specifically, the preset angle range for the synchronous rotation of the first detection unit 11 and the second detection unit 12 by the rotary drive mechanism can be ±30°, and the oscillation mode can be continuous sinusoidal oscillation or step-by-step scanning, performing periodic motion within the preset angle range. By changing the geometric orientation of the first detection unit 11 and the second detection unit 12 relative to the incident muon, sampling of muons with different incident directions can be achieved, thereby obtaining equivalent multi-view observation data under the condition of limited detection area.

[0065] Specifically, the rotary drive mechanism can be implemented in any way available in the prior art. For example, the rotary drive mechanism includes a drive motor and a transmission gear. The drive motor is fixed to the support of the inlet or outlet bracket, and its output shaft is connected to the transmission gear. The transmission gear meshes with a gear ring disposed on the inner side of the annular track. When the drive motor operates, the transmission gear rolls along the gear ring, driving the first support arm and the second support arm to rotate synchronously along the annular track.

[0066] In one embodiment of the present invention, the rotatable muon detection device 1 further includes a translation drive unit 18, which drives the first detection unit 11 and the second detection unit 12 to move along the passage direction or in the opposite direction of the passage reaction. The translation drive unit 18 includes a linear guide rail 181, a first moving member (not shown in the figure), a second moving member (not shown in the figure), and a translation drive mechanism (not shown in the figure). The linear guide rail 181 extends along the central axis and is disposed on the first support arm 142 and the second support arm 143. One end of the first moving member is disposed on the first detection unit 11 and the other end is in sliding or rolling engagement with the linear guide rail 181 on the first support arm 142. One end of the second moving member is disposed on the second detection unit 12 and the other end is in sliding or rolling engagement with the linear guide rail 181 on the second support arm 143. The translation drive unit 18 is configured to drive the first moving member and the second moving member to move along the linear guide rail 181, thereby driving the first detection unit 11 and the second detection unit 12 to move along the passage direction or in the opposite direction of the passage reaction.

[0067] This design allows the two detection units to move along the direction of the inspected item, enabling segmented scanning and full-length coverage of extra-long containers or trains, avoiding the blind spots of fixed detectors. For example, it can meet the customs' need for continuous and comprehensive automated inspection of extra-long items.

[0068] Specifically, the translation drive mechanism includes a translation motor, a lead screw, and a lead screw nut. The translation motor is fixed to the end of the first or second support arm, and its output shaft is coaxially connected to the lead screw. The lead screw extends along the direction of the linear guide rail, and the lead screw nut is sleeved on the lead screw and fixedly connected to the first or second moving member. When the translation motor drives the lead screw to rotate, the lead screw nut drives the moving member to move linearly along the linear guide rail, realizing the precise segmented translation of the detection unit.

[0069] In one embodiment of the present invention, the rotatable muon detection device 1 further includes a signal transmission unit (not shown), a sensor (not shown), and a processor (not shown). The signal transmission unit is configured to have an independent readout circuit connected to each scintillator unit 1311 in the first detection unit 11 and the second detection unit 12, for independently acquiring the output signal of the corresponding scintillator unit 1311. The sensor is configured to acquire rotation angle information or translation information of the first detection unit 11 and the second detection unit 12 in real time. The processor is configured to determine the abnormality of the detected object based on the output signal of the scintillator unit 1311 and the rotation angle information or translation information.

[0070] Optionally, the processor of the rotatable muon detection device 1 can execute the method of embodiment 2 to determine the abnormality of the detected object.

[0071] Optionally, the sensor includes a rotation / oscillation mechanism equipped with an angle encoder for real-time measurement of the attitude angle information of the first detection unit 11 and the second detection unit 12. The angle data output by the angle encoder is synchronized with the processor, ensuring that each muon event corresponds to a unique device attitude parameter. Preferably, a hardware latching method is used to record the current angle value at the moment of triggering, or a high-precision timestamp is used for post-event alignment to ensure the consistency between the angle information and the event data.

[0072] In one embodiment of the present invention, the rotatable muon detection device 1 employs a multi-layer time coincidence triggering mechanism to filter valid muon events. When the trigger signals of the corresponding upper and lower scintillator array groups 13 in the first detection unit 11 and the second detection unit 12 meet a preset time window, it is determined to be a penetration event. Preferably, the time coincidence window is set to 10-50 nanoseconds to balance noise suppression and preservation of real events. The device implements multi-channel triggering determination through logic circuits or FPGAs, and uniformly packages and records events that meet the conditions.

[0073] In one embodiment of the present invention, reference is made to Figure 3 The scintillator array group 13 includes at least one column of scintillator arrays 131, and each scintillator array 131 includes a plurality of scintillator elements 1311 distributed along a central axis. In each layer of the scintillator array group 13, the planes containing the detection areas 132 of the scintillator elements 1311 are coplanar, so that the planes containing the detection areas 132 of the multiple layers of the scintillator array group 13 are parallel to each other. This can be understood as the plane containing the detection area of ​​each scintillator element in the first detection unit being parallel to the plane containing the detection area of ​​each scintillator element in the second detection unit. In each detection unit, the rows and columns of the scintillator elements 1311 are equidistantly arranged in mutually perpendicular X and Y directions, forming a regular grid.

[0074] In one embodiment of the present invention, reference is made to Figure 4 The scintillator array group 13 includes at least one column of scintillator arrays 131, and each scintillator array 131 includes multiple scintillator units distributed along the central axis. In each layer of the scintillator array group 13, multiple columns of scintillator arrays 131 are arranged sequentially in the circumferential direction, and the planes containing the detection areas 132 of adjacent columns of scintillator arrays 131 form a preset angle, so that the plane containing the detection areas of the scintillator array group 13 is set as an arc surface. In the first detection unit or the second detection unit, the opening directions of the arc surface detection areas of the two layers of scintillator array groups 13 are set in the same direction. The openings of the arc surface detection areas of the scintillator array groups of the first detection unit and the scintillator array groups of the second detection unit are set opposite to each other, which means that the detection space is between the openings of the two arc surface detection areas.

[0075] In one embodiment of the present invention, the outer wall of the scintillator unit 1311 is covered with a high reflectivity layer. Optionally, the scintillator unit 1311 is made of plastic, and the high reflectivity layer is polytetrafluoroethylene tape or aluminum foil. Optionally, a front-end signal processing board is provided on one side of the scintillator unit 1311, and a photomultiplier tube mounting groove is provided for mounting a photomultiplier tube. Optionally, the photomultiplier tube is fixed in the photomultiplier tube mounting groove by conductive adhesive or welding.

[0076] In one embodiment of the present invention, the rotatable muon detection device 1 further includes a conveying base plate 19 that allows the passage of the object to be detected.

[0077] In one embodiment of the present invention, high temporal resolution scintillator layers are respectively disposed at the lower part of the first detection unit and the upper part of the second detection unit. The high temporal resolution scintillator layers are made of plastic scintillator material with a fast decay time (e.g., decay time ≤ 1 nanosecond), and are coupled at both ends to silicon photomultiplier tubes (SiPMs) for readout. When a muon passes through, the scintillator generates a fast light pulse, and the arrival time is recorded by a high-frequency oscilloscope or a time-to-digital converter (TDC), with a time measurement accuracy better than 100 picoseconds. The preset distance between the two high temporal resolution scintillator layers is D. The muon velocity and momentum are calculated using the time-of-flight method, and the momentum-scattering angle joint characteristic is calculated.

[0078] Example 2

[0079] This embodiment provides a method for detecting anomalies in an object based on a rotatable muon detection device, the method comprising the following steps:

[0080] From a single muon event, determine two incident representative points where the muon passes through the two-layer scintillator array group of the first detection unit of the rotatable muon detection device, and two exit representative points where the muon passes through the two-layer scintillator array group of the second detection unit. Record the coordinates of the two incident representative points and the two exit representative points in the local coordinate system of the rotatable muon detection device.

[0081] Obtain the rotation angle of the first and second detection units about the central axis of the detection space in the passage direction, and use the rotation angle to transform the coordinates in the local coordinate system to the reference coordinate system to obtain the reference coordinates;

[0082] Calculate the incident direction of the muon event in the reference coordinate system based on the reference coordinate difference between the two incident representative points; calculate the exit direction of the muon event in the reference coordinate system based on the reference coordinate difference between the two exit representative points.

[0083] The scattering angle is calculated based on the incident and exit directions, and the anomalies of the detected object are judged based on the scattering angle.

[0084] This design, by altering the geometric orientation of the first and second detection units relative to the incident muons, enables sampling of muons from different incident directions. This allows for the acquisition of equivalent multi-view observation data within a limited detection area, effectively improving the identification capability of high-atomic-order radioactive materials while reducing detector size and cost. The original coordinates of the impact point are first recorded in a local coordinate system, then transformed to the reference coordinate system using a rotation angle, eliminating interference from rotational motion on positioning. The incident and exit directions are accurately calculated based on the reference coordinate difference, thus yielding the scattering angle. This ensures accurate calculation of the scattering angle in rotating scanning mode, providing fundamental data support for anomaly detection.

[0085] In one embodiment of the present invention, each hit representative point is located on a scintillator element of the scintillator array of the first detection unit or the second detection unit, and each hit representative point can be taken as the geometric center of the area of ​​the corresponding scintillator element hit by the muon. Each muon event records the position coordinates and timestamp of its scintillator element, realizing the acquisition of two-dimensional position and time information of the rotatable muon detection device.

[0086] In one embodiment of the present invention,

[0087] The local coordinate system is set up as follows:

[0088] With the geometric center of the rotatable muon detection device as the origin o, and the central axis of the detection space in the passage direction as the x-axis; two orthogonal directions, namely the y-axis and the z-axis, are set in the cross section perpendicular to the x-axis direction, and the y-axis and the z-axis rotate synchronously with the rotation of the rotatable muon detection device around the x-axis;

[0089] The reference coordinate system is set as follows:

[0090] With the geometric center of the rotatable muon detection device as the origin O, and the central axis of the detection space in the passage direction as the X-axis, two orthogonal directions, namely the Y-axis and the Z-axis, are set in the cross section perpendicular to the X-axis direction. The X-axis and the Y-axis are fixed.

[0091] In one embodiment of the present invention, in each scintillator array group, the planes in which the detection areas of the scintillator units are located are coplanar, so that the planes in which the detection areas of the multi-layer scintillator array groups are located are parallel to each other. This can be understood as the multi-layer scintillator array groups being arranged in parallel to each other.

[0092] Suppose the scintillator is a square with size d, and the element number is... The height of the k-th layer scintillator array group is If the height difference between the scintillator array groups is equal to the distance between the scintillator array groups, then the coordinates of the muon penetrating the k-th scintillator plate are:

[0093] , ,

[0094] In one embodiment of the present invention, the step of "transforming the coordinates in the local coordinate system to the reference coordinate system using the rotation angle to obtain the reference coordinates" includes:

[0095] Based on the rotation angle, obtain the rotation matrix corresponding to the rotation angle, and use the rotation matrix to transform the coordinates in the local coordinate system to obtain the reference coordinates in the reference coordinate system.

[0096] This design ensures that the coordinates of the same physical point can be accurately aligned under different rotation angles, avoiding coordinate drift caused by rotation, and providing reliable data preprocessing support for high-precision calculation of the subsequent incident direction, exit direction and scattering angle.

[0097] Specifically, let the rotation angle be θ. Following the above-described method of setting up the local coordinate system and the reference coordinate system, the rotation matrix is:

[0098] ,

[0099] Using a rotation matrix, the coordinates in the local coordinate system are transformed to obtain the reference coordinates in the reference coordinate system:

[0100] ,

[0101] in, Indicates the reference coordinates in the reference coordinate system. Represents coordinates in a local coordinate system. This represents the rotation matrix.

[0102] Specifically, the rotation angle θ can be ±30°, and the swing mode of the first and second detection units can be continuous sinusoidal swing or step-by-step scanning. The first and second detection units perform periodic movements within a preset angle range.

[0103] In one embodiment of the present invention, the two-layer upper and lower scintillator array group of the upper first detection unit is used to measure the incident direction of the muon before it enters the detection space, and the two-layer upper and lower scintillator array group of the lower second detection unit is used to measure the exit direction of the muon after it leaves the detection space. When the same muon passes through four layers of scintillator array groups in sequence and meets the time compliance condition, it is determined as a muon event, that is, the muon event is a valid scattering event.

[0104] In one embodiment of the present invention, the incident direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between two incident representative points; the exit direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between two exit representative points.

[0105] The vector of the incident direction can be expressed as:

[0106] ,

[0107] in, The vector represents the direction of incidence. P1 represents the reference coordinates of a point representing the incident point, and P2 represents the reference coordinates of another point representing the incident point.

[0108] The vector of the exit direction can be represented as:

[0109] ,

[0110] in, The vector represents the direction of incidence. P3 represents the reference coordinates of the representative point of one outgoing shot, and P4 represents the reference coordinates of the representative point of another outgoing shot.

[0111] In one embodiment of the present invention, the scattering angle is calculated based on the incident direction and the exit direction, and the scattering angle can be expressed as:

[0112] ,

[0113] Where, θ s Indicates the scattering angle. The vector representing the direction of incidence. A vector representing the direction of incidence.

[0114] In one embodiment of the present invention, anomalies of the detected object are determined based on the scattering angle. Since the magnitude of the scattering angle is related to the atomic number and density of the detected object, materials with high atomic numbers typically cause greater scattering. By statistically analyzing the scattering angle distributions of a large number of muon events, the scattering intensity distribution characteristics at different locations within the measured spatial region can be obtained.

[0115] The scattering angle approximately satisfies the following conditions with respect to the material:

[0116]

[0117] Where θ0 represents the scattering angle, X0 represents the radiation length, which is related to the atomic number and is a characteristic of the object itself; β represents the ratio of particle velocity to the speed of light, p represents the momentum of the particle, c represents the speed of light, 13.6 MeV is the empirical constant for multiple Coulomb scattering, and L represents the penetration distance of the particle in the material.

[0118] In one embodiment of the present invention, "judging the anomaly of the detected object based on the scattering angle" includes:

[0119] Anomalies in the detected object can be judged based on the scattering angle by using either a fixed spatial area rotation scanning method or a combination of fixed spatial area rotation scanning and segmented scanning with translation in different spatial areas.

[0120] With this design, two judgment strategies are adopted: "fixed spatial area rotation scanning" or "segmented scanning with translation of different spatial areas". This allows for detailed multi-angle analysis of key areas as well as global coverage of long-distance objects being detected.

[0121] In one embodiment of the present invention, the fixed spatial region rotational scanning includes:

[0122] Multiple scattering angles corresponding to muon events passing through the same spatial region on the detected object at multiple different rotation angles are obtained. The distribution of the comprehensive scattering characteristic value of the same spatial region is calculated based on the multiple scattering angles. The comprehensive scattering characteristic value can be scattering intensity, etc. The distribution of the comprehensive scattering characteristic value is compared with the preset anomaly judgment criteria. When the anomaly condition is met, it is determined that there is an anomaly in the spatial region.

[0123] This design, by fusing scattering angles at multiple rotation angles within the same spatial region, yields a comprehensive scattering characteristic value distribution. This suppresses random noise in single muon measurements and enhances the signal characteristics of high atomic number materials. For example, this method can effectively distinguish between common metals (iron, copper) and special nuclear materials (uranium, lead), reducing customs misreporting rates and minimizing unnecessary inspections.

[0124] Specifically, calculating the distribution of the comprehensive scattering characteristic values ​​of the same spatial region based on multiple scattering angles may include:

[0125] For the current rotation angle θ k All M collected below k Given several muon events, we obtain the set of scattering angles {φ1, φ2, …, φ}. Mk Then, calculate the scattering eigenvalue S at that rotation angle. k Scattering eigenvalue S k This can be the root mean square of the scattering angle (scattering intensity), the arithmetic mean of the scattering angle (average scattering angle), or the variance of the scattering angle (average scattering angle distribution), etc. The scattering characteristic value S calculated at each rotation angle... k The convergence refers to the distribution of the comprehensive scattering characteristic values ​​of the spatial region, which reflects the scattering response characteristics of the region to muons at different detection angles.

[0126] Specifically, the distribution of the comprehensive scattering characteristic value is compared with a preset anomaly judgment standard. The preset anomaly judgment standard could be: at any rotation angle, the scattering characteristic value exceeds a threshold at the corresponding angle; or, the distribution pattern of the comprehensive scattering characteristic value (such as the degree of anisotropy) deviates from the standard distribution of normal materials by more than a set range. When the anomaly conditions are met, the spatial region is determined to be an anomaly, for example, the presence of high atomic number materials (such as uranium or plutonium). This method, through multi-angle detection of the same region, obtains the distribution information of scattering characteristics as a function of angle, effectively suppressing random noise from a single measurement and improving the detection accuracy of special nuclear materials.

[0127] In one embodiment of the present invention, segmented scanning of different spatial regions includes:

[0128] After completing the acquisition of muon data in the current space region, the first and second detection units move a preset step length along the direction of the object being detected or in the opposite direction of the reaction to reach a new space region, and perform a fixed space region rotation scan in the new space region.

[0129] The distribution of the comprehensive scattering feature values ​​collected in each spatial region is correlated with the corresponding spatial region to reconstruct the full-length scattering feature distribution map of the detected object, and anomalies in the full-length range of the detected object are judged.

[0130] This design divides long-distance objects into multiple spatial regions through segmented scanning with translational movement. Rotational scanning is then performed segment by segment, and the feature values ​​of each region are reconstructed into a full-length scattering feature distribution map. This method can intuitively display the location and intensity of abnormal areas within the object, enabling segmented scanning and overall imaging of large-volume targets. For example, it supports customs personnel in quickly locating concealed contraband, and is particularly suitable for the overall screening of large containers or tank trucks.

[0131] Specifically, "reconstructing the eigenvalues ​​of each region into a full-length scattering characteristic distribution map" can be achieved in the following way:

[0132] By using the location (e.g., the location can be obtained at least through translation information) and the feature values ​​of each region as coordinates, two-dimensional or three-dimensional surface plots or scatter plots of location and features can be generated, which facilitates comprehensive analysis.

[0133] In one embodiment of the present invention, "judging the anomaly of the detected object based on the scattering angle" includes:

[0134] For the i-th muon event, based on the scattering angle, muon momentum, and the ratio of muon velocity to the speed of light, a momentum-scattering angle joint feature is constructed:

[0135] ,

[0136] Among them, S i p represents the combined characteristics of momentum and scattering angle. i Denotes muon momentum, β i θ represents the ratio of the muon velocity to the speed of light. i Indicates the scattering angle.

[0137] The test region of the object to be detected is divided into multiple voxels, and the comprehensive scattering index of muon events passing through the voxels is statistically analyzed:

[0138] ,

[0139] in, Indicates the overall scattering index, The number of muons passing through the voxel is represented by Si, which represents the momentum-scattering angle combined characteristic.

[0140] The comprehensive scattering index is compared with data from a preset standard database to determine whether the voxel is abnormal.

[0141] This design constructs a joint momentum-scattering angle feature, effectively eliminating the influence of muon energy differences on the scattering signal and achieving unified calibration of muon events with different energies. Furthermore, through voxelization and statistical averaging, a comprehensive scattering index is obtained and compared with a pre-defined standard database to determine whether any voxels exhibit anomalies. Energy normalization can eliminate interference from muon momentum dispersion, and multi-event averaging improves the signal-to-noise ratio, meeting the stringent requirements of high-reliability applications such as customs.

[0142] Specifically, high temporal resolution scintillator layers are respectively set in the lower part of the first detection unit and the upper part of the second detection unit to record the muon passage times. and Then the flight time is defined as Muzi's speed is , where D is the distance between the two high temporal resolution scintillator layers, and c is the speed of light.

[0143] Let the mass of Mu Zijing be... Then the momentum of the muon is:

[0144] ,

[0145] The above method can provide a momentum estimate for each muon event, thereby eliminating the influence of muon energy differences on scattering angle analysis.

[0146] Specifically, for the i-th muon event, the muon passes through a thickness of L. i When the material is such that the root mean square of its scattering angle satisfies the following physical relationship:

[0147] ,

[0148] Where 13.6 Mev is a constant, p i Denotes muon momentum, β i This represents the ratio of muon velocity to the speed of light, where c represents the speed of light, and X0 represents the radiation length, which is related to the atomic number. Let represent the root mean square angle of the scattering angle corresponding to the i-th muon event.

[0149] Constructing the combined momentum-scattering angle characteristics:

[0150] ,

[0151] Among them, S i p represents the combined characteristics of momentum and scattering angle. i Denotes muon momentum, β i θ represents the ratio of the muon velocity to the speed of light. i Indicates the scattering angle.

[0152] θi Let be the measured scattering angle of the i-th muon event. Then the momentum-scattering angle joint characteristic can be approximated as:

[0153] ,

[0154] Therefore, S i Proportional to the material's equivalent radiation length, it has energy normalization properties, allowing for a unified comparison of muon events with different momentum.

[0155] Specifically, the test area of ​​the analyte is divided into multiple voxels. A voxel is short for volume pixel, representing a tiny cubic unit in three-dimensional space. For each voxel, all muon events passing through that voxel are counted, and the overall scattering index is calculated.

[0156]

[0157] in, Indicates the overall scattering index, The number of muons passing through the voxel is represented by Si, which represents the momentum-scattering angle combined characteristic.

[0158] The comprehensive scattering index is compared with data from a pre-defined standard database to determine whether the voxel exhibits any anomalies. Based on the differences in radiation length among various materials, the following discrimination rule is established: Organic matter: Minimum; aluminum and concrete: Medium; Steel: Larger; radioactive material: Significantly increased. This can be obtained from multiple measurements of various substances. A standardized database will be established, and in practice, customs inspection and... Standardize database comparisons.

[0159] Specifically, "comparing the comprehensive scattering index with data from a preset standard database to determine whether the voxel is abnormal" further includes:

[0160] The standard database contains the average scattering intensity and variance of different substances. Based on the central limit theorem, the comprehensive scattering index is set. It follows a Gaussian distribution, and the Bayesian enhancement index is calculated. When the Bayesian enhancement index of the voxel... If the value is greater than the threshold T, the voxel is determined to contain high atomic order material, and an alarm message is output.

[0161] Specifically, set To standardize the collection of various substances in the database, To synthesize the scattering parameters, according to the central limit theorem, they can be approximated by a Gaussian distribution:

[0162] ,

[0163] in, To standardize the average scattering intensity of substances in the database, To standardize the variance of the scattering intensity of matter in the database, P(Λ) j |M j ) represents the conditional probability density.

[0164] Substituting the above Gaussian distribution into the Bayesian enhancement index formula:

[0165] ,

[0166] in, This indicates the Bayesian enhancement index. This indicates that a hypothesis has been made that the object being tested is a high atomic number item. This indicates that the hypothesis was made that the tested object is a normal, qualified item, P(Λ). j |M highZ The expression indicates that, assuming the voxel contains a high atomic number material (such as uranium), the current value is measured. The probability, P(Λ) j |M bg The ) indicates that, assuming the voxel contains ordinary background material (such as steel), the current value is measured. The probability,

[0167] When the Bayesian enhancement index of voxels When the value exceeds the threshold T, the voxel is determined to contain high atomic number material, and an alarm message is output. The threshold T is a pre-calibrated discrimination threshold of the system, used to characterize the minimum statistical evidence strength required for the high atomic number material hypothesis to be achieved relative to the ordinary material hypothesis.

[0168] The preferred embodiments of the present invention have been described in detail above. However, it should be understood that after reading the above teachings, those skilled in the art can make various alterations or modifications to the present invention. These equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A rotatable muon detection device for customs, characterized in that, The rotatable muon detection device includes a first detection unit, a second detection unit, and a rotation drive unit; The first detection unit and the second detection unit are arranged opposite to each other and form a detection space in the middle that allows the object to be detected to pass through. The first detection unit and the second detection unit each include two layers of scintillator array groups. Each layer of the scintillator array group includes a detection area for receiving muons. The detection area extends along the passage direction of the object to be detected. The rotary drive unit is connected to the first detection unit and the second detection unit respectively. The rotary drive unit is configured to drive the first detection unit and the second detection unit to rotate synchronously by a preset angle around the detection space in the direction of the central axis of the passage direction.

2. The rotatable muon detection device according to claim 1, characterized in that, The scintillator array group includes at least one column of scintillator arrays, and the scintillator array includes multiple scintillator units distributed along the central axis. In each layer of the scintillator array group, the planes containing the detection areas of the scintillator units are coplanar, so that the planes containing the detection areas of the multiple layers of the scintillator array group are parallel to each other. Alternatively, in each layer of the scintillator array group, multiple columns of the scintillator arrays are arranged sequentially along the circumference, and the planes containing the detection areas of adjacent columns of the scintillator arrays form a preset angle, so that the planes containing the detection areas of the scintillator array group are arc-shaped; in the first detection unit or the second detection unit, the opening directions of the arc-shaped detection areas of the two layers of the scintillator array groups are the same; the openings of the arc-shaped detection areas of the scintillator array groups of the first detection unit and the scintillator array groups of the second detection unit are opposite to each other.

3. The rotatable muon detection device according to claim 1, characterized in that, The rotatable muon detection device includes an inlet bracket and an outlet bracket. The inlet bracket includes a support body arranged around the perimeter and an inlet arranged in the middle for the object to be detected to enter the detection space. The outlet bracket includes a support body arranged around the perimeter and an outlet arranged in the middle for the object to be detected to leave the detection space. The rotary drive unit includes a ring track, a first support arm, a second support arm, and a rotary drive mechanism. The annular track includes an inlet-side annular track and an outlet-side annular track. The inlet-side annular track is disposed on the support body of the inlet bracket, and the outlet-side annular track is disposed on the support body of the outlet bracket. The axis of the annular track coincides with the central axis of the detection space. The first support arm extends along the central axis and its two ends are respectively in sliding or rolling engagement with the inlet-side annular track and the outlet-side annular track, and the first detection unit is disposed on the first support arm; the second support arm extends along the central axis and its two ends are respectively in sliding or rolling engagement with the inlet-side annular track and the outlet-side annular track, and the second detection unit is disposed on the second support arm; The rotary drive mechanism is configured to drive the first support arm and the second support arm to move along the annular track, thereby causing the first detection unit and the second detection unit to rotate synchronously.

4. The rotatable muon detection device according to claim 3, characterized in that, The rotatable muon detection device further includes a translation drive unit, which drives the first detection unit and the second detection unit to move along the passage direction or in the opposite direction of the passage reaction. The translation drive unit includes a linear guide rail, a first moving member, a second moving member, and the translation drive unit itself. The linear guide rail extends along the central axis and is disposed on the first support arm and the second support arm. One end of the first moving member is disposed on the first detection unit, and the other end is in sliding or rolling engagement with the linear guide rail on the first support arm. One end of the second moving member is disposed on the second detection unit, and the other end is in sliding or rolling engagement with the linear guide rail on the second support arm. The translation drive unit is configured to drive the first moving member and the second moving member to move along the linear track, thereby causing the first detection unit and the second detection unit to move along the passage direction or in the opposite direction of the passage reaction.

5. The rotatable muon detection device according to claim 3 or 4, characterized in that, The rotatable muon detection device also includes a signal transmission unit, a sensor, and a processor. The signal transmission unit is configured to have an independent readout circuit connected to each scintillator unit in the first and second detection units, for independently acquiring the output signal of the corresponding scintillator unit. The sensor is configured to acquire rotation angle information or translation information of the first detection unit and the second detection unit in real time. The processor is configured to determine the abnormality of the detected object based on the output signal of the scintillator unit and the rotation angle information or the translation information.

6. A detection method for customs, characterized in that, The method includes the following steps: From a single muon event, determine two incident representative points where the muon passes through the two-layer scintillator array group of the first detection unit of the rotatable muon detection device, and two exit representative points where the muon passes through the two-layer scintillator array group of the second detection unit. Record the coordinates of the two incident representative points and the two exit representative points in the local coordinate system of the rotatable muon detection device. Obtain the rotation angle of the first detection unit and the second detection unit about the central axis of the detection space in the passage direction, and use the rotation angle to transform the coordinates in the local coordinate system to the reference coordinate system to obtain the reference coordinates; The incident direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between the two representative points of the incident shots; the exit direction of the muon event in the reference coordinate system is calculated based on the reference coordinate difference between the two representative points of the exit shots. The scattering angle is calculated based on the incident direction and the exit direction, and the anomaly of the detected object is judged based on the scattering angle.

7. The method according to claim 6, characterized in that, "Judging the anomalies of the detected object based on the scattering angle" includes: Anomalies in the detected object are determined based on the scattering angle by employing either a fixed spatial area rotational scanning method or a combination of fixed spatial area rotational scanning and segmented scanning with translation in different spatial areas.

8. The method according to claim 7, characterized in that, The fixed spatial region rotational scanning includes: Multiple scattering angles corresponding to muon events passing through the same spatial region on the object under multiple different rotation angles are obtained. The distribution of the comprehensive scattering feature value of the same spatial region is calculated based on the multiple scattering angles. The distribution of the comprehensive scattering feature value is compared with a preset anomaly judgment standard. When the anomaly condition is met, it is determined that there is an anomaly in the spatial region. Optionally, the segmented scanning of different spatial regions includes: After completing the acquisition of muon data in the current spatial region, the first detection unit and the second detection unit move a preset step length along the direction of the object being detected or in the opposite direction of the passage reaction to reach a new spatial region, and perform the fixed spatial region rotation scan in the new spatial region. The distribution of the comprehensive scattering feature values ​​collected in each spatial region is correlated with the corresponding spatial region to reconstruct the full-length scattering feature distribution map of the detected object, and anomalies in the full-length range of the detected object are judged.

9. The method according to claim 6, characterized in that, The step "transforming the coordinates in the local coordinate system to the reference coordinate system using the rotation angle to obtain the reference coordinates" includes: Based on the rotation angle, the rotation matrix corresponding to the rotation angle is obtained, and the coordinates in the local coordinate system are transformed using the rotation matrix to obtain the reference coordinates in the reference coordinate system.

10. The method according to claim 6, characterized in that, "Judging the anomalies of the detected object based on the scattering angle" includes: For the i-th muon event, based on the scattering angle, muon momentum, and the ratio of muon velocity to the speed of light, a momentum-scattering angle joint feature is constructed: ， Among them, S i p represents the combined characteristics of momentum and scattering angle. i Denotes muon momentum, β i θ represents the ratio of the muon velocity to the speed of light. i Indicates the scattering angle. The test region of the object to be detected is divided into multiple voxels, and the comprehensive scattering index of muon events passing through the voxels is statistically analyzed: ， in, Indicates the overall scattering index, S represents the number of muons passing through the voxel. i This indicates the combined characteristics of momentum and scattering angle. The comprehensive scattering index is compared with data from a preset standard database to determine whether the voxel is abnormal.

Images