A dual-particle time-of-flight encoded radiographic camera and methods of use thereof

Abstract

The application discloses a double-particle time sequence coding ray camera and a use method thereof, and the double-particle time sequence coding ray camera comprises a central detector, a ring-shaped double-mode coding aperture plate, a signal processing and analysis system, a rotating platform control system, a supporting platform and a rotating platform. The application solves the contradiction between the sensitivity and the spatial resolution of the traditional time sequence coding camera design to a great extent, realizes one-dimensional position resolution of particle reaction by using double-end signal reading of the detector, improves the sensitivity of the device by increasing the volume of the detector, and ensures the spatial resolution, and the application can be applied to detection and positioning imaging of out-of-control radioactive sources.

Description

Technical Field

[0001] This invention belongs to the field of radiation detection and imaging, specifically relating to a dual-particle time-coded X-ray camera and its usage method. It can achieve the detection and localization imaging of potential radioactive sources over a large area. Background Technology

[0002] In open spaces such as ports, airports, and customs, radiometric imaging technology has become the most effective means of measuring and locating special nuclear materials, thus gaining attention and widespread research from major countries around the world.

[0003] For radioactive materials that emit neutrons, commonly used localization imaging methods include neutron scattering cameras, neutron-coded aperture cameras, and neutron time-coded X-ray cameras. Among these, time-coded X-ray cameras have advantages over the other two types, such as high detection efficiency, system simplicity, and low cost. However, traditional time-coded X-ray camera designs suffer from a trade-off between sensitivity and spatial resolution; that is, the larger the detector volume, the higher the sensitivity, but the spatial resolution decreases significantly. This invention employs a dual-readout reaction depth detector as the central detector, enabling the detector to have one-dimensional position resolution capability. This largely resolves the trade-off between device sensitivity and spatial resolution and optimizes the design of the annular dual-mode coded aperture plate. Summary of the Invention

[0004] The purpose of this invention is to detect and locate uncontrolled special nuclear materials and radioactive sources, eliminate potential radiation hazards, and propose a dual-particle time-series encoded X-ray camera and its usage method.

[0005] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0006] A dual-particle time-series encoded X-ray camera includes a central detector, an annular dual-mode encoding aperture plate, a signal processing and analysis system, a rotating platform control system, a support platform, and a rotating platform. The annular dual-mode encoding aperture plate is ring-shaped and can simultaneously encode neutrons and gamma rays. The central detector is placed inside the annular dual-mode encoding aperture plate and is coaxially arranged with the annular dual-mode encoding aperture plate. Signals are read out from both ends of the central detector. The annular dual-mode encoding aperture plate is placed on the rotating platform, which is rotatably mounted on the support platform. The rotating platform control system can control the rotation of the rotating platform, causing the annular dual-mode encoding aperture plate to rotate around its own axis. The signal processing and analysis system is connected to the central detector and is used to power the detector, receive the signals read out from both ends of the central detector, determine the reaction position and particle type of particles in the detector, and record the time of signal occurrence.

[0007] To optimize the above technical solution, the specific measures also include:

[0008] The aforementioned annular dual-mode coded aperture plate is provided with coded apertures. Neutrons and gamma rays passing through the coded apertures can irradiate the central detector, while neutrons and gamma rays that do not pass through the coded apertures are shielded by the annular dual-mode coded aperture plate.

[0009] The aforementioned annular dual-mode coded aperture plate consists of two layers, inner and outer. The coded apertures of the inner and outer coded aperture plates are aligned. The outer coded aperture plate can shield neutrons or gamma rays, and correspondingly, the inner coded aperture plate can shield gamma rays or neutrons.

[0010] The aforementioned neutron-shielding coded aperture plate is a hydrogen-rich material plate, while the gamma-ray-shielding coded aperture plate is a heavy metal plate. The hydrogen-rich material plate is a polyethylene plate, an plexiglass plate, or a boron-containing polyethylene plate.

[0011] The aforementioned heavy metal plates are tungsten plates, lead plates, or bismuth plates.

[0012] The aforementioned annular dual-mode encoding perforated plate has its axis set vertically. The encoding hole opening rule on the annular dual-mode encoding perforated plate is: it is generated by combining a horizontal one-dimensional uniform redundant sequence with random rotation. That is, each layer on the horizontal plane is a uniform redundant sequence, but each layer is rotated by a different angle.

[0013] The aforementioned central detector is a columnar plastic scintillator, liquid scintillator, or CLYC scintillator.

[0014] The above-mentioned central detector uses silicon photomultiplier tubes or SiPMs for signal readout at its upper and lower ends.

[0015] The aforementioned rotary platform control system is a stepper motor. The rotary platform is driven by the stepper motor and can rotate at a constant speed with adjustable speed.

[0016] A method for using a dual-particle time-coded ray camera, wherein the field of view is measured using the dual-particle time-coded ray camera.

[0017] During the measurement process, the annular dual-mode coded aperture plate rotates horizontally at a constant speed. The response of the central detector to different positions in the field of view changes with the rotation of the annular dual-mode coded aperture plate, and the response function of the central detector is different at different positions. The response function of the central detector at each position is obtained by Monte Carlo simulation.

[0018] As the coded aperture plate rotates, the signal processing and analysis system obtains the neutron and gamma ray count curves at each position of the central detector over time. If the curves at each position are approximately a horizontal line and the count rate is close to the background count rate, it indicates that there are no potential suspicious radioactive sources within the field of view.

[0019] If the curve fluctuates over time, it indicates the presence of a potential suspected radioactive source within the field of view. By combining the count change curves at various locations of the central detector with the response function, image reconstruction is performed for neutrons and gamma rays using algorithms such as maximum likelihood expectation maximization. Then, the reconstructed images from multiple locations of the detector are filtered and denoised. The filtering process is as follows:

[0020]

[0021] in N The number of intervals divided by the detector used. Fn For the first n Reconstructed images of each detector region, F The optimized image;

[0022] Obtain reconstructed hotspot images of the location of the radiation source.

[0023] The present invention has the following effects:

[0024] This device largely resolves the contradiction between device sensitivity and spatial resolution in traditional time-coded camera designs. It achieves one-dimensional position resolution by reading out the signals from both ends of the detector. While increasing the size of the detector to improve device sensitivity, it also ensures its spatial resolution. It can be used for the detection and localization imaging of runaway radioactive sources. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the device of the present invention;

[0026] Figure 2 This refers to the shape of the coded perforated plate in an embodiment of the present invention;

[0027] Figure 3 This is a curve showing the change of detector measurement count over time in an embodiment of the present invention;

[0028] Figure 4 This is the result of reconstructing the location of the radioactive source in an embodiment of the present invention.

[0029] The attached diagram is labeled as follows: 1. Central detector; 2. Annular dual-mode coded perforated plate; 3. Signal processing and analysis system; 4. Rotating platform control system; 5. Support platform; 6. Rotating platform. Detailed Implementation

[0030] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0031] like Figure 1 As shown,

[0032] The dual-particle time-series encoded X-ray camera of the present invention includes: a central detector 1, a ring-shaped dual-mode encoded aperture plate 2, a signal processing and analysis system 3, a rotating platform control system 4, a support platform 5, and a rotating platform 6. Dual particles refer to neutrons and gamma rays. The central detector 1 has neutron / gamma-ray discrimination capability; that is, when neutrons and gamma rays produce pulses with different shapes in the detector, the particle type can be distinguished based on the shape difference during signal processing. The detector is rod-shaped; increasing the detector length can significantly improve the sensitivity of the device. Silicon photomultiplier tubes are used at both ends of the detector for signal readout. The readout signals are input to the signal processing and analysis system 3, which amplifies and filters the signals, and records the amplitude, shape, and occurrence time of the readout signals at both ends. The type of particle reacting is determined based on the signal shape; by comparing the amplitude and time of the signals at both ends, the longitudinal position of the particle reacting in the detector can be determined, thus achieving one-dimensional position resolution capability of the detector. This is also an important means to resolve the contradiction between device sensitivity and spatial resolution.

[0033] The function of the annular dual-mode coded aperture plate 2 is to distinguish the detector's response to different spatial positions. The essence of the coded aperture plate is to reduce the detector's response to corresponding positions through shielding. Dual-mode refers to the coded aperture plate's shielding effect against both fast neutrons and gamma rays; therefore, hydrogen-rich polyethylene is chosen for fast neutron shielding, and tungsten is chosen for gamma ray shielding. In this invention, the aperture pattern of the coded aperture plate is generated by combining a one-dimensional uniform redundant sequence with random rotation. That is, each layer on the horizontal plane is a uniform redundant sequence, but each layer is rotated by a different angle. During measurement, the coded aperture plate rotates at a constant speed, and the detector's response to different positions in the field of view changes with the rotation of the coded aperture plate, and the response function of the detector at different positions is different. The response functions of the detector at each position are obtained by Monte Carlo simulation.

[0034] The central detector 1 is an EJ276 plastic scintillator with a diameter of 3cm and a length of 15cm; and two SiPMs read out the signals at its two ends.

[0035] The annular dual-mode coded perforated plate 2 is composed of an inner tungsten metal layer and an outer polyethylene layer. The inner tungsten metal layer is 1 cm thick and has an inner diameter of 30 cm; the outer polyethylene layer is 6 cm thick and has an inner diameter of 32 cm. The height of the coded perforated plate is 30 cm. The order of the coded perforated plate is 61×19, and the angle corresponding to each unit in the horizontal direction is 5.9°. Its unfolded schematic diagram is shown below. Figure 2 As shown. The central detector is placed in the center of the encoder plate.

[0036] The signal processing and analysis system 3 can power the SiPM of the central detector and perform amplification, filtering, integration and other processing on its readout signals.

[0037] The rotary platform control system 4 consists of a stepper motor and its control system, which controls the rotation direction and speed of the rotary platform 6.

[0038] The support platform 5 is made of aluminum alloy and is used to fix various parts of the device.

[0039] In specific implementation of this invention, the signal processing system can be purchased from relevant manufacturers, such as the DT5730 / DT5720B manufactured by CAEN.

[0040] When using a two-particle time-coded ray camera, the field of view is measured.

[0041] During the measurement process, as the coded aperture plate rotates, the count curves of neutrons and gamma rays at various locations on the detector can be obtained over time. If the curves at each location are approximately a horizontal line, it indicates that there are no potential suspicious radioactive sources within the field of view; if the curves fluctuate over time, it indicates that there are potential suspicious radioactive sources within the field of view. By combining the count curves of each location on the detector with the response function, images of neutrons and gamma rays can be reconstructed using algorithms such as maximum likelihood expectation maximization. Then, the reconstructed images from multiple locations are filtered for noise reduction. The filtering process is as follows:

[0042]

[0043] in N The number of intervals divided by the detector used. Fn For the first n Reconstructed images of each detector region, F To obtain the optimized image, the process multiplies the corresponding pixels of the reconstructed images at different locations of the detector and then takes the square root.

[0044] Obtain reconstructed hotspot images of the location of the radiation source.

[0045] Example:

[0046] Positioning and imaging measurements of two Cf-252 neutron sources at a distance of 100m

[0047] This example demonstrates the localization and imaging of two Cf-252 neutron sources located 100 m apart. The two sources are positioned at (210°, 27°) and (90°, 0°), respectively, with the former having twice the activity of the latter. During the measurement, the coded aperture rotates at a speed of 360° / 100s, and the measurement lasts for 1000s. The detector is divided longitudinally into five sections, each 3 cm in length. The response function of each section is obtained through simulation. The response functions of the five sections are shown below. Figure 3As shown. After the measurement was completed, the neutron and gamma ray counts of the five detectors were obtained as a function of time. The location of the radiation source was reconstructed using the maximum likelihood expectation-maximization method in conjunction with the response function. Figure 4 The imaging results show the location of the neutron radiation source.

[0048] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A dual-particle time-of-flight encoding gamma camera characterized by: The application relates to a double-particle time-sequence coding ray camera, which comprises a center detector (1), a ring-shaped double-mode coding aperture plate (2), a signal processing and analyzing system (3), a rotating platform control system (4), a supporting platform (5) and a rotating platform (6), the ring-shaped double-mode coding aperture plate (2) is annular and can code neutrons and gamma rays simultaneously, the center detector (1) is arranged on the inner side of the ring-shaped double-mode coding aperture plate (2), the center detector (1) is coaxial with the ring-shaped double-mode coding aperture plate (2), the two ends of the center detector (1) are used for signal reading, the ring-shaped double-mode coding aperture plate (2) is arranged on the rotating platform (6), the rotating platform (6) is rotatably arranged on the supporting platform (5), the rotating platform control system (4) can control the rotating platform (6) to rotate, so that the ring-shaped double-mode coding aperture plate (2) rotates around the axis thereof, the signal processing and analyzing system (3) is connected with the center detector (1) and is used for powering the detector and receiving the signals read by the two ends of the center detector (1), judging the reaction position of particles in the detector and the particle type, and recording the occurrence time of the signals; the ring-shaped double-mode coding aperture plate (2) has two layers, the coding holes of the inner layer coding aperture plate and the outer layer coding aperture plate are aligned, the outer layer coding aperture plate can shield neutrons or gamma rays, and correspondingly, the inner layer coding aperture plate can shield gamma rays or neutrons; the coding aperture plate for shielding neutrons is a hydrogen-rich material plate, the coding aperture plate for shielding gamma rays is a heavy metal plate, the hydrogen-rich material plate is a polyethylene plate or an organic glass plate or a boron-containing polyethylene plate, and the two ends of the center detector (1) are used for signal reading by using a silicon photomultiplier or a SiPM.

2. A dual-particle time-of-flight x-ray camera according to claim 1, wherein: The ring-shaped double-mode coding aperture plate (2) is provided with coding holes, neutrons and gamma rays passing through the coding holes can irradiate the center detector (1), and neutrons and gamma rays not passing through the coding holes are shielded by the ring-shaped double-mode coding aperture plate (2).

3. A dual-particle time-of-flight x-ray camera according to claim 1, wherein: The heavy metal plate is a tungsten plate or a lead plate or a bismuth plate.

4. A dual-particle time-of-flight x-ray camera according to claim 3, wherein: The axis of the ring-shaped double-mode coding aperture plate (2) is vertically arranged, and the coding holes on the ring-shaped double-mode coding aperture plate (2) are regularly opened by a horizontal one-dimensional uniform redundancy sequence combined with random rotation, that is, each layer in the horizontal plane is a uniform redundancy sequence, but each layer is rotated by different angles.

5. A dual-particle time-of-flight x-ray camera according to claim 4, wherein: The center detector (1) is a columnar plastic scintillator, a liquid scintillator or a CLYC scintillator.

6. A dual-particle time-of-flight x-ray camera according to claim 1, wherein: The rotating platform control system (4) is a stepping motor, the rotating platform (6) is driven by the stepping motor, and the rotating platform (6) can rotate at a uniform speed and the rotating speed is adjustable.

7. A method for using a two-particle time-coded ray camera, characterized in that: The double-particle time-sequence coding ray camera is applied to measuring a field of view, During the measurement, the ring-shaped double-mode coding aperture plate (2) rotates at a uniform speed, the response of the center detector (1) to different positions in the field of view changes with the rotation of the ring-shaped double-mode coding aperture plate (2), the response functions of different positions of the center detector (1) are different, and the response functions of the positions of the center detector (1) are obtained by Monte Carlo simulation. With the rotation of the coded aperture, the signal processing analysis system (3) obtains the curve of the neutron and gamma-ray counts of each position of the central detector (1) with time, if the curve of each position is approximately a horizontal line, and the count rate is close to the background count rate, it shows that there is no potential suspicious radioactive source in the field of view; If the curve fluctuates with time, it shows that there is a potential suspicious radioactive source in the field of view, through the curve of the count of each position of the central detector (1) with time, combined with the response function, the maximum likelihood expectation maximization algorithm is used for image reconstruction of neutron and gamma-ray respectively, and then the reconstructed images of multiple positions are filtered and denoised, the filtering process is as follows: wherein N the number of intervals divided for the employed detector, Fn is the reconstructed image of the n interval of the detector, F is the optimized image; The reconstructed hot spot image of the position of the radioactive source is obtained.

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