CN118642155B - Scintillator large-panel type muon detector - Google Patents

Abstract

The invention discloses a scintillator large-flat-plate type muon detector, which relates to the technical field of highway freight detection and comprises a shell, wherein an electronically-controlled DC-DC conversion module, a cable network module, a bias power supply module, a data acquisition and storage module, a signal processing circuit board and a sensitive module are arranged in the shell, the sensitive module is a single layer, a large rectangular flat plate is formed by arranging a plurality of detection units, each detection unit is a 200 cm*15 cm*6 cm cuboid, the material is slow liquid flash or plastic scintillator embedded optical fibers, photoelectric conversion reading plates are arranged at two ends of each detection unit, signals output by the photoelectric conversion reading plates enter a anticompction unit, and the surface of each detection unit is provided with a reflecting layer. The large-plate type muon detector has larger detection sensitivity area and lower cost, and overcomes the bottleneck that the conventional muon imaging detector has small sensitivity area, high manufacturing cost and complex structure and is difficult to be placed in related scenes such as expressway toll stations to develop freight detection application.

Description

A scintillator large flat-plate muon detector

Technical Field

The invention relates to the technical field of highway freight detection, and in particular to a scintillator large flat-plate muon detector.

Background Art

In terms of safety inspection of green agricultural product transport vehicles, traditional inspection methods include manual inspection and radioactive inspection. Manual inspection is time-consuming and labor-intensive and it is difficult to inspect large transport vehicles. Although radioactive inspection methods such as cobalt 60 and x-rays can improve inspection efficiency and accuracy, the cost of inspection equipment is too high and radioactive inspection equipment and radiation sources must undergo environmental impact assessment every year, which results in high subsequent maintenance costs and difficulties.

The mass of a muon is about 207 times that of an electron, and it produces less bremsstrahlung when passing through matter. Therefore, compared with electrons of the same energy, muons have smaller deflections and longer penetration distances. For muons with energies less than 200 GeV, the main form of energy loss is ionization excitation, and the muon energy loss rate is almost only related to the density of the target material. As a natural source of cosmic rays, muons have a wide energy range and strong penetration, and can image and detect the structure of large-scale targets with high resolution. Cosmic ray muon imaging technology does not require a radiation source and does not have risks such as radiation contamination. It is a green nuclear technology. At the same time, because muons are free radiation sources naturally generated by high-energy cosmic rays, the cost of use is low. Due to these advantages of muons in non-destructive testing imaging, muon imaging technology has received widespread attention in recent years and has been gradually applied to various aspects such as scientific research and industry. At present, the application of muon imaging technology in the field of freight inspection has the following main problems: (1) The existing large-scale muon imaging detectors are expensive and are not suitable for large-scale promotion and use in highway toll stations; (2) Muon detectors are not suitable for field detection environments, and the implementation of detection requires a lot of manpower and material resources to complete; (3) In the application scenario of highway freight inspection, new requirements are put forward for detection time, requiring the design of new sensitive detectors that can respond quickly.

Therefore, it is urgent to study a muon detector that can quickly respond to the detection process and realize the application of muon nondestructive testing technology in the field of highway freight inspection.

Summary of the invention

In order to solve the above technical problems, the present invention discloses a scintillator large flat-plate muon detector, which can be placed in highway toll stations and other scenarios where non-destructive internal inspection of large freight vehicles is required. The single-layer flat-plate muon detector not only increases the detection sensitive area but also reduces the cost. The flat-plate muon detector is easy to assemble and maintain, and can work normally when fixed on the ground in the application scenario of highway toll stations without affecting the normal passage of vehicles. The detector includes multiple detection units, which are arranged in sequence. A single detection unit can effectively monitor part of the interior of the car, and the rapid non-destructive inspection of the interior of large freight vehicles can be achieved by summarizing and analyzing the data of each detection unit.

To achieve the above object, the present invention adopts the following technical solutions:

A scintillator large flat-plate muon detector comprises a shell, wherein an electrically controlled DC-DC conversion module, a cable network module, a bias power supply module, a data acquisition and storage module, a signal processing circuit board, and a sensitive module are arranged inside the shell, wherein the sensitive module is a single layer, and is composed of a plurality of detection units arranged to form a large rectangular flat plate, each detection unit is a 200cm*15cm*6cm cuboid, and is made of slow liquid scintillator or a plastic scintillator with an embedded optical fiber, photoelectric conversion readout boards are installed at both ends of the detection unit, and the signal output by the photoelectric conversion readout board enters the anti-coincidence unit, and a reflection layer is provided on the surface of the detection unit for reflecting the scintillation light emitted by the scintillator.

Optionally, a fixing device is mounted on the housing for fixing the detector during the measurement process.

Optionally, the shell is made of metal material to shield excess cosmic ray noise.

Optionally, when the muon passes through the sensitive module, the muon ray deposits energy in the scintillator along the path and is converted into scintillation photons, which are read out by the photoelectric conversion readout plates at both ends of the sensitive module after transmission and converted into electrical signals;

When a muon passes through the detector, the muon direction and incident point determine the emission time and position of the scintillation photons generated along the track, thereby determining the time when the scintillation photons reach the photoelectric conversion readout plate. The time information can be used to infer the impact position of the muon event, and then obtain the muon event count;

The attenuation law of photons in a single medium conforms to the exponential attenuation form, as shown in formula (1):

(1);

In the formula, _N0 is the initial total number of photons, x is the length that the photons travel in the medium, and λ is the attenuation length of the medium material; when the rays enter the scintillator, they interact with the scintillator, deposit energy, and are converted into scintillation photons; the photons are transmitted from the generation position to the two ends of the scintillator, and finally reach the photoelectric conversion readout board, which converts the optical signal into an electrical signal.

Assume that the number of photoelectrons generated by the photoelectric conversion readout plate at one end is _E1 , and the number of photoelectrons generated by the photoelectric conversion readout plate at the other end is _E2 . Assume that the length of the sensitive module is L, and the center position is the origin. When a muon enters the sensitive module and interacts, the interaction point is X. The distance from this point to the two ends of the sensitive module is L/2+X and L/2-X respectively. The number of photoelectrons _E1 and _E2 generated by the photoelectric conversion readout plates at the two ends are:

(2);

(3);

Where, _E0 is the average ionization energy of the generated photons, E _µ is the deposition energy of the muons in the scintillator; P is the probability that a photon is transmitted to both ends and converted into a photoelectron by the photoelectric conversion readout plate; α is the attenuation coefficient, which is the reciprocal of the attenuation length;

By using formulas (2) and (3), we can obtain the position X and the deposited energy E _µ where the muon ray interacts with the sensitive module.

(4);

(5);

The double-end readout method is used to determine the impact position of the muon. A single sensitive unit corresponds to a certain area inside the truck, and the one-dimensional impact position of the muon in a single sensitive unit is quickly given. The information of multiple detection units is integrated, and the muon count distribution can be obtained without calculating the muon track, and the change of the muon count after passing through the vehicle body can be quickly given.

When the incident muon passes through multiple scintillators, the signals triggered by the same event are screened out through coincidence measurement, the interaction position information of each triggered scintillator is calculated, and a muon event count is performed;

The scintillation photons are converted into electrical signals, which are collected and stored by the data acquisition and storage module after shaping, amplification and filtering.

Optionally, when a muon passes through the detector, an electrical signal is generated at the photoelectric conversion readout board at both ends, which is converted into an anti-conformity logic signal after shaping, amplification and filtering, and input into the data acquisition and storage module. If the arrival time of the signals at both ends is within the set time window, a muon event is recorded.

The beneficial effect of the present invention is that the large flat-panel muon detector of the present invention has a large detection sensitive area, and can be applied to the field of freight detection in the "green channel" of highways and related freight transportation safety detection, and the scene of rapid internal detection of related freight vehicles passing through the "green channel". At the same time, the cost is low, which overcomes the bottleneck of the current muon imaging detector with small sensitive area, high cost, complex structure, and difficulty in being placed in relevant scenes such as highway toll stations for freight detection applications. The method of the present invention can be expanded to a wider range of fields, such as customs security inspection. The present invention can effectively avoid the problems of time-consuming and labor-intensive manual inspection, high cost of traditional radioactive detection methods, high environmental protection requirements, and potential safety hazards.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram of the detection principle of a scintillator large flat-plate muon detector according to the present invention;

FIG2 is a flow chart of a scintillator large flat-panel muon detector of the present invention for monitoring and warning freight trucks passing through the “green channel” at a highway toll station;

FIG3 is a schematic diagram of the structure of a scintillator large flat-plate muon detector according to the present invention;

FIG4 is a block diagram of a scintillator large flat-panel muon detector system according to the present invention;

FIG5 is a schematic diagram showing the principle of the detector sensitive unit calculating the muon impact position;

FIG6 is a correlation diagram between the total muon counts and cargo density of trucks loaded with cargo of different densities in the Monte Carlo simulation results;

FIG7 is a correlation diagram between the total count of abnormal body muons and cargo density of a freight vehicle in vegetables doped with different densities in the Monte Carlo simulation results;

Figure 8 shows the difference in muon counts of each detector sensitive unit in the Monte Carlo simulation results when a freight vehicle is doped with abnormal bodies of different densities in vegetables;

Figure 9 shows the difference in muon counts of each detector sensitive unit in the Monte Carlo simulation results when a freight vehicle is doped with abnormal bodies of different densities in vegetables;

Figure 10 shows the difference in muon counts of each detector sensitive unit in the Monte Carlo simulation results when a freight vehicle is doped with abnormal bodies of different densities in vegetables;

Figure 11 shows the difference in muon counts of each detector sensitive unit in the Monte Carlo simulation results for a freight vehicle mixed with vegetables containing abnormal bodies of different densities.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

As shown in Figure 1, when muons pass through matter, they mainly lose energy through ionization and atomic excitation. The average energy loss rate satisfies the Bethe-Block formula, and it can be considered that when muons of the same energy pass through a material, the energy loss rate is linearly related to the density of the material. When muons pass through a freight vehicle, the energy loss of the muons changes with the change in the density of the cargo in the vehicle, so the number of muons reaching the detector will change. When a truck is fully loaded with vegetables, its internal density can be approximately considered to be 1g/ ^cm3 . Using Monte Carlo simulation and experimental methods, freight vehicles of different specifications that are normally fully loaded with various types of vegetables are analyzed to obtain the changes in muon counts under their respective conditions and form a database. During actual measurement, the truck stays above the detector, and the detector obtains the muon flux passing through the truck during this period of time. The muon count and the muon hitting position are analyzed, and the results are compared with the database to determine whether there are density anomalies inside the freight vehicle. The specific process is shown in Figure 2.

A scintillator large flat-plate muon detector, as shown in Figures 3 and 4, includes a shell with a waterproof sealing function and shielding background gamma rays, a DC-DC conversion module, a cable network module, a bias power supply module, a data acquisition and storage module, a signal processing circuit board, and a sensitive module are arranged inside the shell with electronic control connections, wherein the sensitive module is a single layer, and is composed of a plurality of detection units arranged to form a large rectangular flat plate, each detection unit is a 200 cm*15 cm*6 cm cuboid, and is made of slow liquid scintillator or plastic scintillator with embedded optical fiber, photoelectric conversion readout boards are installed at both ends of the detection unit, and the signal output by the photoelectric conversion readout board enters the anti-coincidence unit, and a reflection layer is provided on the surface of the detection unit for reflecting the scintillation light emitted by the scintillator.

Compared with the traditional flat-plate muon detector, the present invention uses a dual-end readout method to determine the muon hit position, and then cooperates with multiple detection units to give the muon count distribution on different detection units. First, the present invention reduces the number of detector layers (traditional flat-plate detectors require 2-4 layers), and only a single layer is needed to achieve the detection function; second, while increasing the detection sensitive area and shortening the detection time, the cost is greatly reduced, making it possible for the invention to be mass-produced to serve domestic highways.

In this embodiment, 40 detection units are combined and arranged into a large muon flat-panel detector with a length of 600 cm, a width of 200 cm, and a height of 6 cm. The detection unit material is composed of slow liquid scintillator or plastic scintillator embedded with optical fiber. Slow liquid scintillator has high energy resolution and high particle identification ability, and can accurately identify muons; optical fiber is embedded in the plastic scintillator to enhance the light signal reaching both ends of the detection unit. The photoelectric readout conversion plate is specially processed and the end receiving photons is placed inside the detection unit.

The detector housing is equipped with a fixing device to prevent the detector from moving during the measurement process. The detector is fixed in a specific area on the detector housing and cannot be moved. Other performance requirements of the detector include: the scintillator must be placed in a light-tight environment; the detector has a waterproof sealing design.

As shown in Figure 5, when a muon passes through a sensitive module, the muon ray deposits energy in the scintillator along the path and is converted into scintillation photons. The scintillation photons are transmitted and read out by the photoelectric conversion readout boards at both ends of the sensitive module, and the optical signals are converted into electrical signals. When a muon passes through a detector, the muon direction and incident point determine the emission time and position of the scintillation photons generated along the track, thereby determining the time when the scintillation photons reach the photoelectric conversion readout board. The time information can be used to infer the impact position of the muon event, and then the muon event count can be obtained.

The attenuation law of photons in a single medium conforms to the exponential attenuation form, as shown in formula (1):

(1);

In the formula, _N0 is the initial total number of photons, x is the length that the photons travel in the medium, and λ is the attenuation length of the medium material; when the rays enter the scintillator, they interact with the scintillator, deposit energy, and convert it into scintillation light; the photons are transmitted from the generation position to the two ends of the scintillator, and finally reach the photoelectric conversion device, which converts the optical signal into an electrical signal.

Assume that the number of photoelectrons generated by the photoelectric conversion readout plate at one end is _E1 , and the number of photoelectrons generated by the photoelectric conversion readout plate at the other end is _E2 . Assume that the length of the sensitive module is L, and the center position is the origin. When a muon enters the sensitive module and interacts, the interaction point is X. The distance from this point to the two ends of the sensitive module is L/2+X and L/2-X respectively. The number of photoelectrons _E1 and _E2 generated by the photoelectric conversion readout plates at the two ends are:

(2);

(3);

In the formula, _E0 is the average ionization energy of the generated photons, E _µ is the deposition energy of the muons in the scintillator; P is the probability that a photon is transmitted to both ends and converted into a photoelectron by the photoelectric conversion readout plate; α is the attenuation coefficient, which is the reciprocal of the attenuation length.

By using formulas (2) and (3), we can obtain the position X and the deposited energy E _µ where the muon ray interacts with the sensitive module:

(4);

(5).

When the incident muon passes through multiple scintillators, the signal triggered by the same event is screened out through coincidence measurement, the interaction position information of each triggered scintillator is calculated, and a muon event count is performed; when the muon passes through the detector, the photoelectric conversion readout plates at both ends generate electrical signals, which are converted into anti-coincidence logic signals after shaping, amplification, and filtering, and input into the data acquisition and storage module. If the arrival time of the signals at both ends is within the set time window, a muon event is recorded.

After the analog signal output by the photoelectric conversion readout board enters the signal processing circuit board, it is converted into a digital signal through digital-to-analog conversion, and the effective events are preliminarily screened through time coincidence. When an effective event occurs, the signal processing circuit board will package the trigger information and the instrument orientation, inclination and other information together and upload them through the network port. The network port of the signal processing circuit board is connected to the cable network module, which modulates the digital signal and loads it onto the 220V AC power line. Another cable network module on the ground is connected to the other end of the power line, and the load signal is demodulated and transmitted to the ground machine through the network port. The ground machine finally stores the data collected by the instrument in the cloud server through network transmission for subsequent data processing and analysis.

Figures 6 to 11 are simulation results for the method of the present invention, which also demonstrate that the invention has good feasibility. Figure 6 is a Monte Carlo simulation result in which a truck is carrying cargo of different densities, and the detector collects a correlation diagram between the muon survival rate and the cargo density. The results show that the muon survival rate is positively correlated with the cargo density. Figure 7 is a Monte Carlo simulation result in which a freight vehicle mixes anomalies of different densities in the vegetable cargo, and the correlation between the total muon count obtained by the detector and the cargo density. Figures 8 to 11 are Monte Carlo simulations in which cargo of different densities is mixed in the middle area of a vegetable truck, and the counts of each sensitive detection unit are compared with the counts of each sensitive detection unit when the truck is fully loaded with vegetables and no anomalies are placed. The results show that after the anomaly is placed, the muon counts of the sensitive detection units in the relevant area will change significantly.

Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims (2)

1. The scintillator large-panel-type muon detector is characterized by comprising a shell, wherein a DC-DC conversion module, a cable network module, a bias power supply module, a data acquisition and storage module, a signal processing circuit board and a sensitivity module which are electrically connected are arranged in the shell, the sensitivity module is a single layer, a large rectangular panel is formed by arranging a plurality of detection units, each detection unit is a cuboid with the thickness of 200cm x 15cm x 6cm, the material is slow liquid flash or plastic scintillator embedded optical fibers, photoelectric conversion reading plates are arranged at two ends of each detection unit, signals output by the photoelectric conversion reading plates enter a reflection unit, and a reflection layer is arranged on the surface of each detection unit and used for reflecting scintillation light emitted by the scintillator;

The shell is provided with a fixing device for fixing the detector in the measuring process;

the shell is made of metal materials and is used for shielding redundant cosmic ray noise;

When the muon passes through the sensitive module, the muon rays deposit energy in the scintillators along the paths and are converted into scintillation photons, and the scintillation photons are read out by photoelectric conversion reading plates at two ends of the sensitive module through transmission and are converted into electric signals;

the attenuation law of photons in a single medium conforms to an exponential decay form as shown in formula (1):

Wherein N ₀ is the initial total photon number, x is the length of the photons passing through the medium, and lambda is the attenuation length of the medium material; when the rays enter the scintillator, the rays interact with the scintillator, deposit energy and are converted into scintillation photons; photons are transmitted from the generating position to two ends of the scintillator and finally reach the photoelectric conversion reading plate to convert the optical signals into electric signals;

Assuming that the length of the sensitive module is L, the center position is the origin, when one muon enters the sensitive module to interact, the interaction point is X, the distances from the point to the two ends of the sensitive module are L/2+X and L/2-X respectively, and the photoelectron numbers E ₁ and E ₂ generated by the photoelectric conversion readout plates at the two ends are respectively:

Wherein E ₀ is the average ionization energy to generate photons, and E _μ is the deposition energy of the muon in the scintillator; p is the probability that photons are transmitted to two ends and are converted into photoelectrons by a photoelectric conversion reading plate; alpha is an attenuation coefficient and the attenuation length is reciprocal;

The interaction point X of the muon rays and the sensitive module and the deposition energy E _μ are obtained through formulas (2) and (3):

Acquiring one-dimensional coordinates of the hit position of the muon by a double-end reading mode, and matching with a plurality of detection units to obtain muon counting distribution so as to realize rapid detection;

When the incident muon passes through a plurality of scintillators, calculating interaction position information of each triggered scintillator by conforming to the signals for measuring and screening the same event trigger, and counting muon events once;

The scintillation photons are converted into electrical signals, shaped, amplified and filtered, and then collected and stored by a data acquisition and storage module.

2. A scintillator large panel type muon detector as set forth in claim 1 wherein when the muon passes through the detector, an electrical signal is generated at the photoelectric conversion readout board, shaped, amplified, filtered, converted into an anti-coincidence logic signal, input to the data acquisition and storage module, and if the arrival time of the signals at both ends is within a set time window, a muon event is recorded.