A neutron detector

Abstract

The application discloses a neutron detector. The neutron detector comprises a cover plate, a base, and a plurality of boron-coated micro-gap chamber electrodes stacked together, the cover plate and the base forming a gas cavity for accommodating the boron-coated micro-gap chamber electrodes; the cover plate is provided with an incident window, and a boron-coated cathode plate is mounted on the inner surface of the incident window; the boron-coated micro-gap chamber electrode comprises a substrate, the surface of the substrate facing the cover plate is provided with a plurality of mutually parallel metal readout strips, the surface of the metal readout strip is provided with a plurality of mutually parallel metal anode strips in a direction perpendicular to the metal readout strip, and the readout strip and the anode strip are separated by an insulating layer; and the surface of the substrate facing the base is coated with a boron film layer. Compared with the existing multilayer boron-coated multi-wire proportional chamber, the neutron detector has higher position resolution and the highest counting rate, and compared with the existing multilayer boron-coated GEM, each layer of the neutron detector has two-dimensional readout capability, does not need to add additional readout electrodes, and is more conducive to the adoption of a multilayer structure to realize high-efficiency neutron detection.

Description

Technical Field

[0001] This application relates to the field of neutron detection equipment, and in particular to a neutron detector. Background Technology

[0002] Neutrons are ideal probes for studying the microscopic structure and dynamic properties of matter. Currently, neutron scattering is widely used in many disciplines, including physics, chemistry, materials science, biology, geology, energy, medicine and health, and environmental protection.

[0003] Position-sensitive neutron detectors are a key component of neutron scattering spectrometers. For a long time, most neutron scattering spectrometers have used high-pressure helium-3 neutron detectors. However, the recent helium-3 gas supply crisis has led countries worldwide to actively explore alternative neutron detection technologies, with boron-10 coated gas detectors being one of the main development directions. As a gas detector, the significant advantage of boron-10 coated neutron detectors is their extremely low gamma-ray sensitivity. However, since the effective detection efficiency of a single layer of boron-10 for thermal neutrons is only about 5%, achieving high neutron detection efficiency is the main key technical problem to be solved for this type of detector.

[0004] To improve the detection efficiency of boron-coated neutron detectors, the main current method is to use multilayer boron-coated 10B thin films, including multilayer boron-coated multifilament proportional cells and boron-coated gas electron multipliers (GEMs). The advantage of multilayer boron-coated multifilament proportional cells is that the detector material scatters neutrons less, but its maximum count rate is relatively low. Current research focuses primarily on the development of neutron detectors based on multilayer boron-coated GEMs. Due to limitations such as the high-voltage stability of the GEM film, the film size, and the technical process of fabricating the 10B coating on the GEM surface, fabricating large-area position-sensitive neutron detectors using multilayer GEM films presents certain difficulties. Summary of the Invention

[0005] The purpose of this application is to provide a structurally improved neutron detector.

[0006] The following technical solution is adopted in this application:

[0007] This application discloses a neutron detector, including a cover plate, a base, and a plurality of stacked boron-coated microgap chamber electrodes installed between the cover plate and the base. The cover plate and the base form a gas cavity for accommodating the boron-coated microgap chamber electrodes. An entrance window is provided on the cover plate, and a boron-coated cathode plate is installed on the inner surface of the entrance window. The boron-coated microgap chamber electrodes include a substrate, and a plurality of parallel metal readout strips are provided on the surface of the substrate facing the cover plate. A plurality of parallel metal anode strips are provided on the surface of the metal readout strips in a direction perpendicular to the metal readout strips. The metal readout strips and the metal anode strips are separated by an insulating layer. A boron thin film layer is coated on the surface of the substrate facing the base.

[0008] It should be noted that in this application, the metal anode strips of each stacked boron-coated microgap chamber electrode have the same orientation, meaning that the metal anode strips of boron-coated microgap chamber electrodes located in different layers are parallel to each other. Compared to existing multilayer boron-coated multi-wire proportional cells, the neutron detector of this application has higher position resolution and the highest count rate. Compared to existing multilayer boron-coated GEMs, each layer of the neutron detector in this application, i.e., each boron-coated microgap chamber electrode, has its own two-dimensional readout capability, eliminating the need for additional readout electrodes and making it easier to achieve high-efficiency neutron detection using a multilayer structure. In one implementation of this application, using 20 stacked boron-coated microgap chamber electrodes can achieve a thermal neutron detection efficiency exceeding 50%.

[0009] In one implementation of this application, the substrate of the boron-coated microgap chamber electrode is an aluminum-based printed circuit board.

[0010] Preferably, the thickness of the aluminum-based printed circuit board is 0.3-1mm.

[0011] In one implementation of this application, the metal readout bar of the boron-coated microgap chamber electrode is a copper bar, and the width of the metal readout bar is 0.5-2 mm.

[0012] In one implementation of this application, the metal anode strip of the boron-coated microgap chamber electrode is made of gold, and the metal anode strip has a thickness of 1-3 μm, a width of 10-20 μm, and a strip spacing of 200-500 μm.

[0013] In one implementation of this application, the thickness of the boron thin film layer of the boron-coated microgap chamber electrode is 0.1-10 μm.

[0014] Preferably, the thickness of the boron thin film layer is 0.5-4 μm, more preferably 1-3 μm.

[0015] In one implementation of this application, among a plurality of stacked boron-coated microgap chamber electrodes, the gap between two boron-coated microgap chamber electrodes is 3-6 mm, preferably 4-5 mm.

[0016] In one implementation of this application, the substrate of the boron-coated cathode plate is an aluminum-based printed circuit board, and the surface of the aluminum-based printed circuit board is coated with... 10 B4C film.

[0017] Preferably, the thickness of the aluminum-based printed circuit board is 0.3-1mm.

[0018] In one implementation of this application, 10 The thickness of the B4C film is 0.1-10 μm, preferably 0.5-4 μm, and more preferably 1-3 μm.

[0019] In one implementation of this application, a high-voltage connector and a signal lead-out connector are provided on the gas chamber, and each electrode is connected to a high-voltage power supply and a signal readout electronics system through the high-voltage connector and the signal lead-out connector, respectively.

[0020] In one implementation of this application, the signal readout electronics system includes a fast charge-sensitive preamplifier and a multi-channel digitizer; the signal position readout of the neutron detector adopts the delay line readout method, with each metal anode bar and metal readout bar connected to the port of the delay line module. The output signals at both ends of the delay line module are amplified and timed by the charge-sensitive preamplifier, respectively. The timing signal output by the charge-sensitive preamplifier is timed by the multi-channel digitizer. The generation position of the pulse current signal, i.e., the incident position of the neutron, is determined by measuring the time difference between the arrival of the signal at both ends of the delay line module.

[0021] It's important to note that the delay line module's function is to establish the time difference between the arrival times of the signals at both ends. The charge-sensitive preamplifier is placed on the two signals output from the series connection of the delay line module. The charge-sensitive preamplifier amplifies the signal from the delay line module, ensuring the signal is strong enough to be detected by the electronics, thus making the time difference between the two ends more clearly visible and enabling more accurate time difference measurement. In short, the delay line module directly introduces the time difference between the signals at both ends, while the charge-sensitive preamplifier amplifies the signal for time difference measurement. Therefore, matching the characteristic impedance of the delay line module with the design of the charge-sensitive preamplifier minimizes or avoids the loss of the original signal while further amplifying it.

[0022] It should also be noted that in this application, the delay line module directly affects the performance of the neutron detector. Using a delay line module chip can save experimental space and ensure the consistency of the delay time between the signal output and the charge-sensitive preamplifier. One implementation of this application uses a 1507-50C delay block chip manufactured by Data Delay Devices. Each delay block chip has ten delay block units, each with a delay time of 5ns, an equivalent inductance of L = 1μH, and an equivalent capacitance of C = 25pF. A single 1507-50C delay block chip has 14 contacts, 10 of which are connected to the metal readout strip; one is either input or output, one is floating, and the last two are grounded.

[0023] In one implementation of this application, the working gas of the neutron detector is argon and carbon dioxide at one atmosphere.

[0024] It should be noted that the working gas is a mixture of argon and carbon dioxide. After the neutrons react with boron, the secondary particles produced mainly undergo primary ionization with Ar molecules in the mixture. Carbon dioxide, as a quenching gas, is mainly used to prevent the detector from sparking and damaging its components.

[0025] In one implementation of this application, the neutron detector includes 2-20 stacked boron-coated microgap chamber electrodes.

[0026] It should be noted that, in one implementation of this application, the thermal neutron detection efficiency of using four stacked boron-coated microgap chamber electrodes can reach 19%, the thermal neutron detection efficiency of eight stacked boron-coated microgap chamber electrodes can reach 30%, and the thermal neutron detection efficiency of twenty stacked boron-coated microgap chamber electrodes can reach more than 50%, which can meet the application requirements of neutron detection and has higher position resolution and the highest count rate.

[0027] It should also be noted that the neutron detector of this application, if not using boron-coated electrodes, can be used in a single-layer structure for X-ray or other particle position measurement. If only neutron counting measurement is required, the reading can be performed solely by the metal anode strips; by connecting all the metal anode strips together as a single output channel, the signal can be amplified and filtered before using a counter or other equipment for neutron counting measurement.

[0028] The beneficial effects of this application are as follows:

[0029] This application's neutron detector innovatively combines a high-count-rate-tolerant two-dimensional micro-gap chamber with multilayer boron coating technology, enabling high count rate, high position resolution, and high-efficiency neutron detection. Compared to existing multilayer boron-coated multi-wire proportional chambers, this application's neutron detector exhibits higher position resolution and a higher count rate. Compared to existing multilayer boron-coated GEMs, each layer of this application's neutron detector possesses built-in two-dimensional readout capability, eliminating the need for additional readout electrodes and facilitating the adoption of multilayer structures for high-efficiency neutron detection. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the principle of the neutron detector in an embodiment of this application;

[0031] Figure 2 This is a schematic diagram of the structure of the neutron detector according to an embodiment of this application;

[0032] Figure 3 The embodiments of this application have different numbers of layers and different thicknesses. 10 Detection efficiency test results of B4C thin film neutron detector. Detailed Implementation

[0033] This application creatively combines a high-count-rate boron-coated microgap chamber electrode, namely a two-dimensional microgap chamber (MGC), with multilayer boron coating technology to achieve high count rate, high position resolution, and high-efficiency neutron detection. To reduce neutron scattering by the detector material, a thin aluminum-based printed circuit board (aluminum-based PCB) is used as the substrate for the MGC. The two-dimensional MGC is fabricated on one surface of the aluminum-based PCB, while the other surface is coated with a boron-10 thin film for neutron conversion. The working principle of the microgap chamber is similar to that of a multi-wire proportional chamber, but this application uses metal microstrips approximately 10 micrometers wide as anode strips. The spacing between the anode strips can be several hundred micrometers, for example, 200-500 μm, thus achieving high position resolution. Furthermore, since the distance from the anode strip to the cathode is only tens of micrometers, the influence of space charge effect after avalanche amplification on the count rate is greatly reduced, thus achieving a high count rate. High neutron detection efficiency can be achieved by stacking multiple layers of two-dimensional boron-coated microgap chambers.

[0034] To achieve two-dimensional position resolution, existing boron-coated multi-wire proportional cells typically require two readout wire planes in addition to the anode wire plane, resulting in a complex structure. The position resolution of multi-wire and micro-gap cells in the direction perpendicular to the anode wire or anode microstrip is mainly determined by the spacing of the anode wires or microstrips. The minimum anode wire spacing in multi-wire cells is approximately 1 mm, making it difficult to achieve high position resolution. In contrast, the neutron detector of this application features a micro-gap cell (MGC) with built-in two-dimensional position resolution in each layer. The smaller spacing of the anode strips enables higher position resolution. Furthermore, due to the smaller distance between the anode and cathode strips in the micro-gap cell, positive ions after avalanche are quickly collected, resulting in a much weaker space charge shielding effect compared to multi-wire cells, thus achieving a high count rate. Moreover, while boron-coated multi-wire proportional cells require a boron-coated cathode plane in addition to the wire plane, the micro-gap cell (MGC) of this application has an anode strip and readout electrode fabricated on one surface and a boron coating on the other, eliminating the need for an additional boron-coated electrode plate.

[0035] Multilayer boron-coated gas detectors achieve high thermal neutron detection efficiency through multilayer boron coating films. In multilayer structures, the total thickness of the boron-coated substrate increases significantly, posing a challenge to the absorption and scattering of incident neutrons. Compared to other structures, the two-dimensional microgap chamber (MGC) used in this application can achieve boron coating itself, thus eliminating the need for additional boron-coated electrodes. Furthermore, this application uses a thin aluminum-based PCB board as the substrate for the MGC; since aluminum has a small neutron scattering cross-section, low neutron scattering characteristics can be achieved.

[0036] The present application will be further described in detail below through specific embodiments. The following embodiments are only for further illustration of the present application and should not be construed as limiting the present application.

[0037] Example

[0038] In this example, the neutron detector, such as Figure 1 and Figure 2 As shown, the device includes a cover plate 1, a base 2, and eight stacked boron-coated microgap chamber electrodes 3 installed between the cover plate 1 and the base 2. The cover plate 1 and the base 2 form a gas cavity for accommodating the boron-coated microgap chamber electrodes 3. An entrance window 11 is provided on the cover plate 1, and a boron-coated cathode plate 12 is installed on the inner surface of the entrance window 11. The boron-coated microgap chamber electrode 3 includes a substrate 31. A plurality of parallel metal readout bars 32 are provided on the surface of the substrate 31 facing the cover plate 1. A plurality of parallel metal anode bars 33 are provided on the surface of the metal readout bars 32 in a direction perpendicular to the metal readout bars 32. The metal readout bars 32 and the metal anode bars 33 are separated by an insulating layer 34. A boron thin film layer 35 is coated on the surface of the substrate 31 facing the base 2.

[0039] Among them, the boron-coated cathode plate 12 is formed by spraying a 1.8μm thick layer of boron onto the surface of a 0.5mm thin aluminum-based printed circuit board (aluminum-based PCB) using magnetron sputtering. 10 A boron-coated cathode plate 12 is formed using a B4C thin film. To reduce neutron scattering by the detector material, a thin aluminum-based printed circuit board (aluminum-based PCB) is used as the substrate 31 for the boron-coated microgap chamber electrode 3, i.e., the microgap chamber (MGC). A two-dimensional microgap chamber (MGC) is fabricated on one surface of the aluminum-based PCB, and a boron-coated neutron conversion layer is fabricated on the other surface. First, an aluminum-based PCB with copper strips on its surface is fabricated. The metal strips serve as signal readout strips, i.e., metal readout strips 32, and their width is determined by the position resolution requirements, for example, a width of 0.5-2 mm, specifically 1 mm in this example. On the surface of the metal readout strips 32 on the aluminum-based PCB, a 2 μm thick insulating film, i.e., insulating layer 34, is first deposited by vacuum evaporation. In this example, SiO2 (diamond thin film) is used, with an evaporation rate of 0.1 nm / s and a substrate temperature of 100 °C. Then, Au gold anode metal microstrips, i.e., metal anode strips 33, are fabricated by etching. The metal anode strip 33 has a thickness of approximately 2 micrometers, for example, 1-3 micrometers, a width of 10-20 micrometers, a strip spacing of 200-500 micrometers, and is perpendicular to the direction of the metal readout strip 32. In this example, the metal anode strip 33 has a thickness of 2 micrometers, a width of 15 micrometers, and a strip spacing of 350 micrometers. After the two-dimensional microgap chamber (MGC) microstrips are fabricated, they are sprayed onto another surface of the aluminum-based PCB board using magnetron sputtering. 10 The neutron conversion layer, namely boron thin film layer 35, is made of B4C thin film with a thickness of 1.8 μm.

[0040] In this example, the boron-coated cathode plate 12 and the eight stacked boron-coated microgap chamber electrodes 3 are placed inside the gas cavity formed by the cover plate 1 and the base 2. The cover plate 1 has an entrance window 11, and the uppermost boron-coated cathode plate 12 is fixed to the inner surface of the entrance window 11 by screws through through holes at its four corners. The eight stacked boron-coated microgap chamber electrodes 3 also have through holes at their four corners, and are fixed together to the base 2 of the cavity by long screws. A 4.5mm thick PCB spacer is placed between every two electrode layers to ensure a 5mm distance between adjacent boron-coated electrodes.

[0041] In this example, the neutron detector uses an Ar / CO2 mixture as the working gas. A high-voltage connector and a signal lead-out connector are installed on the gas chamber. Each electrode is connected to a high-voltage power supply and a signal readout electronics system via the high-voltage and signal lead-out connectors. The readout electronics system includes a fast charge-sensitive preamplifier and a multi-channel digitizer.

[0042] When the detector is operational, a positive voltage of 300-500V is applied to the anode strip, a negative voltage of 1000-2000V is applied to the boron-coated film, and the readout strip is at ground potential. Therefore, the electric field direction is from the anode strip towards the boron-coated film and the readout strip. When neutrons are incident, they will react with boron-10 nuclei in the boron film on the back of the boron-coated cathode or the two-dimensional microgap chamber (MGC), producing alpha particles with a certain energy. 7 The Li nucleus undergoes the following nuclear reaction process:

[0043] n+ 10 B→α(1.47MeV)+ 7 Li (0.84 MeV) + γ (0.48 MeV) (branching ratio 93.7%)

[0044] →α(1.78MeV)+ 7 Li (1.01 MeV) (branching ratio 6.3%)

[0045] alpha particles produced by nuclear reactions and 7 Li nuclei will be emitted in the opposite direction, and under certain emission angle conditions, alpha particles or 7Li is injected into the working gas through the 10B conversion layer, ionizing the working gas. Ionized electrons drift to the vicinity of the anode microstrips under the influence of the electric field, triggering an avalanche effect and ultimately generating a current pulse signal on the corresponding anode and readout strips. The signal position is read out using a delayed-line readout method, with each anode and readout strip connected to a port on the delayed-line module. This example uses a DDD 1507-50C delayed-line module, with each tap having a 5ns delay. The output signals at both ends of the delayed-line module are amplified and timed using a charge-sensitive preamplifier (Mesytec MPR-1). The timing signal output from the charge-sensitive preamplifier (Mesytec MPR-1) is timed using a multi-channel digitizer (CAEN V2740). By measuring the time difference between the arrival times of the signal at both ends of the delayed-line module, the generation position of the pulse current signal, i.e., the incident position of the neutron, can be determined.

[0046] This example uses Geant4 software to simulate the optimal boron coating thickness and the highest achievable neutron detection efficiency for different numbers of boron coating layers. Specifically, simulations were performed for four cases: 2-layer, 4-layer, 8-layer, and 20-layer boron coating micro-gap electrode stacks, with thicknesses ranging from 0.1 to 10 micrometers. 10 The highest neutron detection efficiency achievable with B4C thin films. 10 The B4C thin film was simulated and tested with thickness increases of 0.1 micrometers. The results are as follows: Figure 3 As shown.

[0047] Figure 3 The results showed that 10 Neutron detection can be achieved with B4C thin films ranging from 0.1 to 10 μm in thickness. 10 Four types of neutron detectors exhibit high detection efficiency when the thickness of the B4C thin film is 0.5-4 μm, especially for neutron detectors with 8-layer and 20-layer boron-coated micro-gap electrode stacks. 10 B4C thin films with a thickness of 1-3 μm exhibit high detection efficiency. Experimental results show that as the number of boron-coated micro-gap chamber electrodes increases, the neutron detection efficiency also increases accordingly. A neutron detector with two stacked boron-coated micro-gap chamber electrodes achieves a maximum detection efficiency of only about 10%, a detector with four stacked boron-coated micro-gap chamber electrodes achieves about 19%, a detector with eight stacked boron-coated micro-gap chamber electrodes achieves 30%, and a detector with 20 stacked boron-coated micro-gap chamber electrodes achieves a detection efficiency of over 50%. The detection results for all four neutron detectors show that… 10Within a certain range, such as less than 1.6 micrometers, the detection efficiency of B4C thin films increases with increasing thickness; however, beyond this range, the detection efficiency decreases with increasing thickness and tends to plateau. For example, at a thickness of 7 micrometers, the detection efficiency of a neutron detector with 20 boron-coated micro-gap chamber electrodes stacked together decreases to a level comparable to that of a neutron detector with 8 boron-coated micro-gap chamber electrodes stacked together.

[0048] The above description, in conjunction with specific embodiments, provides a further detailed explanation of this application and should not be construed as limiting the specific implementation of this application to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of this application, and all such modifications or substitutions should be considered within the scope of protection of this application.

Claims

1. A neutron detector, characterized in that: Includes a cover plate (1), a base (2), and several stacked boron-coated microgap chamber electrodes (3) installed between the cover plate (1) and the base (2). The cover plate (1) and the base (2) form a gas cavity that accommodates the boron-coated microgap chamber electrodes (3). An entrance window (11) is provided on the cover plate (1), and a boron-coated cathode plate (12) is installed on the inner surface of the entrance window (11). The boron-coated microgap chamber electrode (3) includes a substrate (31). The surface of the substrate (31) facing the cover plate (1) is provided with a plurality of parallel metal readout bars (32). The surface of the metal readout bars (32) is provided with a plurality of parallel metal anode bars (33) in a direction perpendicular to the metal readout bars (32). Furthermore, the metal readout bars (32) and the metal anode bars (33) are separated by an insulating layer (34). The surface of the substrate (31) facing the base (2) is coated with a boron thin film layer (35). The aforementioned stacked boron-coated microgap chamber electrodes (3) specifically include 4-20 stacked boron-coated microgap chamber electrodes; and the orientation of the metal anode strips of each stacked boron-coated microgap chamber electrode is the same, that is, the metal anode strips of the boron-coated microgap chamber electrodes located in different layers are parallel to each other.

2. The neutron detector according to claim 1, characterized in that: The substrate (31) is an aluminum-based printed circuit board.

3. The neutron detector according to claim 2, characterized in that: The thickness of aluminum-based printed circuit boards is 0.3-1mm.

4. The neutron detector according to claim 1, characterized in that: The metal readout bar (32) is a copper bar, and the width of the metal readout bar (32) is 0.5-2mm.

5. The neutron detector according to claim 1, characterized in that: The metal anode strip (33) is made of gold, and the metal anode strip (33) has a thickness of 1-3 μm, a width of 10-20 μm, and a strip spacing of 200-500 μm.

6. The neutron detector according to claim 1, characterized in that: The thickness of the boron thin film layer (35) is 0.1-10 μm.

7. The neutron detector according to claim 6, characterized in that: The thickness of the boron thin film layer (35) is 0.5-4 μm.

8. The neutron detector according to claim 7, characterized in that: The thickness of the boron thin film layer (35) is 1-3 μm.

9. The neutron detector according to claim 1, characterized in that: In the plurality of stacked boron-coated microgap chamber electrodes (3), the gap between two boron-coated microgap chamber electrodes (3) is 3-6 mm.

10. The neutron detector according to claim 9, characterized in that: The gap between the two boron-coated microgap chamber electrodes (3) is 4-5 mm.

11. The neutron detector according to any one of claims 1-10, characterized in that: The substrate of the boron-coated cathode plate (12) is an aluminum-based printed circuit board, and the surface of the aluminum-based printed circuit board is coated with... 10 B4C film.

12. The neutron detector according to claim 11, characterized in that: The thickness of the aluminum-based printed circuit board is 0.3-1mm.

13. The neutron detector according to claim 11, characterized in that: The 10 The thickness of B4C films ranges from 0.1 to 10 μm.

14. The neutron detector according to claim 13, characterized in that: The 10 The thickness of B4C films is 0.5-4 μm.

15. The neutron detector according to claim 14, characterized in that: The 10 The thickness of B4C films is 1-3 μm.

16. The neutron detector according to any one of claims 1-10, characterized in that: The gas chamber is equipped with a high-voltage connector and a signal lead-out connector. Each electrode is connected to a high-voltage power supply and a signal readout electronics system through the high-voltage connector and the signal lead-out connector, respectively.

17. The neutron detector according to claim 16, characterized in that: The signal readout electronics system includes a charge-sensitive preamplifier and a multi-channel digitizer; The signal position readout of the neutron detector adopts the delay line readout method. Each metal anode bar and metal readout bar is connected to the port of the delay line module. The output signals at both ends of the delay line module are amplified and timed by a charge-sensitive preamplifier, respectively. The timing signal output by the charge-sensitive preamplifier is timed by a multi-channel digitizer. The generation position of the pulse current signal, i.e., the incident position of the neutron, is determined by measuring the time difference between the arrival of the signal at both ends of the delay line module.

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