A coincidence detection device for radioactivity measurement and its use

Abstract

The application discloses a coincidence detection device for radioactivity measurement, comprising a frame, a detector arranged on the frame, and an air inlet and outlet interface; the frame is internally provided with a gas measurement chamber; the frame is a semi-regular polyhedron comprising a triangular face and a square face, and the detector is arranged on the square face; and the detector is a cadmium zinc telluride detector. The detection device is especially suitable for radioactivity measurement of radioactive xenon, solves the defects of a high-purity germanium gamma spectrometer and a NaI+plastic scintillator beta-gamma coincidence detector, such as large volume, large weight, difficult maintenance, and difficulty in realizing portability and on-site measurement, and can achieve a lower detection limit, has higher measurement accuracy than a NaI detector, adopts a semi-regular polyhedral design for the detector shape, guarantees the spatial symmetry of the detectors, obtains a larger 4pi coverage rate of the detector, increases the volume of the measurement chamber, reduces the requirement for air separation and concentration, and solves the problem of the limited measurement chamber of a traditional beta-gamma coincidence detector.

Description

Technical Field

[0001] This invention belongs to the field of radioactive detector technology and relates to the measurement of the radioactive inert gas xenon. Specifically, it relates to a semi-regular polyhedral cadmium zinc telluride coincidence detector for radioactive measurement and the application of the coincidence detector in the radioactive measurement of radioactive inert gases, especially xenon. Background Technology

[0002] Xenon, a radioactive inert gas, is an important nuclide in radioactive effluents that nuclear facilities may release into the environment. Relevant Chinese standards require that nuclear power plants, reprocessing plants, and other nuclear facilities regularly sample and monitor or continuously measure the radioactivity of xenon in their chimney emissions during operation. Furthermore, the fission products of inert gases produced during nuclear explosions can easily leak into the atmosphere. The Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS) uses measurements of radioactive xenon in the air as one of the four techniques for identifying suspected nuclear explosions.

[0003] Considering factors such as fission yield and half-life, the radionuclides that need to be monitored in radioactive xenon isotopes are Xe-131m, Xe-133, Xe-133m, and Xe-135.

[0004] Currently, the main method for measuring xenon radioactivity in China is gamma spectroscopy. This involves sampling the gaseous effluent into a 3L steel cylinder and then measuring it using a high-purity germanium gamma spectrometer. The disadvantages of this method include:

[0005] 1) The gamma-ray emission probabilities of the radioactive isotopes Xe-131m and Xe-133m are low (1.95% and 10%, respectively), resulting in a high detection limit for gamma-ray spectroscopy measurement methods.

[0006] 2) High-purity germanium detectors operate in a laboratory-grade liquid nitrogen cryogenic environment, which results in high maintenance costs and makes on-site measurements difficult.

[0007] Compared to gamma spectroscopy, β-γ coincidence measurement can effectively reduce the background impact of environmental radioactivity. Furthermore, based on the decay characteristics of xenon radioactive isotopes, using X-rays with a higher emission probability for coincidence measurement can achieve a lower detection limit. According to the CTBT's requirements for the detection limit of xenon in air, β-γ coincidence detection systems based on NaI scintillators and plastic scintillators have been developed abroad (such as the SAUNA system developed in Switzerland and the ARSA system developed in the United States). This method measures gamma rays using a NaI scintillator detector and β rays using a plastic scintillator, thus achieving β-γ coincidence measurement. The main disadvantages of this type of measurement system are:

[0008] 1) NaI scintillator detectors have low energy resolution and are subject to significant interference from environmental nuclides, resulting in large statistical errors in measurement results;

[0009] 2) The gas chamber is located inside the plastic scintillator, which is located inside the NaI crystal. Due to the influence of the size of the NaI crystal, the gas chamber volume is relatively small, which places high demands on the separation and concentration of xenon.

[0010] 3) The signals from both the NaI detector and the plastic scintillator detector need to be read out through a photomultiplier tube, resulting in a large overall system size. In addition, both the NaI detector and the plastic scintillator detector are sensitive to ambient gamma radiation. To reduce the background shadow, such systems usually require a large lead shielding system. Summary of the Invention

[0011] In view of this, in order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a semi-regular polyhedral tellurium zinc cadmium coincidence detection device suitable for xenon radioactivity measurement.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] A semi-regular polyhedron tellurium zinc cadmium coincidence detection device suitable for xenon radioactivity measurement includes a frame, a detector mounted on the frame, and gas inlet and outlet interfaces; the frame has a gas measurement chamber; the frame is a semi-regular polyhedron, including triangular faces and square faces, and the detector is mounted on the square face; the detector is a tellurium zinc cadmium detector.

[0014] According to some preferred embodiments of the invention, the semi-regular polyhedron is a small rhombohedral half-cube, consisting of 18 square faces and 8 regular triangular faces.

[0015] According to some preferred embodiments of the invention, the semi-regular polyhedron is a truncated cube, consisting of 6 square faces and 8 equilateral triangular faces.

[0016] According to some preferred embodiments of the invention, the normal of the crystal detection surface of the cadmium zinc telluride detector points towards the center of the gas measurement chamber.

[0017] According to some preferred embodiments of the invention, each of the cadmium zinc telluride detectors on the frame has an equivalent geometric position and the same detection efficiency for the gas in the measurement chamber. That is, the interior of the semi-regular polyhedron detector frame forms a spatially symmetrical semi-regular polyhedron gas measurement chamber. The cadmium zinc telluride detectors mounted on the square face of the semi-regular polyhedron form a spatially symmetrical arrangement for the gas measurement chamber, and each of the cadmium zinc telluride detectors has an equivalent geometric position and the same detection efficiency for the gas in the measurement chamber.

[0018] According to some preferred embodiments of the present invention, a test source probe holder interface and a test source probe holder mounted on the test source probe holder interface are included; the inlet / outlet gas interface and the test source probe holder interface are disposed on the triangular face; the test source probe holder is used to test the performance of the detector. Specifically, the square face is used to mount the cadmium zinc telluride detector, and the triangular face is mainly used to mount the inlet / outlet gas interface and the test source probe holder interface. The test source probe holder is used to verify the main performance parameters and stability of the detector. The adopted test source probe holder design solves the problem that it is difficult to conduct performance testing on gaseous detectors.

[0019] According to some preferred embodiments of the present invention, the test source needle holder sequentially includes a needle holder cap, a sealing ring, a needle holder rod, and a radioactive point source, wherein the needle holder rod is installed at the test source needle holder interface such that the radioactive point source is located in the gas measurement chamber.

[0020] According to some preferred embodiments of the invention, the radioactive point source comprises three types: a radioactive source having β-γ coincidence decay, a γ radioactive source, and a β radioactive source.

[0021] According to some preferred embodiments of the present invention, the outer cover is provided with reserved holes for leading out detector signal lines and power lines.

[0022] According to some preferred embodiments of the present invention, a signal processing system is included, comprising a detector power supply module, a multiplexed preamplifier, a multiplexed high-speed ADC, a filtering module, a peak acquisition module, a coincidence signal recognition module, and a data storage and transmission module. The signal processing system is an FPGA-based β-γ coincidence signal processing system.

[0023] According to some preferred embodiments of the present invention, the detector power supply module is used to provide operating power to the cadmium zinc telluride detector; the multi-channel preamplifier is used to amplify the output pulse signal of the cadmium zinc telluride detector; the multi-channel high-speed ADC is used to acquire pulse shape data and digitize the pulse waveform; pulse shape data refers to converting continuous analog voltage pulse signals into discrete voltage values.

[0024] The coincidence signal recognition module is used to identify the output signals of the multi-channel preamplifier in real time. When any two signals produce a pulse signal within a given coincidence time window, a trigger signal and the coincidence signal channel number are sent to the filtering module and the peak acquisition module, respectively. Upon receiving the trigger signal, the filtering module immediately acquires the pulse waveform data corresponding to the coincidence channel number output by the multi-channel high-speed ADC. The peak acquisition module acquires the peak value in the waveform data and sends the peak value and channel number to the data storage and transmission module. The data storage and transmission module transmits the measurement result information to the host computer at a certain frequency. The coincidence signal recognition module, filtering module, peak acquisition module, and data storage and transmission module are implemented using a programmable gate array (FPGA).

[0025] According to some preferred embodiments of the present invention, the coincidence time window is set within the range of ten ns, which is the difference between the arrival of two coincidence signals at the coincidence signal identification module.

[0026] According to some preferred embodiments of the invention, the channel number corresponds to the number of the two cadmium zinc telluride detectors that generate the coincidence signal, and the peak value is the peak value of the voltage pulse output by the detector, which represents the radiation energy of the decaying radioactive source.

[0027] Due to the adoption of the above technical solutions, the advantages of this invention compared to existing technologies are as follows: The semi-regular polyhedral cadmium zinc telluride coincidence detector of this invention, applicable to xenon radioactivity measurement, solves the defects of high-purity germanium gamma spectrometers and NaI+ plastic scintillator β-γ coincidence detectors, such as large size, heavy weight, difficult maintenance, and difficulty in achieving portable, on-site measurement; the β-γ coincidence measurement technology achieved by using a cadmium zinc telluride detector can achieve a lower detection limit compared to high-purity germanium detectors and has higher measurement accuracy compared to NaI detectors; the detector's shape adopts a semi-regular polyhedral design, ensuring the spatial symmetry of each detector while obtaining a larger detector 4π coverage; the semi-regular polyhedral detector shape design can increase the volume of the measurement chamber, reduce the requirements for air separation and concentration, and solve the problem of limited measurement chamber in traditional β-γ coincidence detectors; it also solves the problem of the symmetry being affected by the arrangement of the gas measurement chamber inlet and outlet. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the frame structure of the detection device in a preferred embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the frame structure of the detection device in another preferred embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the detector cross-sectional structure of the detection device in a preferred embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the test source pin holder structure of the detection device in a preferred embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the β-γ coincidence signal processing system of the coincidence detection device in a preferred embodiment of the present invention;

[0034] In the attached diagram, 10 is the frame of a small rhombic semi-cube detector; 11 is the gas measurement chamber inlet and outlet ports; 12 is the square face of a semi-regular polyhedron; 13 is the cadmium zinc telluride detector receiving slot; 14 is the equilateral triangular face of a semi-regular polyhedron; 15 is the test source needle holder interface; 16 is the connecting rib of the semi-regular polyhedron detector frame; and 17 is the frame of a semi-cube detector.

[0035] 20. Cross-sectional view of the semi-regular polyhedron detector; 21. Pre-drilled hole for the detector outer cover; 22. Fixing screw for the detector outer cover; 23. Detector outer cover; 24. Frame snap-fit ​​part; 25. Cadmium zinc telluride detector; 26. Cadmium zinc telluride crystal detection surface; 27. Gas measurement chamber; 30. Test source needle holder; 31. Needle holder cap; 32. Sealing ring; 33. Needle holder rod; 34. Radioactive point source;

[0036] 40. FPGA-based β-γ coincidence signal processing system; 41. Detector power supply module; 42. Multi-channel preamplifier; 43. Multi-channel high-speed ADC; 44. Filtering module; 45. Peak acquisition module; 46. Coincidence signal recognition module; 47. Data storage and transmission module. Detailed Implementation

[0037] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0038] like Figure 1-5As shown, the semi-regular polyhedral cadmium telluride-zinc coincidence detection device suitable for xenon radioactivity measurement in this embodiment comprises two parts: a spatially symmetrical β-γ coincidence detector consisting of semi-regular polyhedral detector frames 10 and 17 and a cadmium telluride-zinc coincidence detector 25; and an FPGA-based β-γ coincidence signal processing system 40. The semi-regular polyhedral detector frames are of two types: a small rhombohedral truncated cube detector frame 10 or a truncated cube detector frame 17. The cadmium telluride-zinc coincidence detector 25 is installed on the square face of the semi-regular polyhedral detector frames 10 and 17, forming a detector group capable of β-γ coincidence measurement of radioactive gas within the frame. The core modules of the FPGA-based β-γ coincidence signal processing system 40 are a coincidence signal recognition module 46 and a peak acquisition module 45. The specific structure of the detection device is described below:

[0039] (I) Spatially Symmetric β-γ Coincidence Detector

[0040] like Figure 1-4 As shown, the β-γ coincidence detector in this embodiment includes a frame 10 or 17, a cadmium zinc telluride detector 25 disposed on the frame 10 or 17, an air inlet / outlet interface 11, a test source needle holder interface 15, and a test source needle holder 30 mounted on the test source needle holder interface 15.

[0041] The frame 10 or 17 contains a gas measurement chamber 27. The frame 10 or 17 is made of aluminum alloy and is a semi-regular polyhedron, including a triangular face 14 and a square face 12. A frame connecting rib 16 connects the triangular face 14 and the square face 12. The cadmium zinc telluride detector 25 is mounted on the square face 12, while the gas inlet / outlet port 11 and the test source needle holder port 15 are mounted on the triangular face 14. The semi-regular polyhedron frame 10 or 17 is sealed with rubber sealing rings to the detector 25, the gas inlet / outlet port 11, and the test source needle holder mounting port 15, achieving complete sealing and isolation between the entire gas measurement chamber and the outside environment.

[0042] The test source probe holder 30 is used to test the performance of the coincidence detector, mainly including the β detection efficiency, γ detection efficiency of each tellurium zinc detector 25, and the total coincidence detection efficiency of the detector. Stability can be tracked using the total count rate of each detector (the measurement result per unit time). When detector stability testing is required, the necessary radioactive point source 34 is installed at the top of the probe holder rod, and then the test source probe holder 30 is inserted. Different radioactive point sources 34 can be used to test different indicators of the instrument. Instrument testing and sample measurement are performed separately, solving the problem of difficulty in conducting performance testing on gaseous detectors.

[0043] Specifically, such as Figure 4As shown, the test source needle holder sequentially includes a needle cap 31, a sealing ring 32, a needle holder rod 33, and a radioactive point source 34. The needle holder rod 33 passes through the test source needle holder interface 15, placing the radioactive point source 34 within the gas measurement chamber 27. The radioactive point source 34 includes three types: readily available radioactive sources with β-γ coincidence decay, such as Cs-137 and Co-60; γ-radioactive sources such as plastic-sealed Am-241; and β-radioactive sources such as Sr / Y-90. The point source can be prepared by drying a standard solution. The sealing ring and the test source needle holder interface are connected by a threaded seal.

[0044] When it is necessary to conduct instrument performance and stability tests, take out the test source needle holder 30, install the required radioactive point source 34 on the top of the needle holder rod, and then reinsert the test source needle holder 30. Different radioactive point sources 34 can be used to test different indicators of the instrument.

[0045] like Figure 1 As shown, in this embodiment, the semi-regular polyhedron of frame 10 is a small rhombic truncated half-cube, composed of 18 square faces 12 and 8 equilateral triangular faces 14. In some other embodiments, the semi-regular polyhedron of frame 17 is a truncated half-cube, composed of 6 square faces 12 and 8 equilateral triangular faces 14, as shown. Figure 2 As shown. The square face 12 of the two types of semi-regular polyhedral frames is used to install the cadmium zinc telluride detector 25, and the triangular face is mainly used to install the air inlet and outlet interfaces 11 and the test source needle holder interface 15; the square face must be used to install the cadmium zinc telluride detector 25.

[0046] For two application scenarios—xenon radioactivity measurement in typical environments and xenon in gaseous effluents from nuclear facilities—small rhombic semi-cube detector frames 10 (with a larger number of detectors) and semi-cube detector frames 17 (with a smaller number of detectors) can be selected, respectively. Based on current front-end gas enrichment technology and relevant standards and specifications for measurement and detection, the detector model and frame dimensions are designed as follows:

[0047] like Figure 1 As shown, the small rhombic semi-cubic detector frame 10 is made of aluminum alloy or integrally cast. Eighteen hemispherical cadmium telluride (CdT) detectors, each measuring 10mm (length) × 10mm (width) × 5mm (thickness), are installed on the 18 square faces of the frame. The internal chamber dimensions are set as follows: the side length of each regular quadrilateral is 1.2cm (the side length of the equilateral triangles is the same as that of the quadrilaterals). Therefore, the gas measurement chamber volume of the small rhombic semi-cubic detector is 15.1cm³. 3 The 4π coverage of the 18 detectors is 58.2%.

[0048] like Figure 2As shown, the semi-cubic detector frame 17 is made of integrally cast aluminum alloy. Six hemispherical cadmium telluride (CdT) detectors, each measuring 10mm (length) × 10mm (width) × 5mm (thickness), are selected and installed on the six square faces of the small rhombic semi-cubic detector frame. The internal chamber dimensions of the frame are set as follows: the side length of each regular quadrilateral is 2.0cm (the side length of the equilateral triangles is the same as that of the quadrilaterals). Therefore, the gas measurement chamber volume of the small rhombic semi-cubic detector is 8.0cm³. 3 The 4π coverage of the 18 detectors is 25.1%.

[0049] like Figure 3 As shown, the normal of the crystal detection surface 26 of the cadmium zinc telluride detector 25 points towards the center of the gas measurement chamber 27. The interior of the semi-regular polyhedron detector frame forms a spatially symmetrical semi-regular polyhedron gas measurement chamber 27. The cadmium zinc telluride detectors 25 mounted on the square face 12 of the semi-regular polyhedron form a spatially symmetrical arrangement with respect to the gas measurement chamber 27. Each cadmium zinc telluride detector has an equivalent geometric position and the same detection efficiency for the gas in the measurement chamber, which simplifies the detection accuracy and the processing of the multiple β-γ coincidence signals at the back end.

[0050] like Figure 3 As shown, a snap-fit ​​part 24 is provided on the side of the square face 12 closest to the gas measurement chamber 27, and an outer cover 23 is provided on the side away from the gas measurement chamber; a receiving groove 13 for accommodating the cadmium zinc telluride detector 25 is formed between the snap-fit ​​part 24 and the outer cover 23. The outer cover 23 has reserved holes 21 for leading out the detector signal line and power line. A rubber gasket is provided at the connection between the detector outer cover 23 and the cadmium zinc telluride detector 25 and the semi-regular polyhedral detector frame to achieve the purpose of sealing the measurement chamber.

[0051] During installation, the cadmium zinc telluride detector 25 is inserted into the receiving groove 13 from the outside in, and the outer surface of the cadmium zinc telluride detector is fixed by the detector cover 23; the detector cover 23 is fixed to the semi-regular polyhedron detector frame by screws 22.

[0052] (II) FPGA-based β-γ coincidence signal processing system

[0053] like Figure 5 As shown, the β-γ coincidence signal processing system 40 in this embodiment includes a detector power supply module 41, a multi-channel preamplifier 42, a multi-channel high-speed ADC 43, a filtering module 44, a peak acquisition module 45, a coincidence signal recognition module 46, and a data storage and transmission module 47.

[0054] The detector power supply module 41 provides unified power to the cadmium zinc telluride detector 25; the multi-channel preamplifier 42 amplifies the output pulse signal of the cadmium zinc telluride detector; and the multi-channel high-speed ADC 43 acquires pulse shape data and digitizes the pulse waveform. Pulse shape data refers to the conversion of continuous analog voltage pulse signals into discrete voltage values.

[0055] The coincidence signal recognition module 46, filtering module 44, peak acquisition module 45, and data storage and transmission module 47 are implemented using a programmable gate array (FPGA). The coincidence signal recognition module 46 is used to identify the output signals of the multi-channel preamplifier in real time. When any two signals show a pulse signal within a given coincidence time window, it sends a trigger signal and the coincidence signal channel number to the filtering module 44 and the peak acquisition module 45.

[0056] The coincidence time window is set within the range of tens of ns for the possible differences between the arrival times of two coincidence signals at the coincidence signal identification module 46. It is usually determined experimentally.

[0057] After receiving the trigger signal, the filtering module 44 immediately acquires the pulse waveform data corresponding to the channel number output by the multi-channel high-speed ADC 43. The peak acquisition module 45 acquires the peak value in the waveform data and sends the peak value and channel number to the data storage and transmission module 47. The data storage and transmission module 47 transmits the measurement result information to the host computer at a certain frequency.

[0058] The channel number corresponds to the number of the two cadmium zinc telluride detectors that generate the coincidence signal; the peak value is the peak value of the voltage pulse output by the detector, which represents the energy of the radiation source decaying.

[0059] The numerical storage is implemented using the built-in data buffer FIFO (IP core) in the FPGA, and the data transmission method can be either serial port protocol or USB homogeneous protocol.

[0060] This FPGA-based β-γ coincidence signal processing system employs a coincidence signal recognition module 46 based on time window determination. By adjusting the time window, the accuracy of β-γ coincidence signal determination can be improved. Using the coincidence signal determination result as the trigger signal for the filtering module and the peak acquisition module can greatly reduce the signal processing load of the FPGA. The use of a data buffer FIFO can expand the activity measurement range of the detector system.

[0061] The general workflow of the coincidence detection device for radioactivity measurement in this embodiment is as follows:

[0062] (1) After being separated by the separation and concentration system, the radioactive inert gas is carried by the carrier gas (nitrogen) and filled into the gas measurement chamber 27 of the detector equipment through the inlet and outlet gas interfaces 11.

[0063] (2) After filling is complete, begin measurement;

[0064] (3) Monitor the output signals of each zinc cadmium telluride detector through the signal recognition module 46;

[0065] (4) When there are only two detector output signals within a given time interval (time window), it is determined to be a β-γ coincidence signal, and a trigger signal is sent to the filtering module 44 and the peak acquisition module 45.

[0066] (5) Obtain the energy of the signal through the filtering module 44 and the peak acquisition module 45;

[0067] (6) The signal energy information is transmitted to the host computer through the data storage and transmission module 47;

[0068] (7) The host computer identifies the types of nuclides by the coincidence signal energy, plots the coincidence energy spectrum, and completes the calculation of the activity concentration of radioactive gas.

[0069] (8) After the measurement is completed, the radioactive gas sample in the chamber is completely removed by repeatedly filling the gas (carrier gas nitrogen) and evacuating the gas through the separation and concentration system gas path, and then the next measurement can begin.

[0070] The present invention relates to a semi-regular polyhedral cadmium telluride-zinc-cadmium coincidence detection device suitable for xenon radioactivity measurement, comprising two parts: a spatially symmetrical β-γ coincidence detector consisting of a semi-regular polyhedral detector frame and a cadmium telluride-zinc-cadmium detector, and an FPGA-based β-γ coincidence signal processing system. The semi-regular polyhedral detector frame includes two types: a small rhombohedral truncated cube detector frame or a truncated cube detector frame. The cadmium telluride-zinc-cadmium detector is mounted on the square face of the semi-regular polyhedral detector frame, forming a detector group capable of β-γ coincidence measurement of radioactive gas within the frame. The triangular face of the semi-regular polyhedral detector frame is used to install the gas inlet and outlet interfaces and the test source pin holder interface. The FPGA-based β-γ coincidence signal processing system includes a detector power supply module, a multi-channel preamplifier, a multi-channel high-speed ADC, a filtering module, a peak acquisition module, a coincidence signal identification module, and a data storage and transmission module. Compared with the prior art, the advantages of the present invention are:

[0071] (1) The volume of the zinc cadmium telluride detector is much smaller than that of the high-purity germanium detector or NaI detector. Moreover, the zinc cadmium telluride detector operates in a normal temperature environment, which solves the defects of high-purity germanium γ spectrometer and NaI+ plastic scintillator β-γ coincidence measurement and detection system, such as large volume, heavy weight, difficult maintenance, and difficulty in achieving portable and on-site measurement.

[0072] (2) Compared with high-purity germanium gamma spectrometer, zinc-cadmium telluride detector can realize the measurement of beta rays and has better energy resolution than NaI detector. The beta-gamma coincidence measurement technology achieved by zinc-cadmium telluride detector can achieve a lower detection limit than high-purity germanium detector and has higher measurement accuracy than NaI detector.

[0073] (3) The semi-regular polyhedron detector shape design is adopted. Compared with other shape designs such as cube and cuboid, it can ensure the spatial symmetry of each detector, which is conducive to measurement and back-end data processing. On the other hand, it can obtain a larger detector surface coverage under the same measurement chamber volume.

[0074] (4) The use of a zinc cadmium telluride detector can simultaneously measure β-γ rays. Combined with the spatially symmetrical semi-regular polyhedron design, the volume of the measurement chamber can be increased as needed, reducing the requirements for air separation and concentration. This solves the problem of limited measurement chamber in traditional β-γ coincidence detectors.

[0075] (6) The semi-regular polyhedron detector has multiple spatially symmetrical triangular faces in addition to the detector coverage area. This facilitates the arrangement of gas inlets and outlets without affecting the symmetry of the detector. At the same time, the designed test source needle holder solves the problem that radioactive gaseous xenon is not easy to obtain and that gaseous detectors are not easy to perform performance tests.

[0076] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A coincidence detection device for radioactivity measurement, characterized in that, It includes a frame, a detector mounted on the frame, and an inlet / outlet gas interface; the frame has a gas measurement chamber; the frame is a semi-regular polyhedron, including a triangular face and a square face, and the detector is mounted on the square face; the detector is a zinc cadmium telluride detector.

2. The coincidence detection device according to claim 1, characterized in that, The semi-regular polyhedron is a small rhombohedral semi-cube, consisting of 18 square faces and 8 regular triangular faces.

3. The coincidence detection device according to claim 1, characterized in that, The semi-regular polyhedron is a truncated cube, consisting of 6 square faces and 8 equilateral triangular faces.

4. The coincidence detection device according to claim 1, characterized in that, The normal of the crystal detection surface of the cadmium zinc telluride detector points to the center of the gas measurement chamber.

5. The coincidence detection device according to claim 1, characterized in that, Each of the cadmium zinc telluride detectors on the frame has an equivalent geometric position and the same detection efficiency for the gas in the measurement chamber.

6. The coincidence detection device according to claim 1, characterized in that, It includes a test source probe holder interface and a test source probe holder mounted on the test source probe holder interface; the air inlet / outlet interface and the test source probe holder interface are disposed on the triangular surface; the test source probe holder is used to test the performance of the detector.

7. The coincidence detection device according to claim 6, characterized in that, The test source needle holder includes a needle holder cap, a sealing ring, a needle holder rod, and a radioactive point source. The needle holder rod is installed at the test source needle holder interface so that the radioactive point source is located in the gas measurement chamber.

8. The coincidence detection device according to claim 7, characterized in that, The radioactive point source includes a radioactive source with β-γ coincidence decay, a γ radioactive source, and a β radioactive source.

9. The coincidence detection device according to claim 1, characterized in that, A snap-fit ​​portion is provided on the side of the square face closest to the gas measuring chamber, and an outer cover is provided on the side away from the gas measuring chamber; a receiving groove for accommodating the cadmium zinc telluride detector is formed between the snap-fit ​​portion and the outer cover.

10. The coincidence detection device according to any one of claims 1-9, characterized in that, The system includes a signal processing system, which comprises a detector power supply module, a multi-channel preamplifier, a multi-channel high-speed ADC, a filtering module, a peak acquisition module, a coincidence signal recognition module, and a data storage and transmission module.

11. The coincidence detection device according to claim 10, characterized in that, The detector power module is used to provide operating power to the cadmium zinc telluride detector; the multi-channel preamplifier is used to amplify the pulse signal output by the cadmium zinc telluride detector. The multi-channel high-speed ADC is used to acquire pulse shape data and digitize the pulse waveform. The coincidence signal recognition module is used to identify the output signals of the multi-channel preamplifier in real time. When any two signals produce a pulse signal within a given coincidence time window, a trigger signal and a coincidence signal channel number are sent to the filtering module and the peak acquisition module, respectively. After receiving the trigger signal, the filtering module acquires the pulse waveform data of the corresponding coincidence channel number output by the multi-channel high-speed ADC. The peak acquisition module acquires the peak value in the waveform data and sends the peak value and channel number to the data storage and transmission module.

12. The coincidence detection device according to claim 11, characterized in that, The time window refers to the difference between the arrival times of two matching signals at the matching signal recognition module.

13. The coincidence detection device according to claim 11, characterized in that, The channel number corresponds to the number of the two cadmium zinc telluride detectors that generate the coincidence signal; the peak value is the peak value of the voltage pulse output by the detector, which represents the radiation energy of the decaying radioactive source.

14. The application of a coincidence detection device as described in any one of claims 1-13 in the radioactivity measurement of radioactive inert gases.

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