ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration

Abstract

The invention relates to the technical field of counting instruments, and discloses a ZnS (Ag) scintillator alpha counting instrument device for plutonium concentration measurement. Comprising an equipment base, a baking tray is arranged on the upper surface of the equipment base, a shell is fixedly connected to the upper surface of the equipment base, a sample bracket is arranged on the upper surface of the baking tray, a detection crystal is arranged on the upper surface of the sample bracket, and a photomultiplier is arranged on the upper surface of the detection crystal. Aiming at the current measurement situation of the plutonium element in a post-treatment plant, a solution baking tray treatment design is adopted, the influence of the solution matrix effect of the plutonium element to be measured on the measurement process is eliminated, the difference between measurement site equipment is reduced, and a scintillator structure design of spraying zinc sulfide powder on light guide organic glass is adopted, so that the measurement accuracy is improved. According to the invention, the interference of beta / gamma rays on measurement is reduced, the measurement accuracy is improved, the design of double-platform switching measurement is adopted, the measurement efficiency is improved, the labor cost is saved, and the measurement of the concentration of trace plutonium elements in a post-treatment plant is well met.

Description

Technical Field

[0001] The invention relates to the technical field of counters, in particular to a ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration. Background Art

[0002] Spent fuel reprocessing is an important part of the closed cycle of nuclear fuel and an essential step to achieve sustainable development of nuclear energy. The extract and washing liquid in the spent fuel reprocessing process contain trace or trace amounts of plutonium, accounting for about 10% of the total process control sample. Accurately measure the content of plutonium in each process flow to understand the process operation. There are generally spectroscopy, mass spectrometry, hybrid K edge / X fluorescence measurement technology (KED / XRF), α counting method, α energy spectrum method, etc. For the measurement of plutonium in the reprocessing plant, α counting method is currently an advantageous method for determining plutonium in the reprocessing process because of its low requirements for separation effect, reliable analysis results, and convenient equipment maintenance.

[0003] The α scintillator counter is a nuclear radiation detector using ZnS (Ag) scintillator, which is mainly used for the measurement and analysis of the α radioactivity concentration of trace plutonium in post-processing process samples. The α scintillator counter can realize direct sample analysis without the need for pre-processing resources, and can effectively improve sample analysis efficiency and save manpower. It is fast, efficient, accurate and safe.

[0004] The plutonium in the reprocessing process of spent fuel from pressurized water reactors mainly includes Pu-238, Pu-239, Pu-240, Pu-241, and Pu-232, which spontaneously fission and emit alpha particles of about 5 MeV. The range of alpha particles in air is short, about 3.6 cm, and the range in aqueous solution is about 30 μm. The composition of the feed liquid at different process points varies greatly. The concentration of other salts except plutonium varies greatly, and the concentration of nitric acid in the organic phase and the aqueous phase bottom liquid also varies greatly, resulting in different self-absorption of plutonium alpha rays by the solution to be tested. The interference of matrix effects requires the establishment of a separate working curve for the measurement of alpha particles at each measuring point. There are more than 40 measuring points in the reprocessing process, which makes it cumbersome to use and the parameters of instruments at different measuring points vary greatly, making it difficult to maintain and manage them uniformly.

[0005] The plutonium content in the post-processing process is low, and the solution to be tested contains beta-radiating nuclides such as Sr-90, and the activity concentration is high, and the beta activity concentration is nearly a thousand times that of the alpha activity concentration. Many existing alpha scintillator counters have scintillation crystals that respond to beta rays, and the beta radiation has exceeded the alpha and beta discrimination capabilities of existing alpha scintillator counters. The interference of beta radiation causes the measurement error to increase, which interferes with the measurement of the actual plutonium concentration. Therefore, the prior art still lacks alpha scintillator counter equipment suitable for the application scenario. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] In view of the deficiencies of the prior art, the present invention provides a ZnS (Ag) scintillator α counter device for measuring plutonium concentration. In view of the current status of plutonium element measurement in post-processing plants, the invention adopts a solution baking tray processing design to eliminate the influence of the solution matrix effect of the plutonium element to be measured on the measurement process, reduce the difference between the equipment at each measurement site, and facilitate the use and maintenance of the equipment; adopts a scintillator structure design of light-conducting organic glass sprayed with zinc sulfide powder to reduce the interference of β / γ rays on the measurement, improve the measurement accuracy, and increase the reliability of the measurement results; adopts a dual-platform switching measurement design to improve the measurement efficiency and save labor costs. It can well meet the measurement of trace and trace plutonium element concentrations in post-processing plants, has good actual use effects, and is easy to promote and use.

[0008] (II) Technical solution

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions: comprising a device base, a baking tray is arranged on the upper surface of the device base, a housing is fixedly connected to the upper surface of the device base, a sample holder is arranged on the upper surface of the baking tray, a detection crystal is arranged on the upper surface of the sample holder, a photomultiplier tube is arranged on the upper surface of the detection crystal, and the photomultiplier tube is connected to the detection crystal, and the signal processing board is installed inside the housing and above the photomultiplier tube;

[0010] The signal processing board includes a power supply circuit, a communication circuit, a signal amplification and shaping circuit, a main amplification circuit, a pulse discrimination circuit, a preamplification circuit and a high-voltage circuit, and the high-voltage circuit is electrically connected to the photomultiplier tube, the photomultiplier tube is electrically connected to the preamplification circuit, the preamplification circuit is electrically connected to the main amplification circuit, the main amplification circuit is electrically connected to the pulse discrimination circuit, and the signal amplification and shaping circuit is electrically connected to the power supply circuit and the communication circuit.

[0011] Through the above technical scheme, in view of the current status of plutonium measurement in reprocessing plants, a solution baking tray processing design is adopted to eliminate the influence of the solution matrix effect of the plutonium to be measured on the measurement process, reduce the difference between the equipment at each measurement site, and facilitate the use and maintenance of the equipment. The scintillator structure design of photoconductive organic glass sprayed with zinc sulfide powder is adopted to reduce the interference of β / γ rays on the measurement, improve the measurement accuracy, and increase the reliability of the measurement results. The design of dual-platform switching measurement is adopted to improve the measurement efficiency and save labor costs. It can well meet the measurement of trace and trace plutonium concentrations in reprocessing plants, has good actual use effect, and is easy to promote and use.

[0012] Preferably, a detection crystal coating is applied between the baking tray and the detection crystal.

[0013] Through the above technical scheme, it has good chemical stability and alkali resistance, density 4.1g / cm3, refractive index 2.36, maximum luminous wavelength 450nm, scintillation decay time 200ns, wherein a trace amount of silver is added as an activator to improve the luminous efficiency, ZnS (Ag) has a very high detection efficiency for α particles, and the detection efficiency is affected by the coating thickness. If the coating is too thin, the α particles cannot deposit all the remaining energy in the ZnS (Ag), which reduces the utilization rate of the α particles; if the coating is too thick, the photons emitted by the α particles will be absorbed by the ZnS (Ag) and cannot enter the photomultiplier tube. In this embodiment, the detection crystal coating is 20mg / cm 2 The detection efficiency of alpha particles can reach 90%.

[0014] Preferably, the shell is made of stainless steel, and a handle is provided on the side surface of the baking tray.

[0015] Through the above technical solution, the baking tray can be conveniently pulled out using the handle to quickly replace the sample.

[0016] Preferably, the operating voltage of the signal processing board is 12V, which is provided by the power supply circuit.

[0017] The above technical solution is composed of a power supply circuit, a communication circuit and a signal amplification circuit. The signal processing board mainly collects and amplifies the input signal of the detector, counts the amplified pulse signal, obtains a digital signal, and finally transmits the signal to the host computer.

[0018] Preferably, the power supply circuit adopts an external 12V input to distribute the voltage to provide the required corresponding voltages to different components, and the communication circuit adopts RS485 protocol to communicate with the host computer.

[0019] Through the above technical solution, an external power input is adopted, and then power is output to all components of the signal processing board.

[0020] Preferably, the overall operating voltage of the signal amplification and shaping circuit is 12V, which is provided by the power supply circuit.

[0021] Through the above technical solution, it is mainly composed of modules such as preamplifier circuit, main amplifier circuit, pulse discrimination circuit, high-voltage circuit, etc.

[0022] Preferably, the preamplifier circuit is connected to the signal output end of the photomultiplier tube, the main amplifier circuit, and the pulse discrimination circuit in sequence through cables, and then connected to the signal input end of the communication circuit.

[0023] Through the above technical solution, the preamplifier circuit and the main amplifier circuit amplify and shape the radioactive signal detected by the probe.

[0024] Preferably, the high voltage circuit is connected to the high voltage input end of the photomultiplier tube via a cable.

[0025] Through the above technical solution, the high-voltage output of the high-voltage circuit can be controlled by software, and the high-voltage value output by the high-voltage module can also be monitored in real time to ensure normal operation of the circuit.

[0026] Preferably, the housing contains the signal processing board and its component circuits, the photomultiplier tube, the detection crystal, the detection crystal coating and other parts, and the exterior of the housing is in direct contact with the device base.

[0027] Through the above technical solution, the base of the equipment is placed on a horizontal surface, and there is no obvious vibration interference during use.

[0028] Preferably, the photomultiplier tube is coupled to the detection crystal through a silicone grease light guide, and the detection crystal is made of 3mm thick organic glass sprayed with ZnS.

[0029] Through the above technical solution, the Hamamatsu Photonics CR332 photomultiplier tube was selected. This photomultiplier tube is an end-window type photomultiplier tube, which is commonly used in photodetectors and has high sensitivity and amplification. The photomultiplier tube has an absorption peak wavelength of 420nm, which is very close to the ZnS scintillator emission peak wavelength of 450nm, and has good adaptability.

[0030] Compared with the prior art, the present invention provides a ZnS (Ag) scintillator α counter device for measuring plutonium concentration, which has the following beneficial effects:

[0031] 1. Aiming at the current status of plutonium measurement in post-processing plants, the present invention adopts a solution baking tray processing design, eliminates the influence of the solution matrix effect of the plutonium element to be measured on the measurement process, reduces the difference between the equipment at each measurement site, and facilitates the use and maintenance of the equipment; adopts a scintillator structure design of light-conducting organic glass sprayed with zinc sulfide powder to reduce the interference of β / γ rays on the measurement, improves the measurement accuracy, and increases the reliability of the measurement results; adopts a dual-platform switching measurement design to improve the measurement efficiency and save labor costs. It can well meet the measurement of trace and trace plutonium concentrations in post-processing plants, has good actual use effects, and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of the detector of the present invention;

[0033] Figure 2 It is a schematic diagram of the internal structure of the present invention;

[0034] Figure 3 It is a schematic diagram of the structure on the right side of the present invention;

[0035] Figure 4It is a schematic diagram of the software analysis process structure of the present invention.

[0036] Among them: 1. Signal processing board; 2. Power supply circuit; 3. Communication circuit; 4. Signal amplification and forming circuit; 5. Preamplification circuit; 6. Main amplification circuit; 7. Pulse discrimination circuit; 8. High-voltage circuit; 9. Housing; 10. Photomultiplier tube; 11. Equipment base; 12. Detection crystal; 13. Detection crystal coating; 14. Baking tray; 15. Sample holder; 16. Handle. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-4A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration includes a device base 11, a baking tray 14 is arranged on the upper surface of the device base 11, the baking tray 14 is placed on a sample holder 15, and is placed directly opposite to the detector. The solution to be tested is sampled on the baking tray 14, and the bottom liquid is evaporated to eliminate the influence of matrix effects such as salt and acidity. The upper surface of the device base 11 is fixedly connected with a shell 9, and a sample holder 15 is arranged on the upper surface of the baking tray 14. The sample holder 15 is made of stainless steel. Two baking trays 14 are placed in place and can move left and right. When using one side platform for measurement, the baking tray 14 of the sample to be tested can be placed and processed in advance on the other side platform to improve the measurement efficiency. The upper surface of the sample holder 15 The surface is provided with a detection crystal 12, which is a photoconductive organic glass (PMMA) with a layer of silver-doped zinc sulfide powder and phosphorescent material sprayed on the detection sensitive surface. The zinc sulfide powder has good chemical stability and alkali resistance, density 4.1g / cm3, refractive index 2.36, maximum luminous wavelength 450nm, and scintillation decay time 200ns. A trace amount of silver is added as an activator to improve the luminous efficiency. The phosphorescent material is a slow-luminescent photoluminescence phenomenon. When a certain room-temperature substance is irradiated by a certain wavelength of incident light, usually ultraviolet light or X-rays, it absorbs light energy and enters an excited state, which usually has a different spin multiplicity from the ground state, and then slowly de-excites and emits an output longer than the wavelength of the incident light. The photomultiplier tube 10 is arranged on the upper surface of the detection crystal 12, and the photomultiplier tube 10 is connected to the detection crystal 12. The photomultiplier tube 10 selects the Hamamatsu Photonics CR332 photomultiplier tube 10. The photomultiplier tube 10 is an end-window photomultiplier tube 10, which is commonly used in photodetectors and has high sensitivity and amplification. The photomultiplier tube 10 has an absorption peak wavelength of 420nm, which is very close to the emission peak wavelength of 450nm of the ZnS scintillator and has good adaptability. The signal processing board 1 is installed inside the housing 9 and is located above the photomultiplier tube 10. The signal processing board 1 is composed of a power supply circuit 2, a communication circuit 3 and a signal amplification forming circuit. The signal processing board 1 is mainly used for detecting The detector input signal is collected and amplified, and the pulse signal after amplification is counted to obtain a digital signal, and finally the signal is transmitted to the host computer. A detection crystal coating 13 is applied between the baking tray 14 and the detection crystal 12. Between the sample baking tray 14 and the detector, a Mylar film protective layer is wrapped on the surface of the detector probe, and the thickness is 2.5μm. It is resistant to nitric acid and organic solvent corrosion, protects the probe from contamination, and can ensure that α particles are fully transmitted; and the detector is composed of a shell 9, a detection crystal 12 coating, a detector crystal, a photomultiplier tube 10, and an electronic circuit. The detection crystal coating 13 has good chemical stability and alkali resistance, a density of 4.1g / cm3, and a refractive index of 2.36, maximum luminous wavelength 450nm, scintillation decay time 200ns, a small amount of silver is added as an activator to improve luminous efficiency, ZnS (Ag) has a very high detection efficiency for α particles, and the detection efficiency is affected by the coating thickness. If the coating is too thin, the α particles cannot deposit all the remaining energy in the ZnS (Ag), which reduces the utilization rate of the α particles. If the coating is too thick, the photons emitted by the α particles will be absorbed by the ZnS (Ag) and cannot enter the photomultiplier tube 10. The detection crystal coating 13 is 20mg / cm2, and the detection efficiency of α particles can reach 90%. The shell 9 is made of stainless steel, and the side surface of the baking tray 14 is provided with a handle 16. The photomultiplier tube 10 is coupled to the detection crystal 12 through a silicone grease light guide, and the detection crystal 12 is sprayed with a 3mm thick organic glass of ZnS. The photomultiplier tube 10 is coupled to the detection crystal 12 through a silicone grease light guide, and the detection crystal 12 is sprayed with a 3mm thick organic glass of ZnS. .

[0039] The signal processing board 1 includes a power supply circuit 2, which uses an external power input and then outputs power to all components of the signal processing board 1, a communication circuit 3, which supports RS485 communication and RJ45 communication, and transmits the processed signal to the host computer. The host computer controls the circuit output parameters through the supporting data acquisition and analysis software, receives the processed signal and outputs the final counting result of the sample, a signal amplification and shaping circuit 4, a main amplification circuit 6, and a pulse discrimination circuit 7. The pulse discrimination circuit 7 discriminates the pulse amplitude and width of the signal, identifies the α signal according to the different characteristics of the α, β, and γ pulse signals, and then outputs the α ray count value per unit time. The discrimination threshold of the pulse discrimination circuit 7 can be set by software, and the adjustable range is 0 V~5.00V, the threshold is usually set to 0.19V, and the specific parameters are determined by the specific use of the equipment, the preamplifier circuit 5, the preamplifier circuit and the main amplifier circuit 6 amplify and shape the radioactive signal detected by the probe and the high-voltage circuit 8, the high-voltage circuit 8 provides the photomultiplier tube 10 with the working voltage required for normal use, the high-voltage output of the high-voltage circuit 8 can be controlled by software, and the high-voltage value output by the high-voltage module can also be monitored in real time to ensure that the circuit operates normally, the high-voltage output of the high-voltage circuit 8 can be controlled by software, and the high-voltage value output by the high-voltage module can also be monitored in real time to ensure that the circuit operates normally; the adjustable range is 0V~1000V, and the output terminal HVOUT is usually set to output a DC high voltage of about 500V. The specific parameters are determined by the specific equipment. The signal amplification and shaping circuit is mainly composed of a preamplifier circuit, a main amplifier circuit 6, a pulse discrimination circuit 7, a high-voltage circuit 8 and other modules. The photomultiplier tube 10 is electrically connected to the preamplifier circuit 5, the preamplifier circuit 5 is electrically connected to the main amplifier circuit 6, the main amplifier circuit 6 is electrically connected to the pulse discrimination circuit 7, the signal amplification and shaping circuit 4 is electrically connected to the power supply circuit 2 and the communication circuit 3. The working voltage of the signal processing board 1 is 12V, which is provided by the power supply circuit 2. The power supply circuit 2 adopts an external 12V input to distribute the voltage to provide the required corresponding voltage to different components. The communication circuit 3 adopts the RS485 protocol to communicate with the host computer. The overall working voltage of the signal amplification and shaping circuit 4 The voltage is 12V, which is provided by the power supply circuit 2. The preamplifier circuit 5 is connected to the signal output end of the photomultiplier tube 10, the main amplifier circuit 6, and the pulse discrimination circuit 7 in sequence through cables, and then connected to the signal input end of the communication circuit 3. The high-voltage circuit 8 is connected to the high-voltage input end of the photomultiplier tube 10 through cables. The device can control the circuit output parameters, can display the data collected by the equipment in real time and correctly, set the measurement time and the number of measurements, can perform background correction on the detection data, establish a working curve to convert the activity concentration into mass concentration, record the analysis results and form a report, and perform stability analysis on the long-term analysis results. The system can generate reports based on the collected data and print them out. The system uses passwords for authorization management, and different authorizations can only perform operations within the scope of authority.

[0040] When in use, correctly connect all parts of the device, turn on the device, power on and preheat for 10 minutes, place the sample baking tray 14 to be tested on the sample rack, push it into the measuring position, use the software to click to start measuring, the α particles emitted by the plutonium element to be tested react with the zinc sulfide powder of the probe to generate fluorescence, the fluorescent photons enter the photomultiplier tube 10 and interact with the photocathode to emit photoelectrons, the photoelectrons are attracted by the dynode of the electron multiplication part, and after the secondary electron multiplication effect of the dynode, an electron rain is finally formed, and then an observable current signal is generated. After the signal is transmitted to the signal analyzer, it passes through the amplification circuit to generate a voltage pulse signal, and the dual discrimination criteria of amplitude discrimination and width discrimination are adopted to accurately discriminate the α rays, output the α ray count value per unit time, and transmit it to the computer software to calculate the plutonium element concentration.

[0041] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration, comprising a device base (11), characterized in that: A baking tray (14) is arranged on the upper surface of the device base (11), a housing (9) is fixedly connected to the upper surface of the device base (11), a sample holder (15) is arranged on the upper surface of the baking tray (14), a detection crystal (12) is arranged on the upper surface of the sample holder (15), a photomultiplier tube (10) is arranged on the upper surface of the detection crystal (12), and the photomultiplier tube (10) is connected to the detection crystal (12), and the signal processing board (1) is installed inside the housing (9) and is located above the photomultiplier tube (10); The signal processing board (1) comprises a power supply circuit (2), a communication circuit (3), a signal amplification and shaping circuit (4), a main amplification circuit (6), a pulse discrimination circuit (7), a preamplification circuit (5) and a high-voltage circuit (8), wherein the high-voltage circuit (8) is electrically connected to a photomultiplier tube (10), the photomultiplier tube (10) is electrically connected to the preamplification circuit (5), the preamplification circuit (5) is electrically connected to the main amplification circuit (6), the main amplification circuit (6) is electrically connected to the pulse discrimination circuit (7), and the signal amplification and shaping circuit (4) is electrically connected to the power supply circuit (2) and the communication circuit (3).

2. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: A detection crystal coating (13) is applied between the baking tray (14) and the detection crystal (12).

3. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The outer shell (9) is made of stainless steel, and a handle (16) is provided on the side surface of the baking tray (14).

4. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The signal processing board (1) has an operating voltage of 12V, which is provided by the power supply circuit (2).

5. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The power supply circuit (2) uses an external 12V input to distribute the voltage to provide the required corresponding voltages to different components, and the communication circuit (3) uses the RS485 protocol to communicate with the host computer.

6. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The overall operating voltage of the signal amplification and shaping circuit (4) is 12V, which is provided by the power supply circuit (2).

7. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The preamplifier circuit (5) is connected to the signal output end of the photomultiplier tube (10), the main amplifier circuit (6), and the pulse discrimination circuit (7) in sequence through cables, and is then connected to the signal input end of the communication circuit (3).

8. The ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The high-voltage circuit (8) is connected to the high-voltage input end of the photomultiplier tube (10) via a cable.

9. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The housing (9) encloses the signal processing board (1) and its component circuits, the photomultiplier tube (9), the detection crystal (12), the detection crystal coating (13) and other parts, and the outside of the housing (9) is in direct contact with the device base (11).

10. A ZnS (Ag) scintillator alpha counter device for measuring plutonium concentration according to claim 1, characterized in that: The photomultiplier tube (10) is coupled to a detection crystal (12) via a silicone grease light guide, and the detection crystal (12) is made of organic glass with a thickness of 3 mm and sprayed with ZnS.

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