Tritiated water on-line measuring device based on BGO crystal and solid scintillator and working method of tritiated water on-line measuring device

Abstract

The invention belongs to the technical field of nuclear radiation detection, and provides a tritiated water on-line measuring device based on a BGO crystal and a solid scintillator and a working method of the tritiated water on-line measuring device. The measuring device comprises a detector, a waste liquid pool, a rear-end electronics part and a computer, wherein the detector consists of a counting chamber, a photomultiplier tube, a photomultiplier tube seat and a front-end electronics part; the counting chamber is a composite scintillator composed of an outer-layer BGO crystal and an inner-layer solid scintillator, a certain space is reserved in the inner-layer solid scintillator, tritiated water and solid scintillator particles are mixed into a mixed solution according to a certain proportion, the mixed solution flows into a cavity in the composite scintillator through an inflow pipeline before measurement, and the tritiated water and the solid scintillator particles are measured. And keeping for a period of time to count output signals. According to the method, the contact area of the tritium water and the scintillator is increased to the maximum extent so as to improve the detection efficiency of the measurement device, and meanwhile, the counting background of measurement can be greatly reduced, so that the detection lower limit of measurement is reduced, and the measurement capability of the measurement device on low-activity tritium water is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of nuclear radiation detection, and in particular relates to an online measurement device for tritium water based on BGO crystals and solid scintillators and a working method thereof. Background Art

[0002] The beta rays released by tritium decay have low energy, weak penetration, and are easily affected by other radionuclides. The traditional liquid scintillation method requires a large amount of scintillation liquid during measurement, which will produce a large amount of radioactive organic waste after the measurement, and the measurement cost is high.

[0003] With the development of new detection technologies, solid scintillators have been increasingly used in tritium water measurement. This method uses scintillating optical fibers or solid scintillator plates placed in tritium water for measurement, or processes solid scintillators such as CaF2:Eu and plastic scintillators into powder particles, which are mixed with the liquid to be measured for measurement. Solid scintillators can be recycled after measurement. Using solid scintillators to measure tritium water can reduce measurement costs and avoid the generation of radioactive waste. However, there are also some shortcomings. The contact area between solid scintillators and tritium water is limited. The decay of tritium water releases β rays, which makes the efficiency of solid scintillators much lower than that of liquid scintillators. γ rays and cosmic rays in the environment are not effectively shielded, and entering the measurement room increases the background count rate. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies in the above-mentioned prior art and to provide an online measurement device for tritium water based on BGO crystals and solid scintillators and a working method thereof. The method maximizes the contact area between tritium water and the scintillator to improve the detection efficiency of the measuring device, and at the same time can greatly reduce the counting background of the measurement, thereby reducing the detection limit of the measurement and improving the measurement capability of the measuring device for low-activity tritium water. The present invention can be applied to the fields of online monitoring of tritium in nuclear power plant drainage, ocean monitoring, and nuclear waste management.

[0005] The purpose of the present invention is achieved through the following technical measures.

[0006] The invention provides a tritium water online measuring device based on BGO crystal and solid scintillator, comprising a detector consisting of a counting chamber, a photomultiplier tube, a photomultiplier tube holder and a front-end electronic part, a detector shell, a lead-copper shielding body, a waste liquid pool, a back-end electronic part, and a computer; the counting chamber is a composite scintillator consisting of an outer layer of BGO crystal and an inner layer of solid scintillator, a certain space is reserved in the inner layer of the solid scintillator, a solution to be measured flows in, is measured and flows out of the composite scintillator, tritium water and solid scintillator particles are mixed in a certain proportion to form a mixed solution, before measurement, the mixed solution flows into a cavity in the composite scintillator through an inflow pipe, and is kept for a period of time to statistically output a signal, the outflow pipe is connected to the waste liquid pool, the mixed solution flows out of the waste liquid pool through the outflow pipe, and the solid scintillator particles are separated for the next measurement, the photomultiplier tube holder and the front-end electronic part are connected to the back-end electronic part through a connector and a shielded cable, and the back-end electronic part is connected to the computer through the shielded cable to display the measurement result.

[0007] In the above technical solution, the detector housing is made of aluminum lined with polytetrafluoroethylene, the inner surface is coated with a diffuse reflection coating, and interfaces for solution inflow and outflow pipes are left at the top and bottom of the detector housing.

[0008] In the above technical solution, the entire detector is placed in a lead-copper shielding body, which is composed of an outer layer of lead and an inner lining of copper and is installed on the base by multiple sets of fastening bolts. The upper shielding layer and the lower shielding layer are separable to facilitate the assembly of the internal detector.

[0009] In the above technical solution, the BGO crystal and the solid scintillator are both ground and polished, and the gap between the BGO crystal and the solid scintillator is filled with light-guiding silicone oil.

[0010] In the above technical solution, the solid scintillator particles are processed from plastic scintillator or CaF2:Eu, and the solid scintillator particles and the solid scintillator in the inner layer of the composite scintillator are made of the same material.

[0011] The present invention also provides a working method of the above-mentioned online tritium water measuring device based on BGO crystal and solid scintillator: in the online tritium water measurement, batches of tritium water to be measured and a certain proportion of solid scintillator particles are mixed, and enter the counting chamber in the detector through the inflow pipe, the beta rays released by the decay of tritium in the water react with the solid scintillator particles and the solid scintillator to emit light, the photons are converted into electrical signals by the photomultiplier tube and amplified and output to the front-end electronic part, the photomultiplier tube seat and the voltage divider module in the front-end electronic part provide the photomultiplier tube with working high voltage, the signal is amplified, shaped and filtered by the front-end electronic part, and then input into the back-end electronic part to be converted into a digital signal and processed and calculated, and finally displayed and processed on the computer, after the measurement is completed, the outflow pipe is opened by the computer to let the solution flow out to the waste liquid pool, the solid scintillator particles are separated from the solution by the microporous filter, and mixed with the next batch of tritium water for measurement.

[0012] Compared with the prior art, the present invention has the following beneficial effects:

[0013] 1. The present invention uses solid scintillator as the outer shell of the counting chamber, and processes the solid scintillator into particles and mixes them with tritium water to form a solution to be tested. Solid scintillator (CaF2:Eu, plastic scintillator, etc.) has the advantages of being insoluble in water, easy to process, and having a high luminescence yield for the beta rays emitted by tritium decay. Compared with other solid scintillator measurement methods, the present invention greatly improves the measurement efficiency.

[0014] 2. The present invention uses a composite scintillator combined with a BGO crystal to perform anti-coincidence measurement on environmental rays. The BGO crystal completely covers the surface of the solid scintillator counting chamber, and BGO performs anti-coincidence measurement on environmental gamma rays and muons with strong penetration in cosmic rays. Utilizing the different characteristics of the decay time of the luminescent pulses of different crystals and based on the pulse shape discrimination technology, the present invention realizes the discrimination measurement of the β and α signals in the sample and the γ and μ signals in the environment, thereby significantly reducing the background count rate of the measuring device.

[0015] 3. The present invention filters the measured solution to separate the solid scintillator and other operations, recovers the measured solid scintillator particles and uses them for subsequent measurements, thereby greatly reducing the cost of online measurement.

[0016] 4. The present invention does not require additional anti-coincidence detectors and shielding materials, thus reducing the volume and mass of the measuring device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the detector part in the present invention.

[0018] Figure 2 for Figure 1 Cross-section at the center arrow.

[0019] Figure 3 This is an overall schematic diagram of the invented tritium water online measuring device.

[0020] Figure 4 Schematic diagram of an alternative solution of the detector structure in the present invention.

[0021] Among them: 1. Inflow / outflow pipe, 2. Counting chamber, 3. BGO crystal, 4. Solid scintillator and tritium water mixed solution, 5. Photomultiplier tube, 6. Photomultiplier tube socket and front-end electronic part, 7. Detector shell, 8. Lead-copper shielding body, 9. Tritium water to be tested, 10. Solid scintillator particles, 11. Mixed solution, 12. Waste liquid pool, 13. Tritium water after separation, 14. Detector, 14b. Detector, 15. Back-end electronic part, 16. Computer. DETAILED DESCRIPTION

[0022] 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.

[0023] See also Figure 1 , Figure 2 , Figure 3 The embodiment of the present invention provides an online measurement device for tritium water based on BGO crystal and solid scintillator, including a detector 14 composed of an inflow / outflow pipe 1, a counting chamber 2, a BGO crystal 3, a photomultiplier tube 5, a photomultiplier tube holder and a front-end electronic part 6, a detector housing 7, a lead-copper shielding body 8, tritium water to be measured 9, a waste liquid pool 12, a back-end electronic part 15, and a computer 16.

[0024] In this embodiment, the working method of the above-mentioned tritium water online measurement device based on BGO crystal and solid scintillator is as follows:

[0025] In the online measurement of tritium water, the tritium water 9 to be measured is mixed with a certain proportion of solid scintillator particles 10 in batches to form a mixed solution 11, which enters the counting chamber 2 in the detector 14 of the tritium water measuring device through a pipeline. The beta rays released by the decay of tritium in the water react with the solid scintillator particles and the solid scintillator in the counting chamber to emit light, and the photons are converted into electrical signals by the photomultiplier tube 5 and amplified and output to the front-end electronic part 6. The photomultiplier tube base and the voltage divider module in the front-end electronic part 6 provide the photomultiplier tube 5 with a working high voltage. After the signal is amplified, shaped and filtered by the front-end electronic part, it is input to the back-end electronic part 15 and converted into a digital signal for processing and calculation, and finally displayed and processed on the computer 16. After the measurement is completed, the computer 16 controls the pipeline to open, and the solution flows out to the waste liquid pool 12, and the solid scintillator particles are separated from the solution by the microporous filter, and mixed with the next batch of tritium water for measurement.

[0026] In this embodiment, the detector housing 7 is made of aluminum alloy lined with polytetrafluoroethylene, which has good mechanical properties, waterproof properties, electromagnetic shielding properties and is light in weight. The inner wall of polytetrafluoroethylene is sprayed with diffuse reflection materials such as barium sulfate BaSO4 or magnesium oxide or titanium dioxide TiO2 with high reflectivity to improve the light collection efficiency of the counting chamber.

[0027] In this embodiment, the detector shell is a lead-copper shielding body 8, which is composed of an outermost layer of lead, a middle layer of old lead and an inner layer of copper, and can effectively shield a large amount of environmental gamma background.

[0028] In this embodiment, the detector contains a composite scintillator composed of a BGO crystal 3 and a solid scintillator. When the ambient radiation enters the counting chamber and causes luminescence, it will react with the BGO crystal that wraps the solid scintillator to emit light. The light decay time for BGO luminescence is 320ns, and the luminescence time of the solid scintillator is shorter (the luminescence decay time of CaF2:Eu is about 10ns, and the luminescence decay time of the plastic scintillator is about 2.4ns to 200ns). The original signal is amplified and retained by the front-end electronics part, and the obtained pulse signal waveform is related to the luminescence decay time of the scintillator.

[0029] By digitally sampling the pulse signal and reading the pulse waveform parameters of the pulse signal through the back-end electronics part 15, the BGO signal and the solid scintillator signal can be distinguished by the pulse waveform identification method. At this time, the signal of the counting chamber luminescence caused by environmental rays and the BGO crystal luminescence signal will be generated at the same time. By performing anti-coincidence counting processing on the BGO luminescence signal, the luminescence and count caused only by the decay of samples such as tritium water can be obtained, thereby effectively distinguishing cosmic ray muons and environmental background γ signals.

[0030] like Figure 4As shown, another detector structure 14b is shown, in which the BGO crystal and the solid scintillator counting chamber are cylindrical structures, and coincidence measurement is performed through three photomultiplier tubes, which has a higher detection efficiency.

[0031] The present invention also provides another working method. By selecting solid scintillator particles with a larger diameter (such as 1 mm) for measurement, in this mode, a microporous filter is installed at the inlet and outlet of the inflow / outflow pipe 1 respectively, and the diameter of the filter mesh is smaller than the diameter of the solid scintillator particles. The solid scintillator particles are placed in the counting chamber 2, and tritium water only enters / exits through the inflow / outflow pipe 1 for each measurement.

[0032] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0033] The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A tritium water online measurement device based on BGO crystal and solid scintillator, characterized by: The invention comprises a detector consisting of a counting chamber, a photomultiplier tube, a photomultiplier tube holder and a front-end electronic part, a detector shell, a lead-copper shielding body, a waste liquid pool, a back-end electronic part and a computer; the counting chamber is a composite scintillator consisting of an outer layer of BGO crystal and an inner layer of solid scintillator, a certain space is reserved in the inner layer of the solid scintillator, a solution to be tested flows in, is measured and flows out of the composite scintillator, tritium water and solid scintillator particles are mixed in a certain proportion to form a mixed solution, before measurement, the mixed solution flows into a cavity in the composite scintillator through an inflow pipe and is kept for a period of time to statistically output a signal, the outflow pipe is connected to the waste liquid pool, the mixed solution flows out of the waste liquid pool through the outflow pipe to separate the solid scintillator particles for the next measurement, the photomultiplier tube holder and the front-end electronic part are connected to the back-end electronic part through a connector and a shielded cable, and the back-end electronic part is connected to the computer through the shielded cable to display the measurement result.

2. The tritium water online measuring device based on BGO crystal and solid scintillator according to claim 1 is characterized in that: The detector housing is made of aluminum lined with polytetrafluoroethylene, and the inner surface is coated with a diffuse reflection coating. Interfaces for solution inflow and outflow pipelines are left at the top and bottom of the detector housing.

3. The tritium water online measuring device based on BGO crystal and solid scintillator according to claim 1 is characterized in that: The entire detector is placed in a lead-copper shielding body, which consists of an outer layer of lead and an inner lining of copper. It is installed on the base through multiple sets of fastening bolts. The upper shielding layer and the lower shielding layer can be separated to facilitate the assembly of the internal detector.

4. The tritium water online measuring device based on BGO crystal and solid scintillator according to claim 1 is characterized in that: The BGO crystal and the solid scintillator are both ground and polished, and the gap between the BGO crystal and the solid scintillator is filled with light-guiding silicone oil.

5. The online measurement device for tritium water based on BGO crystal and solid scintillator according to claim 1 is characterized in that: The solid scintillator particles are obtained by processing plastic scintillator or CaF2:Eu, and the material of the solid scintillator particles is consistent with that of the solid scintillator in the inner layer of the composite scintillator.

6. A working method of the online measurement device of tritium water based on BGO crystal and solid scintillator as claimed in any one of claims 1 to 5, characterized in that: In the online measurement of tritium water, batches of tritium water to be measured and a certain proportion of solid scintillator particles are mixed and enter the counting chamber in the detector through the inflow pipe. The beta rays released by the decay of tritium in the water react with the solid scintillator particles and the solid scintillator to emit light. The photons are converted into electrical signals by the photomultiplier tube and amplified and output to the front-end electronic part. The photomultiplier tube holder and the voltage divider module in the front-end electronic part provide the photomultiplier tube with working high voltage. After the signal is amplified, shaped and filtered by the front-end electronic part, it is input into the back-end electronic part and converted into a digital signal for processing and calculation, and finally displayed and processed on the computer. After the measurement is completed, the outflow pipe is opened by the computer to let the solution flow out to the waste liquid pool, and the solid scintillator particles are separated from the solution by the microporous filter and mixed with the next batch of tritium water for measurement.

7. The working method according to claim 6, characterized in that: Solid scintillator particles with large diameter are selected for measurement. At the same time, a microporous filter is installed at the inlet / outlet pipe openings respectively. The solid scintillator particles are placed in the counting chamber. Each measurement only allows tritium water to flow in and out through the inlet / outlet pipes.

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