Method for optimizing structure of ionization chamber, ionization chamber and measuring device

Abstract

The application discloses a structure optimization method of an ionization chamber, the ionization chamber and a measuring device. The optimization method comprises the following steps: constructing a finite element model of the ionization chamber; performing finite element multi-physical field analysis based on the finite element model; adjusting structure parameters of the ionization chamber according to each physical field analysis until the uniformity of the physical field meets a preset condition; and determining the structure of the ionization chamber according to the adjusted parameters. The structure parameters of the ionization chamber are optimized through the finite element multi-physical field analysis, the uniformity of multiple physical fields is improved, and the detection efficiency of the ionization chamber is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of radiation detection, and in particular to a structure optimization method of an ionization chamber, an ionization chamber and a measuring device. BACKGROUND

[0002] Some nuclear power plants, target production, neutron generator production or nuclear facility decommissioning and the like will produce a radioactive product, low-energy beta radionuclide H-3, during production and operation. According to the requirements of radiation environment monitoring, the H-3 radiation level is monitored by an ionization chamber.

[0003] In the related art, the lower limit of the ionization chamber for H-3 current detection is pA (10 -12 A) level or fA (10 -15 A) level, for example, the French PREMIUM Analyse and the Canadian TYNE company can reach fA level, but the detection efficiency of H-3 is 69.3% and 77.4% respectively, and the detection efficiency is low. SUMMARY

[0004] Therefore, the embodiments of the present application expect to provide a structure optimization method of an ionization chamber, an ionization chamber and a measuring device to solve the problem of efficient and stable detection of radioactive products such as H-3.

[0005] To achieve the above-mentioned purpose, the technical solutions of the embodiments of the present application are as follows:

[0006] In a first aspect, the present application provides a structure optimization method of an ionization chamber, comprising:

[0007] constructing a finite element model of the ionization chamber;

[0008] performing finite element multi-physical field analysis based on the finite element model;

[0009] adjusting the structure parameters of the ionization chamber according to each of the physical field analysis until the uniformity of the physical field meets a preset condition;

[0010] determining the structure of the ionization chamber according to the adjusted parameters.

[0011] Further, the step of performing finite element multi-physical field analysis based on the finite element model specifically comprises:

[0012] performing finite element electric field analysis based on the finite element model;

[0013] performing finite element gas flow field analysis based on the finite element model.

[0014] Further, the finite element electric field analysis is performed based on the finite element model first, and then the finite element gas flow field analysis is performed based on the finite element model.

[0015] Further, before the step of determining the structure of the ionization chamber according to the adjusted parameters, the optimization method further comprises:

[0016] performing finite element electric field analysis on the finite element model.

[0017] Further, the step of adjusting the structure parameters of the ionization chamber according to each of the physical field analysis until the uniformity of the physical field meets the preset condition specifically comprises:

[0018] adjusting the collecting electrode of the ionization chamber according to the electric field analysis until the electric field uniformity meets a first preset condition;

[0019] adjusting the air port of the ionization chamber according to the gas flow field analysis until the gas flow field uniformity meets a second preset condition.

[0020] Further, the step of adjusting the collecting electrode of the ionization chamber according to the electric field analysis specifically comprises:

[0021] adjusting the length of the collecting electrode in the ionization chamber; and / or,

[0022] performing tip hemispherical processing on the collecting electrode in the ionization chamber.

[0023] Further, the step of adjusting the air port of the ionization chamber according to the gas flow field analysis specifically comprises:

[0024] adjusting the total area of the air inlet and / or the air outlet in the air port; and / or,

[0025] adjusting the position of the air outlet in the air port.

[0026] The second aspect of the present application provides an ionization chamber manufactured according to the above structure optimization method, the ionization chamber comprising:

[0027] a housing having an ionization space and an air inlet and an air outlet respectively communicating with the ionization space, the air inlet being used for the flow of gas containing a detection substance, the housing being used for isolating an amplification circuit from the ionization space;

[0028] an electrode piece arranged on the housing to load a negative high voltage;

[0029] a collecting electrode arranged on the housing and at least partially located in the ionization space, cooperating with the electrode piece to form an electric field, and being used for connecting with the amplification circuit to output a measurement result of the detection substance.

[0030] Further, the housing comprises:

[0031] a barrel having an ionization space with upper and lower openings;

[0032] a seat body sealingly connected to the lower opening of the barrel, the first end of the amplification circuit being packaged in the seat body, the collecting electrode being disposed in the seat body, and the gas outlet being formed on the seat body or the barrel;

[0033] an air inlet assembly sealingly connected to the upper opening of the barrel, the air inlet being formed on the air inlet assembly.

[0034] Further, the air inlet assembly comprises:

[0035] an air inlet plate formed with a plurality of through holes, and a cover being arranged on the upper opening of the barrel;

[0036] a cover body arranged on the air inlet plate, and the air inlet being formed on the cover body;

[0037] a pad arranged between the cover body and the air inlet plate to form a buffer space for buffering the gas.

[0038] Further, the seat body is formed with an upper protrusion, the upper protrusion being disposed in the lower opening of the barrel, the collecting electrode being disposed in the upper protrusion, and the ionization chamber further comprising a first sealing member arranged between the barrel and the upper protrusion.

[0039] Further, the side of the seat body away from the barrel is formed with a plurality of grooves for packaging electronic components of the first end of the amplification circuit.

[0040] Further, the gas outlet has four outlets arranged at equal intervals around the lower outer periphery of the barrel.

[0041] Further, the volume of the ionization space is 180 ml, the height of the ionization space is 100 mm, and the length of the collecting electrode in the ionization space is 90 mm.

[0042] In a third aspect, the present application provides a measuring device, comprising:

[0043] the ionization chamber as described above;

[0044] an amplification circuit electrically connected to the collecting electrode;

[0045] a gas path in communication with the ionization space for introducing a gas containing a detection substance;

[0046] a control system electrically connected to the amplification circuit for displaying the measurement result.

[0047] Further, the measuring device further comprises a shielding shell covering the ionization chamber and the amplification circuit to shield interference.

[0048] The method for optimizing the structure of the ionization chamber provided in the embodiments of the present application comprises the following steps: constructing a finite element model of the ionization chamber, performing finite element multi-physical field analysis based on the finite element model, adjusting the structural parameters of the ionization chamber according to each physical field analysis, and determining the structure of the ionization chamber according to the adjusted parameters until the uniformity of the physical field meets the preset condition. The structural parameters of the ionization chamber are optimized by the finite element multi-physical field analysis, the uniformity of multiple physical fields is improved, and thus the detection efficiency of the ionization chamber is improved. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 A flowchart of a method for optimizing the structure of an ionization chamber provided in the embodiments of the present application;

[0050] Figure 2 A radial electric field intensity distribution diagram of the middle position of the collection electrode with an inner size of 80 mm of the cylinder and a position 10 mm away from the top of the ionization chamber;

[0051] Figure 3 A radial electric field intensity distribution diagram of the middle position of the collection electrode with an inner size of 85 mm of the cylinder and a position 10 mm away from the top of the ionization chamber;

[0052] Figure 4 A radial electric field intensity distribution diagram of the middle position of the collection electrode with an inner size of 90 mm of the cylinder and a position 10 mm away from the top of the ionization chamber;

[0053] Figure 5 A radial electric field intensity distribution diagram of the middle position of the collection electrode with an inner size of 95 mm of the cylinder and a position 10 mm away from the top of the ionization chamber;

[0054] Figure 6 A radial electric field intensity distribution diagram of the middle position of the collection electrode with an inner size of 98 mm of the cylinder and a position 10 mm away from the top of the ionization chamber;

[0055] Figure 7 A radial electric field intensity distribution diagram of a position 10 mm away from the top of the ionization chamber and a position from the tip to the top of the ionization chamber;

[0056] Figure 8 A radial electric field intensity distribution diagram of a position 10 mm away from the top of the ionization chamber and a position from the tip to the top of the ionization chamber;

[0057] Figure 9 A gas flow field cloud diagram of the ionization chamber in the related art;

[0058] Figure 10 A first gas flow field cloud diagram of the ionization chamber provided in the embodiments of the present application;

[0059] Figure 11 A comparison diagram of the gas flow field cloud diagrams of the ionization chambers with different gas outlet positions provided in the embodiments of the present application;

[0060] Figure 12 A second ionization chamber gas flow field cloud map provided by the embodiment of the application;

[0061] Figure 13 A third ionization chamber gas flow field cloud map provided by the embodiment of the application;

[0062] Figure 14 A structure schematic diagram of an ionization chamber provided by the embodiment of the application;

[0063] Figure 15 A Figure 14 A sectional view in A-A direction;

[0064] Figure 16 An ionization chamber measurement current data diagram provided by the embodiment of the application.

[0065] Explanation of reference signs

[0066] Housing 1; ionization space 1a; gas outlet 1b; cylinder body 11; seat body 12; upper convex part 12a; air inlet assembly 13; buffer space 13a; air inlet plate 131; cover body 132; pad 133; electrode 2; collector 3; base 31; anode rod 32; wire 33; insulating seal 34; first seal 4. DETAILED DESCRIPTION

[0067] It should be noted that the embodiments and technical features in the embodiments of the application can be combined with each other without conflict, and the detailed description in the specific embodiments should be understood as the explanation and description of the purpose of the application, and should not be regarded as improper limitation of the application.

[0068] The application will be further described in detail below in combination with the drawings and specific embodiments. The "first", "second" and the like in the embodiments of the application are only for the purpose of description, and should not be understood as indicating or implying relative importance or implicitly including at least one feature. In the description of the embodiments of the application, the meaning of "a plurality of" is at least two, that is, including two and more than two, for example, two or three, and the like, unless otherwise specifically limited.

[0069] The working principle of the ionization chamber is that the incident charged particles interact with the air medium, and the air molecules are ionized to form ion pairs. The physical movement of the ionized electrons and positive ions in the air is diffusion, adsorption, recombination and drift. The ionization chamber detects the ionization charges generated in the gas by using its decay. In order to effectively collect the charges, an electric field must be applied in the ionization space of the ionization chamber, that is, two electrodes are arranged on the ionization chamber, and a voltage is applied to the electrodes to form an electric field, so that the electrons and positive ions drift along the electric field direction to the two poles. Assuming that H-3 forms N0 ion pairs (electrons-positive ions) in the effective air gas space (primary ionization), the relationship between the number of collected ion pairs N and the applied voltage is divided into four working zones: recombination zone, saturation zone, proportional zone, limited proportional zone and G-M zone. The ionization chamber works in the saturation zone. In this zone, the recombination effect disappears, and the primary total ionization number N0 is completely collected by the electrodes and reaches saturation.

[0070] The ionization chamber has many interference factors, such as vibration, turbulent airflow, leakage current, high resistance, and electric field coupling between electronic components, cosmic rays, and natural radioactivity in materials. Specifically, airflow fluctuation is an important influencing factor. In related technologies, a diffusion type gas inlet structure is used for the gas inlet. This structure can reduce vibration and increase the uniformity of the gas in the ionization chamber. However, when the gas flow of the gas pump is unstable, it will also increase the vibration and cause airflow turbulence at the gas inlet. The factors affecting the performance of the ionization chamber belong to the barrel effect. In order to achieve a high-stability and high-detection-efficiency ionization chamber, each factor needs to be optimized to improve the detection efficiency.

[0071] Therefore, with reference to Figure 1 The first aspect of the embodiments of the present application provides a structure optimization method of an ionization chamber, comprising:

[0072] S1, constructing a finite element model of the ionization chamber;

[0073] S2, performing finite element multi-physical field analysis based on the finite element model;

[0074] S3, adjusting the structure parameters of the ionization chamber according to each physical field analysis until the uniformity of the physical field meets the preset condition;

[0075] S4, determining the structure of the ionization chamber according to the adjusted parameters.

[0076] The structure optimization method of the ionization chamber provided by the embodiments of the present application optimizes the structure parameters of the ionization chamber through finite element multi-physical field analysis, improves the uniformity of multiple physical fields, and further improves the detection efficiency of the ionization chamber.

[0077] The ionization chamber manufactured by the structure optimization method provided in the embodiments of the present application can be used for detection of H-3 and radionuclides with similar properties, that is, detection of low-energy beta radionuclides. The processing method of the embodiments of the present application is described in detail below by taking H-3 as an example of the detected substance in combination with specific embodiments.

[0078] S1, constructing a finite element model of the ionization chamber.

[0079] In this step, constructing a finite element model of the ionization chamber means selecting the structure of the ionization chamber in the related art according to the type of the detected substance of the ionization chamber, and then constructing the finite element model with the structure parameters of the ionization chamber in the related art. That is, the detection lower limit of the activity concentration or the micro-current is obtained according to the international advanced level H-3 ionization chamber, and then the finite element model is constructed according to the obtained parameters for subsequent optimization.

[0080] In an embodiment, before constructing the finite element model of the ionization chamber, the steps specifically include: obtaining the detected substance of the ionization chamber; and obtaining the volume of the ionization chamber according to the detected substance. Exemplarily, the detected substance is H-3, the activity concentration detection lower limit C L is 4×10 4 Bq / m 3 , the micro-current detection lower limit I L is 0.1fA or 1fA, the effective working volume V of the ionization chamber is set, the average decay energy E is 5700eV, and the average ionization energy ω of the beta ray in the air is 36±0.4eV. It can be understood that the detection lower limit refers to the minimum value that can be detected in the related art. Under the above effective volume condition, the effective activity A is A=V·C L ; the initial total ionization number N0 is: The collected charge Q0 is: Q0=N0·e, wherein e is the elementary charge; and the average ionization current I is: The effective volume V of the ionization chamber is obtained by combining the above formulas: In this way, the effective volume of the ionization chamber can be calculated as 98.7ml or 987ml. Then, the finite element model is constructed according to the effective volume, the accuracy of the finite element model is improved, and the accuracy of the subsequent finite element analysis is improved.

[0081] In an embodiment, the detected substance is H-3, when the minimum measurement current of the detected substance is 0.1fA, the volume of the ionization chamber is 180ml, and when the minimum detection current of the detected substance is 1fA, the volume of the ionization chamber is 1600ml. That is, when the micro-current detection lower limit I L is 0.1fA, the volume of the ionization chamber is 180ml, and when the micro-current detection lower limit I LWhen the micro-current detection lower limit is 0.1 fA, the volume of the ionization chamber is 1600 ml, which is larger than the calculated 98.7 ml and 987 ml. Thus, the volume of the ionization chamber is left with a margin after the structure is optimized, and the margin is not enough to cause detection failure and failure to verify subsequent finite element analysis. At the same time, when the micro-current detection lower limit is 0.1 fA, there is a margin of 81.3 ml, and when the micro-current detection lower limit is 1 fA, there is a margin of 613 ml. At the same proportion, the margin designed for the micro-current detection lower limit of 0.1 fA is larger. It can be understood that the smaller the micro-current detection lower limit, the lower the detection efficiency, and the larger the margin is designed to reduce the situation that the margin is not enough to cause detection failure and failure to verify subsequent finite element analysis.

[0082] S2, performing finite element multi-physical field analysis based on the finite element model.

[0083] In this step, performing finite element multi-physical field analysis based on the finite element model means performing analysis of multiple physical fields on the finite element model. The multiple physical fields can be a gas flow field or an electric field. It can be understood that the order of performing the analysis of multiple physical fields can be adjusted according to specific conditions.

[0084] In an embodiment, the step of performing finite element multi-physical field analysis based on the finite element model specifically includes: performing finite element electric field analysis based on the finite element model; and performing finite element gas flow field analysis based on the finite element model. Specifically, the analysis order is not limited, and the electric field analysis can be performed first and then the gas flow field analysis, or the gas flow field analysis can be performed first and then the electric field analysis. It can be understood that the uniformity of the electric field and the gas flow field has a greater impact on the detection efficiency of H-3. Through the finite element electric field analysis and the finite element gas flow field analysis, the structure of the ionization chamber can be optimized to effectively improve the detection efficiency of H-3.

[0085] In an embodiment, the finite element electric field analysis is performed based on the finite element model first, and then the finite element gas flow field analysis is performed based on the finite element model. It can be understood that adjusting the structural parameters of the ionization chamber according to the electric field analysis has a greater impact on the uniformity of the gas flow field. The parameters are adjusted after the electric field analysis and then the parameters are adjusted after the gas flow field analysis. In this way, the gas flow field adjustment parameters will not have a greater impact on the results of the electric field analysis, i.e., secondary adjustment is not required, and then the finite element analysis is completed, the time for finite element simulation is reduced, and the efficiency of the structure optimization of the ionization chamber is improved.

[0086] In an embodiment, before the step of determining the structure of the ionization chamber according to the adjusted parameters, the optimization method further comprises: performing finite element electric field analysis on the finite element model. It can be understood that after the finite element multi-physical field analysis based on the finite element model in steps S2 and S3 and the adjustment of the parameters, i.e., after the electric field analysis and the gas flow field analysis and the adjustment of the parameters, the uniformity of the electric field may be affected again. After the multi-physical field adjustment parameter combination of the finite element model is verified, the situation of the electric field being non-uniform after the multi-physical field adjustment parameter combination is reduced, and the detection efficiency of the ionization chamber is improved.

[0087] In an embodiment, the gas flow field analysis is performed based on the finite element model first, and then the finite element electric field analysis is performed based on the finite element model. Before the step of determining the structure of the ionization chamber according to the adjusted parameters, the optimization method further comprises: performing finite element gas flow field analysis on the finite element model. It can be understood that after the gas flow field analysis and the electric field analysis and the adjustment of the parameters, the uniformity of the gas flow field may be affected again. After the multi-physical field adjustment parameter combination of the finite element model is verified, the situation of the electric field being non-uniform after the multi-physical field adjustment parameter combination is reduced, and the detection efficiency of the ionization chamber is improved.

[0088] S3, adjusting the structure parameters of the ionization chamber according to each physical field analysis until the uniformity of the physical field meets the preset condition.

[0089] In this step, adjusting the structure parameters of the ionization chamber according to the physical field analysis means that the influencing factors that have an impact on the finite element analysis are obtained based on the nature of the physical field, and the structure parameters of the influencing factors are adjusted. The structure parameters can be specific structures or sizes, etc. For example, the physical field is the gas flow field, and the determination of the air inlet according to fluid mechanics will have an impact on the finite element analysis. It can be understood that the air inlet refers to the air inlet and the air outlet, and therefore the parameters of the air inlet and the air outlet are adjusted. The uniformity of the physical field meeting the preset condition means that in the process of adjusting the parameters, the most uniform result corresponding to the parameters is output after comparing a plurality of analysis results of the same physical field.

[0090] In an embodiment, the step of adjusting the structural parameters of the ionization chamber according to each physical field analysis until the uniformity of the physical field meets the preset condition specifically comprises: adjusting the collecting electrode of the ionization chamber according to the electric field analysis until the electric field uniformity meets the first preset condition; and adjusting the air port of the ionization chamber according to the gas flow field analysis until the gas flow field uniformity meets the second preset condition. The electric field uniformity meeting the first preset condition refers to a process of outputting the collecting electrode of the ionization chamber corresponding to the most uniform result after comparing a plurality of analysis results in the process of adjusting the collecting electrode of the ionization chamber. The gas flow field uniformity meeting the second preset condition refers to a process of outputting the air port of the ionization chamber corresponding to the most uniform result after comparing a plurality of analysis results in the process of adjusting the air port of the ionization chamber. That is, the electric field uniformity is changed by adjusting the collecting electrode of the ionization chamber, the gas flow field uniformity is changed by adjusting the air port, and then the collecting electrode state corresponding to the most uniform electric field and the air port state corresponding to the most uniform gas flow field are outputted, so as to optimize the ionization chamber structure, improve the uniformity of the physical field, and improve the detection efficiency of the ionization chamber.

[0091] In an embodiment, the step of adjusting the collecting electrode of the ionization chamber according to the electric field analysis specifically comprises: adjusting the length of the collecting electrode in the ionization chamber; and / or, performing a hemispherical treatment on the tip of the collecting electrode located in the ionization chamber. According to the working principle of the ionization chamber and the electric field property, if the electric field formed by the high voltage of the ionization chamber is not uniform, especially at the bottom and top of the ionization chamber, and if the size of the collecting electrode is too short or too long or a sharp tip effect is formed at the upper part of the collecting electrode, the local electric field strength may be too high or too low or the vector direction may be disorderly. If the local electric field strength is too high, the area may have transitioned to the proportional region, causing the collected current to be greater than the saturation current, and the unstable voltage may further cause unstable performance of the detector. If the local electric field strength is too low, some areas may be in the ionization recombination region, causing the collected current to be less than the saturation current, the effective volume of the ionization chamber is too small, and the design requirements cannot be met. If the electric field vector direction is disorderly and not pointing to the collecting electrode, ion recombination may occur, causing the collected current to be less than the saturation current, the effective volume of the ionization chamber is too small, and the design requirements cannot be met. Therefore, by adjusting the size of the collecting electrode to determine the best uniformity, and by performing a hemispherical treatment on the tip of the collecting electrode to eliminate the influence of the sharp tip effect, the uniformity of the electric field is improved, which is simple and effective and easy to implement.

[0092] Specifically, the thickness of the ionization chamber shell is 2 mm, the inner diameter is 48 mm, the inner height is 100 mm, the collecting electrode is a variable parameter, the outer end is 5 mm, and the length of the collecting electrode extending into the ionization chamber is determined by finite element simulation. For example, the length is first determined to be between 80 and 100 mm by bisection method, and then finite element simulation is performed on the lengths of 80 mm, 85 mm, 90 mm, 95 mm, and 98 mm extending into the cylinder, respectively, with reference to the electric field uniformity and the gas flow field uniformity. Figures 2-6 wherein Figures 2-4, Figure 6 The middle light line refers to the radial electric field intensity distribution at the middle position of the collecting electrode, and the dark line refers to the radial electric field intensity at 10 mm from the top of the ionization chamber; Figure 5 The middle light line refers to the radial electric field intensity at 10 mm from the top of the ionization chamber, and the dark line refers to the radial electric field intensity distribution at the middle position of the collecting electrode. Figures 2-6 From the electric field distribution diagram and the field intensity data analysis, it can be known that the length of the collecting electrode is 90 mm.

[0093] Further, the tip of the 90 mm collecting electrode is treated as a hemisphere, and the electric field intensity distribution diagram is shown in FIG. 6. Figures 7-8 wherein, Figure 7 The middle dark line refers to the radial electric field intensity distribution diagram at 10 mm from the top of the ionization chamber, and the light line refers to the radial electric field intensity distribution diagram from the tip to the top of the ionization chamber. Figure 8 The middle darkest line refers to the radial electric field intensity distribution diagram at 10 mm from the top of the ionization chamber, the second dark line refers to the radial electric field intensity distribution diagram from the hemispherical tip to the top of the ionization chamber, and the light line refers to the radial electric field intensity distribution diagram at the middle position of the ionization chamber. From the electric field intensity analysis diagram, it can be known that the electric field intensity of the tip is reduced from 1.45 x 10 5 V / m to 1.40 x 10 5 V / m, which is closer to the electric field intensity of the middle part of the ionization chamber. It can be understood that the electric field of the middle part of the ionization chamber is more uniform, and therefore, the electric field intensity of the tip is close to the electric field intensity of the middle part of the ionization chamber, and the uniformity of the electric field is further improved.

[0094] In an embodiment, the step of adjusting the vent of the ionization chamber according to the gas flow field analysis specifically includes: adjusting the total area of the gas inlet in the vent and / or the gas outlet in the vent; and / or, adjusting the position of the gas outlet in the vent. According to the principle of fluid mechanics, fluid flow is divided into stable flow and unstable flow. Stable flow may induce vibration with the change of the pipe aperture. The strength of the vibration induced by the fluid is comparable to that caused by the mechanical interference source, and the interference signal current caused by mechanical vibration is often at the level of pA or even higher. The fluid causes vibration because the interaction parameters of the fluid and the pipe aperture change, that is, the flow parameter mutation leads to, and the pulsation of the fluid is caused by the vortex, that is, the vortex definitely causes vibration. The boundary fluid separation caused by the mutation of the inlet and outlet of the ionization chamber will further produce vortex and vibration. It can be understood that the vent refers to the gas inlet and the gas outlet. Therefore, in order to reduce the instability of the gas flow field of the ionization chamber, that is, to reduce the influence of vortex and vibration, the uniformity is improved by adjusting the total area of the gas inlet and / or the gas outlet; and / or, adjusting the position of the gas outlet. It can be understood that adjusting the area of the gas inlet can be to set the gas inlet as a multi-hole structure, adjusting the total area of the gas outlet can be to increase the number of gas outlets, and adjusting the position of the gas outlet can be to move the gas outlet up and down by a preset size.

[0095] Specifically, improvements were made to the French PA ionization chamber. First, a gas flow field analysis was performed on the French PA ionization chamber, and the gas flow field cloud diagram is shown below. Figure 9 As shown, the intake plate was then set as a perforated metal plate to reduce the intake velocity and maximize the intake area. The improved gas flow field cloud diagram is shown below. Figure 10 As shown, it is understandable that the comparison Figure 9 and Figure 10 As can be seen from the gas flow field cloud map, setting the air inlet plate as a porous metal plate improves the uniformity of the gas flow field.

[0096] Specifically, adjusting the position of the gas outlet refers to moving the gas outlet up or down. For example, first perform gas flow field analysis on the French PA ionization chamber, then move the gas outlet down by 5 mm or up by 10 mm and perform gas flow field analysis again. The resulting gas flow field cloud map is shown below. Figure 11 As shown, the left image shows the outlet moved down by 5mm, the middle image shows the outlet unchanged, and the right image shows the outlet moved up by 10mm. It is understandable that, comparing the gas flow field contour maps, the gas flow field uniformity is optimal when the outlet position remains unchanged. The outlet of the French PA ionization chamber is located 10mm from the lower end face of the ionization chamber; therefore, the outlet position is set at 10mm from the lower end face of the ionization chamber.

[0097] Specifically, adjusting the total area of ​​the gas outlets refers to increasing the number of gas outlets, for example, by arranging multiple gas outlets at equal intervals around the outer periphery of the ionization chamber. First, a gas flow field analysis is performed on the French PA ionization chamber, such as... Figure 9 As shown, a gas flow field analysis is then performed on the ionization chamber with the added outlets. Please refer to [reference needed]. Figure 12 This yields a gas flow field cloud map. It's understandable that this comparison... Figure 9 and Figure 12 Increasing the number of air outlets improves the uniformity of the gas flow field.

[0098] Specifically, adjusting the position of the gas outlet refers to placing the gas outlet on the side or bottom of the ionization chamber. For example, a gas flow field analysis is first performed on the French PA ionization chamber with an increased number of gas outlets. Figure 12 Then, the outlets are positioned at relatively intervals at the bottom of the ionization chamber to create convection with the inlet, and gas flow field analysis is performed. Please refer to [reference needed]. Figure 13 This yields a gas flow field cloud map. It is understandable that the gas flow field is more uniform when the outlet is located on the side of the ionization chamber.

[0099] Based on the above analysis, the optimized air outlet can be located 10mm from the lower end face of the ionization chamber, with four air outlets arranged equidistantly around the outer periphery of the ionization chamber.

[0100] S4. Determine the structure of the ionization chamber based on the adjusted parameters.

[0101] In this step, the structure of the ionization chamber is determined by the adjusted parameters, thereby improving the detection efficiency of the ionization chamber.

[0102] In a second aspect of the embodiments of the present application, referring to Figures 14-15 , an ionization chamber manufactured according to the above optimization method is provided, which includes a shell 1, an electrode piece 2, and a collecting electrode 3.

[0103] The shell 1 has an ionization space 1a and an air inlet and an air outlet 1b in communication with the ionization space 1a, and the air inlet is used for the flow of a gas containing a detection substance. The shell 1 is used to isolate the amplification circuit from the ionization space 1a, thereby reducing the interference of the amplification circuit on the ionization chamber. It can be understood that the amplification circuit can be arranged on the shell 1 or outside the shell 1.

[0104] The electrode piece 2 is arranged on the shell 1 to load a negative high voltage, and the collecting electrode 3 is arranged on the shell 1 and at least partially located in the ionization space 1a, and cooperates with the electrode piece 2 to form an electric field, and is used to be connected with the amplification circuit to output the measurement result of the detection substance. Specifically, the electrode piece 2 can be an electrode sheet.

[0105] In an embodiment, the shell 1 includes a cylinder 11, a seat 12, and an air inlet assembly 13. The cylinder 11 has an ionization space 1a with an upper and lower opening, and the cylinder 11 can be stainless steel, and exemplarily, the cylinder 11 is 316l stainless steel with low magnetism. The seat 12 is sealingly connected to the lower opening of the cylinder 11, the first end of the amplification circuit is packaged in the seat 12, the collecting electrode 3 is arranged in the seat 12, and the air outlet 1b is formed on the seat 12 or the cylinder 11. That is, the seat 12 is used to isolate the amplification circuit, thereby reducing the mutual interference between the amplification circuit and the ionization chamber. The material of the seat 12 can be aluminum or aluminum alloy, which has no magnetism and good shielding effect, and has sufficient strength and low cost, thereby reducing the production cost. The air inlet assembly 13 is sealingly connected to the upper opening of the cylinder 11, and the air inlet is formed on the air inlet assembly 13. In this way, the ionization space 1a formed by the shell 1 is compact and sealed, thereby improving the detection efficiency of the ionization chamber.

[0106] In an embodiment, the air inlet assembly 13 includes an air inlet plate 131, a cover 132 and a cushion 133. The air inlet plate 131 is formed with a plurality of through holes and covers the upper opening of the cylinder 11. The air inlet plate 131 can be a perforated metal plate with a size equal to the size of the top of the cylinder 11 to increase the air inlet area, ensure the stability and uniformity of the gas flow, reduce vibration interference and increase the sensitive volume and ionization efficiency. The cover 132 covers the air inlet plate 131, and the air inlet is formed on the cover 132. Exemplarily, the cover 132 can be a plastic piece with good insulation and will not affect the uniformity of the electric field. The cushion 133 is arranged between the cover 132 and the air inlet plate 131 to form a buffer space 13a for gas buffering. It can be understood that the buffer space 13a refers to the space surrounded by the cushion 133. Exemplarily, the cushion 133 can be a rubber pad, which forms a 2mm buffer zone with the cover 132. In this way, by forming a plurality of through holes in the air inlet plate 131, the air inlet speed is reduced, the air inlet area is maximized, the detection efficiency is improved, the unstable gas flow is buffered, and the gas flow vibration is reduced.

[0107] In an embodiment, the seat body 12 is formed with an upper protrusion 12a, the upper protrusion 12a penetrates the lower opening of the cylinder 11, the collector 3 penetrates the upper protrusion 12a, and the ionization chamber further includes a first sealing member 4 arranged between the cylinder 11 and the upper protrusion 12a. That is, by arranging the first sealing member 4 between the cylinder 11 and the upper protrusion 12a, the collector 3 is sealed, the air tightness is ensured, the influence of the leakage current is reduced, and the detection efficiency is improved.

[0108] In an embodiment, the side of the seat body 12 away from the cylinder 11 is formed with a plurality of grooves for packaging electronic components of the first end of the amplification circuit. In this way, the electronic components are arranged in the same space, the interference caused by the space distance is reduced, and the coupling interference of the components is prevented. For example, the grooves formed in the seat body 12 include high resistance grooves, capacitor grooves, terminal grooves and delay device grooves, etc., for packaging high resistance, capacitor, terminal and delay device components of the amplification circuit to isolate the amplification circuit, and reduce the interference of the mutual coupling of the high resistance, capacitor, terminal and delay device components on the magnetic field and electric field of the ionization chamber.

[0109] In an embodiment, the air outlet 1b has four, which are arranged at equal intervals around the outer periphery of the lower part of the cylinder 11. According to the finite element analysis of the gas flow field, by increasing the area of the air outlet 1b and the plurality of air outlets 1b to form a stable gas flow, the uniformity of the gas flow field is increased, and the detection efficiency is improved.

[0110] In an embodiment, the volume of the ionization space 1a is 180ml, the height of the ionization space 1a is 100mm, and the length of the collecting electrode 3 located in the ionization space 1a is 90mm. It can be understood that the uniformity of the electric field is best when the length of the collecting electrode 3 located in the ionization space 1a is 90mm, which improves the detection efficiency.

[0111] In an embodiment, the collecting electrode 3 includes a base 31, an anode rod 32, and a wire 33. The base 31 is sealingly connected to the seat body 12, one end of the anode rod 32 is sealingly connected to the base 31, and the other end is at least partially located in the barrel 11. One end of the wire 33 is connected to the end of the anode rod 32 close to the base 31, and the other end is connected to the amplification circuit. The sealing connection can be fusion sealing, which reduces the leakage current and the electric field interference. For example, the anode rod 32 is made of single-crystal oxygen-free copper with better electrical conductivity and thermal conductivity, and the wire 33 can be made of single-crystal oxygen-free copper. The connection to the amplification circuit is by welding, the welding process is flip-over space welding, the welding material is tungsten copper with good thermal and electrical conductivity and good magnetic resistance, and after welding, the surface is sprayed with insulation. In this way, the interference with the detection result is reduced, and the detection efficiency is improved.

[0112] In an embodiment, the collecting electrode 3 further includes an insulating sealing member 34 arranged between the base 31 and the anode rod 32 and / or between the base 31 and the seat body 12. The material of the insulating sealing member 34 is not limited and can be, for example, polytetrafluoroethylene. The insulating sealing member 34 is used to block the leakage current, reduce the electric field interference, and fix the base 31 and the anode rod 32 and / or the base 31 and the seat body 12. In this way, the blocking of the leakage current is completed by the insulating sealing member 34. Compared with the high-temperature ceramic sealing in the related art, which requires high temperature and has a complex process and is prone to cause insufficient sealing and thus fail to achieve the advantage of high resistance of the material, and the collecting electrode 3 wire 33 is extremely thin and is prone to be fused when sealed with ceramic, the insulating sealing member 34 enables the base 31 and the anode rod 32 and / or the base 31 and the seat body 12 to have high bonding, effectively avoiding the adverse effects caused by ceramic sealing.

[0113] In a third aspect of the embodiments of the present application, a measuring device is provided, which includes the ionization chamber, the amplification circuit, the gas path, and the control system. The amplification circuit is electrically connected to the collecting electrode 3, the gas path is in communication with the ionization space 1a and is used to introduce a gas containing a detection substance, and the control system is electrically connected to the amplification circuit and is used to display the measurement result. The control system can be a computer that acquires the measurement result by receiving the electrical signal of the amplification circuit. It can be understood that the amplification circuit and the gas path can be located on the same side or different sides of the ionization chamber, and the amplification circuit can further improve the detection efficiency of the ionization chamber.

[0114] In an embodiment, the measuring device further comprises a shielding shell which is arranged outside the ionization chamber and the amplification circuit to shield interference. It can be understood that the shielding shell prevents electrostatic interference and electromagnetic interference from the ionization chamber and the amplification circuit, the shielding shell can be filled with inert gas, the shielding shell is grounded, and the shielding shell provides necessary conditions for stabilizing a uniform electric field.

[0115] In a fourth aspect of the embodiment of the present application, a measuring method is provided, including: double-ionization chamber subtraction deduction; determining detection efficiency and sensitivity.

[0116] Specifically, the double-ionization chamber is manufactured by the manufacturing method, and includes a measuring ionization chamber and a compensation ionization chamber. The measuring ionization chamber measures the current of H-3 and gamma rays, and the compensation ionization chamber measures the current of gamma rays. The current of the H-3 to be measured is obtained by subtracting the compensation ionization chamber from the measuring ionization chamber.

[0117] In the related art, radioactive interference is generally shielded by metal and background subtraction through MCNP (Monte Carlo N Particle Transport Code) simulation calculation. In order to reduce the interference of radionuclide rays in the material, the minimum thickness of the material is calculated by using a dose material to reduce the interference. Since the shielding thickness of the natural radionuclide gamma ray interference is relatively thick, the design concept of using a shielding layer is not applicable to such an ionization chamber. However, the same batch of materials is used, and the material radioactivity uniformity and local level are determined by using a high-purity germanium gamma spectrometer before use. The same batch of verified materials is used during processing. Double-ionization chamber measurement is used, and background subtraction technology is used. The radioactive gamma ray interference elimination of the present application uses the same batch of materials, and the material radioactivity uniformity and background level are determined by using a high-purity germanium gamma spectrometer before use. The same batch of verified materials is used during processing. Double-ionization chamber measurement is used, and the same anti-coincidence measurement technology and background subtraction technology are used. The background current test is performed in the workplace. The measuring ionization chamber and the compensation ionization chamber are measured every 5 minutes. The experiment is performed for 9 hours, and the experimental data are shown in the following table:

[0118]

[0119]

[0120]

[0121] According to the experimental data, the current measurement graph is as follows Figure 16As shown, the average value of the fA level micro-current measured by the ionization chamber and the compensation ionization chamber is 0.765 fA and 0.930 fA respectively, and the standard deviation is 0.0829 fA and 0.0674 fA respectively, thus the average value of the current of H-3 measured by the ionization chamber is 0.166 fA, and the standard deviation is 0.1038 fA, at the same time, the calibration experiment is carried out by H-3, and it is determined that the collection efficiency of the ionization chamber reaches 93.9%.

[0122] The above merely illustrates the preferred embodiments of the present application, and is not used to limit the present application. Any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present application are included in the protection scope of the present application.

Claims

1. A method of optimizing the structure of an ionization chamber, characterized in that, The method comprises the following steps: building a finite element model of the ionization chamber; performing finite element electric field analysis based on the finite element model; performing finite element gas flow field analysis based on the finite element model; adjusting the collecting electrode of the ionization chamber according to the electric field analysis until the electric field uniformity meets a first preset condition; adjusting the air inlet of the ionization chamber according to the gas flow field analysis until the gas flow field uniformity meets a second preset condition; determining the structure of the ionization chamber according to the adjusted parameters; wherein the step of adjusting the collecting electrode of the ionization chamber according to the electric field analysis specifically comprises: adjusting the length of the collecting electrode in the ionization chamber; and / or, sharpening the tip of the collecting electrode in the ionization chamber; the step of adjusting the air inlet of the ionization chamber according to the gas flow field analysis specifically comprises: adjusting the total area of the air inlet and / or the air outlet in the air inlet; and / or, adjusting the position of the air outlet in the air inlet.

2. The method for structural optimization of claim 1, wherein, The method comprises the following steps:

3. The method of structural optimization according to claim 2, characterized in that, performing finite element electric field analysis based on the finite element model, and then performing finite element gas flow field analysis based on the finite element model. Before the step of determining the structure of the ionization chamber according to the adjusted parameters, the optimization method further comprises:

4. An ionization chamber manufactured by the structure optimization method according to any one of claims 1 to 3, characterized by, performing finite element electric field analysis on the finite element model. The ionization chamber comprises: a shell having an ionization space and an air inlet and an air outlet respectively communicating with the ionization space, the air inlet being used for the flow of gas containing a detection substance, the shell being used for isolating an amplification circuit from the ionization space; an electrode arranged on the shell to load a negative high voltage; 5. The ionization chamber of claim 4, wherein, a collecting electrode arranged on the shell and at least partially located in the ionization space, cooperating with the electrode to form an electric field, and being connected with the amplification circuit to output the measurement result of the detection substance. The shell comprises: a barrel having an ionization space with upper and lower openings; a seat body sealingly connected to the lower opening of the barrel, a first end of the amplification circuit being packaged in the seat body, the collecting electrode being arranged in the seat body, and the air outlet being formed in the seat body or the barrel; 6. The ionization chamber of claim 5, wherein, an air inlet assembly sealingly connected to the upper opening of the barrel, and the air inlet being formed in the air inlet assembly. The air inlet assembly comprises: an air inlet plate formed by a porous medium metal plate, covering the upper opening of the barrel; a cover body covering the air inlet plate, and the air inlet being formed in the cover body; 7. The ionization chamber of claim 5, wherein, a gasket arranged between the cover body and the air inlet plate to form a buffer space for buffering the gas.

8. The ionization chamber of claim 5, wherein, The seat body is formed with an upper protrusion arranged in the lower opening of the barrel, and the collecting electrode is arranged in the upper protrusion, and the ionization chamber further comprises a first sealing member arranged between the barrel and the upper protrusion.

9. The ionization chamber of claim 5, wherein, The side of the seat body away from the barrel is formed with a plurality of grooves for packaging electronic elements of the first end of the amplification circuit.

10. The ionization chamber of claim 4, wherein, The air outlet has four air outlets arranged at equal intervals around the lower outer periphery of the barrel.

11. A measuring device, characterized by The volume of the ionization space is 180 ml, the height of the ionization space is 100 mm, and the length of the collecting electrode in the ionization space is 90 mm. The method comprises the following steps: The ionization chamber according to any one of claims 4-10; An amplification circuit electrically connected to the collector; An air path in communication with the ionization space for passing in a gas containing a detection substance; A control system electrically connected to the amplification circuit for displaying a measurement result.

12. The measuring device of claim 11, wherein, The measurement device further comprises a shielding shell covering the ionization chamber and the amplification circuit to shield interference.

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