Variable chamber time projection chamber for low and medium energy monoenergetic neutron energy measurement

Abstract

The present application relates to a kind of variable chamber time projection chamber of low-energy single-energy neutron energy measurement, low-pressure working gas is filled in sealed chamber inside;Polyethylene support column is installed in sealed chamber, and a plurality of mounting slots are provided on polyethylene support column;Multiple cathode plate support is fixed on the mounting slot of polyethylene support column, and the mounting slot position can be replaced along the direction of polyethylene support column, and the moving step of replacement is centimeter level, anode plate is arranged at the lower bottom plate of sealed chamber;Grid plate support is fixed on the mounting slot of polyethylene support column, and the mounting slot position can be replaced along the direction of polyethylene support column, and the moving step of replacement is millimeter level;Single-energy neutron and low-pressure working gas scatter to form electron-ion pair, and move to anode plate along the direction of electric field.By setting variable chamber time projection chamber, the spacing between grid plate and anode plate can be adjusted, the error of recoil nuclear angle is reduced, the energy resolution is improved, and the neutron energy measurement uncertainty can be reduced to within 10%.

Description

Technical Field

[0001] This invention relates to the field of nuclear technology application technology, and in particular to a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons. Background Technology

[0002] The International Atomic Energy Agency (IAEA) recommends 11 standard cross-section methods, among which 1H(n,n) 1H is the primary standard, applicable to the energy range of 0.1keV to 350MeV. In the monoenergetic neutron radiation field construction region of 0.1keV to 20MeV, the reaction cross-section uncertainty is about 0.2%.

[0003] Currently, time-projection ionization chambers used for measuring the energy of low- and medium-energy monoenergetic neutrons focus on addressing issues such as the uniformity of the electric field in the ionization region, time-projection reproduction algorithms, and electronic readout with high sampling rates and fast response times. However, for the energy measurement of low- and medium-energy monoenergetic neutrons, it is impossible to maintain the pressure of the pressure chamber, which affects the measurement efficiency and measurement uncertainty of low- and medium-energy monoenergetic electrons.

[0004] The above problems urgently need to be addressed. Summary of the Invention

[0005] This invention discloses a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons, aiming to solve the technical problems existing in the prior art.

[0006] This invention employs the following technical solution: a sealed chamber filled with low-pressure working gas, with a neutron inlet on the sealed chamber for projecting monoenergetic neutrons; a polyethylene support column installed vertically within the sealed chamber, with multiple mounting slots on the polyethylene support column; multiple cathode plates installed inside the sealed chamber, near the upper top plate of the sealed chamber, arranged along the direction from the upper top plate to the lower bottom plate, the multiple cathode plates supported and fixed on the mounting slots of the polyethylene support column, the multiple cathode plates can have their mounting slot positions changed along the direction of the polyethylene support column, with a change step size on the order of centimeters, and the uppermost optional cathode plate of the multiple cathode plates is positioned relative to the upper top plate of the sealed chamber. The spacing between the plates is greater than 1 cm; the anode plate is disposed at the bottom plate of the sealed chamber; the grid plate is installed in the sealed chamber and supported and fixed on the mounting groove of the polyethylene support column. The grid plate can be changed in the mounting groove position along the direction of the polyethylene support column, and the change movement step is on the millimeter level. The spacing between the grid plate and the uppermost optional cathode plate is 15 to 20 cm, and the spacing between the grid plate and the anode plate is 200 to 400 micrometers; a high-voltage module is connected to the grid plate, and the voltage between the grid plate and the anode plate is 100V to 400V. The monoenergetic neutrons are scattered with the low-pressure working gas to form electron-ion pairs, and the electrons move to the anode plate along the electric field direction.

[0007] Optionally, the sealed chamber includes: an outer sealed chamber with a wall made of polyethylene and an air inlet on the side wall for introducing the working gas; and an inner sealed chamber located inside the outer sealed chamber with a wall made of polyethylene and multiple openings evenly distributed on the side wall and top plate, wherein the side wall of the inner sealed chamber with the opening is opposite to the side wall of the outer sealed chamber with the air inlet.

[0008] Optionally, the air inlet is disposed on the side wall of the outer sealing cavity and located below the side wall, and the height of the air inlet is at least higher than the thickness of the anode plate.

[0009] Optionally, it also includes: a housing, disposed outside the sealed chamber and in a sealed state, an air inlet pipe disposed at the corresponding position of the air inlet hole, and a needle valve installed on the air inlet pipe for controlling the entry and exit of the working gas.

[0010] Optionally, it also includes: multiple voltage dividing rings, evenly disposed between the cathode plate and the grid plate, for distributing the high voltage between the cathode plate and the grid plate; and voltage dividing resistors connected to the voltage dividing rings, with one voltage dividing ring connected to one voltage dividing resistor.

[0011] Optionally, at least one pressure dividing ring is provided between the plurality of cathode plates, and between each adjacent cathode plate.

[0012] Optionally, the spacing between the plurality of cathode plates is 2 to 4 centimeters; all of the plurality of cathode plates have a centrally radial hollow structure.

[0013] Optionally, the anode plate has a size greater than 10 cm × 10 cm; a pixel array of 256 × 256 is provided on the anode plate; an active pulse clock is triggered outside the anode plate, and the electrons form pulse images on the anode plate according to the time interval of the pulse clock.

[0014] Optionally, for medium-energy monoenergetic neutrons, the working gas adopts... For low-energy monoenergetic neutrons, the working gas is a preset first volume value. and preset second volume value The mixture of gases, wherein the preset first volume value is 40% to 60% of the total volume of the space, and the sum of the preset second volume value and the preset first volume value is the total volume of the space.

[0015] Optionally, it also includes: a barometer, installed inside the sealed chamber and located at a corner of the inner wall; and a thermometer, installed inside the sealed chamber and located at a corner of the inner wall.

[0016] The technical solution adopted in this invention can achieve at least one of the following beneficial effects: In this embodiment of the invention, by setting a variable chamber time projection chamber, the distance between the grid plate and the anode plate can be adjusted, reducing the error of the recoil nucleus angle and improving the energy resolution. The uncertainty of neutron energy measurement can be reduced to less than 10%. At the same time, the variable chamber time projection chamber is not only suitable for monoenergetic neutron energy measurement, but also can obtain the corresponding neutron fluence in effective data acquisition. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below, forming part of the present invention. The illustrative embodiments of the present invention and their descriptions explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings: Figure 1 This is a structural diagram of a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons according to the present invention; Figure 2 This is a structural diagram of the polyethylene support column of a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons according to the present invention.

[0018] Explanation of reference numerals in the attached figures: 1. Sealed chamber; 11. Outer sealed chamber; 12. Air inlet; 13. Inner sealed chamber; 14. Opening; 15. Outer shell; 16. Air inlet pipe; 17. Needle valve; 2. Polyethylene support column; 21. Mounting groove; 22. Pressure dividing ring; 31. Cathode plate; 32. Anode plate; 33. Grid plate; 41. Barometer; 42. Thermometer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. In the description of this invention, it should be noted that the term "or" is generally used to include the meaning of "and / or," unless otherwise expressly indicated.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or a magnetic connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, "a plurality of" means at least two, such as two, three, or more, unless otherwise explicitly specified.

[0021] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] To address the problems existing in related technologies, this application provides a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons.

[0023] This embodiment provides a variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons, such as... Figure 1 and Figure 2 As shown, Figure 1 This is a structural diagram of a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons according to the present invention. Figure 2 This is a structural diagram of the polyethylene support column 2 of a variable chamber time projection chamber for measuring the energy of low- and medium-energy monoenergetic neutrons according to the present invention. The structure includes: A sealed chamber 1 is filled with low-pressure working gas. A neutron inlet is provided on the sealed chamber 1 for projecting monoenergetic neutrons. A polyethylene support column 2 is installed inside the sealed chamber 1, placed vertically, and has multiple mounting slots 21. Multiple cathode plates 31 are installed inside the sealed chamber 1, near the upper top plate, and arranged along the direction from the upper top plate to the lower bottom plate. The multiple cathode plates 31 are supported and fixed on the mounting slots 21 of the polyethylene support column 2. The mounting slots 21 of the multiple cathode plates 31 can be changed along the direction of the polyethylene support column 2, with a moving step size on the order of centimeters. The distance between the uppermost optional cathode plate 31 and the upper top plate of the sealed chamber 1 is greater than 1 centimeter. Meters; an anode plate 32, disposed at the lower bottom plate of the sealed chamber 1; a grid plate 33, installed in the sealed chamber 1 and supported and fixed on the mounting groove 21 of the polyethylene support column 2, the grid plate 33 can be changed in the mounting groove 21 along the direction of the polyethylene support column 2, the moving step of the change is on the order of millimeters, the grid plate 33 is spaced 15 to 20 centimeters apart from the uppermost optional cathode plate 31, the grid plate 33 is spaced 200 to 400 micrometers apart from the anode plate 32; a high-voltage module is connected to the grid plate 33, the voltage between the grid plate 33 and the anode plate 32 is 100V to 400V, the monoenergetic neutrons are scattered with the low-pressure working gas to form electron-ion pairs, and the electrons move along the electric field direction to the anode plate 32.

[0024] Optionally, the sealed chamber 1 is equipped with a cathode plate 31, a grid plate 33, and an anode plate 32. The sealed chamber 1 is spaced more than 1 cm from the uppermost optional cathode plate 31, the uppermost cathode plate 31 is spaced 15 to 20 cm from the grid plate 33, and the optional cathode plates 31 are spaced 2 to 4 cm apart. All optional cathode plates 31 have a centrally radial hollow structure, and a suitable negative voltage is selected during operation.

[0025] Optionally, the field cage inside the sealed chamber 1 is supported by polyethylene support columns 2. Multiple voltage dividing rings 22 are arranged between the cathode plate 31 and the grid plate 33, and each voltage dividing ring 22 is connected to a voltage dividing resistor. The voltage of the grid plate 33 does not require voltage division and is directly provided by the high-voltage module. The voltage of the grid plate 33 is at 0 potential. The grid plate 33 has a grid of 10μm to 50μm with uniformly distributed mesh. In addition, the grid plate 33 is externally connected to a preamplifier and a main amplifier for signal acquisition. The voltage between the grid plate 33 and the anode plate 32 is set to 100V to 400V, and the voltage gradient in the drift region must be 500 to 1000V / cm. The distance between them is 200μm to 400μm. The anode plate 32 is larger than 10cm × 10cm and is divided into at least a 256 × 256 imaging array. An externally self-triggered pulse clock is connected, and imaging is performed once every 20ns to complete the operation of the time projection chamber.

[0026] In addition, millimeter-level mounting grooves 21 are opened on the polyethylene support column 2 near the grid plate 33 to support grid movement in 2mm increments. After the grid is installed, it should be sealed and reinforced. For drift chamber specifications of 15cm to 20cm, the distance between the cathode plate 31 and the grid should be adjusted to achieve a gap adjustment of 10cm to 15cm with an interval of 1cm ± 2mm.

[0027] Optionally, after filling the variable chamber with a negative pressure working gas, the cathode plate 31 of the variable chamber can be adjusted during operation, thereby changing the volume of the entire sensor, i.e., the chamber is variable. The cathode plate 31 is at a negative voltage, the grid plate 33 is at 0 potential, and the anode plate 32 is at a positive potential. The voltage divider ring 22 is responsible for the voltage distribution between the cathode plate 31 and the grid plate 33. The neutron to be measured enters the variable chamber along the axial direction and undergoes elastic collisions in the low-pressure working gas to form recoil nuclei. The recoil nuclei ionize the working gas to form electron-ion pairs, which drift between the cathode plate 31 and the grid plate 33. The grid plate 33 has micropores, and the distance between the grid plate 33 and the anode plate 32 is on the order of μm, resulting in an extremely strong electric field. Electrons multiply after passing through the micropores of the grid plate 33. Anode plate 32 is a 256×256 dot array detector connected to a self-triggered electronics system. It captures images sequentially on the array every 20 ns. The initial X and Y coordinates of the recoil nucleus are determined by fitting the image segmentation slices. For the Z coordinate, ionization signals are synchronously acquired on grid plate 33. The total time is obtained by multiplying the number of slices captured by anode plate 32 by 20 ns. The electron drift velocity in the working gas can be calculated using srim or Garfiel++, specifically 21.4 μm / ns, thus yielding the initial Z coordinate. Drift and diffusion corrections are not considered here. Therefore, the X, Y, and Z coordinates of the particle are obtained. Combining this with the relationship of the projected track, the drift angle, i.e., the recoil angle after the elastic collision, can be obtained. At this point, the known quantities are the recoil angle and the recoil nucleus energy (i.e., the signal intensity on grid plate 33). Without considering quenching, the incident neutron energy can be calculated using the recoil equation for elastic neutron collisions.

[0028] The variable chamber, by changing the spacing between the cathode plate 31, the grid plate 33 and the anode, is matched with fast-response electronics to ensure that particles of different energies between the grid plate 33 and the anode plate 32 can obtain at least 10 projected pixel images, thereby improving reconstruction accuracy.

[0029] In the particle projection process, the particle drift velocity needs to be considered, as it is related to the working medium, electric field strength, and air pressure. Multiple hollow, selectable cathode plates 31 are used to adjust the distance between the cathode plates 31 and the grid plate 33, thereby changing the sensor volume. Together with the voltage divider ring 22 of the field cage, different working voltage conditions are set while ensuring the electric field gradient, allowing for particle energy measurement based on different voltages, ultimately obtaining the particle's projected Z-coordinate. This effectively reduces the uncertainty of neutron energy, resulting in a more accurate particle projection.

[0030] Optionally, the electronic components of the variable chamber time projection chamber include finished high-voltage plug-in supplying cathode voltage, voltage divider resistor voltage, field cage electrode voltage, grid plate 33 voltage, imaging plate voltage, etc., and signal readout includes fast signal acquisition preamplifier, main amplifier, etc.

[0031] In some preferred embodiments, the sealed chamber 1 includes: an outer sealed chamber 11, the chamber wall of which is made of polyethylene material, and an air inlet 12 is provided on the side wall for introducing the working gas; and an inner sealed chamber 13, which is disposed inside the outer sealed chamber 11, the chamber wall of which is made of polyethylene material, and a plurality of openings 14 are uniformly provided on the side wall and the top plate, wherein the side wall of the inner sealed chamber 13 with openings 14 is opposite to the side wall of the outer sealed chamber 11 with air inlet 12.

[0032] Optionally, the outer sealing cavity 11 mainly provides a passage for supplying working gas to ensure the sealing effect of the double-layer chamber. An air inlet 12 is opened on the outer sealing cavity 11. The upper part and side of the inner sealing cavity 13 have air inlet holes 12, i.e., openings 14, which must be strictly offset from the air inlet 12 of the outer sealing cavity 11 to reduce airflow disturbance.

[0033] Optionally, the inner sealed cavity 13 serves as the main body of the time projection chamber. The cathode plate 31 is tightly attached to the top surface of the inner sealed cavity 13. The distance between the cathode plate 31 and the grid plate 33 is 15 to 20 cm. Multiple annular PCBs are evenly distributed to provide uniform high voltage within the field cage. The distance between the grid plate 33 and the anode plate 32 is 200 μm to 400 μm. The effective area of ​​the anode plate 32 needs to be >10 cm × 10 cm, and the imaging interval <350 μm to ensure the subsequent imaging effect. The outer sealed cavity 11 mainly ensures airtightness, provides a working gas charging interface, and allows adjustment of the distance between the grid plate 33 and the imaging anode plate 32.

[0034] In some preferred embodiments, the air inlet 12 is disposed on the side wall of the outer sealing cavity 11 and located below the side wall, and the height of the air inlet 12 is at least higher than the thickness of the anode plate 32.

[0035] Optionally, the air inlet 12 should be slightly higher than the surface of the outer shell 15, the air passage of the inner sealing cavity 13 and the outer sealing cavity 11 is the same, and openings 14 are provided on the upper wall and side wall of the inner sealing cavity 13 to ensure that the working gas enters the sensor body evenly and stably.

[0036] In some preferred embodiments, the system further includes: a housing 15 disposed on the outside of the sealed chamber 1 and in a sealed state; an air inlet pipe 16 disposed at the corresponding position of the air inlet 12; and a needle valve 17 installed on the air inlet pipe 16 for controlling the entry and exit of the working gas.

[0037] Optionally, an outer shell 15 is provided on the outer surface of the outer sealing cavity 11. The outer shell 15 is made of stainless steel. A needle valve 17 is provided on the air inlet pipe 16 on the stainless steel outer shell 15. The needle valve 17 is a Swagelok needle valve 17, which is used to control the filling and closing of the working gas.

[0038] In some preferred embodiments, the system further includes: a plurality of voltage dividing rings 22, evenly disposed between the cathode plate 31 and the grid plate 33, for distributing the high voltage between the cathode plate 31 and the grid plate 33; and voltage dividing resistors connected to the voltage dividing rings 22, with one voltage dividing ring 22 connected to one voltage dividing resistor.

[0039] In some preferred embodiments, at least one pressure dividing ring 22 is provided between the plurality of cathode plates 31, and between each adjacent cathode plate 31.

[0040] Optionally, the variable chamber mainly realizes the adjustment of the distance between the grid plate 33 and the cathode plate 31. Since the distance between the grid plate 33 and the cathode plate 31 is on the order of cm, in addition, the field cage formed between the cathode plates 31 is spaced by 1 to 2 cm. For easy adjustment, multiple optional cathodes are provided, and there is also a pressure dividing ring 22 supported by polyethylene between each optional cathode. Each cathode plate 31 is separated from each other and insulated.

[0041] In some preferred embodiments, the spacing between the plurality of cathode plates 31 is 2 to 4 centimeters; the plurality of cathode plates 31 are all hollow structures with a central radial orientation.

[0042] Optionally, the spacing between multiple cathode plates 31 is 2 to 4 cm, which can effectively control the uniformity of the electric field; the cathode plates 31 are set with a centrally radial hollow structure, which can reduce weight, increase the effective reaction area, and reduce the possibility of ion pair collisions.

[0043] In some preferred embodiments, the anode plate 32 has a size greater than 10 cm × 10 cm; a pixel array of 256 × 256 is provided on the anode plate 32; an externally triggered pulse clock is provided on the anode plate 32, and the electrons form pulse images on the anode plate 32 according to the time interval of the pulse clock.

[0044] In some preferred embodiments, for medium-energy monoenergetic neutrons, the working gas adopts For low-energy monoenergetic neutrons, the working gas is a preset first volume value. and preset second volume value The mixture of gases, wherein the preset first volume value is 40% to 60% of the total volume of the space, and the sum of the preset second volume value and the preset first volume value is the total volume of the space.

[0045] Optionally, for monoenergetic neutron points in the range of 144 keV to 1.2 MeV, the working gas is pure. For 24keV monoenergetic neutrons, the percentage is 40% to 60%. and Mixed gas, with a working gas pressure of 40 mbar to 60 mbar.

[0046] In some preferred embodiments, the device further includes: a barometer 41, installed inside the sealed chamber 1 and located at a corner of the inner wall; and a thermometer 42, installed inside the sealed chamber 1 and located at a corner of the inner wall.

[0047] Optionally, a thermometer 42 and a barometer 41 with a measurement error better than 0.1% are provided at one corner of the inner sealing cavity 13 to ensure that the pressure and temperature of the working gas are stable during measurement.

[0048] Optionally, to enhance chamber sealing, both the inner sealing cavity 13 and the outer sealing cavity 11 have interlocking grooves, sealed with sealing strips, and connected to the stainless steel outer shell 15 to prevent leakage. A helium mass spectrometer is used to detect leaks in the inner sealing cavity 13; the leakage rate of the inner sealing cavity 13 should be less than 10%. -5 Pa·m 3 ·s -1 .

[0049] Optionally, the number of cable leads can be reduced. The cables are led out from the same port to the outer wall of the outer sealing cavity 11. A cable lead-out plate is embedded in the outer sealing cavity 11. The upper and lower sealing plates of the cable lead-out plate are connected by a flange. At the same time, a rubber ring is gasketed inside to enhance the sealing performance. The electronic or high-voltage power supply module is then connected.

[0050] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons, characterized in that, include: A sealed chamber (1) is filled with low-pressure working gas. A neutron inlet is provided on the sealed chamber (1) for projecting monoenergetic neutrons. A polyethylene support column (2) is installed in the sealed chamber (1) and placed vertically. Multiple mounting slots (21) are provided on the polyethylene support column (2). Multiple cathode plates (31) are installed inside the sealed chamber (1), near the upper top plate of the sealed chamber (1), and arranged along the direction from the upper top plate to the lower bottom plate. The multiple cathode plates (31) are supported and fixed on the mounting groove (21) of the polyethylene support column (2). The multiple cathode plates (31) can change the position of the mounting groove (21) along the direction of the polyethylene support column (2), and the moving step of the change is in centimeters. An anode plate (32) is disposed at the bottom plate of the sealed chamber (1); The grid plate (33) is installed in the sealed chamber (1) and supported and fixed on the mounting groove (21) of the polyethylene support column (2). The grid plate (33) can change the position of the mounting groove (21) along the direction of the polyethylene support column (2), and the moving step of the change is in millimeters. A high-voltage module is connected to the grid plate (33). The monoenergetic neutrons are scattered with the low-pressure working gas to form electron-ion pairs. The electrons move along the electric field direction to the anode plate (32).

2. The variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, The grid plate (33) is spaced 15 to 20 cm from the uppermost optional cathode plate (31), and the grid plate (33) is spaced 200 to 400 micrometers from the anode plate (32); The interval between the uppermost optional cathode plate (31) of the plurality of cathode plates (31) and the upper top plate of the sealed chamber (1) is greater than 1 cm.

3. The variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, The voltage between the grid plate (33) and the anode plate (32) is 100V to 400V.

4. The variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, The sealed chamber (1) includes: The outer sealing cavity (11) has a wall made of polyethylene and an air inlet (12) on the side wall for introducing the working gas. The inner sealing cavity (13) is located inside the outer sealing cavity (11). The cavity wall is made of polyethylene material. Multiple openings (14) are evenly provided on the side wall and the top plate. The side wall of the inner sealing cavity (13) with openings (14) is opposite to the side wall of the outer sealing cavity (11) with air inlet (12).

5. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 4, characterized in that, The air inlet (12) is located on the side wall of the outer sealing cavity (11) and below the side wall. The height of the air inlet (12) is at least higher than the thickness of the anode plate (32).

6. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 4, characterized in that, Also includes: The outer shell (15) is located outside the sealed chamber (1) and is in a sealed state. An air inlet pipe (16) is provided at the corresponding position of the air inlet (12). A needle valve (17) is installed on the air inlet pipe (16) to control the entry and exit of the working gas.

7. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, Also includes: Multiple pressure-dividing rings (22) are evenly disposed between the cathode plate (31) and the grid plate (33) to distribute the high voltage between the cathode plate (31) and the grid plate (33); A voltage divider resistor is connected to the voltage divider ring (22), and one voltage divider ring (22) is connected to one voltage divider resistor.

8. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 7, characterized in that, At least one pressure dividing ring (22) is provided between each of the plurality of cathode plates (31) and between each adjacent cathode plate (31).

9. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, The spacing between the plurality of cathode plates (31) is 2 to 4 centimeters; The plurality of cathode plates (31) are all hollow structures with a central radial shape.

10. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, The anode plate (32) has a size greater than 10 cm × 10 cm; A pixel array is provided on the anode plate (32), and the pixel array is 256×256; The anode plate (32) is externally contacted with an active pulse clock, and the electrons form pulse images on the anode plate (32) according to the time interval of the pulse clock.

11. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, For medium-energy monoenergetic neutrons, the working gas adopts ; For low-energy monoenergetic neutrons, the working gas is a preset first volume value. and preset second volume value The mixture of gases, wherein the preset first volume value is 40% to 60% of the total volume of the space, and the sum of the preset second volume value and the preset first volume value is the total volume of the space.

12. A variable chamber time projection chamber for measuring the energy of low-to-medium energy monoenergetic neutrons according to claim 1, characterized in that, Also includes: A barometer (41) is installed inside the sealed chamber (1) and located at the corner of the inner wall; The thermometer (42) is installed inside the sealed chamber (1) and located at the corner of the inner wall.

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