A field cage for time projection ionization chamber

Abstract

The present invention belongs to the technical field of neutron metrology, and specifically relates to a field cage for a time projection ionization chamber, which is arranged on a neutron detector equipped with a GEM film, and comprises a rectangular parallelepiped cage body with a first opening at the bottom, a copper coating is arranged on the lower surface of a top plate (1) of the cage body, and a plurality of copper electrodes (6) are arranged on the inner surface of a side plate of the cage body. The present invention can make the electric field between the cathode and the GEM film of a large-volume time projection ionization chamber uniformly distributed, and can make all areas inside the field cage be in an ionization zone, thereby greatly improving the sensitive volume of the time projection ionization chamber.

Description

Technical Field

[0001] The invention belongs to the technical field of neutron metrology, and in particular relates to a field cage used in a time projection ionization chamber. Background Art

[0002] In the field of neutron metrology, fluence is not only an important physical quantity that characterizes the number of neutrons, but also one of the important parameters for calculating the neutron emission rate, neutron ambient dose equivalent, and personal dose equivalent in some measurement methods. Since the fluence response of most neutron detectors will change with energy, it is necessary to calibrate the response under a monoenergetic neutron reference radiation field. Since the 1960s, major metrology institutions around the world have begun research on neutron fluence measurement.

[0003] As research deepens, it is found that the energy range of several keV to 100 keV is one of the difficulties in absolute measurement of neutron flux. The main difficulties are mainly from three aspects. First, in this range, many reaction cross sections are in the resonance energy region, and the uncertainty of the cross section is relatively large, which is difficult to use for absolute measurement. In the 1990s, researchers found that the uncertainty of the cross section of 6Li and neutrons was relatively small, so they used this reaction to develop the LiF-SSD detector [1,5] as the primary standard for this energy range. The second difficulty is that most international metrology institutions use the two energy points of 8keV and 24keV in this range. Both energies are produced by accelerating protons to hit Sc targets, and the reaction yield is low. When the efficiency of the detector is low, it may cause a significant increase in statistical uncertainty and measurement time. The main problem of the LiF-SSD detector lies in this. Third, in the process of expanding the neutron energy range downward, it is increasingly difficult to distinguish the neutron signal from the γ background and electronic noise. How to improve the signal-to-noise ratio and perform n / γ discrimination is the key to expanding the energy limit.

[0004] In 2010, IRSNC. Golabek et al. of France introduced the time projection ionization chamber into the field of neutron fluence measurement, hoping to make some breakthroughs in the energy range of several keVˉ100keV. Time projection ionization chamber was originally used in the field of high energy physics and has some advantages that traditional gas detectors do not have. The special feature of its structure is that it combines the ionization chamber and the proportional tube together, combining the advantages of both: the ionization chamber has a relatively large sensitive volume, so the detection efficiency is high; and the proportional tube has a good signal-to-noise ratio due to signal amplification. In addition, it has another important advantage in that it can measure the track of charged particles, and the neutron energy spectrum can be inferred based on the kinematic relationship without spectrum decomposition. It can also identify particles by the energy deposition of particles on a unit path, so the background caused by γ or other particles can be reduced. For large-volume time projection ionization chambers, especially ionization chambers with a large distance between the cathode and the GEM membrane, how to make the power plant evenly distributed between the two poles is one of the key designs. The field cage can greatly improve the uniformity of the electric field between the cathode and the GEM membrane, allowing the time projection ionization chamber to develop in the direction of larger volume and higher detector efficiency. At present, there are two main methods: PCB field cage and metal field cage. Their main advantages and disadvantages are as follows. The advantage of PCB field cage is that it is simple and convenient to make. The disadvantage is that it often uses hydrogen-containing materials. Since the reaction between neutrons and hydrogen will produce recoil protons, hydrogen-containing materials should be avoided as much as possible during the measurement process. The advantage of metal field cage is that metal materials have little effect on neutron measurement. The disadvantage is that it is difficult to process, it is difficult to keep the electrodes parallel and uniform, and the installation of voltage divider resistors is also difficult. Summary of the invention

[0005] An object of the present invention is to provide a device capable of improving the uniformity of the electric field between the cathode and the GEM membrane of a large-volume time projection ionization chamber, so as to improve the signal stability of the large-volume time projection ionization chamber.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is a field cage for a time projection ionization chamber, which is arranged on a neutron detector equipped with a GEM film, wherein the field cage comprises a rectangular cage body with a first opening at the bottom, the lower surface of the top plate of the cage body is provided with a copper coating, and the inner surface of the side plate of the cage body is provided with a plurality of copper electrodes.

[0007] Furthermore, the top plate is a square PCB board, and the copper plating layer can withstand a high voltage of 5000V and a current of 100μA.

[0008] Furthermore, the side plate is a PCB board, the copper electrode is rectangular and parallel to the top plate, and the copper electrode can withstand a high voltage of 5000V and a current of 100μA.

[0009] further,

[0010] The adjacent copper electrodes are connected via a chip resistor;

[0011] The copper electrode closest to the top plate is connected to the copper plating layer through a chip resistor, and a first pad is provided on the upper surface of the top plate for connecting an external device;

[0012] The copper electrode farthest from the top plate is also provided with a chip resistor for connecting to an external device, and a second soldering pad is provided on the outer surface of the side plate for connecting to an external device.

[0013] Furthermore, the chip resistor connected to the copper plating layer is arranged on the upper surface of the top plate, and the remaining chip resistors are arranged on the outer surface of the side plate; the resistance value of the chip resistor is 5MΩ.

[0014] Furthermore, it also includes a fixing bar arranged on the edge of the first opening at the bottom of the cage body, the fixing bar is a rectangular PCB board, and a second opening corresponding to the position of the first opening and consistent with the size is provided in the center, and the second opening matches the GEM membrane; through holes are provided at the four corners of the fixing bar for fixing the cage body and the detector, the second opening has a side length of 50 mm, the fixing bar has a side length of 75 mm, the through hole has a diameter of 4 mm, and the distance between adjacent through holes is 64 mm.

[0015] Furthermore, the width of the copper electrode is 1 mm, and the interval between adjacent copper electrodes is 4 mm.

[0016] Furthermore, it also includes a connector for fixedly connecting the side panels, the top panel and the fixing strip, the connector being arranged between the top panel and the side panels, and also between the side panels and the fixing strip, the connector being a right-angled stainless steel strip, and being fixedly arranged on the side panels, the top panel and the fixing strip by welding.

[0017] Furthermore, the side length of the top plate is 50 mm; the side plates have three specifications, all of which are 50 mm in length; the side plates with a height of 30 mm are provided with 6 copper electrodes; the side plates with a height of 50 mm are provided with 9 copper electrodes; and the side plates with a height of 80 mm are provided with 15 copper electrodes.

[0018] Furthermore, the top plate, the first side plate, the second side plate, the third side plate, the fourth side plate and the fixing strip are all made of ceramic materials.

[0019] The beneficial effects of the present invention are:

[0020] 1. All electrode circuits in the field cage can withstand 5000V voltage and 100μA current, meeting the voltage requirements of the ionization zone of a large-volume time projection ionization chamber.

[0021] 2. The copper electrodes and chip resistors (voltage divider resistors) evenly distributed on the side panels make the electric field between the cathode and the GEM membrane of the large-volume time projection ionization chamber evenly distributed, so that all areas inside the field cage are in the ionization zone, greatly improving the sensitive volume of the time projection ionization chamber.

[0022] 3. Due to the improvement of the uniformity of the electric field distribution, the plateau area of ​​the time projection ionization chamber is greatly increased, the plateau slope is improved (smaller plateau slope, better plateau characteristics), and the signal stability of the time projection ionization chamber is significantly improved.

[0023] 4. The design heights of the side panels are 30mm, 50mm and 80mm respectively, which can meet the requirements of different gas conditions and different detection efficiencies.

[0024] 5. The total resistance of the chip resistors (voltage divider resistors) are 35MΩ, 50MΩ and 80MΩ, respectively, which match the cathode voltage of the field cages at different heights so that the current therein does not exceed 100μA.

[0025] 6. The top plate 1, the first side plate 2, the second side plate 3, the third side plate 4, the fourth side plate 5 and the fixing bar 8 of the field cage are all made of ceramic materials, which can reduce the influence of H atoms on neutron measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the upper surface of a top plate 1 of a field cage for a time projection ionization chamber described in the specific implementation mode of the present invention;

[0027] Figure 2 It is a schematic diagram of the outer surface of the first side plate 2 described in the specific implementation mode of the present invention (the connecting portion provided with the copper electrode 6);

[0028] Figure 3 It is a schematic diagram of the outer surface of the second side plate 3 described in the specific implementation mode of the present invention (the connecting portion provided with the copper electrode 6);

[0029] Figure 4 It is a schematic diagram of the outer surface of the third side plate 4 described in the specific implementation mode of the present invention (the connecting portion provided with the copper electrode 6);

[0030] Figure 5 It is a schematic diagram of the outer surface of the fourth side plate 5 described in the specific implementation mode of the present invention (the connecting portion provided with the copper electrode 6);

[0031] Figure 6It is a schematic diagram of the inner surface of the side plate described in the specific implementation mode of the present invention (the main part provided with the copper electrode 6);

[0032] Figure 7 is a schematic diagram of the fixing strip 8 described in the specific implementation mode of the present invention;

[0033] Figure 8 It is a time projection ionization chamber plateau curve test diagram of a field cage for a time projection ionization chamber provided by the present invention, which is illustrated in the specific implementation mode of the present invention;

[0034] In the figure: 1-top plate, 2-first side plate, 3-second side plate, 4-third side plate, 5-fourth side plate, 6-copper electrode, 7-chip resistor, 8-fixing bar, 9-through hole, 10-connector, 11-first pad, 12-second pad. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0036] The present invention provides a field cage for a time projection ionization chamber, which is arranged on a neutron detector equipped with a GEM film, and includes a rectangular cage body with a first opening at the bottom, the lower surface of the top plate 1 of the cage body is provided with a copper coating, and the inner surface of the side plate of the cage body is provided with a plurality of copper electrodes 6 by printing.

[0037] like Figure 1 As shown, the top plate 1 is a square PCB board, and the copper plating layer can withstand a high voltage of 5000V and a current of 100μA.

[0038] like Figures 2 to 6 As shown, the side plate is a PCB board, the copper electrode 6 is rectangular and parallel to the top plate 1, and the copper electrode 6 can withstand a high voltage of 5000V and a current of 100μA.

[0039] Adjacent copper electrodes 6 are connected via a chip resistor 7;

[0040] The copper electrode 6 closest to the top plate 1 is connected to the copper plating layer through a chip resistor 7, and a first pad 11 is provided on the upper surface of the top plate 1 for connecting to an external device;

[0041] The copper electrode 6 farthest from the top plate 1 is also provided with a chip resistor 7 for connecting to an external device, and a second soldering pad 12 is provided on the outer surface of the side plate for connecting to an external device.

[0042] The chip resistor 7 connected to the copper plating layer (the chip resistor 7 connected to the copper electrode 6 closest to the top plate 1 and the copper plating layer) is arranged on the upper surface of the top plate 1, and the remaining chip resistors 7 are arranged on the outer surface of the side plate; the resistance value of the chip resistor 7 is 5MΩ.

[0043] like Figure 7 As shown, it also includes a fixing bar 8 arranged on the edge of the first opening at the bottom of the cage body. The fixing bar 8 is a rectangular PCB board, and a second opening corresponding to the position of the first opening and having the same size is provided in the center, and the second opening matches the GEM membrane; through holes 9 are provided at the four corners of the fixing bar 8 for fixing the cage body to the detector (inner wall), the second opening has a side length of 50 mm, the fixing bar 8 has a side length of 75 mm, the through hole 9 has a diameter of 4 mm, and the distance between adjacent through holes 9 is 64 mm.

[0044] The width of the copper electrodes 6 was 1 mm, and the interval between adjacent copper electrodes 6 was 4 mm.

[0045] The copper electrode 6 includes a main body part and a connecting part. The main body part of the copper electrode 6 is arranged on the inner surface of the side plate, and the connecting part of the copper electrode 6 is arranged between adjacent side plates to connect the main bodies of the copper electrodes 6 on adjacent side plates to form a rectangular copper electrode 6 together.

[0046] It also includes a connector 10 for fixing the side panel, the top panel 1 and the fixing bar 8. The connector 10 is arranged between the top panel 1 and the side panel, and also between the side panel and the fixing bar 8. The connector 10 is a right-angled stainless steel bar, which is fixed on the side panel, the top panel 1 and the fixing bar 8 by welding. The specific method is to use the welding pads prefabricated on the side panel, the top panel 1 and the fixing bar 8, and use the connector 10 to weld the side panel, the top panel 1 and the fixing bar 8 together (add the fixing bar 8 to the solder) to increase the strength and stability. Since the neutron detector contains special gas inside, the impurity gas will affect the measurement performance of the neutron detector. Therefore, the connector 10 should be made of a material that does not release gas and has less interference with neutron measurement, such as stainless steel.

[0047] The side length of the top plate 1 is 50 mm; there are three specifications of the side plates, the length (the distance between the two sides perpendicular to the top plate 1) is 50 mm, the height (the distance from one side of the side plate connected to the top plate 1 to the opposite side) is 30 mm, and there are 6 copper electrodes 6; the side plate with a height of 50 mm is provided with 9 copper electrodes 6; the side plate with a height of 80 mm is provided with 15 copper electrodes 6. If the height of the side plate is less than 30 mm, the width and spacing of the copper electrodes 6 and the chip resistor 7 can be appropriately reduced to maintain the uniformity of the electric field inside the field cage.

[0048] The top plate 1 , the first side plate 2 , the second side plate 3 , the third side plate 4 , the fourth side plate 5 and the fixing strip 8 are all made of ceramic material.

[0049] High voltage is provided to the top plate 1 and the copper electrode 6 via a coaxial cable.

[0050] An example is given to illustrate the practical application of a field cage for a time projection ionization chamber provided by the present invention (see Table 1 and Figure 8 ):

[0051] After the field cage with a side plate height of 30 mm was filled with 1 atm of methane, the plateau area of ​​the time projection ionization chamber was -400V to 3000V, the plateau length was 2600V, and the plateau slope was 0.103%.

[0052] The side plate height is 50mm. After the field cage is filled with 1atm methane, the plateau area of ​​the time projection ionization chamber is -800V~3000V, the plateau length is 2200V, and the plateau slope is 0.317%.

[0053] After the field cage with a side plate height of 30 mm is filled with 1 atm methane and 1 atm helium, the plateau area of ​​the time projection ionization chamber is -1400V~2000V, the plateau length is 600V, and the plateau slope is 1.591%.

[0054] The side plate height is 50mm, the field cage is filled with 0.5atm methane and 1atm helium, and after adding the GEM film, the plateau area of ​​the time projection ionization chamber is -937.5V~1250V, the plateau length is 312.5V, and the plateau slope is 2.767%.

[0055] Table 1. Time projection ionization chamber plateau curve characteristics

[0056]

[0057] The device described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the technical innovation scope of the present invention.

Claims

1. A field cage for a time projection ionization chamber, arranged on a neutron detector equipped with a GEM membrane, characterized in that: It comprises a rectangular parallelepiped cage with a first opening at the bottom, the lower surface of the top plate (1) of the cage is provided with a copper coating, and the inner surface of the side plate of the cage is provided with a plurality of copper electrodes (6); The top plate (1) is a square PCB board, and the copper plating layer can withstand a high voltage of 5000V and a current of 100μA; The side plate is a PCB board, the copper electrode (6) is rectangular and parallel to the top plate (1), and the copper electrode (6) can withstand a high voltage of 5000V and a current of 100μA; the side plate comprises a first side plate (2), a second side plate (3), a third side plate (4) and a fourth side plate (5); It also includes a fixing strip (8) arranged on the edge of the first opening at the bottom of the cage body, the fixing strip (8) is a rectangular PCB board, and a second opening corresponding to the position of the first opening and having the same size is arranged at the center, and the second opening matches the GEM membrane; The top plate (1), the first side plate (2), the second side plate (3), the third side plate (4), the fourth side plate (5) and the fixing strip (8) are all made of ceramic material.

2. A field cage for a time projection ionization chamber as claimed in claim 1, characterized in that: Adjacent copper electrodes (6) are connected via a chip resistor (7); The copper electrode (6) closest to the top plate (1) is connected to the copper plating layer via a chip resistor (7), and a first solder pad (11) is provided on the upper surface of the top plate (1) for connecting to an external device; The copper electrode (6) farthest from the top plate (1) is also provided with a chip resistor (7) for connecting to an external device, and a second solder pad (12) is provided on the outer surface of the side plate for connecting to an external device.

3. A field cage for a time projection ionization chamber as claimed in claim 2, characterized in that: The chip resistor (7) connected to the copper plating layer is arranged on the upper surface of the top plate (1), and the remaining chip resistors (7) are arranged on the outer surface of the side plate; the resistance value of the chip resistor (7) is 5MΩ.

4. A field cage for a time projection ionization chamber as claimed in claim 3, characterized in that: The four corners of the fixing bar (8) are provided with through holes (9) for fixing the cage body to the detector, the second opening has a side length of 50 mm, the fixing bar (8) has a side length of 75 mm, the through hole (9) has a diameter of 4 mm, and the hole spacing between adjacent through holes (9) is 64 mm.

5. A field cage for a time projection ionization chamber as claimed in claim 4, characterized in that: The width of the copper electrode (6) is 1 mm, and the interval between adjacent copper electrodes (6) is 4 mm.

6. A field cage for a time projection ionization chamber as claimed in claim 5, characterized in that: It also includes a connector (10) for fixedly connecting the side panels, the top panel (1) and the fixing strip (8); the connector (10) is arranged between the top panel (1) and the side panels, and also between the side panels and the fixing strip (8); the connector (10) is a right-angled stainless steel strip, and is fixedly arranged on the side panels, the top panel (1) and the fixing strip (8) by welding.

7. A field cage for a time projection ionization chamber as claimed in claim 6, characterized in that: The side length of the top plate (1) is 50 mm; the side plates have three specifications, all of which are 50 mm in length; the side plates with a height of 30 mm are provided with 6 copper electrodes (6); the side plates with a height of 50 mm are provided with 9 copper electrodes (6); and the side plates with a height of 80 mm are provided with 15 copper electrodes (6).

Images