CN117976511A

CN117976511A - Gas ionization chamber

Info

Publication number: CN117976511A
Application number: CN202410015321.2A
Authority: CN
Inventors: 刘毅娜; 何逾洋; 刘蕴韬; 王志强; 李春娟; 徐新宇; 王红玉
Original assignee: China Institute of Atomic of Energy
Current assignee: China Institute of Atomic of Energy
Priority date: 2024-01-04
Filing date: 2024-01-04
Publication date: 2024-05-03

Abstract

The embodiment of the application provides a gas ionization chamber which comprises a shell, an anode plate, a cathode plate and a window assembly. The casing is cylindric, and inside is provided with holds the chamber, and the casing is provided with entrance and exit respectively along axial both ends, and the direction of entrance to exit is the neutron beam incident direction. The anode plate is arranged in the accommodating cavity and is perpendicular to the incident direction of the particle beam. The cathode plate is arranged in the accommodating cavity and is perpendicular to the incident direction of the particle beam. At least one of the entrance and exit ports is hermetically provided with a window assembly comprising a window mylar film in sealing engagement with the housing through which the particle beam passes into and out of the receiving chamber. The gas ionization chamber provided by the embodiment of the application effectively reduces the structural materials which need to be penetrated by the particle beam entering and exiting the accommodating cavity, reduces the amount of substances on the particle beam when the particle beam is measured, and can effectively reduce the strong interference signals generated by the actions of neutrons, gamma and substances on the beam, thereby improving the energy resolution of the gas ionization chamber.

Description

Gas ionization chamber

Technical Field

The application relates to the technical field of radioactivity measurement, in particular to a gas ionization chamber.

Background

The energy range of a common white light neutron source is wider, for example, the energy range of CSNS/Back-n is 0.2 eV-200 MeV, so that the accurate measurement of the full area cannot be completed by using one detector, and the energy-division area measurement is required to be measured by a plurality of neutron detection systems. In the related art, detectors widely used for neutron spectrum measurement in the energy region below 1MeV mainly include scintillation detectors, semiconductor detectors and ionization chamber type detectors based on two reactions of ¹⁰ B (n, α) and ⁶ Li (n, t). ⁶ The time characteristic of the Li glass scintillation detector matched with the fast photomultiplier is suitable for a neutron flight time method, but the lithium glass has high gamma ray detection efficiency, and for a high-flux white light neutron source, such as CSNS-back n, the instant of proton targeting has strong instant gamma-flash, and the instant saturation of light output can be caused. In the related art, how to inhibit the influence of gamma-flash on a high-flux white light neutron source radiation field is achieved, and the problem that under the high-flux white light neutron source radiation field, a strong gamma-flash generated at the moment of proton targeting causes saturated signals in a measuring device, namely strong interference signals generated, so that neutron signals cannot be effectively collected and the result of energy measurement range cutoff appears is a difficult problem.

Disclosure of Invention

In view of the foregoing, it is desirable to provide a gas ionization chamber that can reduce the generation of interference signals, thereby improving the energy resolution of the gas ionization chamber.

To achieve the above object, an embodiment of the present application provides a gas ionization chamber including:

The shell is cylindrical, a containing cavity is formed in the shell, an entrance port and an exit port are respectively formed in two ends of the shell along the axial direction, and the direction from the entrance port to the exit port is the incidence direction of neutron beams;

the anode plate is arranged in the accommodating cavity and is perpendicular to the incident direction of the particle beam;

The cathode plate is arranged in the accommodating cavity and is perpendicular to the incident direction of the particle beam;

The window assembly is arranged on at least one of the entrance opening and the exit opening in a sealing mode, the window assembly comprises a window Mylar film, the window Mylar film is in sealing fit with the shell, and particle beams enter and exit the accommodating cavity through the window Mylar film.

In some embodiments, the window mylar film has a thickness of 10 μm to 80 μm.

In some embodiments, the window mylar film has a thickness of 20 μm to 60 μm.

In some embodiments, the window assembly further comprises a mounting ring coupled to the housing and sandwiching the window mylar therebetween.

In some embodiments, both sides of the window mylar film are provided with a smooth window aluminum coating having a thickness of 35nm-45nm.

In some embodiments, the anode plate comprises an anode mylar film with smooth anode aluminum plating on both sides of the anode mylar film.

In some embodiments, the anode mylar film has a thickness of 6 μm to 23 μm.

In some embodiments, the anode plate includes two anode connection rings that clamp the anode mylar film therebetween, and the anode connection rings are PCB rings.

In some embodiments, the cathode plate comprises a cathode mylar film, smooth cathode aluminum plating is provided on both sides of the cathode mylar film, and a target is provided on the outside of the cathode aluminum plating.

In some embodiments, the cathode mylar film has a thickness of 6 μm to 23 μm.

In some embodiments, the cathode plate further comprises two cathode connection rings, the two cathode connection rings clamp the cathode mylar film therebetween, and the cathode connection rings are PCB rings.

In some embodiments, the gas ionization chamber further includes two gate plates, the number of the anode plates is two, and the two gate plates are respectively disposed at two ends of the cathode plate along the axial direction of the housing, and the two gate plates are respectively disposed between the two anode plates and the cathode plate.

In some embodiments, the anode plate, the cathode plate, the gate plate, and the window mylar are all circular.

In some embodiments, the grid plate comprises a PCB plate fixing ring and grid wires connected with the PCB plate fixing ring.

In some embodiments, the gas ionization chamber further includes a connecting member and a plurality of spacers sleeved on the connecting member, the anode plate, the cathode plate and the gate plate are sleeved on the connecting member, and the anode plate, the cathode plate and the gate plate are arranged at intervals by the spacers.

The embodiment of the application provides a gas ionization chamber, which comprises a shell, an anode plate, a cathode plate and a window assembly. The casing is cylindric, and inside is provided with holds the chamber, and the casing is provided with entrance and exit respectively along axial both ends, and the direction of entrance to exit is the neutron beam incident direction, that is to say, the particle beam gets into and holds the chamber through the entrance to hold the chamber from exit outflow, particle beam incident direction is all perpendicular with anode plate and negative plate. The window assembly is arranged to comprise the window Mylar film, the window Mylar film is in sealing fit with the shell, and the particle beam enters and exits the accommodating cavity through the window Mylar film, so that structural materials which need to be penetrated by the particle beam entering and exiting the accommodating cavity are effectively reduced, the amount of substances on the particle beam is reduced when the particle beam is measured, and strong interference signals generated by the actions of neutrons, gamma and the substances on the beam can be effectively reduced, so that the energy resolution of the gas ionization chamber is improved. In addition, the window mylar film has better ductility than common metals (such as aluminum, stainless steel and the like), is beneficial to realizing a smooth and flat mirror effect, and can further reduce the generation of interference signals.

Drawings

FIG. 1 is a schematic diagram of a gas ionization chamber according to an embodiment of the present application;

FIG. 2 is a schematic view showing a connection structure between a window assembly and a housing according to an embodiment of the present application;

FIG. 3 is a schematic view of a mounting ring according to an embodiment of the present application;

fig. 4 is a schematic structural diagram of an anode plate according to an embodiment of the application;

FIG. 5 is a schematic view of a cathode plate according to an embodiment of the application;

FIG. 6 is a schematic diagram of a gate plate according to an embodiment of the present application;

FIG. 7 is a diagram of performance tuning electronics in an embodiment of the application;

FIG. 8 is a ²³⁹Pu-²⁴¹Am-²⁴⁴ Cm mixed alpha source pulse amplitude spectrum in an embodiment of the application;

FIG. 9 is a pulse amplitude spectrum of particles produced by a ²⁴¹ Am source and ⁶ Li (n, α) T nuclear reactions, respectively, in an embodiment of the application;

fig. 10 is a waveform of the output energy signal E and the time signal T of the anode plate according to an embodiment of the application.

Description of the reference numerals

1. A housing; 1a, a containing cavity; 1b, an entrance port; 1c, an exit port; 2. a particle beam; 3. an anode plate; 31. an anode mylar film; 32. an anode connecting ring; 4. a cathode plate; 41. cathode mylar film; 42. a cathode connecting ring; 43. a target; 5. a window assembly; 51. window mylar; 52. a mounting ring; 6. a gate plate; 61. a PCB fixing ring; 62. a grid wire; 100. a gas ionization chamber.

Detailed Description

It should be noted that, in the case of no conflict, the embodiments of the present application and the technical features of the embodiments may be combined with each other, and the detailed description in the specific embodiments should be interpreted as an explanation of the gist of the present application and should not be construed as unduly limiting the present application.

The terminology used in the description of the application herein is for the purpose of describing the application only and is not intended to indicate or imply that the devices or elements so referred to must be in a particular orientation, be constructed and operate in a particular orientation, and is therefore not to be construed as limiting the application.

In the embodiments of the present application, the "upper", "lower", "top", "bottom" orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and the "central axis" is based on the orientation shown in the drawings, it should be understood that these orientation terms are merely for convenience in describing the present application and simplifying the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present application. The application will be described in further detail with reference to the accompanying drawings and specific examples. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

The time-of-flight method is based on basic physical quantity time and distance measurement energy spectrum, has high accuracy, and the international spallation neutron source adopts the time-of-flight method to measure neutron beam energy spectrum parameters. According to the neutron nuclear reaction standard section recommended by the international atomic energy organization (IAEA), the neutron measurement of the energy region below 1MeV is currently widely used for ¹⁰B(n,α)⁷Li、⁶ Li (n, t) alpha and ²³⁵ U (n, f) nuclear reaction standard sections. The detector types based on the nuclear reaction detection principle mainly comprise ⁶ Li glass scintillator detectors, ⁶ Li-Si semiconductor detectors, ¹⁰ B and ⁶ Li ionization chamber type detectors, fission ionization chambers and the like. ⁶ The Li glass scintillation detector is matched with a fast photomultiplier, has a fast time resolution characteristic, and is suitable for neutron measurement by a time-of-flight method. ⁶ The Li-Si semiconductor detector has good energy resolution effect and spatial resolution effect. The ionization chamber type detector has the advantages of high detection efficiency (100%), insensitivity to gamma rays, no radiation damage problem and the like, and is suitable for measuring the neutron beam energy spectrum of a white light source.

The energy range of a common white light neutron source is wider, for example, the energy range of CSNS/Back-n is 0.2 eV-200 MeV, so that the accurate measurement of the full area cannot be completed by using one detector, and the energy-division area measurement is required to be measured by a plurality of neutron detection systems. In the related art, detectors widely used for neutron spectrum measurement in the energy region below 1MeV mainly include scintillation detectors, semiconductor detectors and ionization chamber type detectors based on two reactions of ¹⁰ B (n, α) and ⁶ Li (n, t). ⁶ The time characteristic of the Li glass scintillation detector matched with the fast photomultiplier is suitable for a neutron flight time method, but the lithium glass has high gamma ray detection efficiency, and for a high-flux white light neutron source, such as CSNS-back n, the instant of proton targeting has strong instant gamma-flash, and the instant saturation of light output can be caused. The ionization chamber type detector to be adopted by the invention has time resolution inferior to that of a scintillator detector, but the neutron flight 78m in an energy region below 1MeV requires about several mu s, so the ionization chamber type detector with time resolution of hundred nanoseconds can also be used for neutron flight time measurement experiments, and thus, various measuring devices based on different principles can mutually verify.

In the related art, how to inhibit the influence of gamma-flash on a high-flux white light neutron source radiation field is achieved, and the problem that under the high-flux white light neutron source radiation field, a strong gamma-flash generated at the moment of proton targeting causes saturated signals in a measuring device, namely strong interference signals generated, so that neutron signals cannot be effectively collected and the result of energy measurement range cutoff appears is a difficult problem.

Referring to fig. 1 to 6, the embodiment of the present application provides a gas ionization chamber 100, which includes a housing 1, an anode plate 3, a cathode plate 4, and a window assembly 5. The shell 1 is cylindrical, a containing cavity 1a is arranged in the shell, an entrance port 1b and an exit port 1c are respectively arranged at two ends of the shell 1 along the axial direction, and the direction from the entrance port 1b to the exit port 1c is the incidence direction of neutron beams. The anode plate 3 is disposed in the accommodating chamber 1a and perpendicular to the incident direction of the particle beam 2. The cathode plate 4 is disposed in the accommodating chamber 1a and perpendicular to the incident direction of the particle beam 2. At least one of the entrance port 1b and the exit port 1c is hermetically provided with a window assembly 5, the window assembly 5 includes a window mylar film 51, the window mylar film 51 is hermetically fitted with the housing 1, and the particle beam 2 enters and exits the accommodating chamber 1a through the window mylar film 51.

Referring to fig. 1 and 2, the housing 1 has a cylindrical shape, and the housing 1 forms a general external appearance of the gas ionization chamber 100, that is, the gas ionization chamber 100 has a generally cylindrical shape.

The direction from the entrance port 1b to the exit port 1c is the neutron beam incident direction, that is, the particle beam 2 enters the accommodating chamber 1a through the entrance port 1b and flows out of the accommodating chamber 1a from the exit port 1 c.

The sealed arrangement of the window assembly 5 at least one of the entrance port 1b and the exit port 1c means that the window assembly 5 may be sealed arrangement of the entrance port 1b, the window assembly 5 may be sealed arrangement of the exit port 1c, or the window assembly 5 may be sealed arrangement of both the entrance port 1b and the exit port 1 c.

The window assembly 5 comprises a window Mylar film 51, i.e. a portion of the window assembly 5 is formed of Mylar film (Mylar film), so that the window assembly 5 can be thinned, the amount of material on the particle beam 2 is reduced when measuring on the particle beam 2 line, and the strong interference signals generated by neutrons and gamma acting on the material on the beam can be effectively reduced.

Window mylar film 51 refers to a portion of a window formed from mylar film.

The particle beam 2 enters and exits the accommodating chamber 1a through the window mylar film 51, that is, the particle beam 2 passes through the window mylar film 51 to enter and exit the entrance port 1b and the exit port 1c.

The window assembly 5 is made using a micrometer thick aluminized Mylar film. Mylar films have excellent thermal stability, chemical resistance, electrical insulation, and high tensile strength (mechanical properties), and a wide range of service temperatures. The window assembly 5 has certain strength, can play a role of sealing and is not easy to break.

The embodiment of the application provides a gas ionization chamber 100 which comprises a shell 1, an anode plate 3, a cathode plate 4 and a window assembly 5. The shell 1 is cylindrical, a containing cavity 1a is arranged in the shell, an entrance port 1b and an exit port 1c are respectively arranged at two ends of the shell 1 along the axial direction, the direction from the entrance port 1b to the exit port 1c is the neutron beam incident direction, that is, the particle beam 2 enters the containing cavity 1a through the entrance port 1b and flows out of the containing cavity 1a from the exit port 1c, and the incident direction of the particle beam 2 is perpendicular to the anode plate 3 and the cathode plate 4. By arranging the window assembly 5 to include the window mylar film 51, the window mylar film 51 is in sealing fit with the housing 1, and the particle beam 2 enters and exits the accommodating cavity 1a through the window mylar film 51, so that structural materials which the particle beam 2 needs to penetrate through to enter and exit the accommodating cavity 1a are effectively reduced, and when the particle beam 2 is measured on a line, the amount of substances on the particle beam 2 is reduced, and strong interference signals generated by the actions of neutrons and gamma and the substances on the beam can be effectively reduced, so that the energy resolution of the gas ionization chamber 100 is improved. In addition, the window mylar film 51 has better ductility than conventional metals (such as aluminum, stainless steel, etc.), which is advantageous in achieving a smooth and flat mirror effect, and can further reduce the generation of interference signals.

Note that the thickness of window mylar film 51 is not limited herein, and in some embodiments, window mylar film 51 is 10 μm to 80 μm thick, for example. For example 10 μm, 15 μm, 20 μm, 26 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm etc.

The window mylar film 51 having the thickness in this range can provide the window mylar film 51 with a certain tensile strength and ductility, and can reduce the interference signal generated by the particle beam 2 passing through the window mylar film 51 as much as possible.

Further, the thickness of the window mylar film 51 is 20 μm to 60 μm.

In some embodiments, referring to fig. 2-3, window assembly 5 further includes a mounting ring 52, where mounting ring 52 is coupled to housing 1 and sandwiches window mylar 51 therebetween.

The window assembly 5 further includes a mounting ring 52, and an avoidance region for avoiding the window mylar film 51 is formed in the middle of the mounting ring 52, so that the particle beam 2 passes through the window mylar film 51 via the avoidance region.

The specific manner of connecting the mounting ring 52 to the housing 1 is not limited herein, and may be, for example, a connection manner such as a snap connection, a fastening connection, or a plug connection.

Wherein the fastening connection includes, but is not limited to, a screw connection, a bolt connection, a rivet connection, or the like.

In the embodiment of the application, six fastening holes are arranged on the mounting ring 52 at intervals along the circumferential direction, six fastening holes are correspondingly arranged at positions of the housing 1 corresponding to the fastening holes of the mounting ring 52, and the six fastening holes are fastened and connected through screws. By virtue of the tightening effect of the screws and the ductility of the window mylar film 51, the front and rear windows can achieve a mirror effect after installation, and the generation of interference signals can be further reduced.

In some embodiments, both sides of window mylar film 51 are provided with a smooth window aluminum coating having a thickness of 35nm-45nm.

Smooth window aluminum plating layers are arranged on two sides of the window Mylar film 51, and the arrangement of the window aluminum plating layers can lead the bottom lining (the window Mylar film 51) to be conductive and lead the window Mylar film 51 to have mirror effect.

The thickness of the aluminum window coating is 35nm-45nm, such as 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, 41nm, 42nm, 43nm, 44nm or 45nm, etc.

By providing smooth window aluminum plating layers on both sides of the window mylar film 51, the substrate (window mylar film 51) can be made conductive, and the window mylar film 51 can be made to have a mirror effect, which is simple in structure and advantageous in reducing the generation of interference signals.

In some embodiments, the mounting ring 52 is provided with an annular groove in the circumference of the side facing the window mylar film 51, and the window assembly 5 further includes a sealing ring sealingly sandwiched between the wall of the annular groove and the window mylar film 51 for sealing the gap between the mounting ring 52 and the window mylar film 51.

In some embodiments, referring to fig. 4, the anode plate 3 includes an anode mylar 31, and both sides of the anode mylar 31 are provided with a smooth anode aluminum coating.

The anode mylar 31 refers to a portion of an anode made up of mylar.

The particle beam 2 passes through the anode mylar 31 during transport.

Smooth anode aluminum plating layers are arranged on two sides of the anode Mylar film 31, and the arrangement of the anode aluminum plating layers can lead the bottom lining (the anode Mylar film 31) to be conductive and lead the anode Mylar film 31 to have mirror effect.

By providing the anode plate 3 to include the anode mylar film 31, that is, a portion of the anode plate 3 is formed of the mylar film (Mylay film), the anode plate 3 can be thinned, the amount of the substance on the particle beam 2 can be further reduced when the measurement is performed on the particle beam 2 line, and the strong interference signals generated by the actions of neutrons and γ and the substance on the beam can be effectively reduced.

In some embodiments, the thickness of the anode mylar 31 is 6 μm-23 μm. For example 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm or 23 μm etc.

The anode mylar 31 having the thickness in this range can provide the anode mylar 31 with a certain tensile strength and ductility, and can reduce the interference signal generated by the particle beam 2 passing through the anode mylar 31 as much as possible.

In some embodiments, anode plate 3 includes two anode connection rings 32, two anode connection rings 32 sandwich anode mylar 31 therebetween, and anode connection rings 32 are PCB rings.

The anode plate 3 includes two anode connection rings 32, and an avoiding area for avoiding the anode mylar 31 is formed in the middle of the anode connection rings 32, so that the particle beam 2 passes through the anode mylar 31 through the avoiding area.

The anode connecting ring 32 is a PCB ring, that is, the anode plate 3 is a two-piece lightweight PCB ring, so that the anode plate 3 can be thinned and lightened, and the amount of substances on the particle beam 2 is further reduced when the particle beam 2 is measured on the line, so that strong interference signals generated by the actions of neutrons and gamma and substances on the beam are further reduced.

The PCB ring is for example FR-4 board.

FR-4 is a designation of a flame-retardant material grade, and represents a material specification that means that a resin material must self-extinguish after being burned, not a material name, but a material grade, so that FR-4 grade materials used for general circuit boards are very various, but most are composite materials made of so-called tetra-functional (Tera-functional) epoxy resin plus Filler (Filler) and glass fiber.

Illustratively, the anode plate 3 is formed by an AB glue between an anode connecting ring 32 and an anode Mylar film 31.

In some embodiments, referring to fig. 1 and 5, the cathode plate 4 includes a cathode mylar film 41, smooth cathode aluminum plating is provided on both sides of the cathode mylar film 41, and a target 43 is provided on the outside of the cathode aluminum plating.

That is, the cathode plate 4 has substantially the same structure as the anode plate 3, except that a target 43 is provided outside the cathode aluminum plating layer of the cathode plate 4.

The specific type of target 43 is not limited herein, and is, for example, ⁶ Li target 43 and/or ¹⁰ B target 43.

The specific manner of disposing the target 43 outside the cathode aluminum plating layer is not limited herein, and the ⁶ Li target 43 and/or ¹⁰ B target 43 is illustratively prepared by, for example, a vacuum evaporation method or an Atomic Layer Deposition (ALD) method.

Illustratively, targets 43 are provided on both sides of the cathode plate 4, i.e. two targets 43 are placed in a "back-to-back" manner for simultaneous measurement.

In some embodiments, the cathode mylar film 41 has a thickness of 6 μm-23 μm. For example 6 μm, 8 μm, 10 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm or 23 μm etc.

The cathode mylar film 41 having the thickness in this range can provide the cathode mylar film 41 with a certain tensile strength and ductility, and can reduce the disturbance signal generated by the particle beam 2 passing through the cathode mylar film 41 as much as possible.

In some embodiments, the cathode plate 4 further includes two cathode connection rings 42, the two cathode connection rings 42 sandwich the cathode mylar film 41 therebetween, and the cathode connection rings 42 are PCB rings.

The cathode plate 4 includes two cathode connection rings 42, and an avoiding region for avoiding the cathode mylar film 41 is formed in the middle of the cathode connection rings 42, so that the particle beam 2 can pass through the cathode mylar film 41 through the avoiding region.

The cathode connection ring 42 is a PCB ring, that is, the cathode plate 4 is a two-piece light PCB ring, so that the cathode plate 4 can be thinned, and the amount of substances on the particle beam 2 is further reduced when the particle beam 2 is measured on the line, so that strong interference signals generated by the actions of neutrons, gamma and substances on the beam are further reduced.

The PCB ring is for example FR-4 board.

In some embodiments, referring to fig. 1 and 6, the gas ionization chamber 100 further includes two gate plates 6, the number of anode plates 3 is two, and the two gate plates 6 are respectively disposed between the two anode plates 3 and the cathode plate 4 and are respectively disposed at two ends of the cathode plate 4 along the axial direction of the housing 1.

The cathode plate 4 corresponds to a substrate of the neutron nuclear reaction target 43.

The two anode plates 3 correspond to two collectors.

The screen grid ionization chamber is characterized in that a wire-shaped or net-shaped grid electrode is added between a cathode and an anode of a common parallel plate ionization chamber, and the purpose of adding the grid electrode is to shield the anode, so that when electrons move between the cathode and the grid electrode, an induction signal is basically not generated on the anode; only after the electrons pass through the gate will a pulse signal be generated at the anode. However, since the shielding effect of the screen grid on the anode cannot be completely absolute, when positive ions drift between the cathode and the grid, partial induced charges still flow into the anode through the load, so that the incident position of particles affects the amplitude of the output voltage pulse, and the energy resolution of the ionization chamber of the screen grid is poor. In practice, therefore, the gate has a certain problem of shield failure, generally indicated by a shield failure factor sigma,

Wherein:

E _A —electric field strength between gate and anode;

E _C -electric field strength between cathode and gate;

p-gate-anode spacing;

d-the spacing of the grid wires 62;

r—the radius of the grid wire 62.

According to a theoretical formula, the shielding failure factor can be effectively reduced by increasing the distance between the grid and the anode; reducing the ratio of the spacing of the grid wires 62 to the radius of the grid wires 62 may also reduce the shield failure factor, but the denser the grid wires 62 the greater the probability of electrons being trapped. Gold-plated tungsten wires with the diameter of 0.1mm are comprehensively considered as the grid wires 62, and a light PCB (FR-4 board) ring is adopted as a fixing ring of the polar plate. Illustratively, when the grid wire 62 pitch is 2mm, and the grid-anode pitch is 3mm, 5mm, 8mm or 10mm, the shielding failure factor σ of the grid is calculated from formulas (1.1), (1.2) and (1.3) to be 0.085, 0.051, 0.032 or 0.026, respectively.

That is, the two gate plates 6 are symmetrically disposed on both sides of the cathode plate 4 in the axial direction of the gas ionization chamber 100, the two anode plates 3 are also symmetrically disposed on both sides of the cathode plate 4 in the axial direction of the gas ionization chamber 100, and the gate plate 6 is located between the cathode plate 4 and the anode plates 3.

In some embodiments, referring to fig. 1-6, the anode plate 3, the cathode plate 4, the gate plate 6, and the window mylar 51 are all circular.

In this way, the anode mylar 31 of the anode plate 3, the cathode mylar 41 of the cathode plate 4, the grid wire 62, and the window mylar 51 can all be positioned on the transport path of the particle beam 2. By thinning the window assembly 5, the anode plate 3 and the cathode plate 4, structural materials which are required to be penetrated by the particle beam 2 entering and exiting the accommodating cavity 1a are effectively reduced, and the amount of substances on the particle beam 2 is reduced when the particle beam 2 is measured on a line, so that strong interference signals generated by the actions of neutrons, gamma and the substances on the beam can be effectively reduced, and the energy resolution of the gas ionization chamber 100 is improved.

In some embodiments, referring to fig. 6, the gate plate 6 includes a PCB board fixing ring 61 and a gate wire 62 connected to the PCB board fixing ring 61.

The grid plate 6 comprises a PCB fixing ring 61, and an avoidance area for avoiding the grid wires 62 is formed in the middle of the PCB fixing ring 61 and is used for enabling the particle beam 2 to penetrate through gaps among the grid wires 62 through the avoidance area.

The grid plate 6 adopts the light PCB fixing ring 61, so that the grid plate 6 can be thinned and lightened, and the amount of substances on the particle beam 2 is further reduced when the measurement is carried out on the particle beam 2, thereby further reducing the strong interference signals generated by the actions of neutrons, gamma and substances on the beam.

The PCB ring is for example FR-4 board.

Illustratively, a gold-plated tungsten wire with a diameter of 0.1mm is used as the grid wire 62, and a lightweight PCB (FR-4 board) ring is used as the plate securing ring.

Illustratively, the grid wires 62 are spaced 2mm apart.

In some embodiments, the gas ionization chamber 100 further includes a connector and a plurality of spacers sleeved on the connector, and the anode plate 3, the cathode plate 4 and the gate plate 6 are spaced by the plurality of spacers.

The length of the spacers is 1mm,2mm,5mm,8mm or 20mm, respectively, etc., which is advantageous for flexibly adjusting the gap between the anode plate 3, the cathode plate 4 and the gate plate 6.

The anode plate 3, the cathode plate 4 and the grid plate 6 are supported and fixed through connecting pieces with good insulating property and high hardness and light weight, and the anode plate 3, the cathode plate 4 and the grid plate 6 are arranged at intervals through a plurality of spacing pieces with good insulating property and high hardness and light weight, so that the structural reliability of the gas ionization chamber 100 is improved.

For example, the material of the casing 1 may be, for example, an aluminum alloy, which has a high structural strength and a lower density than stainless steel, so that the weight of the casing 1 can be effectively reduced, and compared with the stainless steel material, the total weight can be reduced by 2/3, which is beneficial to installation and debugging. The different parts of the shell 1 are in an O-ring press seal structure. The height of the inside of the shell 1 is 250mm, the electrode spacing is convenient to adjust, and the wall thickness is 5mm.

Illustratively, 3 gas control valves are mounted on the housing 1 and connected to an external gas circuit via a 6mm diameter hose. The screen grid ionization chamber adopts a gas flowing working mode, and experiments prove that the gas flow rate is too large and influences the movement track of particles, so that the track position of the peak in the pulse amplitude spectrum is influenced. On the premise that the cavity is filled with working gas and the influence of gas flow on the detection result is negligible, the position of the channel address where the peak appears in the pulse amplitude spectrum measured under the same test condition is unchanged. Therefore, the gas flow rate needs to be controlled during the experiment to ensure a single variable. On the premise of ensuring that the cavity is filled with working gas, the gas flow rate is as small as possible, so that the influence of gas flow on the particle motion track is reduced, and meanwhile, the waste of the working gas can be reduced.

Through multiple test tests, on the premise of ensuring that the air in the cavity is exhausted and the working gas is filled, the gas mass flow is controlled to be about 15mL/min, so that the cavity is always filled with the working gas and the detected signal is not influenced by the gas flow. According to the processing size, the volume of the cavity of the screen grid ionization chamber is calculated to be 7.9L, so that during experiments, working gas is introduced into the cavity for 10min at a high flow rate (2L/min) to exhaust air in the cavity. Then, a gas mass flowmeter (ALICAT MCS-100 SCCM) is adopted to control the flow rate of the working gas to 15mL/min for experiment.

1 ²³⁹Pu/²⁴¹Am/²⁴⁴ Cm mixed alpha-plane source (the diameter of the active area is smaller than 5mm, the total activity is about 1.784 multiplied by 103 Bq) is attached to the cathode plate, signal debugging is carried out on the screen grid ionization chamber, and an adopted electronic circuit system is shown in figure 7. The grid electrode is grounded, and positive high voltage and negative high voltage are respectively applied to the anode and cathode electrode plates. The anode signal is led out and then passes through a pre-amplifier and a main amplifier, and then the pulse amplitude spectrum of the alpha particles can be displayed and recorded on a multi-channel analyzer. The time signal waveform of the screen ionization chamber can be viewed by displaying the T output waveform of the preamplifier of the anode signal input through the oscilloscope MDO 3014.

²³⁹Pu、²⁴¹ The main energies of the alpha particles emitted by Am and ²⁴⁴ Cm are 5.16MeV, 5.48MeV and 5.81MeV, respectively. The working gas was P10, the cathode-gate spacing was 50mm, the gate-anode spacing was 10mm, and the measured amplitude spectrum of the mixed alpha source pulse was shown in fig. 8. From the experimental data calculations, the energy resolution of alpha particles by the front 142PC ionization chamber was 193keV@5.48MeV (3.5%). The screen grid ionization chamber detection system developed by the work has good alpha particle energy resolution capability.

A thermal neutron target 43 signal measurement experiment of a double-screen ionization chamber was performed between plasma boron concentration measurements (neutron fluence rate at full power 3×10 ⁶cm^-2s^-1) of a hospital neutron irradiator based on a mini-nuclear reactor. A ⁶ Li target 43 was mounted at the cathode of the double-screen ionization chamber to measure the alpha particles generated by ⁶ Li (n, alpha) T nuclear reaction. The cathode-gate spacing was 50mm, the gate-anode spacing was 10mm, and the pulse amplitude spectra of particles generated by the ²⁴¹ Am source and ⁶ Li (n, α) T nuclear reactions, respectively, detected by a dual-screen gate ionization chamber under the same test conditions, were shown in fig. 9 for P10 as the working gas. Neutron striking ⁶ Li target 43 produces alpha particles while also producing ³ H particles, both of which have energies of 2.05MeV and 2.74MeV, respectively. The screen grid ionization chamber detection system developed by the work can well detect particles generated by ⁶ Li (n, alpha) T nuclear reaction, and can better distinguish alpha particles from ³ H particles. The waveforms of the anode signal output are shown in fig. 10, and the output pulse has a width of about 0.5 μs, and can be used as a time-of-flight measurement signal of neutrons below 1MeV, so as to realize neutron energy spectrum measurement.

In the description of the present application, reference to the term "one embodiment," "in some embodiments," "in other embodiments," "in yet other embodiments," or "exemplary" etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the application. In the present application, the schematic representations of the above terms are not necessarily for the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, the various embodiments or examples described in the present application and the features of the various embodiments or examples may be combined by those skilled in the art without contradiction.

The various embodiments/implementations provided by the application may be combined with one another without contradiction.

The above description is only of the preferred embodiments of the present application and is not intended to limit the present application, but various modifications and variations can be made to the present application by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A gas ionization chamber, comprising:

2. A gas ionization chamber according to claim 1, wherein said window mylar film has a thickness of 10 μm to 80 μm.

3. A gas ionization chamber according to claim 2, wherein said window mylar film has a thickness of 20 μm to 60 μm.

4. The gas ionization chamber of claim 1, wherein said window assembly further comprises a mounting ring connected to said housing and sandwiching said window mylar film therebetween.

5. A gas ionization chamber according to claim 1, wherein both sides of the window mylar film are provided with a smooth window aluminum coating having a thickness of 35nm-45nm.

6. The gas ionization chamber of claim 1, wherein said anode plate comprises an anode mylar film provided with a smooth anode aluminum coating on both sides of said anode mylar film.

7. The gas ionization chamber of claim 6, wherein said anode mylar film has a thickness of 6 μm to 23 μm.

8. The gas ionization chamber of claim 6, wherein said anode plate comprises two anode connection rings sandwiching said anode mylar film therebetween, and said anode connection rings are PCB rings.

9. The gas ionization chamber of claim 1, wherein said cathode plate comprises a cathode mylar film, smooth cathode aluminum plating is provided on both sides of said cathode mylar film, and a target is provided on the outside of said cathode aluminum plating.

10. The gas ionization chamber according to claim 9, wherein said cathode mylar film has a thickness of 6 μm to 23 μm; and/or the cathode plate further comprises two cathode connecting rings, the two cathode connecting rings clamp the cathode Mylar film between the two cathode connecting rings, and the cathode connecting rings are PCB rings.

11. The gas ionization chamber according to claim 1, further comprising two gate plates, the number of the anode plates being two, and being disposed at both ends of the cathode plate in the axial direction of the housing, respectively, the two gate plates being disposed between the two anode plates and the cathode plate, respectively.

12. The gas ionization chamber of claim 11, wherein said anode plate, said cathode plate, said gate plate, and said window mylar film are all circular.

13. The gas ionization chamber of claim 11 wherein said gate plate comprises a PCB plate retaining ring and a gate wire connected to said PCB plate retaining ring.

14. The gas ionization chamber according to claim 1, further comprising a connector and a plurality of spacers sleeved on the connector, wherein the anode plate, the cathode plate and the gate plate are sleeved on the connector, and the anode plate, the cathode plate and the gate plate are arranged at intervals by the spacers.