CN211907381U - A flat-panel ionization chamber for high-energy electron beam dosimetry - Google Patents

Abstract

The utility model discloses a flat plate ionization chamber for high-energy electron beam dose measurement, comprising an outer electrode and an inner electrode; the outer electrode is a cap-mounted structure made of an air equivalent material, which forms a The airtight flat air cavity is provided with an insulating plate at the bottom of the air cavity; the inner electrode is fixed on the insulating plate, and a protective ring is surrounded on the periphery. The air equivalent material used by the utility model is used as the external electrode, and the measurement is more accurate; the problem of measuring the electron beam dose in the prior art is solved, and the gradient change of the radiation beam can be truly reflected; the fixed cap edge structure is adopted, and the assembly is simple and the contact Good, less air voids, improve cavity ionization chamber consistency, increase product yield, while achieving product robustness and durability.

Description

A flat-panel ionization chamber for high-energy electron beam dosimetry

technical field

The utility model relates to the technical field of electron beam dose measurement, in particular to a flat plate ionization chamber used for high-energy electron beam dose measurement.

Background technique

In 1958, Shonka, F.R, Rose, J.E, Failla, G, etc. published an article on the equivalent structure of conductive plastics, air, and polystyrene, which opened up the research on air-equivalent plastics and applied air-equivalent materials to the ionization chamber. make. The wall of the ionization chamber is made of air-equivalent material, which has approximately the same absorption coefficient for primary radiation and air, and approximately the same atomic blocking ability for secondary electrons. The physical properties are firm, durable and stable. of excellent material.

The development of air-equivalent materials abroad started very early, and there are already ready-made products, such as C-552 air-equivalent materials. Air-equivalent materials have been used in the production of standard ionization chambers abroad, such as FC23-C Farmer, PR-06C Farmer, PR-06G Farmer, etc. In China, Sichuan Zhongshi Radiation Technology Co., Ltd. is engaged in the research and development of this material. The CT long rod ionization chamber produced has been used for CT dose measurement, and the energy response is less than 3%. It has applied for a patent [pen-type ionization chamber for CT index measurement. , Patent No.: ZL200520036437.7].

In view of the domestic research on air-equivalent materials and the production of ionization chambers, China Institute of Testing Technology has carried out research on the production process of ionization chambers, and developed a finger-shaped ionization chamber with a volume of 0.6cm ³ for absolute dose measurement in radiotherapy , this ionization chamber is robust, durable, and stable, but cannot be used for high-energy electron beam dosimetry.

A medical linear accelerator is an acceleration device that uses a microwave electromagnetic field to accelerate electrons and has a linear motion track. It is mainly used for radiotherapy of tumor patients and has been widely used now. However, for the dose detection of high-energy electron beam rays, a finger-shaped ionization chamber is usually used. Since high-energy electron beam rays are mainly used for the treatment of superficial tumors on the skin surface, and their dose decay gradients vary greatly, it is not suitable to measure the absorbed dose of electron beams with lower energy ≤ 10MeV using a finger-shaped ionization chamber.

To sum up, there are two main disadvantages of the existing technology:

1. Usually, a finger-shaped ionization chamber is used for measurement. At present, a finger-shaped ionization chamber is usually used to measure the absorbed dose of water in China, but when the electron beam energy is low, the finger-shaped ionization chamber cannot truly reflect the characteristics of the radiation beam gradient.

2. Plexiglass-coated graphite is used as the chamber wall material. There are flat ionization chambers abroad for measuring the absorbed dose of water with low electron beam energy, but the wall of the chamber is coated with a graphite conductive layer of plexiglass, and its effective atomic number is slightly smaller than that of air, so it is generated in the cavity. The ionization charge is slightly less than that of the free air ionization chamber.

Utility model content

In view of the above problems, the purpose of the present invention is to provide a flat plate ionization chamber for high-energy electron beam dose measurement with compact structure, small intra-cavity scattering disturbance effect, small disturbance influence, and easy determination of effective measurement points.

The technical scheme of the utility model is as follows: a flat plate ionization chamber for high-energy electron beam dose measurement, comprising an outer electrode and an inner electrode; the outer electrode is a cap-mounted structure made of an air equivalent material, which is connected with the lower outer electrode The rear cover forms a closed flat air cavity, and an insulating plate is arranged at the bottom of the air cavity; the inner electrode is fixed on the insulating plate, and a protective ring is surrounded on the periphery.

Further, a first insulating support ring and a second insulating support ring are also supported between the insulating plate and the outer electrode; the second insulating support ring is located on the outer ring, and an inner concave ring is arranged on the inner side of its bottom; the first insulating support ring is located in the inner ring, the outer side of the bottom is provided with an outer concave ring, and the inner side is provided with an inner concave ring; the protection ring is embedded between the inner concave ring of the second insulating support ring and the outer concave ring of the first insulating support ring; the The inner electrode is embedded in the inner concave ring with the first insulating support ring, and is on the same plane as the protection ring.

Furthermore, the outer edge of the bottom of the outer electrode is provided with a concave platform, and the outer edge of the rear cover of the outer electrode is provided with a boss that is fitted with the concave platform.

Further, it also includes the front end of the strut, one end of which is connected to the outer electrode through a thread, and the other end of the front end of the strut is fixedly connected to the rear end of the strut.

Furthermore, the insulating plate is provided with a small groove for wiring the inner electrode and the guard ring and filling the ionization cavity on the back.

Further, the inner electrode is plexiglass-coated graphite with a diameter of 10 mm, and a gold-plated pressing sheet is arranged on the edge thereof; the thickness of the incident window is 1 mm.

Further, the width of the protection ring is not less than 1.5 times the height of the air cavity.

The beneficial effects of the utility model are as follows: the utility model adopts the air equivalent material as the outer electrode, and the measurement is more accurate; the problem of measuring the electron beam dose in the prior art is solved, and the gradient change of the radiation beam can be truly reflected; the outer electrode and the The rear cover of the outer electrode adopts a fixed cap edge structure, which is easy to assemble, has good contact, and has few air gaps, which improves the consistency of the cavity ionization chamber, improves the qualification rate of the product, and at the same time realizes the sturdiness and durability of the product.

Description of drawings

FIG. 1 is a top view of a novel flat-panel ionization chamber for high-energy electron beam dose measurement.

FIG. 2 is a cross-sectional view at B-B in FIG. 1 .

In the figure: 1-outer electrode; 2-outer electrode back cover; 3-protection ring; 4-inner electrode; 5-pillar front end; 6-pillar rear end; 7-insulating plate; 8-first insulating support ring; 9 -Second insulating support ring.

Detailed ways

The present utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Figure 1, a flat plate ionization chamber for high-energy electron beam dose measurement includes an outer electrode 1 and an inner electrode 4; the outer electrode 1 is a cap-mounted structure made of an air equivalent material, which is connected with the lower The outer electrode rear cover 2 forms a closed flat air cavity, and an insulating plate 7 is arranged at the bottom of the air cavity; the inner electrode 4 is fixed on the insulating plate 7, and a protective ring 3 is surrounded on the periphery.

In this embodiment, air-equivalent plastic is used as the chamber wall material, and epoxy resin is used as the adhesive, which has the advantages of small distance between poles, small disturbance influence, and easy determination of effective measurement points. There are obvious advantages and higher measurement accuracy in the measurement of areas with large directional dose gradient changes.

As shown in FIG. 2, a first insulating support ring 8 and a second insulating support ring 9 are also supported between the insulating plate 7 and the outer electrode 1 in this embodiment; the second insulating support ring 9 is located on the outer ring, and the inner bottom of the second insulating support ring 9 is provided The inner concave ring; the first insulating support ring 8 is located in the inner ring, the outer side of the bottom is provided with an outer concave ring, and the inner side is provided with an inner concave ring; the protection ring 3 is embedded in the inner concave ring of the second insulating support ring 9 and the first Between the outer concave rings of the insulating support ring 8 ; the inner electrode 4 is embedded in the inner concave ring of the first insulating support ring 8 , and is on the same plane as the protection ring 3 . The first insulating support ring 8 and the second insulating support ring 9 are made of high-insulation polytetrafluorochloroethylene, and the guard ring and the inner electrode are placed in the machined concave ring to ensure that the guard ring and the inner electrode are on the same plane; The ring 3 and the inner electrode 4 achieve high insulation isolation, the machined surface is smooth, and the leakage loss is reduced.

The ionization chamber of this embodiment uses air-equivalent material as the ionization outdoor electrode to maintain the sturdiness and durability of the ionization chamber; there is a flat air cavity with a height of 2 mm, the inner electrode is surrounded by a protection ring, and the width of the protection ring is not less than 1.5 times the height of the air cavity, in order to reduce the influence of radial beam inhomogeneity, the diameter of the inner electrode is small, 10mm, and the thickness of the incident window is 1mm.

The outer electrode of this embodiment is made of air equivalent material, and cooperates with the back cover to form an independent electric field space and reduce the interference of the external electric field. Specifically, the outer edge of the bottom of the outer electrode 1 is provided with a concave platform, and the outer edge of the outer electrode rear cover 2 is provided with a convex platform that cooperates with the concave platform. , simple assembly, good contact, less air voids, improve the consistency of the cavity ionization chamber, improve the qualification rate of the product, and at the same time achieve the firmness and durability of the product; epoxy resin is used for the external joints of the ionization chamber Bonding ensures good water resistance.

The inner electrode is made of plexiglass coated graphite with a diameter of 10mm, which is easy to process and has small deformation. Its sensitive height is determined by the insulating support rings 1 and 2. ionized charge. The graphite coated on the inner electrode has good electrical conductivity and reduces the loss of collected charges.

The guard ring is made of pure copper gold-plated for easy soldering, with a width of 3mm to ensure that the electric field at the edge of the sensitive volume remains uniform and reduces leakage loss; there are small grooves on the insulating plate, which are used for the wiring of the inner electrode and the guard ring and to fill the ionization space on the back. cavity to prevent the addition of additional ionization volume. The addition of guard poles reduces leakage losses and ensures that the electric field remains uniform at the edge of the sensitive volume.

It also includes a strut front end 5 whose one end is connected to the outer electrode 1 through threads, and the other end of the strut front end 5 is fixedly connected to the strut rear end 6 . The front end 5 of the pillar and the rear end 6 of the pillar are made of aluminum alloy, which are connected to the high-voltage pole of the cable, and are connected to the outer electrode through the thread, which can realize the non-attenuated conduction of the voltage, and protect the cable from being damaged by external force. The clamp realizes the fixing effect.

Claims (7)

1. A flat plate ionization chamber for high-energy electron beam dose measurement, characterized in that it comprises an outer electrode (1) and an inner electrode (4); the outer electrode (1) is a cap made of an air equivalent material structure, which forms a closed flat air cavity with the lower outer electrode back cover (2), and an insulating plate (7) is arranged at the bottom of the air cavity; the inner electrode (4) is fixed on the insulating plate (7), and the periphery is surrounded by With guard ring (3). 2 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , wherein a first insulating support ring is further supported between the insulating plate ( 7 ) and the outer electrode ( 1 ). 3 . (8) and the second insulating support ring (9); the second insulating support ring (9) is located on the outer ring, and an inner concave ring is arranged on the inner side of its bottom; the first insulating support ring (8) is located on the inner ring, and the outer side of its bottom is provided There is an outer concave ring, and the inner side is provided with an inner concave ring; the protection ring (3) is embedded between the inner concave ring of the second insulating support ring (9) and the outer concave ring of the first insulating support ring (8); The inner electrode (4) is embedded in the inner concave ring with the first insulating support ring (8), and is on the same plane as the protection ring (3). 3 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , wherein the outer edge of the bottom of the outer electrode ( 1 ) is provided with a concave platform, and the outer electrode rear cover ( 2 ) is outside the outer edge of the outer electrode. 4 . The edge is provided with a boss fitted with the concave platform. 4 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , further comprising a strut front end ( 5 ), one end of which is connected to the outer electrode ( 1 ) through a thread, and the strut front end The other end of (5) is fixedly connected with the rear end (6) of the strut. 5 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , wherein the insulating plate ( 7 ) is provided with an inner electrode ( 4 ) and a guard ring ( 3 ). 6 . Trace the wires and the small slots that fill the ionization cavity on the back. 6 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , wherein the inner electrode ( 4 ) is a plexiglass-coated graphite with a diameter of 10 mm, and its edge is provided with a gold-plated ionization chamber. 7 . Tablet; the thickness of the incident window is 1mm. 7 . The flat plate ionization chamber for high-energy electron beam dose measurement according to claim 1 , wherein the width of the protection ring ( 3 ) is not less than 1.5 times the height of the air cavity. 8 .

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