阅读说明：本技术 一种用于高能电子束剂量测量的平板电离室 (Flat ionization chamber for high-energy electron beam dose measurement ) 是由 龚岚 周媛媛 程金星 王庆波 于艾 于 2020-05-23 设计创作，主要内容包括：本发明公开一种用于高能电子束剂量测量的平板电离室,包括外电极和内电极；所述外电极为空气等效材料制成的帽装结构,其与下方的外电极后盖构成一个密闭的扁平气腔,气腔底部设有绝缘板；所述内电极固定于绝缘板上,外围环绕有保护环。本发明采用的空气等效材料作为外电极,测量更加准确；解决现有技术中用于测量电子束剂量测量的难题,能真实反映辐射束梯度变化；采用固定帽缘结构,装配简单、接触良好、空气空隙少,改善了空腔电离室的一致性,提高了产品的合格率,同时实现了产品的坚固性和耐用性。(The invention discloses a flat ionization chamber for measuring high-energy electron beam dosage, which comprises an outer electrode and an inner electrode; the outer electrode is a cap structure made of air equivalent material, and forms a closed flat air cavity together with the lower outer electrode rear cover, and the bottom of the air cavity is provided with an insulating plate; the inner electrode is fixed on the insulating plate, and a protective ring is surrounded on the periphery of the inner electrode. The air equivalent material is used as the outer electrode, so that the measurement is more accurate; the problem of measuring electron beam dosage in the prior art is solved, and the gradient change of a radiation beam can be truly reflected; adopt fixed cap reason structure, the assembly is simple, the contact is good, the air space is few, has improved the uniformity of cavity ionization chamber, has improved the qualification rate of product, has realized the tightness and the durability of product simultaneously.)

1. A flat ionization chamber for high energy electron beam dosimetry, characterized by comprising an outer electrode (1) and an inner electrode (4); the outer electrode (1) is a cap structure made of air equivalent material, and forms a closed flat air cavity together with the lower outer electrode rear 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 of the inner electrode is surrounded by the protection ring (3).

2. A flat-plate ionization chamber for high-energy electron beam dosimetry according to claim 1, characterized in that between the insulating plate (7) and the outer electrode (1) there are further supported a first insulating support ring (8) and a second insulating support ring (9); the second insulating support ring (9) is positioned on the outer ring, and the inner side of the bottom of the second insulating support ring is provided with an inner concave ring; the first insulating support ring (8) is positioned at the inner ring, the outer side of the bottom of the first insulating support ring is provided with an outer concave ring, and the inner side of the first insulating support ring is provided with an inner concave ring; the protection ring (3) is embedded between the inner concave ring of the second insulation support ring (9) and the outer concave ring of the first insulation support ring (8); the inner electrode (4) is embedded in the inner concave ring with the first insulation support ring (8) and is positioned on the same plane with the protection ring (3).

3. The flat-plate ionization chamber for high-energy electron beam dosimetry according to claim 1, characterized in that 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 which is matched with the concave platform.

4. The flat-plate ionization chamber for high-energy electron beam dosimetry according to claim 1, further comprising a strut front end (5) having one end connected to the outer electrode (1) by a screw thread, the other end of the strut front end (5) being fixedly connected to the strut rear end (6).

5. A flat-panel ionization chamber for high-energy electron beam dosimetry according to claim 1, characterized in that the insulating plate (7) is provided with small grooves for the routing of the inner electrode (4) and the guard ring (3) and for filling the ionization cavity at the back.

6. The flat ionization chamber for high-energy electron beam dosimetry according to claim 1, characterized in that the inner electrode (4) is plexiglas-coated graphite with a diameter of 10mm, provided with gold-plated preforms at its edges; the thickness of the entrance window is 1 mm.

7. The flat-plate ionization chamber for high-energy electron beam dosimetry according to claim 1, characterized in that the width of the guard ring (3) is not less than 1.5 times the air cavity height.

Technical Field

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

Background

In 1958, article of conductive plastic equivalent tissue, air and polystyrene was published by Shonka, F.R, Rose, j.e, Failla, G and the like, research on air equivalent plastic was developed, and air equivalent material was applied to the manufacturing of ionization chambers. The wall of the ionization chamber is made of air equivalent material, has approximately the same absorption coefficient to primary radiation and air and approximately the same atomic stopping power to secondary electrons, has firm, durable and stable physical characteristics, and is an excellent material for manufacturing the ionization chamber.

The development of air equivalent materials in foreign countries starts very early, and existing products are available, such as: c-552 air equivalent material. Air equivalent materials have been used abroad for the production of standard ionization chambers, such as FC23-C Farmer, PR-06CFarmer, PR-06G Farmer, and the like. The radiation technology limited company for measuring in Sichuan is engaged in the research and development of the material, the produced CT long-rod ionization chamber is already used for CT dose measurement, the energy response is less than 3%, and the patent is applied for (pen-shaped ionization chamber for CT index measurement, patent number: ZL 200520036437.7.

In view of the research on the equivalent materials of air in China and the manufacturing situation of the ionization chamber, the research on the manufacturing process of the ionization chamber is carried out by the research institute of Chinese test technology, and a volume of 0.6cm is developed³The finger ionization chamber of (a) is used for radiation therapy absolute dosimetry, and the ionization chamber is firm, durable and stable, but cannot be used for high-energy electron beam dosimetry.

The medical linear accelerator is an accelerating device which accelerates electrons by using a microwave electromagnetic field and has a linear motion track, is mainly used for radiotherapy of tumor patients, and is widely used at present. However, for the dose detection of high-energy electron beam radiation, a finger-type ionization chamber is generally used. Since high-energy electron beam radiation is mainly used for treating superficial tumors on the skin surface, the dose attenuation gradient of the high-energy electron beam radiation is greatly changed, and the measurement of the absorbed dose of the electron beam with lower energy less than or equal to 10MeV is not suitable for the measurement by using a finger ionization chamber.

In summary, the disadvantages of the prior art are two main:

1. typically using a finger ionization chamber. At present, a finger-shaped ionization chamber is generally adopted for measuring the water absorption dose in China, but under the condition that the energy of an electron beam is lower, the characteristic of the gradient change of a radiation beam cannot be truly reflected by the finger-shaped ionization chamber.

2. Organic glass coated graphite is used as a chamber wall material. Foreign countries have flat ionization chambers for measuring the amount of water absorbent with low electron beam energy, but the walls of the chambers are made of organic glass coated with a graphite conductive layer, and the effective atomic number of the graphite conductive layer is slightly smaller than that of air, so that the ionization charge generated in the cavity is slightly less than that of a free air ionization chamber.

Disclosure of Invention

In view of the above problems, the present invention aims to provide a flat ionization chamber for high-energy electron beam dosimetry, which has a compact structure, a small intra-cavity scattering perturbation effect, a small perturbation effect, and an easily determined effective measurement point.

The technical scheme is as follows: a flat ionization chamber for high energy electron beam dosimetry comprising an outer electrode and an inner electrode; the outer electrode is a cap structure made of air equivalent material, and forms a closed flat air cavity together with the lower outer electrode rear cover, and the bottom of the air cavity is provided with an insulating plate; the inner electrode is fixed on the insulating plate, and a protective ring is surrounded on the periphery of the inner electrode.

Furthermore, a first insulating support ring and a second insulating support ring are supported between the insulating plate and the outer electrode; the second insulating support ring is positioned on the outer ring, and an inner concave ring is arranged on the inner side of the bottom of the second insulating support ring; the first insulating support ring is positioned on the inner ring, an outer concave ring is arranged on the outer side of the bottom of the first insulating support ring, and an inner concave ring is arranged on the inner side of the first insulating support ring; the protection ring is embedded between the inner concave ring of the second insulation support ring and the outer concave ring of the first insulation support ring; the inner electrode is embedded in the inner concave ring of the first insulating support ring and is positioned on the same plane with the protection ring.

Furthermore, the outer edge of the bottom of the outer electrode is provided with a concave table, and the outer edge of the outer electrode rear cover is provided with a boss which is matched with the concave table.

Furthermore, the device also comprises a strut front end, one end of the strut front end is connected with the outer electrode through threads, and the other end of the strut front end is fixedly connected with the strut rear end.

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

Furthermore, the inner electrode is organic glass coated graphite with the diameter of 10mm, and the edge of the inner electrode is provided with a gold-plated pressing sheet; the thickness of the entrance window is 1 mm.

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

The invention has the beneficial effects that: according to the invention, the air equivalent material is used as the outer electrode, so that the measurement is more accurate; the problem of measuring electron beam dosage in the prior art is solved, and the gradient change of a radiation beam can be truly reflected; the outer electrode and the outer electrode rear cover adopt a fixed cap edge structure, the assembly is simple, the contact is good, air gaps are few, the consistency of the cavity ionization chamber is improved, the qualification rate of products is improved, and the firmness and the durability of the products are realized.

Drawings

FIG. 1 is a top view of a flat panel ionization chamber for high energy electron beam dosimetry according to the present invention.

Fig. 2 is a cross-sectional view taken at B-B in fig. 1.

In the figure: 1-an outer electrode; 2-rear cover of external electrode; 3-a guard ring; 4-an inner electrode; 5-pillar front end; 6-post rear end; 7-an insulating plate; 8-a first insulating support ring; 9-second insulating support ring.

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

As shown in fig. 1, a flat ionization chamber for high energy electron beam dosimetry comprises an outer electrode 1 and an inner electrode 4; the outer electrode 1 is a cap structure made of air equivalent material, and forms a closed flat air cavity together with the lower outer electrode rear 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 of the inner electrode is surrounded by the protection ring 3.

In the embodiment, air equivalent plastic is used as a chamber wall material, epoxy resin is used as an adhesive, the method has the advantages of small inter-polar distance, small disturbance influence, easy determination of effective measurement points and the like, and has obvious advantages and high measurement accuracy on the calibration of the absorbed dose of the electron beam and the measurement of the area with large dose gradient change along the incident direction of the electron beam.

As shown in fig. 2, a first insulating support ring 8 and a second insulating support ring 9 are supported between the insulating plate 7 and the outer electrode 1; the second insulating support ring 9 is positioned on the outer ring, and the bottom of the inner side of the second insulating support ring is provided with an inward concave ring; the first insulating support ring 8 is positioned on the inner ring, the outer side of the bottom of the first insulating support ring is provided with an outer concave ring, and the inner side of the first insulating support ring is provided with an inner concave ring; the protection ring 3 is embedded between the inner concave ring of the second insulation support ring 9 and the outer concave ring of the first insulation support ring 8; the inner electrode 4 is embedded in the concave ring with the first insulating support ring 8 and is positioned on the same plane with the protection ring 3. The first insulating support ring 8 and the second insulating support ring 9 are processed by high-insulating polytetrafluoroethylene, and the processed concave rings are respectively provided with a protection ring and an inner electrode to ensure that the protection ring and the inner electrode are positioned on the same plane; high insulation isolation is realized on the protection ring 3 and the inner electrode 4, the processed surface is smooth, and the leakage loss is reduced.

The ionization chamber of the embodiment adopts an air equivalent material as an ionization chamber outer electrode, so that the firmness and durability of the ionization chamber are maintained; the height of the air cavity is 2mm, the inner electrode is surrounded by the protection ring, the width of the protection ring is not less than 1.5 times of the height of the air cavity, the diameter of the inner electrode is smaller and 10mm, and the thickness of the entrance window is 1mm in order to reduce the influence of the nonuniformity of the radial ray beams.

The outer electrode of the embodiment adopts an air equivalent material and is matched with the rear cover to form an independent electric field space, so that the interference of an external electric field is reduced. Specifically, the outer edge of the bottom of the outer electrode 1 is provided with a concave table, the outer edge of the outer electrode rear cover 2 is provided with a convex table which is matched with the concave table, and the formed cap edge structure is convenient to process, accurate in position control during installation, simple in assembly, good in contact and less in air gap, improves the consistency of a cavity ionization chamber, improves the qualification rate of products, and meanwhile realizes the firmness and durability of the products; seams outside the ionization chamber are bonded by epoxy resin to ensure good waterproof performance.

The inner electrode is made of organic glass coated graphite with the diameter of 10mm, the inner electrode is easy to process and small in deformation, the sensitivity height of the inner electrode is determined through the insulating support rings 1 and 2, and the edge of the inner electrode is made of a gold-plated pressing sheet and used for collecting ionization charges on the inner electrode by a welding lead. The graphite coated on the inner electrode has good conductivity and reduces the loss of collected charges.

The protection ring is plated with gold by adopting pure copper so as to be convenient for welding, the width is 3mm, the electric field at the edge of the sensitive volume is ensured to be uniform, and the leakage loss is reduced; the insulating plate is provided with a small groove for routing the inner electrode and the protection ring and filling the ionization cavity on the back, so that the additional ionization volume is prevented from being increased. And a protective electrode is added, the leakage loss is reduced, and the electric field at the edge of the sensitive volume is ensured to be uniform.

The electrode holder further comprises a strut front end 5, one end of which is connected with the outer electrode 1 through threads, and the other end of the strut front end 5 is fixedly connected with a strut rear end 6. Pillar front end 5 and pillar rear end 6 adopt the aluminum alloy to make, link to each other with the high-voltage pole of cable, through threaded connection to outer electrode, can realize the non-decay of voltage and switch on to the protection cable is not damaged by external force, can realize the fixed action through anchor clamps.