A flat-plate ionization chamber for ultra-high pulsed dose rate measurement

Abstract

This invention discloses a flat-plate ionization chamber for ultra-high pulse dose rate measurement, comprising an incident electrode plate, an inner electrode plate, and a chamber wall. The incident electrode plate and the inner electrode plate are fixedly disposed within the chamber wall. A disc-shaped high-voltage electrode is disposed at the center of the incident electrode plate. The inner electrode plate includes a collecting electrode and a protective electrode. The incident electrode plate and the inner electrode plate have a two-layer parallel structure. The air inside the incident electrode plate and the inner electrode plate is formed into a disc-shaped air cavity by the chamber wall. External signal lines are connected to the high-voltage electrode, the collecting electrode, and the protective electrode, respectively. This invention improves the charge collection efficiency of the ionization chamber, enables accurate charge measurement, achieves simple assembly and strong stability, reduces leakage current in the ionization chamber, and ensures good uniformity of the internal electric field.

Description

Technical Field

[0001] This invention can be applied in the field of ionization measurement technology, specifically a flat-plate ionization chamber for ultra-high pulse dose rate measurement. Background Technology

[0002] There are many methods for treating tumors, mainly including surgery, radiotherapy, chemotherapy, targeted drug therapy, and organ transplantation. Radiotherapy uses ionizing radiation such as X-rays, gamma rays, or proton beams to irradiate tumor tissue and kill tumor cells. Flash radiotherapy, which delivers ultra-high pulsed dose rates to tumors, can better protect surrounding normal tissues under the same tumor treatment conditions.

[0003] The devices used to measure water absorbed dose in flash radiotherapy are generally finger-type ionization chambers and flat-plate ionization chambers. However, because the dose rate of flash radiotherapy is 40 Gy / s, which is 200 times higher than that of conventional radiotherapy, and because the pulse output time of flash radiotherapy is on the order of microseconds, the single pulse dose is 1–10 Gy / pulse. Conventional water absorbed dose measurement devices suffer from high ion recombination loss (below 70%) under such ultra-high pulse dose rate conditions, resulting in an excessively large ion radiation loss correction factor. This leads to low collection efficiency of the ionization chamber and large measurement deviations, making them unsuitable for measuring water absorbed dose in flash radiotherapy. Although passive dosimeters, such as film dosimeters and thermoluminescent dosimeters, are available for dose measurement, these methods are passive. After the radiation has deposited energy in the passive dosimeter, a specific readout device is required for reading, which takes a long time and cannot directly display the dose value of the radiation beam in real time.

[0004] In summary, the disadvantages of the existing technology are: (1) The existing finger-shaped ionization chamber or plate ionization chamber is no longer suitable for ultra-high pulse dose rate measurement. When the ionization chamber is irradiated at ultra-high dose rate, the ion recombination loss is serious and it cannot truly reflect the measured water absorbed dose value. (2) The existing passive dose measurement method has the disadvantages of low measurement efficiency and long time consumption, and is not suitable for real-time dose value measurement.

[0005] Existing flat-plate ionization chambers, with an electrode spacing of 1 mm, exhibit severe ion recombination loss under ultra-high dose rate conditions. Furthermore, existing theories and methods for correcting ion recombination loss are no longer applicable, resulting in measurement results that do not accurately reflect the absorbed dose of water. Therefore, existing measuring devices are no longer suitable for measuring high pulse doses. To address the problem of excessive ion recombination loss, this invention provides a flat-plate ionization chamber and method for measuring ultra-high pulse dose rates. Summary of the Invention

[0006] This invention provides a flat-plate ionization chamber for ultra-high pulse dose rate measurement to solve the problem of excessive ion recombination loss mentioned above.

[0007] This invention includes an incident electrode plate, an inner electrode plate, and a chamber wall. The incident electrode plate and the inner electrode plate are fixedly disposed within the chamber wall. A disc-shaped high-voltage electrode is disposed at the center of the incident electrode plate. The inner electrode plate includes a collecting electrode and a protective electrode. The incident electrode plate and the inner electrode are parallel structures of two layers. The collecting electrode and the protective electrode are located in the same concentric circular structure plane and are isolated by a slotted structure. The high-voltage electrode is attached to the upper part of the collecting electrode. The chamber wall forms a disc-shaped air cavity with the air inside the incident electrode and the inner electrode. External signal lines are connected to the high-voltage electrode, the collecting electrode, and the protective electrode, respectively.

[0008] Furthermore, the chamber wall is provided with a groove for accommodating the inner electrode plate, the inner electrode plate is fixed in the chamber wall by screws, and a second step is provided on the groove for engaging the incident electrode plate.

[0009] Furthermore, a matching through groove is provided at the connection between the incident electrode plate and the inner electrode plate, and it penetrates the side wall of the chamber wall. A channel for connecting through holes is provided at the center of the collecting electrode of the inner electrode plate. The channel is filled with conductive graphite. A second groove extends from the edge of the high voltage electrode of the incident electrode plate to the through groove. The channel, the through groove, and the through groove are all filled with conductive graphite for connection with the signal line.

[0010] Furthermore, the width of the protective ring is 20 times that of the sensitive volume air gap.

[0011] Furthermore, the high-voltage electrode is a PEEK substrate high-voltage electrode with a graphite layer sprayed on its surface.

[0012] Furthermore, the width of the protective electrode ring is the same as the length of the collecting electrode radius.

[0013] Furthermore, the distance between the high-voltage electrode and the collecting electrode is 0.25 mm.

[0014] Furthermore, a conductive metal sheet is fixedly disposed on the inner electrode plate.

[0015] Furthermore, the width ratio of the gas cavity formed between the high-pressure electrode and the collecting electrode to the width of the collecting electrode is 1:1.5.

[0016] Compared with the prior art, the beneficial effects of this invention are as follows:

[0017] (1) This invention improves the charge collection efficiency of the ionization chamber, solves the problem of existing FLASH ultra-high pulse dose measurement, and enables accurate charge measurement.

[0018] (2) The core structure of the ionization chamber of this invention is divided into three parts, which achieves the characteristics of simple assembly and strong stability. The overall insulation material of the ionization chamber is high-insulation PEEK, which reduces the leakage current of the ionization chamber. At the same time, the collecting electrode and the protection electrode are designed as an integral structure, which ensures good uniformity of the internal electric field.

[0019] (3) In this invention, a groove insulation structure is used between the collecting electrode and the protection electrode, which has a good isolation effect and further reduces the leakage current of the ionization chamber. Attached Figure Description

[0020] Figure 1 This is a physical diagram of the ionization chamber of the flat-plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention;

[0021] Figure 2 The above is a linear graph of dose measurement in the electron Flash radiation field for the flat plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention.

[0022] Figure 3 This is a leakage current diagram of the flat plate ionization chamber used for ultra-high pulse dose rate measurement in this invention within ±4fA;

[0023] Figure 4 This is an overall structural diagram of the flat-plate ionization chamber for ultra-high pulse dose rate measurement according to the present invention;

[0024] Figure 5 This is a schematic diagram of the incident electrode plate of the flat plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention;

[0025] Figure 6 This is a schematic diagram of the inner electrode plate of the flat plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention;

[0026] Figure 7 This is a schematic diagram of the ionization chamber wall of the flat-plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention;

[0027] Figure 8 This is a schematic diagram of the conductive metal sheet of the flat plate ionization chamber used for ultra-high pulse dose rate measurement according to the present invention;

[0028] Wherein: 1-incident electrode plate, 2-inner electrode plate, 3-chamber wall, 4-conductive metal sheet, (1-1)-high voltage electrode, (1-4)-second groove, (2-1)-collecting electrode, (2-2)-protective electrode, (4-2)-screw, (2-3)-channel Detailed Implementation

[0029] To more clearly illustrate the technical solution of the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0030] like Figure 1-8As shown, the present invention includes an incident electrode plate 1, an inner electrode plate 2, and a chamber wall 3. The incident electrode plate 1 and the inner electrode plate 2 are fixedly disposed inside the chamber wall. A disc-shaped high-voltage electrode 1-1 is disposed at the center of the incident electrode plate 1. The inner electrode plate 2 includes a collecting electrode 2-1 and a protective electrode 2-2. The incident electrode plate 1 and the inner electrode 2 are parallel structures with upper and lower layers. The collecting electrode 2-1 and the protective electrode 2-2 are located in the same concentric circular structure plane and are isolated by a slotted structure. The high-voltage electrode 1-1 is attached to the upper part of the collecting electrode 2-1. The chamber wall 3 forms a disc-shaped air cavity for the air inside the incident electrode 1 and the inner electrode 2. The external signal lines are connected to the high-voltage electrode, the collecting electrode, and the protective electrode, respectively.

[0031] The ionization chamber structure consists of a high-voltage electrode, a collecting electrode, and a protective electrode. The portion directly opposite the high-voltage and collecting electrodes is the sensitive volume of the ionization chamber. A positive high voltage and a negative high voltage (or 0V) are applied to the high-voltage and collecting electrodes, respectively, generating an electric field within the sensitive volume. The X-rays interact with the air, generating positive and negative charges. These charges move along the electric field lines under the influence of the electric field, generating induced charges during this movement. These induced charges are then collected via signal lines.

[0032] The chamber wall 3 is provided with a groove to accommodate the inner electrode plate 2. The inner electrode plate 2 is fixed in the chamber wall 3 by screws. A second step is provided on the groove to engage the incident electrode plate 1.

[0033] The connection between the incident electrode 1 and the inner electrode 2 is provided with a matching through groove that penetrates the side wall of the chamber wall. The center of the collecting electrode 2-1 of the inner electrode 2 is provided with a channel 2-3 for connecting through holes. The channel 2-3 is filled with conductive graphite. The edge of the high voltage electrode 1-1 of the incident electrode 1 extends into the through groove via a second groove 1-4. The channel 2-3, the through groove, and the second groove 1-4 are all filled with conductive graphite for connection with the conductive metal sheet.

[0034] Among them, the conductive metal sheet 4 is connected to the high voltage electrode 1-1, the collecting electrode 2-1 and the protective electrode 2-2.

[0035] In this embodiment, the distance between the high-voltage electrode 1-1 and the collecting electrode 2-1 is 0.25 mm, meaning the gap within the sensitive volume of the ionization chamber is 0.25 mm. This reduces the trajectory of the charge within the air cavity, increases the internal electric field strength, and thus improves charge collection efficiency. The collecting electrode 2-1 and the protective electrode 2-2 are located on the same electrode plate, strictly ensuring that the two structures are on the same plane and guaranteeing the uniformity of the electric field inside the ionization chamber.

[0036] In this example, the incident electrode 1 is made of highly insulating PEEK material with a radius of 35 mm and a stepped surface. At the very top is a circular structure with a radius of 10 mm, which serves as the high-voltage electrode 1-1. The surface of the high-voltage electrode is coated with a graphite layer for conductivity. Graphite has excellent conductivity and is also an air-equivalent material, replacing metal as the conductive material and reducing radiation attenuation caused by metal. Using PEEK as the base material for the high-voltage electrode 1-1 improves the robustness and radiation resistance of the ionization chamber. A channel-shaped groove extends from the edge of the high-voltage electrode 1-1 to the edge of the incident electrode 1. The groove is filled with conductive graphite. The high-voltage electrode 1-1 is connected to the conductive metal sheet 4 via a triaxial signal line.

[0037] The inner electrode plate 2 is divided into two concentric circular parts: the inner part is the collecting electrode 2-1, and the outer part is the protective electrode 2-2. Both surfaces are coated with graphite, which provides high conductivity and excellent electrical performance. A circular groove, 0.25 mm wide and 0.2 mm deep, separates the collecting electrode 2-1 and the protective electrode 2-2, ensuring isolation between them. The collecting electrode 2-1 and the protective electrode 2-2 are on the same structural block and share the same plane. The ring width of the protective electrode 2-2 is the same as the radius of the collecting electrode 2-1, ensuring uniformity of the electric field inside the ionization chamber. The groove structure also effectively reduces leakage current in the ionization chamber by isolating the collecting electrode 2-1 and the protective electrode 2-2. The width of the protective ring 2-2 is 20 times the size of the air gap in the sensitive volume, further improving the uniformity of the electric field inside the ionization chamber.

[0038] The ionization chamber has a modular, block-shaped structure. The high-voltage electrode is designed using PEEK substrate coated with graphite. The collecting electrode and the protective electrode are located within the same structural plane and are isolated by a slotted structure. The structural plane is a concentric circle structure.

[0039] The inner electrode plate 2 has a channel on its side, which is directly connected to the collector electrode 2-1. The channel is filled with graphite, which can connect the collector electrode 2-1 to the outside. Graphite has good conductivity. The signal generated during the movement of charge inside the ionization chamber is transmitted through the graphite as a conductor, without causing signal loss.

[0040] The conductive metal sheet 4 is fixed to the inner electrode plate 2 by screws 4-2. Screws 4-2 are made of insulating PEEK material, which has good insulation effect. The square metal sheet 4-2 in the conductive metal sheet 4 is in close contact with the inner electrode plate 2. The inner electrode plate 2 is coated with graphite on the outside of the protective electrode 2-2. Signal conduction is achieved through the graphite and the square metal sheet 4-2, connecting to the conductive metal sheet 4.

[0041] The part directly opposite the high-voltage electrode 1-1 and the collecting electrode 2-1 is the sensitive volume of the ionization chamber. The gap between the air cavities inside is 0.25mm, which reduces the trajectory of charge movement generated in the air cavity, lowers the probability of recombination of positive and negative ions, and helps to improve charge collection efficiency.

[0042] The chamber wall 3 has a groove within which the inner electrode plate 2 can be placed precisely. Four threaded holes are located at the bottom of the groove, through which the inner electrode plate 2 is fixed. A larger step is provided on the groove, through which the incident electrode plate 1 is placed inside the chamber wall 3, with its bottom surface positioned precisely at the step. A threaded hole is located on the side of the chamber wall 3, through which a conductive metal sheet 4 connects to the high-voltage electrode 1-1, the collecting electrode 2-1, and the protective electrode 2-2. This design allows for accurate positioning and simple assembly during installation.

[0043] The ionization chamber adopts a three-part block structure, which is simple in construction, highly functional, easy to assemble, and quick to position. The positioning of the block structure enables accurate positioning of the air gap with high accuracy.

[0044] In this embodiment, an ionization chamber with a distance of 0.25 mm between the high-voltage electrode and the collecting electrode was designed. The actual ionization chamber is shown below. Figure 1 As shown. Experimental measurements of the ionization chamber were conducted using a Flash electron beam accelerator. The results showed good linearity within the range of 0.2–2.25 Gy / pulse, with a linearity R² = 0.99994, indicating good measurement results under ultra-high pulsed dose conditions. The results were calculated for a pulsed dose of DPP = 2.18 Gy / pulse.

[0045] Formula for calculating ion collection efficiency

[0046]

[0047] In the formula, a0 = 1.022, a1 = -0.363, a2 = 0.341, resulting in ks = 1.037 and a collection efficiency of 96.43%, indicating that the collection efficiency of the ionization chamber in this invention is significantly improved under high pulse dose conditions.

[0048] Table 1. Experimental Measurement Results of the Ionization Chamber of the Invention

[0049] Operating voltage Charge value / nC Collection efficiency -100V -19.44 96.43％

[0050] The ionization chamber of this invention features a 0.25mm gap in the sensitive volume, reducing the tracks of positive and negative charges generated within the sensitive volume and shortening the charge movement time within it. The designed collecting electrode radius of the ionization chamber is 5mm, effectively reducing the impact of uneven beam illumination. The sensitive volume is approximately 19.6mm³, reducing the amount of ionized charge within the ionization chamber, thereby lowering the probability of recombination effects and improving charge collection efficiency. This design allows for application in high-pulse dose rate radiation fields, solving the problem of measuring doses in high-pulse radiation fields. The collecting and protective electrodes of the ionization chamber are designed within the same structure, effectively ensuring that they are on the same plane and guaranteeing the uniformity of the electric field inside the ionization chamber. A groove structure between the collecting and protective electrodes effectively isolates them, reducing leakage current in the ionization chamber.

[0051] The ionization chamber structure adopts a stepped structure as a limiting structure, which makes it easier to control and position, and will not cause the components to shift. It keeps the air gap in the sensitive volume of the ionization chamber at a fixed value, improving the repeatability of the measurement results. The main core structure of the ionization chamber adopts a block-integrated design, which is simple in structure, easy to install, and has strong stability.

[0052] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A flat-plate ionization chamber for ultra-high pulsed dose rate measurement, characterized in that, The device includes an incident electrode plate, an inner electrode plate, and a chamber wall. The incident electrode plate and the inner electrode plate are fixedly disposed within the chamber wall. A disc-shaped high-voltage electrode is disposed at the center of the incident electrode plate. The inner electrode plate includes a collecting electrode and a protective electrode. The incident electrode plate and the inner electrode are parallel structures in two layers. The collecting electrode and the protective electrode are located in the same concentric circular structure plane and are isolated by a slotted structure. The high-voltage electrode is disposed above the collecting electrode. The chamber wall forms a disc-shaped air cavity between the air inside the incident electrode and the inner electrode. External signal lines are connected to the high-voltage electrode, the collecting electrode, and the protective electrode, respectively. A matching through groove is provided at the connection between the incident electrode plate and the inner electrode plate, penetrating the side wall of the chamber wall. A channel for connecting through holes is provided at the center of the collecting electrode of the inner electrode plate. The channel is filled with conductive graphite. A second groove extends from the edge of the high-voltage electrode of the incident electrode plate to the through groove. The channel, the through groove, and the through groove are all filled with conductive graphite for connection with the signal line. The chamber wall is provided with a groove to accommodate the inner electrode plate, and the inner electrode plate is fixed in the chamber wall by screws. The groove is provided with a second step to lock the incident electrode plate. The width of the protective ring is 20 times the air gap of the sensitive volume. The distance between the high-voltage electrode and the collecting electrode is 0.25 mm.

2. The flat-plate ionization chamber for ultra-high pulse dose rate measurement according to claim 1, characterized in that, The high voltage electrode is a PEEK substrate high voltage electrode with a graphite layer sprayed on its surface.

3. A flat-plate ionization chamber for ultra-high pulse dose rate measurement according to claim 1, characterized in that, The width of the protective ring is the same as the length of the radius of the collecting electrode.

4. A flat-plate ionization chamber for ultra-high pulse dose rate measurement according to claim 1, characterized in that, A conductive metal sheet is fixedly disposed on the inner electrode plate, and the external signal line is connected to the inner electrode plate through the conductive metal sheet.

5. A flat-plate ionization chamber for ultra-high pulse dose rate measurement according to claim 1, characterized in that, The ratio of the thickness of the gas cavity formed between the high-pressure electrode and the collecting electrode to the width of the collecting electrode is 1:1.5.

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