A thin-film air ionization chamber for proton and heavy-ion position detection

Abstract

The present invention discloses a thin-film air ionization chamber for proton and heavy-ion position detection, which is characterized by comprising a parallel-plate ionization detector and a signal extraction structure; the top of the parallel-plate ionization detector is an incident window, and the bottom is an exit window. Between the incident window and the exit window are successively a first high-voltage electrode film, a readout electrode film, and a second high-voltage electrode film; the substrate of the readout electrode film is a polyimide film, and readout electrodes are plated on both its upper and lower surfaces; wherein, the substrates of the first and second high-voltage electrode films are polyimide films, and conductive films are plated on the surfaces facing the readout electrode film for accessing high-voltage electrical signals; two chambers are formed between the first and second high-voltage electrode films and the readout electrode film for ionizing incident particles; the signal extraction structure is connected to the two readout electrodes for outputting the signals generated by the two readout electrodes. The present invention can achieve large-area and high-position-accuracy particle beam detection.

Description

Technical Field

[0001] The present invention belongs to the fields of nuclear technology applications and ionizing particle detection, and relates to a thin-film air ionization chamber for proton and heavy ion position detection, which can be used in scientific research, radiation detection, especially in radiology. Background Art

[0002] Ionization chambers are a type of ionizing radiation detector that have been developed earlier and more perfectly, and are one of the basic technologies for radiation measurement. The basic working principle of an ionization chamber is that when an ionizing particle passes through a gas medium, ionization occurs, generating positively charged ions and negatively charged free electrons. When there is no external electric field, the positive ions and electrons will pair up again; while when there is an external electric field, the electrons and ions will move in opposite directions, generating an induced current on the electrodes, thus forming a signal. Ionization chambers have various shapes and gas components, and play a significant role in scientific research, radiation measurement, medicine and other fields.

[0003] In use, ionization chambers generally use gases with strong ionization and weak electronegativity to ensure that the signals of the ionization chambers are read out in the form of pulse signals. The main gas substances used in traditional ionization chambers are inert gases - such as argon, neon, xenon, etc. When using these gases, gas sealing measures need to be taken, which to a certain extent limits the use of ionization chambers. And using free air as the working gas has the following advantages: the properties of air are stable, and gas sealing is not required, which is beneficial to reducing costs and making the system simpler. However, free air has strong electronegativity, that is, it is easy to capture electrons to form negative ions, thus weakening the signal.

[0004] When high-energy particles pass through the chamber of the ionization chamber, ionization effects are generated and a series of secondary ionizations are triggered, thus forming a signal. Induced currents will be generated on the electrode planes on both sides during the movement of electrons and ions. When the ionization number is large, a signal will be formed on the electrode plate. The electrons generated when strongly ionizing particles interact with air particles or electrodes will trigger a shower. Although each free electron will quickly combine with air molecules, the signal can still be detected after amplification. Therefore, free air ionization chambers can be applied in high-dose situations such as radiation dose measurement and nuclear medicine.

[0005] The sensitive area of traditional free air ionization chambers is generally a relatively small closed cavity, with different sizes according to their sensitivity and radiation intensity requirements. Currently, free air ionization chambers have been widely used in dose detection. For example, various cylindrical free air ionization chambers for X-ray monitoring, etc. In recent years, with the research and development and promotion of proton and heavy ion therapy equipment, higher requirements have been put forward for the position detection accuracy of rays.

[0006] Protons and heavy ions have strong ionization ability, with extremely high energy loss in thick and heavy substances, and there will be a certain position shift. Typical ionization chambers use conductors as electrode materials, and common materials such as copper and aluminum will have a strong blocking effect on high-energy protons and heavy ions. In addition, for some electrodes, glass, plates, etc. with conductive coatings on the surface can be used. Although the atomic number is lower than that of typical metals, the interaction with particles is still relatively obvious. Summary of the Invention

[0007] Aiming at the technical problems existing in the prior art, the purpose of the present invention is to provide a thin-film air ionization chamber for proton and heavy ion position detection, which belongs to a large-area parallel plate ionization chamber with high position accuracy, and provides a powerful technical means for accurately measuring the positions of ionizing particle beams such as heavy ions and protons. The present invention is an integral part of a multi-disciplinary and systematic device. The three parts of the system include: a parallel plate ionization chamber detector, an ultra-multi-channel signal readout and processing system, and a supporting software system. Among them, the present invention relates to the parallel plate ionization chamber system in the system, including a large-area flat thin-film ionization chamber detector and a supporting signal extraction structure.

[0008] The technical solution of the present invention is as follows:

[0009] A thin-film air ionization chamber for proton and heavy ion position detection, characterized in that it includes a parallel plate ionization detector and a signal extraction structure; the top of the parallel plate ionization detector is an incident window, and the bottom is an exit window. Between the incident window and the exit window are successively a first high-voltage electrode film, a readout electrode film, and a second high-voltage electrode film; the substrate of the readout electrode film is a polyimide film, and readout electrodes are plated on both its upper and lower surfaces; wherein,

[0010] The substrate of the first high-voltage electrode film is a polyimide film, and a conductive film is plated on the surface facing the readout electrode film for accessing high-voltage electrical signals; a first chamber is formed between the upper surface of the first high-voltage electrode film and the readout electrode film for ionizing the particles incident through the incident window.

[0011] The substrate of the second high-voltage electrode film is a polyimide film, and a conductive film is plated on the surface facing the readout electrode film for accessing high-voltage electrical signals; a second chamber is formed between the lower surface of the readout electrode film and the second high-voltage electrode film for ionizing the incident particles passing through the readout electrode film.

[0012] The signal extraction structure is connected to the two readout electrodes for outputting the signals generated by the two readout electrodes.

[0013] Further, the readout electrodes are multiple electrode strips arranged in parallel, and the electrode strips on the upper surface of the readout electrode film are perpendicular to the electrode strips on the lower surface.

[0014] Further, the signal extraction structure includes a double-layer support frame and a needle row for clamping and connecting the readout electrodes; a plurality of through holes and readout strips are provided on one side frame of the double-layer support frame; holes are respectively machined at positions on the readout electrodes corresponding to the through holes on the side frame, a conductive unit is applied around each hole, and each conductive unit is respectively electrically connected to a pair of perpendicular electrode strips on the upper and lower surfaces of the readout electrode film; each needle in the needle row respectively passes through the through hole and the corresponding hole and is electrically connected to the conductive unit, and each readout strip is respectively electrically connected to one needle in the needle row for reading signals generated when the particle beam passes through the position corresponding to the electrode strip.

[0015] Further, the material of the double-layer support frame is PCB; the conductive unit is conductive adhesive, graphite layer or copper foil.

[0016] Further, the thickness of the polyimide film is less than or equal to 100 microns.

[0017] Further, a support frame is respectively arranged on the outer sides of the first high-voltage electrode film and the second high-voltage electrode film.

[0018] Further, the air gap widths of the first chamber and the second chamber are both 4 mm - 10 mm.

[0019] Further, the thicknesses of the incident window and the exit window are 100 - 900 microns.

[0020] Further, the conductive film is a copper thin film or an aluminum thin film.

[0021] The advantages of the present invention are as follows:

[0022] Traditional detectors often use materials such as metals to form electrode materials. The presence of relatively large metal components will cause energy shift and energy attenuation of particles. In order to reduce the influence of the constituent materials of the detector on the particle beam and achieve high-position-accuracy detection of the particle beam, the present invention proposes a thin, large-area, radiation-resistant ionization detector with two-dimensional position resolution ability for proton and heavy particle beams.

[0023] For example, for a typical GeV-energy proton beam or heavy ion beam, its penetration depth in metal is generally at the centimeter level. If a metal window or electrode is used, it generally has a thickness of more than millimeters, which will cause attenuation of the ray energy. In the present invention, the electrode films all use materials with a thickness of less than one hundred microns, so there is almost no influence on the energy and distribution of the particle beam; the electrodes on the surface of the electrode film are plating layers or printing layers, and the thickness is even smaller.

[0024] This system uses dry air as the signal layer and does not require the replacement of gas with an inert gas mixture like traditional detectors. Therefore, this system is easy to operate, without the need for an additional gas system, which is conducive to combining with other devices. Brief Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the ionization chamber structure of the present invention.

[0026] Figure 2 It is a schematic diagram of the structure of the double-sided readout electrode of the present invention.

[0027] Figure 3 It is a schematic diagram of the signal extraction structure.

[0028] Reference Signs: 1 - High-voltage electrode film, 2 - Readout electrode film, 3 - Incident window, 4 - High-voltage ionization region, 5 - Exit window, 6 - Readout electrode film or electrode strip, 7 - Support frame, 8 - Contact piece, 9 - Pin header, 10 - Pad. Detailed Description of the Invention

[0029] The present invention will be further described in detail below with reference to the drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0030] The core component of the present invention is two chambers isolated by three layers of electrode films. As Figure 1 shown, the core components of the ionization chamber are three parallel electrode films. The two on the sides are high-voltage electrodes, and the middle one is the readout electrode. The electrode film is square, with a width of 10 - 100 cm to meet various actual detection requirements. Between the high-voltage electrode and the readout electrode, there is a high-voltage ionization region, and the air gap width is between 4 mm and 10 mm. In this interval, the electric field can be ensured to be uniform and the signal to be stable. On the outside of the core part of the ionization chamber, incident and exit windows are made of radiation-resistant materials with a thickness of several hundred micrometers, which play a role in isolating the internal air from the external air.

[0031] The base material of the electrode film is a polyimide film. The thickness of the film needs to be selected to be less than or equal to 100 micrometers according to actual requirements such as hardness. A layer of conductive metal, such as copper or aluminum, is plated on the surface of the film. The high-voltage electrode film 1 uses a large-area coating process, and high voltage is connected to the coating on the surface to form a complete high-voltage plane.

[0032] Both sides of the readout electrode film 2 need to be plated with multiple parallel conductive metal strips, and the conductive metal strips on the upper surface are perpendicular to those on the lower surface. With such a design, ionization occurring at any position can be received only by the electrode strips at this position. By reading the signals from both sides of the detector, the position where the ionization particle beam passes can be determined through the position of the signals.

[0033] The readout electrode film 2 can be fabricated with parallel-distributed electrode readout strips using flexible PCB technology, micro-etching grooves or micro-printing processes, as shown in Figure 2 . The inventors have successfully realized the process and production of the copper readout strip electrode film and have completed the electrical connection. Subsequently, electrode films made of materials such as aluminum will also be developed. The electrode film is an effective guarantee for the ultimate realization of the design of this ionization chamber.

[0034] Different from the readout electrode film 2, the high-voltage electrode film 1 can adopt a whole-surface conductive film. The high-voltage electrode film 1 requires a conductive layer on the side facing the readout electrode film 2, while the other side has no requirements. The manufacturing process of the high-voltage electrode film 1 can be shared with the readout electrode film 2.

[0035] To support the electrodes, a square support frame is designed on the outside of the high-voltage electrode film 1 to make it flat. The fixing method of this support frame to the electrode film can adopt mechanical crimping, mechanical stretching, or a combination with adhesive. The frame needs to have high strength and be non-conductive. In summary, various rigid plastics and plates, etc., can be considered for the frame, or PCB materials can be used for manufacturing.

[0036] On the basis of fixing the electrodes, signal extraction is required. Considering the need for signal extraction, PCB should be used as the external frame. For the readout electrode extraction, pads or holes for connecting to the electrode strips are fabricated on the PCB, with one end in contact with the electrode strip and the other end led out to a standard interface, such as a 2.54 mm connector, etc. Then, a dedicated connector cable is made to lead the signal from the standard interface to the detector housing. The detector housing is made of hard plastic or aluminum alloy, and the two surfaces for particle incidence and exit also adopt thin plates or plastics with low blocking performance, and at the same time need to have a certain hardness to play a basic protection role.

[0037] Considering the above requirements, the present invention designs a feasible signal extraction structure, as shown in Figure 3 . The frame of the signal extraction structure uses PCB material, and through-holes and readout strips are designed at specific positions. At the positions corresponding to the welding holes on the two PCB boards, a hole is also machined on the electrode film, and a conductive adhesive, graphite layer or copper foil is applied around the hole. Then, a pin is passed through the two PCBs and the intermediate film, and the pin is welded at this position. Thus, the signal on the readout electrode can reach the outer pads of the PCB frame through the conductive adhesive and the pin, and finally the readout is completed through the connector on the PCB. Each electrode strip is equipped with a readout hole for reading the signal when the particle beam passes through here. Note that both sides of the pin are welded, so signals can be read from both sides of the pin. During use, only one side is read, and corresponding protection needs to be taken on the other side.

[0038] For the high-voltage electrode films 1 on both sides, a similar method can also be used to connect them to high voltage. The two high-voltage electrode films can be connected to positive high voltage respectively, or to negative high voltage respectively, or one to positive and the other to negative. There is no difference in use, only a difference in signal polarity.

[0039] The above is the parallel plate ionization detector invented by us. There is also a high-voltage power supply system and a multi-channel electronics readout system outside the detector, thus forming a two-dimensional flat panel detector for detecting the position of the beam. The present invention can fill the gaps in the relevant domestic fields and provide a simple, stable and accurate positioning tool for the scientific research and application of heavy ion and proton beams.

[0040] Although specific embodiments of the present invention are disclosed for illustrative purposes, which are intended to help understand the content of the present invention and implement it accordingly, those skilled in the art can understand that: without departing from the spirit and scope of the present invention and the appended claims, various substitutions, changes and modifications are possible. Therefore, the present invention should not be limited to the content disclosed in the best embodiments, and the scope of protection claimed by the present invention shall be defined by the scope of the claims.

Claims

1. A thin-film air ionization chamber for proton and heavy ion position detection, characterized in that, It includes a parallel plate ionization detector and a signal extraction structure; the top of the parallel plate ionization detector is an incident window, and the bottom is an exit window. Between the incident window and the exit window are, in sequence, a first high-voltage electrode film, a readout electrode film, and a second high-voltage electrode film; the substrate of the readout electrode film is a polyimide film, and readout electrodes are plated on both its upper and lower surfaces; the readout electrodes are a plurality of electrode strips arranged in parallel, and the electrode strips on the upper surface of the readout electrode film are perpendicular to the electrode strips on the lower surface; among them, the substrate of the first high-voltage electrode film is a polyimide film, and a conductive film is plated on the surface facing the readout electrode film for accessing high-voltage electrical signals; a first chamber is formed between the first high-voltage electrode film and the upper surface of the readout electrode film for ionizing the particles incident through the incident window; the substrate of the second high-voltage electrode film is a polyimide film, and a conductive film is plated on the surface facing the readout electrode film for accessing high-voltage electrical signals; a second chamber is formed between the lower surface of the readout electrode film and the second high-voltage electrode film for ionizing the incident particles passing through the readout electrode film; the signal extraction structure is connected to the two readout electrodes for outputting the signals generated by the two readout electrodes; the signal extraction structure includes a double-layer support frame and pin headers for clamping and connecting the readout electrodes; a plurality of through holes and readout strips are provided on one side frame of the double-layer support frame; holes are respectively machined at positions on the readout electrodes corresponding to the through holes on the frame, and conductive units are applied around each hole, and each conductive unit is electrically connected to a pair of perpendicular electrode strips on the upper and lower surfaces of the readout electrode film respectively; each pin in the pin headers passes through the through hole and the corresponding hole and is electrically connected to the conductive unit, and each readout strip is electrically connected to one pin in the pin headers for reading the signals generated at the positions where the particle beam passes through the corresponding electrode strips.

2. The thin-film air ionization chamber according to claim 1, characterized in that, The material of the double-layer support frame is PCB; the conductive unit is conductive adhesive, graphite layer or copper foil.

3. The thin-film air ionization chamber according to claim 1, characterized in that, The thickness of the polyimide film is less than or equal to 100 microns.

4. The thin-film air ionization chamber according to any one of claims 1 to 3, characterized in that, A support frame is respectively provided outside the first high-voltage electrode film and the second high-voltage electrode film.

5. The thin-film air ionization chamber according to any one of claims 1 to 3, characterized in that, The air gap widths of the first chamber and the second chamber are both 4 mm - 10 mm.

6. The thin-film air ionization chamber according to any one of claims 1 to 3, characterized in that, The thicknesses of the incident window and the exit window are 100 - 900 microns.

7. The thin-film air ionization chamber according to any one of claims 1 to 3, characterized in that, The conductive film is copper thin film or aluminum thin film.

Images