A shielding structure for use in small linear accelerators

Abstract

This invention belongs to the field of radiation shielding technology and discloses a shielding structure for a small linear accelerator. The shielding structure includes an upper shield and a lower shield, with the upper shield surrounding the accelerator. The lower shield has an internal cavity for placing the object to be irradiated. The outer wall thickness varies in different local areas of the shielding structure. This invention ensures effective shielding while conserving shielding material.

Description

Technical Field

[0001] This invention belongs to the field of radiation shielding technology, and particularly relates to a shielding structure for use in small linear accelerators. Background Technology

[0002] The accelerator has an energy range of 0.5 MeV to 3.5 MeV and a power range of 0.5 kW to 3 kW. Considering that the electron beam generated by the accelerator will produce X-rays, and that X-rays have strong penetrating power, heavy metal materials must be installed for shielding on both sides of the internal space and in any area that X-rays can directly penetrate. Conventional accelerator shielding structures are mostly made of concrete, which occupies a large area; once built, they are difficult to move, let alone move together with the accelerator. If the accelerator is removed, the shielding structure cannot be reused. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, this invention provides a shielding structure for small linear accelerators. By optimizing the material and outer wall thickness of the shielding structure, it can be made smaller and lighter while maintaining the shielding effect, making transportation possible.

[0004] To achieve the above objectives, one or more embodiments of the present invention provide a shielding structure for a small linear accelerator, the shielding structure comprising an upper shield and a lower shield, the upper shield surrounding the accelerator; the lower shield having an internal cavity for placing an object to be irradiated; and the outer wall thickness of different local areas in the shielding structure being different.

[0005] In some embodiments, the material of the shielding structure is lead, lead-antimony, or a lead alloy.

[0006] In some embodiments, the accelerator includes an electron gun, an accelerating tube, a bellows, and a scanning box arranged from top to bottom, with a waveguide provided on one side of the accelerating tube.

[0007] In some embodiments, the method for optimizing the thickness of the outer wall of the shielding structure is as follows:

[0008] The analysis space is defined with the shielding structure as the center.

[0009] Set the X-ray energy value and mark the point with the highest irradiation dose as the X-ray source point;

[0010] The initial thickness of the shielding structure is set, and the radiation dose rate received on the boundary of the analysis space under the initial thickness is calculated.

[0011] Based on the radiation dose rate threshold set for the analysis space boundary, the thickness of the shielding structure is optimized to ensure that the radiation dose rate threshold is met when the radiation source point reaches the analysis space boundary.

[0012] In some embodiments, the upper shielding body includes a shielding body body, the inner cavity shape of which is adapted to the accelerator; a first shielding block is added to the upper surface of the shielding body body at the position corresponding to the electron gun of the accelerator; a second shielding block is added to the outer surface of one side wall of the shielding body body at the position corresponding to the waveguide, and a third shielding block is added at the position corresponding to the titanium pump.

[0013] In some embodiments, the lower shield includes a side shield and a bottom shield, and the upper surface of the bottom shield is provided with a shielding block for placing the object to be irradiated.

[0014] In some embodiments, the shielding block comprises multiple shielding plates of the same shape but different sizes stacked together, with the largest shielding plate in contact with the bottom shielding body, and the topmost shielding plate used to place the object to be irradiated.

[0015] In some embodiments, at least one side of the lower shield is configured as a shielding door.

[0016] In some embodiments, the top two sides of the shielding door are provided with guide holes, and a horizontal guide rail is provided through the guide holes. The upper surface of the horizontal guide rail is a rack, and column supports are provided on both sides of the horizontal guide rail, respectively located on both sides of the shielding door. The upper surface of the guide hole is open, and a gear that meshes with the rack is provided in the opening. The central axis of the gear is connected to an operating handle, and the operating handle can drive the gear to rotate in the opening.

[0017] In some embodiments, the object to be irradiated is a water box, which is used to store the water to be irradiated, and the upper surface of the water box is provided with a radiation receiving area.

[0018] In some embodiments, one side of the lower shield is provided with an inlet and an outlet for installing the water inlet and outlet pipes of the water box.

[0019] By optimizing the materials and outer wall thickness of the shielding structure, it is possible to make the shielding structure smaller and lighter while ensuring the shielding effect, thus making transportation possible. Attached Figure Description

[0020] The dimensions and scales in the accompanying drawings do not represent the actual dimensions and scales of the product. The drawings are for illustrative purposes only, and some non-essential elements or features have been omitted for clarity.

[0021] Figure 1 This is a schematic diagram of the overall irradiation shielding structure in an embodiment of the present invention;

[0022] Figure 2This is a schematic diagram of the internal structure of the irradiation shielding structure in an embodiment of the present invention;

[0023] Figure 3 This is a schematic diagram of the internal structure of the irradiation shielding structure in an embodiment of the present invention from another perspective;

[0024] Figure 4 This is a top view of the irradiation shielding structure in an embodiment of the present invention;

[0025] Figure 5 This is a three-dimensional rendering of the overall irradiation shielding structure in an embodiment of the present invention;

[0026] Figure 6 This is a schematic diagram illustrating the principle of optimizing the outer wall thickness of the irradiation shielding structure in an embodiment of the present invention.

[0027] In the diagram, 1. Upper shield, 2. Lower shield, 3. Accelerator, 4. Inlet, 5. Outlet, 1-1. First shielding block, 1-2. Second shielding block, 1-3. Third shielding block, 2-1. Bottom shield, 2-2. T-stage shielding block, 3-1. Electron gun, 3-2. Accelerator tube, 3-3. Corrugated tube, 3-4. Waveguide window, 3-5. Waveguide, 3-6. Scanning magnet, 3-7. Titanium pump, 3-8. Scanning box, 6. Shielding door, 7. Horizontal guide rail, 8. Column support, 9. Rack, 10. Gear, 11. Operating handle, 12. Water box. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] In this invention, terms such as "upper," "lower," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are merely relational terms determined for the convenience of describing the structural relationship of the various components or elements of this invention, and do not specifically refer to any component or element in this invention, and should not be construed as limiting this invention.

[0032] In this invention, terms such as "connection" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of the above terms in this invention based on the specific circumstances, and they should not be construed as limitations on this invention.

[0033] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0034] One or more embodiments of the present invention provide a shielding structure for use in a small linear accelerator 3, such as Figures 1-5 As shown, the shielding structure includes an upper shield 1 and a lower shield 2. The upper shield 1 is arranged to surround the accelerator 3. The lower shield 2 has an internal cavity for placing the object to be irradiated.

[0035] As an example, such as Figure 3 As shown, the object to be irradiated is a water box 12, which is used to store the water to be irradiated. The upper surface of the water box 12 is provided with a radiation receiving area. One side of the lower shield 2 is provided with a water inlet 4 and a water outlet 5, which are used to install the water inlet pipe and the water outlet pipe of the water box 12.

[0036] The shielding structure is made of at least one of lead, lead-antimony, and lead alloys. X-rays with a nominal energy of 3 MeV attenuate by 1 / 10 in lead material every 40 cm. Therefore, a dose attenuation of seven orders of magnitude requires at least 28 cm of lead, lead-antimony, or lead alloy material. If shielding material of this thickness is installed along all X-ray radiation directions, the overall weight will reach 50–160 tons. Considering the varying shielding thickness from the source to different angles in space, some angles will be superimposed due to different channels, and others will increase after dividing by the cosine of the included angle. Therefore, the shielding thickness at many locations can be reduced accordingly. Based on this, in some embodiments, the shielding structure is divided into zones, with different outer wall thicknesses in each local area.

[0037] As a specific implementation method, such as Figure 6 As shown, with the shielding structure as the center, the analysis space range (e.g., the space within 3 meters of the irradiation area) is set; the X-ray energy value is set, and the point with the largest irradiation dose is recorded as the radiation source point; the initial thickness of the shielding structure is set, and the irradiation dose rate received on the boundary of the analysis space under the initial thickness is calculated; according to the irradiation dose rate threshold set for the boundary of the analysis space, the thickness of the shielding structure is optimized to ensure that the irradiation dose rate threshold is met when the radiation source point reaches the boundary of the analysis space. Figure 6 Middle ①- As an example of a sample point for calculating the radiation dose rate at the boundary of the analysis space, if the radiation dose rate at a certain point on the analysis boundary is greater than the set radiation dose rate threshold, the thickness of the outer wall along the path from the radiation source point to that point can be appropriately reduced. Conversely, if the radiation dose rate at a certain point on the analysis boundary is less than the set radiation dose rate threshold, the thickness of the outer wall along the path from the radiation source point to that point needs to be increased. As an example, the radiation dose at the exit of the accelerator tube 3-2 is the highest, followed by the high-dose radiation reaching the radiation receiving area at the top of the water box 12, where the X-rays are reflected. Therefore, the exit of the accelerator tube 3-2 and the radiation receiving area at the top of the water box 12 are used as radiation source points. The top, side, and bottom radiation dose rates of the analysis space are set, for example, to 100 μSv / h, 2.5 μSv / h, and 5 mSv / h, respectively. After structural optimization, the overall weight of the shielding body is between 12 and 28 tons, showing a significant reduction and meeting transportation requirements. To facilitate the fabrication of the shielding structure, in some embodiments, the outer wall thickness of the shielding structure is optimized by partitioning based on the radiation dose rate received at the analysis boundary. The shielding structures corresponding to adjacent samples with similar radiation dose rates are also located in similar areas. Therefore, a cross-overlapping design is adopted. Adjacent shielding structure areas with similar required thicknesses use a single shielding block, which reduces the fabrication difficulty. This not only reduces the overall quality of the self-shielding but also achieves effective shielding, ensuring that the environmental radiation dose outside the self-shielding body meets the requirements of domestic and international radiation protection standards, thus protecting the safety of the environment and personnel.

[0038] As an example, the accelerator 3 includes, from top to bottom, an electron gun 3-1, an accelerating tube 3-2, a bellows 3-3, and a scanning box 3-8. The scanning box 3-8 is externally surrounded by a scanning magnet 3-6. The upper shield 1 and the lower shield 2 are bounded by the scanning box 3-8 of the accelerator 3. The electron gun 3-1 is a device that generates electrons; when a high voltage is applied, the electrons are accelerated and injected into the accelerating tube 3-2. A waveguide 3-5 is provided on one side of the accelerating tube 3-2, and a waveguide window 3-4 is provided at the connection between the accelerating tube 3-2 and the waveguide 3-5. The waveguide 3-5 is used to transmit microwave power, which is fed into the accelerating tube 3-2 through the waveguide window 3-4. The accelerating tube 3-2 is a resonant cavity array for accelerating electrons, which can establish an alternating accelerating electric field to continuously accelerate electrons. The bellows 3-3 is a component connecting the accelerating tube 3-2 and the scanning box 3-8, and is an important channel for electron beam drift, which has the function of solving thermal expansion problems and adjusting accumulated errors during equipment installation. The scanning box 3-8 is used to provide the vacuum space required for the formation of the fan-shaped electron beam. The lower surface of the scanning box 3-8 is provided with a titanium window (50 micrometers thick), which can ensure the vacuum while allowing electrons to pass through smoothly. A titanium pump 3-7 is located on one side of the scanning box 3-8 to maintain the vacuum inside the accelerating tube 3-2 and the scanning box 3-8. Under the control of the triangular wave current, the scanning magnet 3-6 generates an alternating magnetic field, which deflects the electrons and forms a fan-shaped electron beam.

[0039] Specifically, the scanning box 3-8 is an internal ion pump type scanning box 3-8 (see patent document CN1207729C for specific structure). By directly integrating the vacuum system on the scanning box 3-8, the flow resistance loss of the vacuum system can be reduced, resulting in high efficiency, high pumping speed, small size, regular shape, and easy radiation protection shielding, providing a basis for the overall miniaturization of the shielding body.

[0040] Furthermore, by placing the scanning magnet 3-6 outside the scanning box 3-8, the scanning and beam uniformity are improved, resulting in a beam non-uniformity of less than ±5% after scanning. The scanning magnet coil is an inductive load, and the voltage waveform of the coil power supply is a square wave. This allows us to obtain the current waveform of the scanning magnet 3-6 coil and the magnetic field distribution of the scanning magnet 3-6, further improving scanning uniformity.

[0041] As a specific implementation method, such as Figure 3 and Figure 5As shown, the upper shield 1 includes a shield body. The shape of the inner cavity of the shield body is adapted to the accelerator 3. For example, the inner cavity corresponding to the top of the electron gun 3-1 has a groove, and the inner cavity corresponding to the transverse waveguide 3-5 also has a groove. Furthermore, the initial outer wall thickness meets a certain threshold. The overall shape of the upper shield 1 is similar to that of the accelerator 3. The cross-sectional area is smallest in the height range corresponding to the electron gun 3-1, and the cross-sectional area increases sequentially in the height ranges corresponding to the accelerating tube 3-2 and the bellows 3-3, and the scanning box 3-8. A first shielding block 1-1 is added to the upper surface of the shield body at the position corresponding to the electron gun 3-1 of the accelerator 3. A second shielding block 1-2 is added to the outer surface of one side wall of the shield body at the position corresponding to the waveguide 3-5, and a third shielding block 1-3 is added to the outer surface corresponding to the titanium pump 3-7, i.e., the position from the outlet of the accelerating tube 3-2 to the scanning magnet 3-6. For example, the waveguide 3-5, connecting pipes, ventilation pipes, etc., can be embedded in the upper shield 1 by pre-embedding pipes.

[0042] like Figure 2 and Figure 3 As shown, the lower shield 2 includes a side shield and a bottom shield 2-1. The upper surface of the bottom shield 2-1 is provided with a T-shaped shield block 2-2. The T-shaped shield block 2-2 includes multiple flat shield plates of the same shape but different sizes. The multiple shield plates are stacked in descending order of size at the center of the upper surface of the bottom shield 2-1, and the largest shield plate is in contact with the bottom shield 2-1. The uppermost shield plate is used to place the object to be irradiated.

[0043] The aforementioned shielding blocks and shielding plates represent a specific implementation of optimizing the outer wall thickness of the shielding structure. This ensures that, regardless of its location outside accelerator 3, the radiation dose rate remains below the target radiation source at a certain distance. This structural optimization makes mobile transportation possible.

[0044] To facilitate the placement of the object to be irradiated, at least one side of the lower shield 2 is configured as a shielding door 6. As an example, the top two sides of the shielding door 6 are provided with guide holes, and a horizontal guide rail 7 runs through the guide holes. Column supports 8 are provided on both sides of the horizontal guide rail 7, respectively located on both sides of the shielding door 6. A rack 9 is provided on the upper surface of the horizontal guide rail 7. The upper surface of the guide holes is open, and a gear 10 meshes with the rack 9 within the opening. The central axis of the gear 10 is connected to an operating handle 11, which drives the gear 10 to rotate within the opening. A roller guide mechanism is provided between the bottom of the shielding door 6 and the bottom shield 2-1 to support the shielding door 6. Therefore, the shielding door 6 can be opened or closed under the control of the operating handle 11. In some embodiments, two opposite sides of the lower shield 2 are configured as shielding doors 6.

[0045] The scope of protection of this invention is defined only by the claims. Thanks to the teachings of this invention, those skilled in the art will readily recognize that alternative structures to the structures disclosed herein can be used as feasible alternative implementations, and that the implementations disclosed herein can be combined to produce new implementations, which also fall within the scope of the appended claims.

Claims

1. A shielding structure for use in a small linear accelerator, characterized in that, The shielding structure includes an upper shield and a lower shield. The upper shield surrounds the accelerator. The lower shield has an internal cavity for placing the object to be irradiated. The outer wall thickness varies in different local areas of the shielding structure. The upper shielding body includes a shielding body main body, the inner cavity shape of which is adapted to the accelerator; a first shielding block is added to the upper surface of the shielding body main body at the position corresponding to the electron gun of the accelerator; a second shielding block is added to the outer surface of one side wall of the shielding body main body at the position corresponding to the waveguide, and a third shielding block is added at the position corresponding to the titanium pump. The lower shield includes a side shield and a bottom shield. The upper surface of the bottom shield is provided with a shielding block for placing the object to be irradiated. The shielding block comprises multiple shielding plates of the same shape but different sizes stacked together, with the largest shielding plate in contact with the bottom shielding body, and the topmost shielding plate used to place the object to be irradiated. At least one side of the lower shield is configured as a shielding door; the top two sides of the shielding door are provided with guide holes, and a horizontal guide rail is provided through the guide holes. The upper surface of the horizontal guide rail is a rack, and column supports are provided on both sides of the horizontal guide rail, respectively located on both sides of the shielding door; the upper surface of the guide hole is open, and a gear that meshes with the rack is provided in the opening. The central axis of the gear is connected to an operating handle, and the operating handle can drive the gear to rotate in the opening.

2. The shielding structure for a small linear accelerator as described in claim 1, characterized in that, The material of the shielding structure is lead, lead-antimony, or lead alloy.

3. The shielding structure for a small linear accelerator as described in claim 2, characterized in that, The accelerator includes an electron gun, an accelerating tube, a bellows, and a scanning box arranged from top to bottom, with a waveguide on one side of the accelerating tube.

4. The shielding structure for a small linear accelerator as described in claim 3, characterized in that, The method for optimizing the thickness of the outer wall of the shielding structure is as follows: The analysis space is defined with the shielding structure as the center. Set the X-ray energy value and mark the point with the highest irradiation dose as the X-ray source point; The initial thickness of the shielding structure is set, and the radiation dose rate received at the boundary of the analysis space under the initial thickness is calculated. Based on the radiation dose rate threshold set for the analysis space boundary, the thickness of the shielding structure is optimized to ensure that the radiation dose rate threshold is met when the radiation source point reaches the analysis space boundary.

5. The shielding structure for a small linear accelerator as described in claim 1, characterized in that, The object to be irradiated is a water box, which is used to store the water to be irradiated. The upper surface of the water box is provided with a radiation receiving area. One side of the lower shield is provided with a water inlet and a water outlet for setting up the water inlet pipe and water outlet pipe of the water box.

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