Chopping wheel and back scattering imaging device

Abstract

The invention provides a chopper wheel and a back scattering imaging device, the chopper wheel comprises a first surface and a second surface which are opposite to each other, the chopper wheel is provided with at least one slit, and the width d2 of the slit on the second surface is greater than the width d1 of the slit on the first surface; the slit comprises a first part and a second part, an opening of the first part is rectangular, and an opening of the second part is isosceles trapezoid. According to the invention, the slit in the shape of the isosceles trapezoid is arranged in the thickness direction of the chopper wheel, so that the problem of non-uniform X-ray emission along with the change of the rotation angle of the chopper wheel is solved to a certain extent, the intensity of an optical signal detected by a detector is more uniform, and the imaging quality of the back scattering device is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of backscatter imaging, and in particular to a chopper wheel and a backscatter imaging device. Background Art

[0002] An X-ray backscatter imager is a non-contact detection instrument based on Compton backscattering. It uses the Compton scattering effect between X-rays and the extranuclear electrons of the target object to generate backscattered X-ray signals for imaging, thereby obtaining information on the electron density distribution in the shallow layers of the target object. Handheld backscatter imagers are attracting attention in the security inspection field due to their small size, ease of operation, fast detection speed, non-contact nature, and the ability to be placed on the same side of the target object.

[0003] The chopper is the core component of a backscatter imager. Chopper structures can generally be categorized as disc-shaped, cylindrical, or flying ring-shaped. Choppers are typically made of metal with a high X-ray absorption rate. In handheld backscatter imager systems, a disc-shaped chopper structure is generally preferred. Centripetal slits are typically uniformly and angularly arranged on the disc structure. The X-ray beam emitted by the X-ray machine is a cone-shaped beam, which first passes through a pre-collimator and then forms a fan-shaped beam that irradiates the chopper disc. Except for the intersection with the slit, where X-rays are transmitted, all other fan-shaped X-ray beams are absorbed by the chopper disc. Driven by the chopper motor, the slit and the fan-shaped collimating slit of the radiation source form an intersection that moves up and down. Rays emerge from this intersection to form a flying-point beam that scans up and down. Simultaneously, the object moves left and right, thereby enabling scanning of different locations of the target.

[0004] In order to achieve a better shielding effect, the chopper disk requires a certain thickness. Therefore, if the slit is designed as a standard centripetal rectangle, the cross-section of the beam will be greatly affected by the rotation angle of the chopper disk during the rotation scanning process of the chopper disk. The formed X-ray spot will shrink and deform as the rotation angle increases, resulting in uneven distribution of signal intensity at different positions in the obtained backscattered image, causing the imaging quality of the backscattered scanning image to deteriorate. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the present invention provides a chopper wheel and a backscatter imaging device. The chopper wheel comprises a first surface and a second surface facing each other, and at least one slit is provided on the chopper wheel. The width d2 of the slit on the second surface is greater than the width d1 of the slit on the first surface. The slit comprises a first portion and a second portion, with the opening of the first portion being rectangular and the opening of the second portion being an isosceles trapezoid. By providing the isosceles trapezoidal slit in the thickness direction of the chopper wheel, the present invention, to a certain extent, solves the problem of uneven X-ray emission as the chopper wheel rotates at different angles. This makes the intensity of the light signal detected by the detector more uniform, thereby improving the imaging quality of the backscatter imaging device.

[0006] To achieve the above-mentioned and other related objectives, the present invention provides a chopper wheel, comprising a first surface and a second surface opposite to each other, wherein the chopper wheel is provided with at least one slit, wherein a width d2 of the slit on the second surface is greater than a width d1 of the slit on the first surface; the slit comprises a first portion and a second portion, wherein the first portion is connected to the first surface, and the second portion is connected to the second surface, and in the thickness direction of the chopper wheel, the opening shape of the first portion is a rectangle, and the opening shape of the second portion is an isosceles trapezoid.

[0007] Optionally, the chopper wheel is provided with N slits, and the N slits are distributed at equal angles on the chopper wheel, where N is an integer greater than or equal to 2.

[0008] Optionally, the width d1 of the slit on the first surface is between 0.3 mm and 0.4 mm.

[0009] Optionally, the width d2 of the slit on the second surface is between 0.3 mm and 0.4 mm.

[0010] Optionally, the thickness of the first portion is between 1 mm and 1.2 mm.

[0011] Optionally, the thickness of the chopping wheel is between 2.4 mm and 3 mm.

[0012] The present invention further provides a backscatter imaging device, which comprises:

[0013] A light source, wherein the light beam emitted by the light source is a cone-shaped light beam;

[0014] A sector collimator, wherein a collimating diaphragm is provided on the sector collimator, and the cone-shaped light beam is emitted as a fan-shaped light beam after passing through the collimating diaphragm, and the optical axis of the sector collimator is coaxial with the optical axis of the light source;

[0015] A chopper wheel, wherein the chopper wheel is the chopper wheel according to any one of claims 1 to 6, wherein the fan-shaped light beam is emitted as a flying spot light beam after passing through the slit;

[0016] The flying spot light beam is irradiated onto the surface to be detected and then scattered to form scattered light which enters the detector.

[0017] Optionally, the first surface of the chopper wheel faces the sector collimator, and the second surface of the chopper wheel faces the detector.

[0018] Optionally, the distance between the light source and the chopper wheel is between 20 mm and 35 mm.

[0019] Optionally, the distance between the light source and the surface to be detected is between 90 mm and 110 mm.

[0020] The chopper wheel and backscatter device provided by the present invention have at least the following beneficial effects:

[0021] The present invention provides an isosceles trapezoidal slit in the thickness direction of the chopper wheel, thereby solving to a certain extent the problem of uneven X-ray emission as the rotation angle of the chopper wheel changes, making the intensity of the light signal detected by the detector more uniform, and improving the imaging quality of the backscatter device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The backscatter imaging device provided in the second embodiment is shown.

[0023] Figures 2a-2b It shows the slit structure form in the prior art.

[0024] Figure 3 Shown is a schematic structural diagram of the slits on the chopper wheel provided in Example 1.

[0025] Figure 4a Shown is a curve showing the change of the X-ray spot size with the chopper wheel rotation angle for different slit structures in Example 1.

[0026] Figure 4b Shown are the signal intensity distribution curves of different slit structures in Example 1.

[0027] Component number description

[0028] 100 light sources

[0029] 200 Sector Collimator

[0030] 300 Chopping Wheel

[0031] 400 detectors

[0032] 500 Surfaces to be tested

[0033] 301 Chopping Wheel Side 1

[0034] 302 The second side of the chopping wheel

[0035] 30 Slit

[0036] 31 The first part of the slit

[0037] 32 The second part of the slit DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] It should be noted that the illustrations provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Although the illustrations only show components related to the present invention and are not drawn according to the number, shape and size of components in actual implementation, the form, quantity, positional relationship and proportion of each component in actual implementation can be changed at will under the premise of realizing the technical solution of this party, and the component layout form may also be more complicated.

[0040] Example 1

[0041] like Figure 1 As shown, a backscatter imaging device generally consists of a light source 100, a sector collimator 200, a chopper wheel 300, and a detector 400. The light source 100 is an X-ray source, which can be regarded as a point light source, and its emission angle is less than 180°, so the X-ray beam it emits is a cone-shaped beam; the center of the collimating aperture (not shown in the figure) provided in the sector collimator 200 is located on the optical axis, and the opening of the collimating aperture is perpendicular to the incident surface of the cone-shaped beam. The collimating aperture blocks a portion of the incident cone-shaped beam, and the output is a fan-shaped beam; the fan-shaped beam emitted by the collimating aperture is incident on the chopper wheel 300, that is, on the slit (not shown in the figure), but only a part of the slit can overlap with the fan-shaped beam, and the rest will be blocked. As an example, the part where the fan-shaped beam overlaps with the slit is defined as the beam incident area.

[0042] Since the chopper wheel 300 is in a rotating state when working, it drives the slit to rotate. When the slit is at different rotation angles θ, the position where it overlaps with the incident light beam is different, that is, the position of the light beam incident area is different; and the incident light beam is a fan-shaped light beam, and the outgoing light beam will appear as a flying spot light beam, wherein the light beam exit area S of the flying spot light beam is θ There will be a periodic change pattern (the beam exit area S θ The periodic change of the slit corresponds to the periodic change of the rotation angle θ). The rotation angle when the central axis of the slit passes through the optical axis of the fan beam is defined as 0°, and the limit angle at which the slit can overlap with the incident beam is defined as the maximum rotation angle ±θ max , when the slit is a long rectangular shape and satisfies -θ max ≤θ≤+θ max When the absolute value of the rotation angle θ is larger, the beam exit area S of the flying spot beam is larger.θ The smaller.

[0043] Figures 2a-2b Two different slit structures in the prior art are shown, both of which adopt a vertical section opening method.

[0044] Figure 2a The aperture method sets a long strip slit of appropriate width according to the designed spot size. However, during the imaging scanning process, as the chopper wheel 300 rotates, this structure takes the slit and the fan-shaped beam as the zero angle when it is perpendicular to the fan-shaped beam. When the slit deviates from the center of the fan-shaped beam by about ±20°, the fan-shaped beam will be completely blocked, resulting in a reduction in the actual scanning range and a significant reduction in the imaging range.

[0045] Figure 2b The structure shown in Figure 2a Based on the structure shown above, an improvement has been made by increasing the width of the slit on the outer diameter of the chopper wheel 300. This solves the problem of the fan-shaped beam being completely blocked when the slit deviates from the center of the fan-shaped beam, thereby increasing the scanning range. However, this slit structure will cause the light spot irradiated on the object to be measured to be unstable during the scanning process. This is specifically manifested in two aspects. First, when the slit leaves the center of the fan-shaped beam, the luminous flux of the light spot will undergo a sudden change, which will lead to a sudden change in the brightness of the image, which is difficult to completely repair during later correction. Second, as the chopper wheel rotates to the edge, the shape of the light spot gradually deforms, gradually becoming longer and narrower from a square. This causes the image resolution to gradually deteriorate, and this phenomenon cannot be corrected by later signal processing methods.

[0046] This embodiment provides a chopper wheel, such as Figure 1 As shown, the chopper wheel 300 includes a first surface 301 and a second surface 302 that are opposed to each other. During use, the first surface 301 faces the sector collimator 200, and the second surface 302 faces the detector 400. The chopper wheel 300 is provided with at least one slit 30, which may be one or more slits. When the number of slits 30 is two or more, each slit 30 is equally spaced. In this embodiment, the chopper wheel 300 is provided with four slits 30, and the angles between adjacent slits 30 are 90°.

[0047] like Figure 3As shown, the slit 30 includes a first portion 31 and a second portion 32. The first portion 31 is connected to the first surface 301, and the second portion 32 is connected to the second surface 302. The width d2 of the slit 30 on the second surface 302 is greater than the width d1 on the first surface 301. In the thickness direction of the chopper wheel 300, the opening of the first portion 31 is rectangular with a width d1. The opening of the second portion 32 is an isosceles trapezoid with an upper base width equal to the width of the first portion 31 and a lower base width d2. Considering that a fan-shaped beam propagates obliquely when off-center, the slit 30 is divided into two portions. The second portion 32 increases the amount of fan-shaped beam output when the chopper wheel 300 rotates at excessive angles, thereby reducing the difference in center and edge spot size during scanning. Furthermore, the first portion 31 reduces X-ray scattering caused by thinning the shielding material, thereby ensuring that the spot does not deform, maintaining image resolution, and preventing radiation leakage.

[0048] As an example, d1 is between 0.3 mm and 0.4 mm, and d2 is between 0.3 mm and 0.4 mm. The specific values ​​should be related to the specific design requirements and depend on the size of the physical resolution at the designed shooting position.

[0049] As an example, the thickness h of the first portion 31 is between 1 mm and 1.2 mm, and its specific value is adjusted according to the designed energy of the light source 100 to ensure sufficient shielding thickness when the slit 30 is perpendicular to the collimating aperture on the sector collimator 200 .

[0050] As an example, the thickness of the chopper wheel 300 is between 2.4 mm and 3 mm. It is made of high-density metal, such as tungsten, which can effectively shield X-rays and prevent X-rays from penetrating the blocking area.

[0051] In order to compare the imaging effects of the chopper wheel provided in this embodiment with those of the chopper wheel in the prior art, this embodiment makes a comparison in terms of X-ray flux and signal intensity:

[0052] 1) First, follow Figure 1 In the application scenario shown, the surface to be tested 500 is used as the test surface, and three simulation models of chopper wheel slits are established using Geant4, including Figures 2a-2b The two prior art chopper wheel slits and the chopper wheel slit provided by this embodiment are shown; then, the scanning process of the chopper wheel rotation is simulated, and 100,000 photon examples are run when each chopper slit structure is rotated to different angles. The number of photons received on the detection surface is analyzed to obtain the changes in the X-ray flux of the three slit structures during the chopper wheel scanning process. Figure 4a As shown, curve 1 represents Figure 2a The test results of the structure shown, curve 2 represents Figure 2bThe test results of the structure shown in FIG3 are shown in FIG4 . Curve 3 represents the test results of the structure provided by this embodiment. It can be seen from the figure that, compared with the two slit structures in the prior art, the X-ray flux is increased by 299.59% and 75.98% respectively by using the chopper wheel provided by this embodiment.

[0053] 2) First, follow Figure 1 In the application scenario shown, the chopper wheel 300 uses the chopper wheel provided in this embodiment, starts the scanning process, scans and images the surface to be detected 500, and measures the backscattered signal intensity of the surface to be detected 500; then, replace Figures 2a-2b The chopper wheel shown in the figure was re-measured, and the actual signal intensity distribution data of the three slit opening methods were finally obtained. Figure 4b As shown, curve 1 represents Figure 2a The test results of the structure shown, curve 2 represents Figure 2b The test results of the structure shown in FIG. 3 are shown. Curve 3 represents the test results of the structure provided by this embodiment. As can be seen from the figure, compared with the two slit structures in the prior art, the signal distribution curve obtained by using the chopper wheel provided by this embodiment is smoother. That is to say, during the rotation of the chopper wheel, the light spot irradiated on the surface to be tested changes less, and the imaging quality is better.

[0054] Example 2

[0055] This embodiment provides a backscatter imaging device, such as Figure 1 As shown, the optical system includes a light source 100, a sector collimator 200, a chopper wheel 300 and a detector 400 in sequence.

[0056] As an example, the light source 100 is used to generate a light beam. In this embodiment, the light beam emitted by the light source 100 is a cone-shaped light beam.

[0057] As an example, a sector collimator 200 is disposed at the front end of the light source 100. A collimating aperture (not shown) is provided on the sector collimator 200. After passing through the collimating aperture, the cone-shaped light beam is emitted as a fan-shaped light beam. In addition, the optical axis of the sector collimator 200 is coaxial with the optical axis of the light source 100. In this embodiment, the sector collimator 200 can be a W metal pre-collimator or a Cu metal pre-collimator.

[0058] As an example, the chopper wheel 300 is arranged on a side of the sector collimator 200 away from the light source 100 and is arranged parallel to the sector collimator 200. The fan-shaped light beam is emitted as a flying spot beam after passing through the slit 30. In this embodiment, the chopper wheel 300 is the chopper wheel provided in Example 1. The chopper wheel 300 includes a first surface 301 and a second surface 302 relative to each other. In the backscatter imaging device, the first surface 301 faces the sector collimator 200, and the second surface 302 faces the detector 400. The chopper wheel 300 is provided with at least one slit 30, and the slit 30 includes a first portion 31 and a second portion 32. In the thickness direction of the chopper wheel 300, the opening shape of the first portion 31 is rectangular, and the opening shape of the second portion 32 is an isosceles trapezoid. As an example, the distance between the chopper wheel 300 and the light source 100 is between 20 mm and 35 mm. Please refer to the description of Example 1 for the specific structure of the chopper wheel 300, which will not be repeated here.

[0059] As an example, the detector 400 is positioned on the side of the chopper wheel 300 away from the sector collimator 200, and the surface to be inspected 500 is placed on the side of the detector 400 away from the chopper wheel 300. After the flying spot beam impinges on the surface to be inspected 500, it is scattered, forming scattered light that enters the detector 400. In this embodiment, the distance between the surface to be inspected 500 and the light source 100 is between 90 mm and 110 mm; the spot size formed on the surface to be inspected 500 is between 1 mm and 1.5 mm.

[0060] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A chopper wheel, characterized in that: The chopper wheel includes a first surface and a second surface facing each other. At least one slit is provided on the chopper wheel. The width d2 of the slit on the second surface is greater than the width d1 of the slit on the first surface. The slit includes a first portion and a second portion, wherein the first portion is connected to the first surface and the second portion is connected to the second surface. In the thickness direction of the chopper wheel, the opening shape of the first portion is a rectangle, and the opening shape of the second portion is an isosceles trapezoid.

2. The chopper wheel according to claim 1, characterized in that The chopper wheel is provided with N slits, and the N slits are distributed at equal angles on the chopper wheel, where N is an integer greater than or equal to 2.

3. The chopper wheel according to claim 1, wherein: The width d1 of the slit on the first surface is between 0.3 mm and 0.4 mm.

4. The chopper wheel according to claim 1, wherein: The width d2 of the slit on the second surface is between 0.3 mm and 0.4 mm.

5. The chopper wheel according to claim 1, wherein: The thickness of the first portion is between 1 mm and 1.2 mm.

6. The chopper wheel according to claim 1, characterized in that The thickness of the chopper wheel is between 2.4 mm and 3 mm.

7. A backscatter imaging device, characterized in that: The backscatter imaging device comprises in sequence: A light source, wherein the light beam emitted by the light source is a cone-shaped light beam; A sector collimator, wherein a collimating diaphragm is provided on the sector collimator, and the cone-shaped light beam is emitted as a fan-shaped light beam after passing through the collimating diaphragm, and the optical axis of the sector collimator is coaxial with the optical axis of the light source; A chopper wheel, wherein the chopper wheel is the chopper wheel according to any one of claims 1 to 6, wherein the fan-shaped light beam is emitted as a flying spot light beam after passing through the slit; The flying spot light beam is irradiated onto the surface to be detected and then scattered to form scattered light which enters the detector.

8. The backscatter imaging device according to claim 7, characterized in that: A first surface of the chopper wheel faces the sector collimator, and a second surface of the chopper wheel faces the detector.

9. The backscatter imaging device according to claim 7, characterized in that: The distance between the light source and the chopper wheel is between 20 mm and 35 mm.

10. The backscatter imaging device according to claim 7, characterized in that: The distance between the light source and the surface to be detected is between 90 mm and 110 mm.

Images