JP4420190B2 - X-ray equipment - Google Patents

Description

  The present invention relates to an X-ray apparatus including an X-ray generator that can easily generate X-rays having a wide beam width.

Inspection devices using X-ray transmission (X-ray devices) are used in a wide range of fields, including medical fields, inspection of products in factories, security checks of belongings at airports, and inspection of cargo by customs at ports. .
In general, this type of inspection apparatus irradiates X-rays generated from an X-ray generation unit toward an inspection object (including a subject) and detects X-rays transmitted through the object using a line sensor. In addition, the inside of the inspection object is examined by imaging the difference in transmission intensity.

Among these, the X-ray generation unit causes an electron beam emitted from an electron gun (cathode) in a container kept in a vacuum to collide with an X-ray conversion target (anode), and from the X-ray conversion target to X It emits a line, and various improvements have been added from the past (see, for example, Patent Document 1).
JP 2003-7236 A

By the way, in the inspection of cargo in a container, etc., it is necessary to irradiate and transmit X-rays to every corner of a large inspection object (cargo in a container). Width ") must be sized to accommodate large objects.
The X-ray generation unit (see FIG. 1) is basically configured so that the X-ray conversion target 2 irradiated with the linear electron beam e from the electron gun 1 generates X-rays x from the irradiation position. Is done. The X-ray x generated by the X-ray target 2 goes straight in a conical shape at a predetermined spread angle from one point irradiated with the electron beam e. The spread angle of the X-ray x is about 45 degrees at the maximum. Therefore, in order to obtain X-rays having a beam width suitable for the large inspection object 3 as described above, the distance L1 between the X-ray generation unit (X-ray conversion target 2) and the inspection object 3 is set as follows. It had to be long enough. For example, when the height of the inspection object is 10 m, in order to perform inspection by one X-ray generation unit, the inspection object 3 and the X-ray generation unit (X-ray conversion target 2) are 12 m (distance L1). It is necessary to separate them above. However, it is not easy to secure such a wide space at the actual inspection place, and therefore it is necessary to shorten the distance L1 between the inspection object 3 and the X-ray generation unit (X-ray conversion target 2). Become.

As a means for shortening the distance L1 between the inspection object and the X-ray generation unit, as shown in FIG. 2A, a plurality of X-ray generation units are arranged side by side and cannot be covered by one X-ray generation unit. It is conceivable that the X-ray irradiation range is covered by another X-ray generation unit. Alternatively, as shown in FIG. 2B, for example, it is conceivable to perform an inspection while moving one X-ray generation unit in the height direction. However, when a plurality of X-ray generators are used, the X-ray ends from adjacent X-ray generators overlap as shown as region A in FIG. Since the shadow (image) of the object is erased by the other X-ray, there is a drawback that the image becomes unclear. Further, when the X-ray generation unit is moved, not only a complicated moving mechanism is required but also a moving time is required. In addition, imaging while moving is the same as using a large number of X-ray generators, so that the captured image becomes unclear.

  In consideration of the above-described problems, in the present invention, even when a large inspection object is inspected, the separation distance between the inspection object and the X-ray generation unit can be shortened, and clear X-rays can be obtained. It is an object to provide an X-ray apparatus suitable for obtaining an image.

In order to achieve the above object, according to a first aspect of the present invention, there is provided an electron gun for generating an electron beam, deflection means for deflecting and scanning the electron beam over a predetermined width in a predetermined direction , and deflection scanning. An X-ray generation surface having a rod-like or plate-like shape having a predetermined length that is inclined with respect to a beam surface formed by the electron beam and is provided over a deflection width of the electron beam. An X-ray conversion target that generates X-rays from an irradiation site of the electron beam on the generation surface, and an X-ray conversion target that is provided opposite to the X-ray conversion target and that emits the X-rays generated by the X-ray conversion target. A collimator aligned in parallel, and the deflecting means controls the deflection speed of the electron beam beam on the surface of the electron beam beam so as to output X-rays having a uniform distribution over a predetermined width through the collimator. Slow at both ends X-ray apparatus characterized by faster at the central portion of the beam surface is provided with.

Preferably, the collimator is provided in parallel with a predetermined gap therebetween, and a long X-ray shielding plate that forms X-rays generated by the X-ray conversion target in a strip shape into a sheet shape, and irradiates the X-rays. It is desirable to configure with a plurality of girders made of X-ray shields provided between the X-ray shield plates in parallel along the power direction.

In the X-ray apparatus of the present invention, in order to deflect and scan the electron beam, the electron beam which forms a pseudo plane is irradiated to the X-ray conversion target in a straight line instead of a single point. For this reason, X-rays are not generated so as to spread from one point of the X-ray conversion target, but are generated from all parts of the linear generation source and go straight while forming a belt-like X-ray beam surface. Therefore, the beam width of the belt-like X-ray coincides with the length of the linear source, which is the deflection width (deflection angle) of the electron beam, and the distance between the deflection start point of the electron beam and the X-ray conversion target. Is set by That is, since the X-ray beam width can be set regardless of the distance between the X-ray generation unit and the inspection object, it is possible to inspect a large inspection object while keeping the distance between the inspection object and the X-ray generation unit short. Necessary large beam width X-rays can be obtained. For example, an X-ray having an arbitrary beam width is formed by forming an X-ray generation surface having a predetermined length in the deflection scanning direction of the electron beam by deflecting and scanning the electron beam over a predetermined width in a predetermined direction. Can be obtained.

In addition, depending on the normal X-ray generation unit, the X-ray components traveling with a predetermined spread overlap each other, so that the X-ray images cancel each other, and the X-ray images become unclear. End up. However, in the X-ray apparatus of the present invention, the X-ray component other than the predetermined direction is blocked by the installation of the collimator, so that the photographed image is not obscured. In addition, in the deflecting means, the deflection speed of the electron beam is slowed at both ends of the electron beam beam surface and fast at the center of the beam surface, so that X having a uniform distribution over a predetermined width. The line can be output through the collimator, and a clear image can be obtained.

Hereinafter, an embodiment of the X-ray apparatus of the present invention will be described with reference to the drawings.
FIG. 3 is a schematic configuration diagram showing an X-ray generation unit 10 which is a main part of the X-ray apparatus according to the present invention. Since devices other than the X-ray generation unit are known, description thereof is omitted. The X-ray generator 10 includes an electron gun 11 that generates an electron beam e0, and a pair of electromagnets 12a and 12b that are disposed in front of the electron gun 11 on opposite sides of the electron beam irradiation axis of the electron gun 11. And, from the X-ray conversion target 13 that generates X-rays from the irradiation site of the electron beam e0, and the X-rays generated by the X-ray conversion target 13, X-rays other than X-rays parallel to a predetermined direction are cut off, And a collimator 20 that forms parallel sheet X-rays. All of these devices, except for the collimator 20, are sealed in a vacuum container (not shown) having a window portion for extracting X-rays to the outside.

The electron gun 11 emits a linear electron beam by applying a cathode voltage.
A voltage is alternately applied to the electromagnets 12a and 12b by a control circuit (not shown) to generate a magnetic field between the electromagnets 12a and 12b, and the electron beam e0 is directed along the opposite direction of the electromagnets 12a and 12b. It plays the role of deflection scanning with a predetermined width like a pendulum.
The X-ray conversion target 13 is composed of a rod or plate having an X-ray generation surface 13a having a predetermined length in the deflection scanning direction of the electron beam e0, and in particular, this X-ray generation surface 13a is deflected. The fan-shaped beam plane E formed by the electron beam e0 is parallel to the longitudinal direction and the other direction is inclined with respect to the fan-shaped beam plane E at a predetermined angle α. And it positions so that the fan-shaped beam surface E may make a straight line F and cross. The length in the longitudinal direction of the X-ray generation surface 13a is set to be at least the same as or longer than the beam width of the X-ray generated. In the drawing, the fan-shaped beam plane E is illustrated in a state intersecting with the straight line F, and thus is illustrated as a triangle instead of a fan.

  The X-ray conversion target 13 includes a cooling device (not shown) for suppressing the temperature rise of the X-ray generation surface 13a due to electron beam irradiation. Further, the material of the X-ray generation surface 13a of the X-ray conversion target is capable of generating X-rays by collision of electron beams, and has sufficient heat resistance even in consideration of temperature rise due to electron beam irradiation heating. For example, molybdenum, copper, etc. can be preferably used in addition to tungsten.

By the way, the collimator 20 will be described below. The collimator 20 is disposed on the downstream side of the belt-shaped X-ray generated by the X-ray conversion target 13 so as to face the X-ray conversion target 13. The collimator 20 is disposed in parallel at a predetermined pitch between two long shielding plates 21a and 21b arranged in parallel with each other with a slight gap h, and the shielding plates 21a and 21b. And a number of girders 22 that secure the shielding plates 21a and 21b to each other. The girder 22 also has an X-ray shielding capability. The shielding plates 21a and 21b and the two girder plates 22 form a plurality of rectangular tubular small sections 23 open at both ends. As shown in FIG. 4, the direction of the collimator 20 is determined so that an axis 23a passing through the small section 23 is parallel to a straight line K that is a direction in which the X-ray X2 should be irradiated. Here, the straight line K includes the straight line F and the fan beam vertical plane perpendicular to the fan beam plane E and the X-ray beam center plane G which is symmetric to the fan beam plane E with respect to the symmetry plane D perpendicular to the X-ray generation surface 13a. A straight line formed by intersection with J. The reason why the collimator 20 is arranged so that the axis 23a of the small section 23 is parallel to the straight line K is that the X-ray intensity generated from the X-ray conversion target 13 is maximized in the direction parallel to the straight line K. .

Explaining the size of the collimator, the width L3 (see FIG. 3) in the longitudinal direction of the collimator 20 is made substantially equal to the length of the straight line F described above. The gap height h between the shielding plates 21a and 21b is set according to the required thickness of the sheet-like X-rays emitted from the X-ray generation unit.
Further, a method for setting the arrangement pitch p of the two girder plates 22 will be described with reference to FIG. FIG. 5 shows only one of the plurality of small sections 23 of the collimator 20 extracted for explanation. The arrangement pitch p is set so that the maximum angle γ that the X-rays passing through the small section 23 can make with respect to the axis of the small section 23 is not more than a predetermined value. As the maximum angle γ is reduced, the number of X-rays other than the X-rays parallel to the straight line K decreases, and a clearer X-ray image can be obtained. Therefore, the maximum angle γ is set in consideration of clarity, and the arrangement pitch p is set based on the maximum angle γ. The following relational expression is established between the maximum angle γ, the arrangement pitch p, the gap h, and the depth length L4 of the collimator 20.

Tan (γ) = (p ² + h ² ) ^1/2 / L4 (1) Formula The thicknesses of the shielding plates 21a and 21b and the girder plate 22 are the X-rays generated in the X-ray generation unit 10. In consideration of the energy, X-ray intensity, shielding ability of shielding plates and girders, etc., it is determined so that unnecessary X-ray components can be blocked. Note that lead or tungsten can be suitably used as the material of the shielding plates 21a and 21b and the girder plate 22. However, when the gap between the shielding plates 21a and 21b and the arrangement pitch of the girder plates 22 are reduced, tungsten with less deformation is used. Can be used more suitably.

Next, the operation of the X-ray generator 10 will be described.
The X-ray generator 10 deflects and scans the linear electron beam e0 generated from the electron gun 11 by the electromagnets 12a and 12b to form a flat electron beam (fan beam plane E). The X-ray conversion target 13 is irradiated with the planar electron beam, and X-rays are generated from the entire straight line F that is the electron beam irradiation site. That is, according to the present invention, X-rays do not spread from one point as in the prior art, but a wide X-ray generation source is formed in a straight line on the X-ray generation surface 13a. X-rays can be generated. Note that it is difficult to obtain a wide X-ray by deflecting and scanning the X-ray itself. However, since an electron beam for generating X-rays can be easily deflected and scanned by means of an electromagnet or the like and the X-ray generation source is made linear, X-rays having a wide beam width can be generated. The same effect as that of the deflection scanning can be obtained.

  In addition, the X-rays generated as described above form a belt-like band shape that has a linear generation source, but also includes an X-ray component that extends in part. These X-ray components in the expanding direction are blocked by the collimator 20 and emitted from the X-ray generation unit 10 as X-rays parallel to a predetermined direction. According to such parallel X-rays, a clear and less distorted X-ray image can be obtained.

Below, the effect | action of the X-ray generation part 10 is demonstrated in detail.
The electron beam position closest to the electromagnet 12a is e1, the electron beam position closest to the electromagnet 12b is e2, and the angle formed by the electron beams e1 and e2 is the deflection angle β. The deflection angle β can be determined by adjusting the electron acceleration voltage of the electron beam and the strength of the magnetic field generated by the voltage applied to the electromagnets 12a and 12b.

  Since the electron beam e0, which is originally a linear beam, is deflected at a deflection angle β, if the deflection speed is high, it is a fan-like planar beam having electron beam positions e1 and e2 as two sides. Acts as if. The fan beam plane E intersects the X-ray generation surface 13a of the X-ray conversion target 13 with an angle α. At this time, the fan beam plane E and the X-ray generation surface 13a intersect to form a straight line F parallel to the longitudinal direction of the X-ray generation surface 13a, and X-rays are emitted using the straight line F as a generation source.

As shown in FIG. 6, the X-ray emission direction is distributed within a certain angular range with the X-ray beam center plane G as the center. That is, the X-ray X1 enters the collimator 20 while forming a triangular prism shape having the straight line F as one side.
The X-ray X1 incident on the collimator 20 is converted into a sheet-like X-ray X2 that hardly spreads by the rectification action of the collimator 20 (that is, the X-rays other than the X-rays parallel to the straight line K described above). Released.

As described above, when inspecting a large object, it is important to increase the X-ray beam width, but the beam width of the sheet-like X-ray X2 is substantially equal to the length of the straight line F. The length of the straight line F is expressed by the following formula.
Length of straight line F = L2 × 2 × Tan (β / 2) (2) where L2 is the distance from the starting point S of electron beam deflection to the straight line F.

  As is clear from the equation (2), the length of the straight line F becomes longer and output as the deflection angle β is increased and the distance from the deflection starting point S to the X-ray conversion target 13 is increased. The X-ray beam width is also increased. That is, according to the X-ray generator 10, the acceleration voltage of the electron beam e that determines the deflection angle β, the magnetic field strength of the electromagnets 12a and 12b, and the distance from the deflection start point of the electron beam to the X-ray conversion target are adjusted. Thus, X-rays having an arbitrary beam width can be obtained. Therefore, X-rays having an arbitrary beam width can be obtained regardless of the distance between the X-ray generation unit and the inspection object.

Further, depending on the X-ray generation unit 10, as described above, since the X-ray generation source is not a point as in a normal apparatus but a straight line, a band-shaped X-ray that originally has little spread is generated. Since the X-ray is further rectified by the collimator 20, the emitted sheet-like X-ray has a strong property as a parallel X-ray.
Therefore, in addition to the above-described effect that the beam width can be arbitrarily adjusted, the following two effects are also provided.

The first effect is that a clear image can be obtained because X-rays other than parallel X-rays overlap each other and the X-ray images formed by the X-rays do not cancel each other. As described above, the arrangement pitch p of the collimator 20 is important in order to obtain a clear X-ray image.
The second effect is that no distortion occurs in an X-ray image by parallel X-rays. That is, as shown in FIG. 7A, when the X-ray X3 has a property of expanding like the normal X-ray X3, the image S1 of the object B1 close to the X-ray generation source is enlarged, and the distant object B2 The image S2 is hardly enlarged. For this reason, as an X-ray image, the images of the objects B1 and B2 having different sizes may be shown in almost the same size. In other words, image distortion occurs in ordinary X-rays having a spreading property. On the other hand, in the case of parallel X-rays (sheet-like X-rays) X4 generated by the X-ray generator 10, the images S3 and S4 of the large and small objects B3 and B4 are enlarged as shown in FIG. Never match the actual size, so the image will not be distorted.

If the deflection speed (angular velocity) of the electron beam e is constant regardless of the position of the electron beam on the fan beam plane E, the generated X-ray beam is an X-ray as shown in FIG. Shows an intensity distribution in which the center of the beam width swells and the both ends are small (XC in FIG. 8 indicates the X-ray center, and XT1 and XT2 indicate both ends of the X-ray). However, it is generated by slowing the deflection speed of the electron beam e near the both edges e1 and e2 of the fan beam plane E and increasing it near the center e3 (see FIG. 3) of the fan beam plane E. It is also possible to uniformly distribute the X-ray intensity distribution as shown in FIG. For this purpose, the voltage applied to the electromagnets 12a and 12b may be input as a sine wave, for example.

According to the present invention, it is possible to irradiate X-rays having a wide beam width with a single unit. However, a plurality of this apparatus are arranged adjacent to each other in the beam width direction of a sheet-like X-ray to irradiate a wider X-ray. It is also possible.
Since the present invention can obtain X-rays having an arbitrary beam width without requiring a wide space and can obtain a clear X-ray image, an X-ray apparatus for a large inspection object such as container cargo inspection. It is suitable as. Moreover, since a very clear X-ray image can be obtained as an effect of parallel X-rays, it can be suitably used as a small X-ray apparatus such as a security check inspection apparatus in an airport or the like.

It is a conceptual diagram which shows the X-ray inspection method by the conventional X-ray generation part. It is a figure which shows the concept of the method of test | inspecting a large sized test target object using the conventional X-ray generation part. It is a conceptual block diagram which shows one Embodiment concerning the X-ray apparatus of this invention. It is a conceptual diagram which shows the positional relationship of the fan-shaped beam plane E, the X-ray generation surface 13a, and the collimator 20 of FIG. It is a conceptual diagram which shows the dimension of the small division 23 of FIG. It is a conceptual diagram which shows the relationship between the X-ray conversion target 13 of FIG. 3, the X-ray | X_line X1 generated from it, and the collimator 20 into which X-ray | X_line X1 injects. It is a conceptual diagram explaining the principle of the magnitude | size and distortion of the image obtained by the conventional X-ray apparatus and the X-ray apparatus which concerns on this invention. It is a conceptual diagram which shows distribution of the X-ray generated from the X-ray generation part of the X-ray apparatus concerning this invention.

Explanation of symbols

10 X-ray generator 11 Electron gun 12a, 12b Electromagnet (deflection means)
13 X-ray conversion target 13a X-ray generation surface 20 Collimators 21a, 21b Shielding plates (shielding plates)
22 Girder plate (shield plate)
E Fan-shaped beam plane (beam surface)

Claims (2)

An electron gun that generates an electron beam;
Deflection means for deflecting and scanning the electron beam in one direction ;
A rod-shaped or plate-shaped X-ray generating surface having a predetermined length that is inclined with respect to a beam surface formed by the electron beam that has been deflected and scanned and that is provided over a deflection width of the electron beam; An X-ray conversion target for generating X-rays from the irradiation site of the electron beam on the ray generation surface ;
A collimator provided opposite to the X-ray conversion target and aligning the irradiation direction of the X-ray generated by the X-ray conversion target in parallel;
The deflection means slows the deflection speed of the electron beam at both ends of the electron beam surface and outputs the X-ray having a uniform distribution over a predetermined width through the collimator. X-ray apparatus characterized by speeding up at the center of the X-ray. The collimator is provided in parallel with a predetermined gap, and a long X-ray shielding plate that forms X-rays generated by the X-ray conversion target in a strip shape into a sheet shape, and a direction in which the X-rays should be irradiated The X-ray apparatus according to claim 1 , comprising a plurality of girders made of X-ray shields provided between the X-ray shield plates in parallel with each other.

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