JP2006024522A - X-ray generation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray generation device which can change the focus where an electron beam collides with a target easily while maintaining X-ray dose. <P>SOLUTION: A first deflection coil 11 and a second deflection coil 13 are installed at two stages along the axis A to unite a cathode 1 and the target 3. A collision position changing control part 21 changes the direction of the center orbit E of the electron beam e which enters into a throttle hole 8 by interlockingly operating these deflection coils 11, 13 while the center orbit E of the electron beam e passes through the throttle hole 8. By this, there is no possibility that the generated X-ray dose is reduced because the electron amount which passes through the throttle hole 8 and which arrives at the target 3 does not decrease. Furthermore, by making the direction of the center orbit E of the electron beam e which enters into the throttle hole 8 be changed, the position of the focus F can be changed easily and freely. Therefore, even if the focus is damaged, the position of the focus F can be changed easily. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an X-ray generator used in the industrial field, the medical field, and the like, and more particularly to a technique for deflecting an electron beam generated from an electron source.

  Conventionally, as this type of apparatus, there are transmissive and reflective X-ray generators depending on the X-ray generation method. FIG. 3A illustrates a transmissive X-ray generator. The electron beam e generated from the cathode 31 collides with the target 33 and is converted into X-rays. A focus coil 35 that focuses the electron beam e is provided between the cathode 31 and the target 33, and the focal point F at which the electron beam e collides with the target 33 is miniaturized. Further, an aperture 37 for cutting an unnecessary electron beam e is inserted in the focus coil 35.

  In the case of the transmission type, for example, a tungsten film having a thickness of several microns is deposited on the surface of the target 33 using an aluminum plate as a base material on the cathode 31 side. When the electron beam e hits the tungsten film, most of the kinetic energy of the electrons is converted into thermal energy except that a few percent of the kinetic energy becomes X-rays. Therefore, the tungsten film is subjected to a shock due to electron collisions as well as a high temperature. When X-rays are generated for a long time, the tungsten film at the focal position is damaged, such as a hole, and the electron beam e directly hits the exposed aluminum plate, so that X-rays are not generated.

  When the target 33 is damaged, the operation of the X-ray generator is stopped, and the target 33 is moved manually to adjust the focal position on the target 33 so that the electron beam e collides with the tungsten film again. Do.

  Increasing the thickness of the tungsten film may be expected to increase the life of the target 33, but is preferable because the generated X-rays are absorbed by the tungsten film itself and a desired X-ray dose cannot be obtained. Absent.

On the other hand, in the case of the reflection type, the heat conduction of the target is relatively good, so that the target does not reach a high temperature and the target is not severely damaged compared to the transmission type. Therefore, it can endure use for a longer time. However, the surface of the target is rough and no X-rays are finally generated, as in the transmissive type (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 6-1888092

  However, the conventional example having such a configuration has the following problems.

  That is, in the conventional apparatus, it takes time and labor to shift the focus F at which the electron beam e collides with the target 33, which is troublesome.

  Therefore, as shown in FIG. 3B, a configuration in which a deflection coil 41 is provided between the cathode 31 and the focus coil 35 to deflect the electron beam e can be considered. According to this, the focus F can be shifted without moving the target 33.

  However, as the electron beam e is deflected, the center trajectory E of the electron beam e is displaced from the aperture hole 38 of the aperture 37, so that the amount of the electron beam e passing through the focus coil 35 is reduced. As a result, the dose of X-rays generated also decreases, causing a problem that the projected image and the like become dark.

  The present invention has been made in view of such circumstances, and provides an X-ray generator capable of easily changing a focal point at which an electron beam collides with a target while maintaining a dose of X-rays. For the purpose.

  In order to achieve such an object, the present invention has the following configuration.

  That is, the invention described in claim 1 is disposed between an electron source that generates an electron beam, a target that is opposed to the electron source and generates X-rays by collision of the electron beam, and the electron source. A plurality of deflectors arranged between the electron source and the diaphragm means and deflecting the electron beam in an X-ray generator having a diaphragm means formed with a diaphragm hole so as to limit the range of the electron beam that passes through The position at which the electron beam collides with the target by operating the plurality of deflecting means in an interlocking manner so that the direction of the central orbit of the electron beam incident on the aperture is changed while the central orbit of the electron beam passes through the aperture And a collision position change control means for changing.

  [Operation / Effect] According to the first aspect of the present invention, since a plurality of deflecting means are provided, the electron beam can be deflected at least twice. Therefore, by operating the plurality of deflection means in conjunction with the collision position change control means, the center trajectory of the electron beam can pass through the aperture hole of the aperture means. For this reason, the amount of electrons passing through the aperture and reaching the target does not decrease. Therefore, the dose of X-rays generated at the target does not decrease. Furthermore, by changing the direction of the center orbit of the electron beam incident on the aperture, the position of the focal point where the electron beam that has passed through the aperture hits the target can be easily and freely changed. Therefore, even if the focus is damaged, the position of the focus can be easily changed.

  According to a second aspect of the present invention, in the X-ray generation apparatus according to the first aspect, the collision position change control means is based on each deflection means based on arrangement information of the plurality of deflection means and the diaphragm means. A plurality of deflection means are operated so that the deflection angle of the electron beam satisfies a predetermined correlation with each other.

  [Operation / Effect] When the center trajectory of the electron beam passes through the aperture hole, the deflection angle of the electron beam by each deflecting means has a predetermined correlation with each other, and this correlation is obtained between the plurality of deflecting means and the aperture means. It is based on the arrangement information. Therefore, according to the second aspect of the present invention, the collision position change control means is based on the arrangement information of the plurality of deflection means and the diaphragm means, so that the center trajectory of the electron beam passes through the diaphragm hole and Changing the direction of the central trajectory of the electron beam incident on the hole can be suitably realized.

  In addition, this specification also discloses the invention which concerns on the following X-ray generators.

  (1) An electron source that generates an electron beam, a target that is disposed opposite to the electron source and generates X-rays by collision of the electron beam, and a focusing unit that is disposed between the electron source and the target and focuses the electron beam. And a plurality of deflecting means for deflecting the electron beam, and the center trajectory of the electron beam passes through the central portion of the focusing means and is focused. And a collision position change control means for changing the position where the electron beam collides with the target by interlocking operation of the plurality of deflection means so as to change the direction of the central trajectory of the electron beam incident on the means. Line generator.

  (Operation / Effect) In the case of an X-ray generator not provided with a diaphragm means, there is no problem of the present application. However, even when the aperture means is not provided, the following problems exist in the X-ray generator provided with the focusing means. That is, the farther the range through which the electron beam passes from the central part of the annular focusing means, the more difficult the focusing means can focus the electron beam. As a result, the size of the focal point on the target becomes large, and there is a problem that an image with a high magnification cannot be obtained with the X-rays generated at this time. Therefore, according to the invention described in (1) above, since the center trajectory of the electron beam can pass through the central portion of the focusing means, the focusing means can focus the electron beam suitably. The focal point can be easily and freely changed by changing the direction of the central trajectory of the electron beam incident on the focusing means, as in the first aspect of the invention. Therefore, even if the focus is damaged, the position of the focus can be easily changed.

  According to the X-ray generator of the present invention, since the plurality of deflecting means are provided, the electron beam can be deflected at least twice. Therefore, the collision position change control means can operate the plurality of deflection means in conjunction with each other so that the center trajectory of the electron beam can pass through the aperture hole of the aperture means. Thereby, the amount of electrons passing through the aperture hole does not decrease. Therefore, the dose of X-rays generated at the target does not decrease. Furthermore, by changing the direction of the center orbit of the electron beam incident on the aperture, the position of the focal point where the electron beam that has passed through the aperture hits the target can be easily and freely changed. Therefore, even if the focus is damaged, the position of the focus can be easily changed. As described above, it is possible to easily change the focal point at which the electron beam collides with the target while maintaining the X-ray dose.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view illustrating a configuration of an X-ray tube according to an embodiment.

  The X-ray tube according to this embodiment is a so-called transmission type microfocus X-ray tube. The X-ray tube includes a cathode 1 that generates an electron beam e, and a target 3 that is disposed opposite to the cathode 1 and generates X-rays by the collision of the electron beam e. A focus coil 5 that focuses the electron beam e is provided between the cathode 1 and the target 3. An aperture 7 that restricts the range of the passing electron beam e is inserted in the focus coil 5. Between the cathode 1 and the aperture 7 (focus coil 5), deflection coils 11 and 13 for deflecting the electron beam e are provided in two stages along the axis A connecting the cathode 1 and the target 3. . Among these, the cathode 1 side is referred to as the first deflection coil 11 and the aperture 7 side is referred to as the second deflection coil 13 for distinction. The X-ray tube corresponds to the X-ray generator in this invention.

As the cathode 1, a filament formed of a thin tungsten wire, or a single crystal or sintered chip formed of lanthanum hexaboride (LaB ₆ ), cerium hexaboride (CeB ₆ ), or the like is used. The cathode 1 corresponds to the electron source in the present invention.

  An accelerating electrode (not shown) or the like is provided on the side of the cathode 1 that irradiates the electron beam e, and accelerates thermoelectrons drawn from the cathode 1 in a high temperature state toward the target 3. In FIG. 1, a state in which the electron beam e travels and spreads is schematically represented by a two-dot chain line.

  The target 3 is made of a light metal with little X-ray absorption such as beryllium (Be) or aluminum (Al) as a base material, and X-ray generation such as tungsten (W) or molybdenum (Mo) is generated on the cathode 1 side surface of the base material. An efficient heavy metal thin film (for example, 3 μm to 5 μm thick) is formed by vapor deposition. The target 3 corresponds to the target in the present invention.

  When the electron beam e collides with the target 3, X-rays are generated in the heavy metal thin film. The generated X-rays are emitted from the side of the target 3 opposite to the cathode 1.

  The focus coil 5 is formed in an annular shape around the axis A, and focuses the electron beam e passing through the focus coil 5. The focal point F is a point where the electron beam e is focused on the target 3. The size of the focus F is reduced by controlling the current flowing through the focus coil 5. The focus coil 5 corresponds to the focusing means in this invention.

  The aperture 7 is formed with an aperture 8 having a predetermined diameter along the axis A at the center thereof. Then, the electron beam e focused by the focus coil 5 is limited to only the electron beam e passing through the aperture 8. The aperture 7 corresponds to the diaphragm means in this invention.

  The first deflection coil 11 has a pair of X deflection coils (11xn, 11xs) symmetrical in the left and right (X axis direction) about the axis A in the XZ plane. Similarly, although not shown, the first deflection coil 11 is a pair of Y deflection coils (symmetric about the axis A about the axis A on the same XY plane as the X deflection coil in the YZ plane ( 11yn, 11ys). Therefore, the first deflection coil 11 includes four coils (11xn, 11xs, 11yn, and 11ys).

  The pair of opposing X deflection coils (11xn, 11xs) deflects the traveling direction of the electron beam e passing between them in the X-axis direction. The pair of opposing Y deflection coils (11yn, 11ys) deflects the traveling direction of the electron beam e in the Y-axis direction. Further, the electron beam e can be deflected in an arbitrary direction by combining the X deflection coil and the Y deflection coil. In the following description, when there is no need to distinguish between them, they are collectively referred to as “first deflection coil 11”.

  Similarly to the first deflection coil 11, the second deflection coil 13 also has an X deflection coil (13xn, 13xs) and a Y deflection coil (13yn, 13ys) (not shown). Hereinafter, when there is no need to distinguish between them, they are collectively referred to as “second deflection coil 13”. The first deflection coil 11 and the second deflection coil 13 correspond to the deflection means in this invention.

  Further, the deflection angle of the electron beam e is in accordance with the magnitude of the current flowing through the first deflection coil 11 and the second deflection coil 13, respectively.

  The first deflection coil 11 and the second deflection coil 13 are electrically connected to and fed with a first power source 15 and a second power source 17, respectively. The first power supply 15 and the second power supply 17 are further controlled by a collision position change control unit (hereinafter referred to as “change control unit” as appropriate) 21. That is, the change control unit 21 controls the current flowing through the first deflection coil 11 and the second deflection coil 13 by controlling the amount of power supplied from the first power source 15 and the second power source 17. The change control unit 21 corresponds to the collision position change control means in this invention.

  Here, the change control unit 21 will be described in detail.

  The change control unit 21 controls the first power source 15 (first deflection) so as to change the direction of the central trajectory E of the electron beam e incident on the aperture 8 while the central trajectory E of the electron beam e passes through the aperture 8. The coil 11) and the second power source 17 (second deflection coil 13) are controlled.

  Please refer to FIG. FIG. 2 is a cross-sectional view of an X-ray tube schematically showing only the central orbit E of the electron beam e. Note that the deflection by the first deflection coil 11 and the second deflection coil 13 will be described only in the X-axis direction for convenience of explanation.

First, the distance between the first deflection coil 11 and the second deflection coil 13 is L1, and the distance between the second deflection coil 13 and the aperture 7 (focus coil 5) is L2. Further, the deflection angles of the electron beams by the first deflection coil 11 and the second deflection coil 13 are defined as a deflection angle θ ₁ and a deflection angle θ ₂ , respectively. The direction of the central orbit E of the electron beam e incident on the aperture 8 corresponds to the incident angle θ ₃ . Hereinafter, two cases will be described according to the relationship between L1 and L2.

(1) When L1 and L2 are Equal In this case, when the center trajectory of the electron beam e passes through the aperture 8 of the aperture 7, the following expression (1) is established.

θ ₂ = 2θ ₁ (1)
Further, when the deflection angles (θ ₁ , θ ₂ ) are increased or decreased while satisfying the predetermined correlation shown in the equation (1), the incident angle θ ₃ can be changed.

In FIG. 2, by changing the deflection angles (θ ₁ , θ ₂ ) to the deflection angles (θ ₁ ′, θ ₂ ′), the incident angle θ ₃ is changed to the incident angle θ ₃ ′. F schematically represents a shift to the focal point F ′.

Thus, changing the control unit 21, the deflection angle (theta _1, theta ₂₎ while the maintaining the predetermined correlation, the deflection angle (theta _1, theta ₂₎ a to change respectively, the first deflection coil 11 second The current flowing through the two deflection coils 13 may be controlled. Thus, the direction of the central orbit E of the electron beam e incident on the aperture 8 can be changed while the central orbit E of the electron beam e passes through the aperture 8.

  As apparent from FIG. 2, the change control unit 21 continuously changes the direction of the center orbit E of the electron beam e incident on the aperture 8, whereby the focus F can be continuously shifted. Here, for the convenience of limiting the deflection direction of the electron beam e to the X-axis direction, the focal point F moves on a straight line XL passing through the intersection O of the axis A and the target 3 and parallel to the X-axis. However, if the electron beam e is deflected in the Y-axis direction in addition to the X-axis direction, the focal point F can be freely changed to an arbitrary position on the target 3.

(2) When L1 and L2 are not equal In this case, when the center trajectory of the electron beam e passes through the aperture 8 of the aperture 7, the following equation (2) is established.

θ ₂ = θ ₁ (1 + L1 / L2) (2)
As shown in Expression (2), a predetermined correlation between the deflection angle θ ₁ and the deflection angle θ ₂ based on the arrangement of the first deflection coil 11, the second deflection coil 13, and the aperture 7 (focus coil 5). Exists. The incident angle θ ₃ can be changed by changing the deflection angles (θ ₁ , θ ₂ ) while satisfying the predetermined correlation. Therefore, the change control unit 21 changes the deflection angles (θ ₁ , θ ₂ ) while maintaining the predetermined correlation between the deflection angles (θ ₁ , θ ₂ ). What is necessary is just to control the electric current which flows into the deflection | deviation coil 13. FIG. Thus, the direction of the central orbit E of the electron beam e incident on the aperture 8 can be changed while the central orbit E of the electron beam e passes through the aperture 8.

  If L1 = L2 is substituted into equation (2), equation (1) is derived. Therefore, even when L1 and L2 are equal, as in the case where L1 and L2 are not equal, the correlation between the deflection angles is the relationship between the first deflection coil 11, the second deflection coil 13, and the aperture 7 (focus coil 5). This is based on the arrangement information.

  As described above, according to the X-ray tube shown in the present embodiment, since the first deflection coil 11 and the second deflection coil 13 are provided as the deflection coils in two stages, the electron beam e is deflected twice. Can do. Therefore, the central orbit E of the electron beam e can pass through the aperture hole 8 of the aperture 7. Therefore, the amount of electrons reaching the target 3 does not decrease, and the dose of X-rays to be converted does not decrease.

  Further, since the direction of the central orbit E of the electron beam e incident on the aperture 8 can be changed while the central orbit E of the electron beam e passes through the aperture 8, the position of the focal point F on the target 3 can be arbitrarily set. Can be changed. That is, the change control unit 21 can control the focal position of the electron beam e on the target 3 by operating the first deflection coil 11 and the second deflection coil 13 in conjunction with each other. Therefore, even if the focus F on the target 3 is damaged, the position of the focus F can be easily shifted. Therefore, it is not necessary to stop the X-ray tube just because the focal point F on the target 3 is damaged, and the X-ray tube can be continuously operated.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In each of the above-described embodiments, the X-ray generation method is a transmissive X-ray tube, but it can also be applied to a reflective X-ray tube.

  (2) In each of the above-described embodiments, the deflection coil is provided with the first deflection coil 11 and the second deflection coil 13 in two stages along the axis A. However, the deflection coil is provided in three stages or more along the axis A. The structure provided may be sufficient.

  (3) In each of the above-described embodiments, both the first deflection coil 11 and the second deflection coil 13 are configured to include two pairs of coils arranged to face the X-axis direction and the Y-axis direction. However, the number of coils arranged opposite to each other may be one or three or more.

  (4) In the above-described embodiments, the aperture 7 is provided. However, the change control unit 21 and the like of this embodiment can be applied to an X-ray tube that does not include the aperture 7. That is, the change control unit 21 may control the center orbit E of the electron beam e to change the direction of the center orbit E of the electron beam e incident on the focus coil 5 while passing through the center of the focus coil 5. . Thereby, the focus coil 5 can focus the electron beam e on a micro focus.

  (5) In the above-described embodiment, the case where the focal point F is damaged is operated so that another position is set as the focal point F. However, the electron beam e is moved to the target 3 while continuously shifting the position of the focal point F. You may make it drive | operate so that it may collide.

It is a schematic sectional drawing which shows the structure of the X-ray tube which concerns on an Example. (A) The schematic sectional drawing of the X-ray tube which shows typically the mode of deflection | deviation of the electron beam e, (b) The top view of the target 3 which shows typically a mode that the focus F shift | deviates. It is a schematic sectional drawing which shows the structure of the conventional X-ray tube.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Cathode 3 ... Target 5 ... Focus coil 7 ... Aperture 8 ... Diaphragm hole 11 ... 1st deflection coil 13 ... 2nd deflection coil 21 ... Collision position change control part

Claims (2)

  An electron source that generates an electron beam, a target that is disposed opposite to the electron source, generates X-rays by collision of the electron beam, and is disposed between the electron source and the target so as to limit the range of the electron beam that passes through In the X-ray generator comprising the aperture means in which the aperture hole is formed, a plurality of deflection means arranged between the electron source and the aperture means for deflecting the electron beam, and the central trajectory of the electron beam is the aperture hole A collision position change control means for changing the position at which the electron beam collides with the target by operating the plurality of deflecting means in an interlocking manner so as to change the direction of the center orbit of the electron beam incident on the aperture hole while passing through An X-ray generator characterized by that. 2. The X-ray generation apparatus according to claim 1, wherein the collision position change control means has a predetermined correlation between the deflection angles of the electron beams by the deflection means based on arrangement information of the plurality of deflection means and the diaphragm means. An X-ray generator characterized by operating a plurality of deflection means so as to satisfy

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