X-RAY GENERATOR

Abstract

An X-ray generator capable of reliably reducing an X-ray focal spot size without depending on the focal spot size of an electron beam on a target. Providing, within the irradiation range of an electron beam B of a target laminated structure 3 comprising a target 2 and an X-ray irradiation window 1, a low X-ray absorptivity region 3a of localized low X-ray absorptivity in the irradiation direction of the electron beam B results in the suppression of emission to the outside of X-rays from among the X-rays generated as a result of the irradiation of the electron beam B onto the target 2 that are from regions other than the low X-ray absorptivity region 3a, and an X-ray focal spot of a size corresponding to the size of the low X-ray absorptivity region 3a is obtained regardless of the size of the irradiation region of the electron beam B.

Claims

1-6. (canceled)

7. An X-ray generator comprising: the X-ray generator that extracts an X-ray generated by irradiating a target disposed in a vacuum container with an electron beam to an outside in a direction along an irradiation direction of the electron beam through an X-ray irradiation window on which the target is integrally stacked and formed, wherein an X-ray low absorption rate part in which an X-ray absorption rate is locally low in the irradiation direction of the electron beam is formed in an irradiation region of the electron beam in a target stacked structure including the target and the X-ray irradiation window.

8. The X-ray generator according to claim 7, wherein the X-ray absorption rate in the irradiation direction of the electron beam in the target stacked structure decreases continuously or stepwise toward the X-ray low absorption rate spot at least in a predetermined region around the X-ray low absorption rate spot.

9. The X-ray generator according to claim 7, wherein a thickness of the target in the X-ray low absorption rate part is larger than an electron diffusion distance in the target.

10. The X-ray generator according to claim 7, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the target.

11. The X-ray generator according to claim 7, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the X-ray irradiation window.

12. The X-ray generator according to claim 7, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from stacking an X-ray absorption layer for varying the X-ray absorption rate in the target stacked structure.

13. The X-ray generator according to claim 8, wherein a thickness of the target in the X-ray low absorption rate part is larger than an electron diffusion distance in the target.

14. The X-ray generator according to claim 8, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the target.

15. The X-ray generator according to claim 9, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the target.

16. The X-ray generator according to claim 8, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the X-ray irradiation window.

17. The X-ray generator according to claim 9, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from a difference in thickness of the X-ray irradiation window.

18. The X-ray generator according to claim 8, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from stacking an X-ray absorption layer for varying the X-ray absorption rate in the target stacked structure.

19. The X-ray generator according to claim 9, wherein a difference in the X-ray absorption rate in the irradiation direction of the electron beam between positions in the target stacked structure results from stacking an X-ray absorption layer for varying the X-ray absorption rate in the target stacked structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of an embodiment of the invention and a graph indicating an X-ray profile released to the outside by this configuration.

[0029] FIG. 2 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of another embodiment of the invention.

[0030] FIG. 3 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of still another embodiment of the invention.

[0031] FIG. 4 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of still another embodiment of the invention.

[0032] FIG. 5 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of an embodiment of the invention having a function of facilitating alignment of an irradiation position of the electron beam.

[0033] FIG. 6 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of another embodiment of the invention having a function of facilitating alignment of an irradiation position of the electron beam.

[0034] FIG. 7 is a schematic cross-sectional view of a portion around an electron beam irradiation region in a target stacked structure of still another embodiment of the invention having a function of facilitating alignment of an irradiation position of the electron beam.

[0035] FIG. 8 is a schematic cross-sectional view illustrating a configuration example of an X-ray generator using a transmission type target.

[0036] FIG. 9 is an enlarged view of a portion around a region in which a target is irradiated with an electron beam in FIG. 8 and a graph indicating an X-ray profile released to the outside by this configuration.

[0037] FIG. 10 is a schematic cross-sectional view of a portion around a region in which a target is irradiated with an electron beam in a conventional X-ray generator having a structure in which a fine columnar target is held in an X-ray irradiation window, and a graph indicating an X-ray profile released to the outside by this configuration.

MODE FOR CARRYING OUT THE INVENTION

[0038] Hereinafter, embodiments of the invention will be described with reference to drawings.

[0039] FIG. 1 is a schematic cross-sectional view of a main part of an embodiment of the invention and a graph indicating an X-ray profile emitted to the outside by this configuration. In this embodiment, a basic configuration as an X-ray generator is the same as that illustrated in FIG. 8, and a great feature is that a target stacked structure is changed from that illustrated in FIG. 9 to that illustrated in FIG. 1.

[0040] A target stacked structure 3 fixed to close one end portion of a vacuum container includes an X-ray irradiation window 1 and a target 2 stacked on an inner surface side of the container similarly to that of FIG. 9. Further, an electron beam B accelerated and focused from an electron gun in the vacuum container is emitted onto the target 2 to generate an X-ray. In general, W, Mo, Cu, etc. is used as a material of the target 2, and Al, Be, diamond, etc. is used for the X-ray irradiation window 1. In FIG. 1 to FIG. 10, an arrow in the electron beam B indicates an irradiation direction of the electron beam.

[0041] In the target stacked structure 3, an X-ray low absorption rate part 3a in which an X-ray absorption rate in an irradiation direction (X-ray extraction direction) of the electron beam B is locally low is formed in a region in which the target 2 is irradiated with the electron beam B. The X-ray low absorption rate part 3a in this example is formed by reducing a thickness of the target 2.

[0042] An element contained in the X-ray irradiation window 1 is a light element when compared to an element contained in the target 2. Further, when compared to an X-ray passing through an arrow a in the figure in the X-ray low absorption rate part 3a, an X-ray passing through an arrow b in another part is attenuated due to more absorption. As a result, the intensity of an X-ray profile emitted to the outside through the X-ray irradiation window 1 relatively increases around a center corresponding to a formation position of the X-ray low absorption rate part 3a as illustrated in FIG. 1. For this reason, the X-ray focal spot diameter becomes smaller when compared to a case of using the target having a uniform thickness illustrated in FIG. 9.

[0043] According to this configuration, an electron incident on the X-ray low absorption part 3a diffuses and an X-ray generated to reach the target 2 other than the part attenuates. Therefore, this configuration is particularly suitable to obtain an X-ray focal spot diameter less than or equal to 1 μm. In addition, due to the electron beam B incident on the X-ray low absorption rate part 3a, an X-ray obliquely emitted therefrom attenuates similarly to an X-ray passing through a part other than the X-ray low absorption rate part 3a, and thus this configuration is suitable for a case of reducing an X-ray irradiation angle.

[0044] In the above embodiment, the X-ray low absorption rate part 3a is formed by locally reducing the thickness of the target 2, more specifically, by providing a depression on a surface of the target 2 on a side at which the target 2 comes into contact with the X-ray irradiation window 1. However, the X-ray low absorption rate part may be formed by structures illustrated in FIG. 2 to FIG. 4 below.

[0045] In a target stacked structure 13 illustrated in FIG. 2, an X-ray low absorption rate part 13a is formed by providing a depression on a surface on an opposite side from a surface of a target 12 on a side at which the target 12 comes into contact with an X-ray irradiation window 11, and thus on a surface of the target 12 on an irradiation side of an electron beam B.

[0046] According to the structure illustrated in FIG. 2, an influence due to electron diffusion of the electron beam B incident on the X-ray low absorption rate part 13a to another part may not be reduced. However, the structure is suitable for a case of increasing an X-ray irradiation angle.

[0047] In a target stacked structure 23 illustrated in FIG. 3, an X-ray absorbing material 24 is stacked between an X-ray irradiation window 21 and a target 22, and a hole is provided in the X-ray absorbing material 24, thereby forming an X-ray low absorption rate part 23a in which an X-ray absorption rate is relatively low. A metal having a higher X-ray absorption rate than that of the target 22 is preferably used as a material of the X-ray absorbing material 24. For example, Pb may be used when W is used for the target 22, and W may be used when Cu is used for the target 22. According to the structure illustrated in FIG. 3, the same effect as that of the example illustrated in FIG. 1 may be obtained.

[0048] In a target stacked structure 33 illustrated in FIG. 4, a target 32 has a uniform thickness, and an X-ray transmitting member 35 made of a material having a lower X-ray absorption rate than that of a material of an X-ray irradiation window 31 is partially embedded in the X-ray irradiation window 31, thereby forming an X-ray low absorption rate part 33a in the target stacked structure 33. For example, Be may be used as the material of the X-ray transmitting member 35 when Al or diamond is used for the X-ray irradiation window 31. According to this configuration, the same effect as that of the example illustrated in FIG. 1 may be obtained.

[0049] It is possible to employ a configuration in which a depression is provided in the X-ray irradiation window 31, that is, a configuration in which air is used as the X-ray transmitting member 35 without using the X-ray transmitting member 35.

[0050] In each of the above embodiments, the X-ray low absorption rate part needs to be located inside an irradiation region of the electron beam B with respect to the target. However, in the invention, the X-ray focal spot diameter may be reduced without narrowing the electron beam. Therefore, when the irradiation region of the electron beam is set to be wide, positions thereof may not be particularly adjusted.

[0051] However, when X-ray intensity is increased, the density of the electron beam needs to be increased. When the density of the electron beam is increased while the irradiation region of the electron beam is widened, there arises another problem such as an increase in necessary power, an increase in the amount of heat generation of the target, etc. Therefore, it is useful to narrow the irradiation region by narrowing the electron beam to some extent. In this case, the irradiation position of the electron beam needs to be adjusted to the X-ray low absorption rate part. A configuration for facilitating position adjustment of the electron beam and the X-ray low absorption rate part will be described below.

[0052] In a target stacked structure 43 illustrated in FIG. 5, an X-ray low absorption rate part 43a is formed by forming a depression on a surface of a target 42 on an X-ray irradiation window 41 side similarly to the example of FIG. 1, and a portion around the X-ray low absorption rate part 43a on the surface of the target 42 on the same side is configured as a slope surface 46, so that an X-ray absorption rate gradually decreases toward the X-ray low absorption rate part 43a. In this way, when the irradiation position of the electron beam B is adjusted, it is sufficient to change the irradiation position of the electron beam B such that the X-ray intensity increases, and adjustment work is facilitated.

[0053] In a target stacked structure 53 illustrated in FIG. 6, a stepped surface 57 in which a thickness of a target decreases stepwise toward an X-ray low absorption rate part 53a is formed on a surface of the target 52 on an X-ray irradiation window 51 side around the X-ray low absorption rate part 53a formed in the same manner as that in the above description. The same effect as that in the above description may be obtained by this configuration.

[0054] As described above, the configuration in which the X-ray absorption rate decreases toward the X-ray low absorption rate part may be applied to the target stacked structure corresponding to the structures illustrated in FIG. 2 to FIG. 4. In the structure of FIG. 2, the same slope surface as that of the FIG. 5 or the stepped surface may be formed on the surface of the target 12 on the irradiation side of the electron beam B. In addition, in the structure of FIG. 4, an upper surface may be configured as a slope surface or a stepped surface such that the thickness of the X-ray irradiation window 31 increases toward an outer side. Further, in the structure of FIG. 3, as illustrated in FIG. 7, in a target stacked structure 63 in which an X-ray absorbing material 64 is stacked between an X-ray irradiation window 61 and a target 62, a thickness of the X-ray absorbing material 64 may be decreased toward an X-ray low absorption rate part 63a.

[0055] Here, in each of the above embodiments, a shape of an outline of the X-ray low absorption rate part viewed in the irradiation direction of the electron beam B is not particularly restricted, and may be set to an arbitrary shape such as a circle, a square, a polygon, etc. In addition, the slope surface and the stepped surface may be set to arbitrary shapes such as a cone and a circular stepped shape, a pyramid or a prismatic stepped shape, etc.

[0056] In addition, in each of the above embodiments, it is desirable to set the thickness of the target in the X-ray low absorption rate part to be larger than an electron diffusion distance. In this way, an electron incident on the X-ray low absorption rate part does not reach the X-ray irradiation window beyond the target. Therefore, it is possible to prevent a defect that an electron widely diffuses in the X-ray irradiation window and an X-ray is generated from a relatively wide region which is weak and unintended, thereby making the effect of the invention more reliable. The electron diffusion distance in the target differs depending on the material or acceleration energy of the electron beam, and thus an appropriate form or size may be employed according to a device specification.

INDUSTRIAL APPLICABILITY

[0057] The invention improves an X-ray focal spot using a target stacked structure including a target and an X-ray irradiation window of a transmission type X-ray generator. Unlike a technology of providing a collimator for shielding an X-ray in an unnecessary direction on the outside of an X-ray irradiation window, no structure is required on the outside of a vacuum container in the invention. Thus, it is possible to achieve the desired effect while a structure is simple and compact.

REFERENCE SIGNS LIST

[0058] 1, 11, 21, 31, 41, 51, 61: X-ray irradiation window

[0059] 2, 12, 22, 32, 42, 52, 62: target

[0060] 3, 13, 23, 33, 43, 53, 63: target stacked structure

[0061] 3a, 13a, 23a, 33a, 43a, 53a, 63a: X-ray low absorption rate part

[0062] 24, 64: X-ray absorbing material

[0063] 35: X-ray transmitting member

[0064] 46: slope surface

[0065] 57: stepped surface

[0066] 100: vacuum container

[0067] 101: X-ray irradiation window

[0068] 102: target

[0069] 103: target stacked structure

[0070] 104: electron gun

[0071] B: electron beam