Patent Application
20120087475
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-229572, filed on Oct. 12, 2010; the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a method for generating an X-ray with high brightness and to an apparatus for generating the same X-ray.
2. Description of the Related Art
In the X-ray diffraction measurement or the like, it is often required that an X-ray with an intensity as high as possible is irradiated onto a sample so as to realize the X-ray diffraction measurement. As such an X-ray generating apparatus as being employed for the X-ray diffraction measurement, an X-ray generating apparatus of rotating anticathode target is conventionally well known.
The rotating anticathode X-ray generating apparatus is configured such that an electron beam is irradiated onto the outer surface of the columnar anticathode target while the columnar anticathode target is rotated under the condition that a cooling medium is flowed in the columnar anticathode target. The rotating anticathode X-ray generating apparatus has an extreme high cooling efficiency because the irradiating portion of the electron beam is varied with time in comparison with an X-ray generating apparatus of stationary target. Therefore, an electron beam can be irradiated onto the anticathode target under the condition of large current to generate an X-ray with high intensity (high brightness).
In this case, however, the intensity of the electron beam to be irradiated per unit area on the target is increased, causing the partial melting for the target and the splashing of the melted target. Therefore, theoretically, the brightness of the x-ray can be increased based on the aforementioned relation, but practically, is restrictive due to the melting point of the target.
In view of the aforementioned problem, such an attempt is made in Reference 1 as irradiating an electron beam onto the inner side of the cylindrical portion of a rotating anticathode X-ray generating apparatus so as to heat the irradiating portion to a temperature equal to or near the melting point of the anticathode target and generate an X-ray with high brightness. In this case, since the irradiating portion of the electron beam is heated to a temperature around the melting point of the rotating anticathode target, the electron beam irradiating portion is at least partially melted. However, since the electron beam irradiating portion is kept against the cylindrical portion by the centrifugal force generated by the rotation of the rotating anticathode target, the partially melted portion of the target, originated from the electron beam irradiation, cannot be splashed outward from the cylindrical portion.
According to Reference 1, therefore, since the intensity of the electron beam to be irradiated can be increased per unit area of the target under the condition that the melting and splashing of the rotating anticathode target are prevented, an X-ray with an relatively higher brightness can be obtained as compared with a conventional one.
In view of high resolution analysis and examination, however, it is required to realize the X-ray with higher brightness. Moreover, it is desired to realize the X-ray with higher brightness under the condition of low electric power.
It is an object of the present invention to provide a new X-ray generating method and apparatus which can generate an X-ray with high brightness.
In order to achieve the object, the present invention relates to a method for generating an X-ray, including the steps of:
The present invention also relates to An X-ray generating apparatus, including:
Here, the incident angle β and the output angle α are measured by defining the surface of the target as a standard.
The inventor had intensely studied so as to achieve the above-mentioned object. As a result, the inventor has found out that the incident angle of an energy beam, that is, an electron beam so as to generate an X-ray and the output angle of the X-ray importantly affect the brightness of the X-ray. Namely, in a conventional X-ray generating method and apparatus, an electron beam for generating an X-ray is incident on the surface of a target at an angle of about 90 degrees and only the X-ray falling within an output angle range of about 5 to 6 degrees is selectively taken out of the target.
However, when the electron beam is irradiated under the aforementioned condition to take the thus obtained X-ray out of the target, the electron beam is deeply penetrated into the target (electron range re) so that the X-ray generated at the deep portion of the target travels in the target by a long distance (re/sin α) until the X-ray is taken out of the surface of the target. Therefore, the thus generated X-ray is largely absorbed by the target so that the intensity (brightness) of the X-ray is also decreased.
The aforementioned phenomenon becomes conspicuous as the energy of the electron beam, that is, the accelerating voltage for the electron beam is increased.
For example, when an electron beam with an energy of 80 keV is irradiated on a Cu target, the electron beam is penetrated into the Cu target by a depth of about 14 μm. If the output angle of the thus obtained X-ray is 5.7 degrees, the X-ray travels in the target by a distance of 140 μm (about 14 μm/sin 5.7). As a result, the intensity (brightness) of the X-ray is decreased about one-thousandth as high as the intensity (brightness) of an X-ray with no absorption.
In view of the aforementioned fact, therefore, the inventor has investigated variously the brightness of the X-ray by changing the incident angle of the electron beam relative to the target and the output angle, that is, the taking out-angle of the X-ray variously. As a result, the inventor has found out that the brightness of the X-ray can be easily rendered higher by setting the incident angle β of the electron beam relative to the target to a predetermined angle, concretely within a range of 60 degrees or less and setting the output angle (taking out-angle) α of the X-ray to an angle so as to satisfy the relation of −30 degrees≦β−α≦60 degrees.
In other words, the inventor has found out that the X-ray with a high intensity can be easily obtained by improving the corresponding X-ray generating apparatus so as for the incident angle β of the electron beam relative to the target for generating the X-ray and the output angle α of the x-ray to satisfy the above-described relations without a large-scaled improvement for the X-ray generating apparatus.
As is apparent from the aforementioned description, the present invention is realized on the try and error and the finding of the aforementioned phenomenon by the inventor, so that the present invention encompasses the finding of the aforementioned phenomenon.
In an aspect of the present invention, the X-ray can be generated and taken out so as to satisfy the relation of 0 degree≦β−α≦60 degrees. In this case, even if the electron beam with a high energy is irradiated onto the target, the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
In another aspect of the present invention, the X-ray can be generated and taken out so as to satisfy the relation of 30 degrees≦β−α≦50 degrees. In this case, even if the electron beam with a low energy is irradiated onto the target, the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
Here, the requirement of the output angle α of the X-ray XR when the electron beam with a low energy is irradiated is restricted in comparison with the requirement of the output angle α of the X-ray when the electron beam with a high energy is irradiated. This is because the brightness of the X-ray to be generated and taken out is not much dependent on the output angle α of the X-ray since the electron beam with the low energy is not deeply penetrated into the target. In order to obtain the X-ray with the high brightness under such a relaxed condition as described above, therefore, it is required that the output angle α of the X-ray is strictly selected, resulting in the above-described restriction.
In still another aspect of the present invention, the incident angle β is controlled by adjusting an arrangement of the electron beam source disposed in or outside the chamber or deflecting an orbit of the electron beam using a deflecting magnet disposed in the chamber.
In a further aspect of the present invention, the output angle α is controlled by adjusting a position of formation of an X-ray transparent window.
As described above, according to the present invention can be provided the new X-ray generating method and apparatus which can generate an X-ray with high brightness.
For better understanding of the present invention, reference is made to the attached drawings.
hereinafter, the present invention will be described in detail with reference to the drawings.
An X-ray generating apparatus illustrated in
The chamber 11 may be made of, e.g., a stainless steel (SUS). The target 12 may be made of Cu, Co, W, Mo, Cr or the like depending on a wavelength of an X-ray to be generated. The X-ray transparent film 16 may be made of Be, Al or the like. Here, the electron beam source 13 and the deflecting magnet 14 may be made of ones commercially available.
In the X-ray generating apparatus 10 illustrated in
In this case, if the X-ray XR is taken out of the target 12 by setting the incident angle β of the electron beam EB to be irradiated onto the target 12 within a range of 60 degrees or less and satisfying the relation of −30 degrees≦β−α≦60 degree if the output angle of the X-ray is defined as “α”, the absorption of the X-ray XR by the target 12 is prevented so as to increase the brightness of the X-ray XR.
Here, the lower limited value of the incident angle β of the electron beam EB is not restrictive only if the electron beam EB can be incident onto the target 12 to generate the X-ray XR. Therefore, the incident angle β may be set to 0 degree or more, practically to 5 degrees.
Since the X-ray XR is taken out of the X-ray transparent film (X-ray transparent window) 16, the position of the formation of the X-ray transparent film (X-ray transparent window) 16 is determined commensurate with, the output angle α satisfying the relation of −30 degrees≦β−α≦60 degree.
Here, the incident angle β and the output angle α are measured by defining the surface of the target 12 as a standard.
The incident angle β of the electron beam EB for the target 12 can be set within the aforementioned range by changing the magnetic field and position of the deflecting magnet 14 depending on the energy (accelerating voltage) of the electron beam EB.
The X-ray can be generated and taken out so as to satisfy the relation of 0 degree≦β−α≦60 degrees. In this case, even if the electron beam EB with a high energy is irradiated onto the target 12, the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
The X-ray can be generated and taken out so as to satisfy the relation of 30 degrees≦β−α≦50 degrees. In this case, even if the electron beam EB with a low energy is irradiated onto the target 12, the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
Here, the requirement of the output angle α of the X-ray XR when the electron beam EB with a low energy is irradiated is restricted in comparison with the requirement of the output angle α of the X-ray XR when the electron beam EB with a high energy is irradiated. This is because the brightness of the X-ray XR to be generated and taken out is not much dependent on the output angle α of the X-ray XR since the electron beam EB with the low energy is not deeply penetrated into the target 12. In order to obtain the X-ray XR with the high brightness under such a relaxed condition as described above, therefore, it is required that the output angle α of the X-ray XR is strictly selected, resulting in the above-described restriction.
As described, above, in the X-ray generating apparatus 10 in this embodiment, the X-ray with the high brightness can be obtained by improving the apparatus 10 so as for the incident angle β of the electron beam EB for the target 12 and the output angle α of the X-ray XR to satisfy the aforementioned relations.
In this embodiment, the electron beam source 13 is disposed in the chamber 11, but may be disposed outside of the chamber 11 so that the electron beam RE can be introduced into the chamber 11 through an electron beam introducing window or au electron beam inlet formed at the chamber 12.
An X-ray generating apparatus 20 illustrated in
The rotating anticathode 22 includes a cylindrical portion 22a made of Cu (copper) or the like, a circular plate 22b formed so as to close the one opening of the cylindrical portion 22a, and a rotating shaft 23 with a center shaft shared with the cylindrical portion 22a and the circular plate 22b which are integrally formed. The interior of the circular plate 22b is formed in air hole. An electron beam irradiating portion is defined on the inner wall of the cylindrical portion 22a.
The rotating shaft 23 of the rotating anticathode 22 is supported rotatably by a pair of bearings 28a and 28b which are provided in the rotation driving portion 28. The rotating anticathode 22 is rotated by the rotation of the rotating shaft 23 so that a centrifugal force is generated outward from the rotating anticathode 22, that is, a cylindrical portion 22a.
At the root of the rotating shaft 23 near the circular plate 22b is provided a rotating shaft-sealing member 29 for maintaining the interior of the anticathode chamber 21 in a state of vacuum by maintaining the rotating shaft 23 and the anticathode chamber 21 under an air-tight condition by the rotating shaft-sealing member 29.
In the rotating anticathode 22a is inserted a stationary separating member 22c for flowing a cooling water along the inner wall of the electron beam irradiating portion. The stationary separating member 22c is formed in a cylindrical shape commensurate with the shape of the rotating shaft 23, enlarged along the shape of the circular shape 22b and elongated short of the right and left edges of the inner wall of the cylindrical portion 22a.
In other words, the stationary separating member 22c divides the interior space of the rotating anticathode 22 so as to be a double tube structure. The outer side of the double tube structure is communicated with a cooling water inlet.
Therefore, the introduced cooling water is flowed in the outer side of the double tube structure, returned from the right edge of the inner wall of the cylindrical portion 22a and flowed in the inner side of the double tube structure. In this case, the inner wall of the electron beam irradiating portion is cooled by the cooling water, and the remnant cooling water is flowed in the inner side and discharged from a cooling water outlet.
The cathode 32 includes an insulating structural portion 33, a filament 34, a wehnelt 35 and the like, and configured such that the electron beam ER can be irradiated onto the rotating anticathode 22 by the supply of high voltage electric power with several ten kV from a high voltage electric power introducing portion 37 and the supply of filament electric power.
In this case, if the X-ray XR is taken out of the rotating anticathode 22 (cylindrical portion 22a) by setting the incident angle β of the electron beam EB to be irradiated onto the rotating anticathode 22 within a range of 60 degrees or less and satisfying the relation of −30 degrees≦β−α≦60 degree if the output angle of the X-ray is defined as “α”, the absorption of the X-ray XR by the rotating anticathode 22 (cylindrical portion 22a) is prevented so as to increase the brightness of the X-ray XR.
Here, the lower limited value of the incident angle β of the electron beam EB is not restrictive only if the electron beam EB can be incident onto the rotating anticathode 22 (cylindrical portion 22a) to generate the X-ray XR. Therefore, the incident angle β may be set to 0 degree or more, practically to 5 degrees.
Since the X-ray XR is taken out of the X-ray transparent film (X-ray transparent window) 26, the position of the formation of the X-ray transparent film (X-ray transparent window) 26 is determined commensurate with the output angle α satisfying the relation of −30 degrees≦β−α≦60 degree.
Here, the incident angle β and the output angle α are measured by defining the surface of the rotating anticathode 22 (cylindrical portion 22a) as a standard.
The incident angle β of the electron beam EB for the rotating anticathode 22 (cylindrical portion 22a) is controlled by adjusting the position of the cathode 32. In this embodiment, the position of the formation of the cathode chamber 31 relative to the anticathode chamber 21 is adjusted so as to control the incident angle β of the electron beam EB.
The X-ray can be generated and taken out so as to satisfy the relation of 0 degree≦β−α≦60 degrees. In this case, even if the electron beam EB with a high energy is irradiated onto the rotating anticathode 22 (cylindrical portion 22a), the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
The X-ray can be generated and taken out so as to satisfy the relation of 30 degrees≦β−α≦50 degrees. In this case, even if the electron beam EB with a low energy is irradiated onto the rotating anticathode 22 (cylindrical portion 22a), the brightness of the X-ray can be easily increased by appropriately selecting and taking out the X-ray with the output angle α satisfying the aforementioned relation.
Here, the requirement of the output angle α of the X-ray XR when the electron beam EB with a low energy is irradiated is restricted in comparison with the requirement of the output angle α of the X-ray XR when the electron beam EB with a high energy is irradiated. This is because the brightness of the X-ray XR to be generated and taken out is not much dependent on the output angle α of the X-ray XR since the electron beam EB with the low energy is not deeply penetrated into the target 12. In order to obtain the X-ray XR with the high brightness under such a relaxed condition as described above, therefore, it is required that the output angle α of the X-ray XR is strictly selected, resulting in the above-described restriction.
As described above, in the X-ray generating apparatus 20 in this embodiment, the X-ray with the high brightness can be obtained by improving the apparatus 20 so as for the incident angle β of the electron beam EB for the rotating anticathode 22 (cylindrical portion 22a) and the output angle α of the X-ray XR to satisfy the aforementioned relations.
In the X-ray generating apparatus 20 of this embodiment, moreover, the electron beam irradiating portion of the cylindrical portion 22a of the rotating anticathode 22 is kept against the cylindrical portion 22a, that is, the rotating anticathode 22 by the centrifugal force generated in the direction outward from the cylindrical portion 22a and generated by the rotation of the rotating shaft 23. In the case where the electron beam EM with a high brightness is irradiated onto the rotating anticathode 22, therefore, even if the electron beam irradiating portion is partially melted, the melted portion cannot be splashed outward since the melted portion is kept by the centrifugal force generated at the cylindrical portion 22a. In the X-ray generating apparatus 20 in this embodiment, therefore, the X-ray with a high brightness can be easily generated also due to the structural characteristic of the apparatus 20.
The brightness of an X-ray (an actually measured brightness I relative to a theoretical brightness I0) was investigated dependent on the incident angle β of an electron beam and the output angle α of the X-ray by using the x-ray generating apparatus 10 illustrated in
I/I
0=(sin β/sin α)exp(−μX)
Here, the term “(sin β/sin α)” means a ratio in cross section of the electron beam to the X-ray and the term “μ” means an absorption coefficient of a target. The term “X” gleans a range of the X-ray from the inside to the surface of the target and can be represented as “re(sin β/sin α)” using a range re of the electron beam in the target.
Conventionally, since the electron beam is irradiated vertically on the surface of the target (at an angle of 90 degrees), the incident angle β of the electron beam, which is introduced for the first time in the present invention, is not considered as a variable in view of the brightness of the X-ray. In the present invention, however, since the incident angle β of the electron beam is changed and thus required to be used as a variable, the aforementioned equation is introduced. The aforementioned equation is obvious because the range of the generated X-ray from the inside to the surface of the target is represented as re(1/sin α) in “BRIEF SUMMARY OF THE INVENTION”.
The target 12 is made of Cu and the unit system is represented by “μm”. In this case, the term “μ” is 0.041. Moreover, the energy (accelerating voltage) of the electron beam is set to 40 keV. In this case, the range r, of the electron beam in the Cu target is 5.36 μm. The calculated (simulated) results are listed in Table 1.
In the examples, the brightness (I/I0) is often beyond 1 because the term “(sin β/sin α)” is introduced. Namely, if the relation of β>α is satisfied within a range of 0 to 90 degrees, the term “(sin β/sin α)” is beyond 1, so that in the case where the value of the exponential part of the aforementioned equation is relatively large, the brightness (I/I0) is often beyond 1 because the brightness (I/I0) is represented by the multiplication of the term “(sin β/sin α)” and the exponential part.
As is apparent from Table 1, in the examples, if the incident angle β of the electron beam is set to 60 degrees or less and the output angle of the X-ray satisfies the relation of 30 degrees≦β−α≦50 degrees, the brightness of the X-ray can be increased in comparison with the conventional ones because the energy of the electron beam is set relatively small to 40 keV.
In the X-ray generating apparatus 20 illustrated in
The brightness of an X-ray (an actually measured brightness I relative to a theoretical brightness I0) was investigated dependent on the incident angle β of an electron beam and the output angle α of the X-ray by using the X-ray generating apparatus 10 illustrated in
As is apparent from Table 2, in the examples, if the incident angle β of the electron beam is set to 60 degrees or less and the output angle of the X-ray satisfies the relation of −30 degrees≦β−α≦60 degrees, the brightness of the X-ray can be increased in comparison with the conventional ones because the energy of the electron beam is set relatively large to 60 keV.
In the X-ray generating apparatus 20 illustrated in
The brightness of an X-ray (an actually measured brightness I relative to a theoretical brightness I0) was investigated dependent on the incident angle β of an electron beam and the output angle α of the X-ray by using the X-ray generating apparatus 10 illustrated in
As is apparent from Table 3, in the examples, if the incident angle β of the electron beam is set to 60 degrees or less and the output angle of the X-ray satisfies the relation of 0 degree≦β−α≦60 degrees, the brightness of the X-ray can be increased in comparison with the conventional ones because the energy of the electron beam is set relatively large to 80 keV.
In the X-ray generating apparatus 20 illustrated in
Although the present invention was described in detail with reference to the above examples, this invention is not limited to the above disclosure and every kind of variation and modification may be made without departing from the scope of the present invention.
For example, in the examples, the Cu target is employed because the Cu target is easily available and not expensive, but another target such as a Co target, a W target, a Mo target, a Cr target or commercially available may be employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-229572 | Oct 2010 | JP | national |
