JP5299739B2 - Refraction lens unit for X-rays and method for manufacturing a refraction lens for X-rays - Google Patents

Description

  The present invention relates to a refractive condensing lens optimal for synchrotron radiation X-rays and a method for manufacturing the same.

  X-rays are widely used for structural analysis such as X-ray diffraction, fluorescence measurement, and X-ray absorption fine structure (XAFS) because they have high penetrating power and are capable of nondestructive measurement. In particular, the appearance of synchrotron radiation X-rays has dramatically improved performance, and it has become possible to achieve measurements with high spatial resolution and detection of extremely low concentration substances, which were impossible before. Recently, free-electron laser oscillation has been realized, and it is expected that coherent X-rays can be used several years ahead.

The biggest problem with X-rays is that special ingenuity is required for beam focusing and imaging. Infrared light, visible light, and ultraviolet light can be easily collected and imaged by a glass refraction lens, whereas application of a similar refraction lens is extremely difficult for X-rays. This is based on the fact that the difference in refractive index between the solid and the atmosphere is extremely small from 10 ⁻⁴ to 10 ⁻⁷ in the X-ray region.
Therefore, conventionally, as an X-ray condensing element, an X-ray is grazingly incident on an elliptical mirror (see, for example, Non-Patent Document 1) or a Fresnel zone plate (FZP) which is a diffractive condensing element in which a concentric pattern is formed on a thin film. ) Is generally used (see, for example, Non-Patent Document 2).

  Recently, attempts to use refractive lenses for the purpose of condensing X-rays have also been reported. An example is shown in FIG. The material of this lens is beryllium (Be). As shown in FIG. 3A, one unit 101 of this lens is prepared by preparing cylindrical beryllium as a lens material 102, polishing the central portion of the two cylindrical end faces 103, and processing the spheroid hole 104. (For example, see Patent Document 1). X-rays have a refractive index in a solid smaller than that in the atmosphere (opposite to visible light). Therefore, the spheroid hole (concave lens) as shown in FIG. 3A functions as a condenser lens for X-rays.

However, since the difference in refractive index between Be and the atmosphere is very small, it is difficult to achieve the target focal length with a single lens unit. Therefore, as shown in FIG. 3B, a lens 105 having a desired focal length is realized by stacking the lens units 101 in series and accommodating them in a lens case 106.
Namioka, Yamashita, “X-ray imaging optics”, Baifukan (1999), p. 113 Same as above, page 96 JP 2005-207962 A

  In the prior art described above, the method using an elliptical mirror is problematic in that it is difficult to produce a precise elliptical shape, resulting in astigmatism. Moreover, there is a limit to the light collecting performance due to insufficient smoothness of the processed surface. FZP has a high light condensing performance, and an element with a short focal length can be manufactured relatively easily. Therefore, it has recently been widely used as an X-ray condensing / imaging element. However, since the diffraction efficiency of FZP is limited to 20 to 30%, there is light that passes through without being condensed (zero-order light). Therefore, in using FZP, how to block the zero-order light is a big problem. FZP is known to deteriorate in a short time when used with high-intensity X-rays using an undulator as a light source. Therefore, even if free electron lasers are put into practical use in the future and even higher-intensity X-rays can be used, it is considered that FZP is difficult to apply due to its durability problem.

  The problem of the X-ray refractive lens is processing accuracy. As described above, since the difference in refractive index between the atmosphere and the solid is very small, the radius of curvature of the lens must be 100 μm or less in order to obtain a short focal length. Precise machining of fine holes to achieve this is extremely difficult. In addition, it is extremely difficult to obtain the desired light collecting performance due to the shift of the central axis when the lens units are stacked in series.

  The present invention has been made in order to solve the above-described problems of the conventional X-ray condensing / imaging element, and has an excellent durability with a sufficient condensing performance with a single unit. The purpose is to provide.

The present invention has been made to solve the above problems. That is, the X-ray refractive lens unit according to the present invention includes a lens frame having a penetrating cylindrical hole and a concave meniscus formed by melting and solidifying a metal inside the cylindrical hole in order to achieve the above object. It is what has.
The X-ray refractive lens unit according to the present invention preferably has a concave radius of curvature of 100 μm or less.
The X-ray refractive lens unit according to the present invention is preferably such that the concave surface has a spherical accuracy of 0.1 μm or less.
The X-ray refractive lens unit according to the present invention preferably has a contact angle of 45 ° or less when the metal is melted with respect to the material of the lens frame.
In the X-ray refractive lens unit according to the present invention, the cylindrical hole preferably has a diameter of 1000 μm or less.
In the X-ray refractive lens unit according to the present invention, the depth of the cylindrical hole is preferably larger than the diameter of the cylindrical hole.
In the refractive lens unit for X-rays according to the present invention, the material of the lens frame is preferably gold, silver, copper or brass, and the metal is preferably a solder material.
The method of manufacturing a refractive lens for X-ray according to the present invention includes a step of placing a lens frame material having a cylindrical hole therethrough in contact with a heating source, and a lens material having high wettability with respect to the lens frame material. It includes a step of filling the inside of the cylindrical hole, heating and melting, and a step of cooling and solidifying the concave meniscus formed by the molten lens material at the opening end of the cylindrical hole.
In the method for producing a refractive lens for X-ray according to the present invention, the cooling rate of the cooling and solidification is preferably 10 ° C./min or less.
In the method for producing a refractive lens for X-rays according to the present invention, it is preferable to perform the heating and melting and cooling and solidification in an inert gas.

  Since the refractive lens for X-rays according to the present invention has a concave surface with a small radius of curvature, a single unit can obtain a focal length of 1 m or less. Further, the concave surface formed by the meniscus is a precise spherical surface, and is flat at the atomic level, so that high light condensing performance can be obtained. Furthermore, water cooling is possible, and it is possible to easily cope with heat generated by high-intensity X-rays. Therefore, the present invention can provide a refractive lens for X-rays having a sufficient light collecting performance with a single unit and excellent in durability.

As a lens frame material used for the X-ray refractive lens according to the present invention, for example, a refractory metal plate processed and formed with a fine cylindrical hole can be employed.
The cylindrical hole is usually a through hole. The diameter of the cylindrical hole is a factor that determines the radius of curvature of the lens, and is preferably 1000 μm or less. If it exceeds 1000 μm, it may be difficult to form an accurate spherical surface due to the weight of the metal melt. The depth of the cylindrical hole is preferably larger than the diameter of the cylindrical hole. The cylindrical hole can be formed using a laser drill or electron beam machining.
The refractory metal used as the lens frame material is preferably a metal having a melting point higher than the melting point of the solder material (200 ° C. to 300 ° C.) and a solder wetting angle (contact angle) of 45 ° or more. Specifically, gold, silver, copper or brass is preferable.

The low melting point metal used as the lens material is not particularly limited as long as it has high wettability with respect to the high melting point metal and has a lower melting point than the high melting point metal. From the viewpoint of the difference in refractive index from the low melting point metal, tin-silver solder and tin-lead solder are preferable.
A concave surface having a smaller radius of curvature is obtained as the wettability is higher and the contact angle (wetting angle) is smaller. Therefore, it is preferable that the lens frame material has a contact angle (wetting angle) of 45 ° or less when the lens frame material is melted. In this specification, the contact angle is measured by cross-sectional observation using a stereomicroscope or a scanning electron microscope.

  The method of manufacturing a refractive lens for X-rays according to the present invention fills the inside of the cylindrical hole with a lens material that has high wettability with respect to the lens frame material, and preferably has a contact angle at the time of melting within the above range. And heating and melting. The heating temperature depends on the melting point of the low melting point metal used as the lens material, but is preferably about 300 ° C. in order to prevent thermal shrinkage during cooling. From the viewpoint of preventing oxidation of the molten metal surface, melting and solidification are preferably performed in an inert gas atmosphere such as nitrogen or argon. The filling amount of the lens material is preferably such that the volume at the time of melting is smaller than the volume of the cylindrical hole so as not to overflow in order to form a concave meniscus at the end of the cylindrical hole.

  The X-ray refractive lens manufacturing method according to the present invention includes a step of cooling and solidifying the concave meniscus formed by the molten lens material at the two opening ends of the cylindrical hole. The cooling rate is desirably 10 ° C./min or less. When cooled rapidly, the molten metal may solidify locally and a precise spherical surface may not be obtained.

  The concave lens obtained by the method for producing a refractive lens for X-ray according to the present invention is also one aspect of the present invention. The concave lens obtained by the method for manufacturing a refractive lens for X-rays according to the present invention may be taken out from the lens frame material, or may be used as it is formed in the lens frame material. The refractive lens unit for X-rays according to the present invention is a single unit and has a sufficiently short focal length, but may be used in combination as a composite lens in series.

Since the refractive lens unit for X-ray according to the present invention has a concave surface with a small radius of curvature and can be 100 μm or less, a single unit can obtain a focal length of 1 m or less. The lower limit of the radius of curvature of the concave surface is determined by the radius of the smallest cylindrical hole. Since the minimum radius of the cylindrical hole by electron beam machining is about 50 nm, the lower limit of the radius of curvature of the concave surface is also about 50 nm.
The concave lens surface of the X-ray refractive lens unit according to the present invention forms a precise spherical surface, and the spherical accuracy measured by cross-sectional observation using the scanning electron microscope can be several nm or less.

The refractive lens unit for X-ray according to the present invention can be suitably used for condensing X-rays whose refractive index in solid is smaller than the refractive index in air, and is particularly suitable for condensing X-rays of 10 keV to 100 keV. Can be used.
As an application of the refractive lens unit for X-rays according to the present invention, it can be suitably employed for X-ray CT, X-ray diffractometer and the like.

  The X-ray refractive lens according to the present invention is a lens in which two concave surfaces are formed in the vicinity of two openings in a cylindrical hole that penetrates as described above, but a cylindrical hole that does not penetrate is formed, After obtaining a one-surface concave lens having a concave surface formed at one opening end of the cylindrical hole, a two-surface concave lens is combined back to back to obtain an X-ray refractive lens having two concave surfaces. You can also.

Hereinafter, the present invention will be described in detail based on examples.
FIG. 1 shows a first embodiment. As a lens frame member 1, a 30 μm thick copper plate (Cu) was drilled using a laser drill to form a cylindrical through hole 2 having a diameter of 20 μm. The obtained copper plate having a cylindrical through hole was fixed to the heater block in the gas distribution container with a screw. As the lens material 5, a solder mainly composed of tin (Sn) (composition Sn 96.5%, Ag 3%, Cu 0.5% Ag, product number: HS-302, manufactured by HOZAN) was used. A predetermined amount of the lens material is filled to the extent that it does not overflow into the through hole 2, heated to about 250 ° C. together with the lens frame material 1 on the heater block in a nitrogen atmosphere, and cooled at a cooling rate of 5 ° C./min. A lens 5 having concave meniscuses 3 and 4 as shown in FIG. 1 was formed in the through hole of the lens frame member 1. The radii of curvature of the meniscuses 3 and 4 were about 10 μm. In this embodiment, the photon energy of X-rays is E = 10 keV. At this energy, the refractive index difference between the atmosphere and Sn is 1−n≈10 ⁻⁵ . Therefore, from the relational expression of the radius of curvature R, the refractive index n, and the focal length f,
f = R / (1-n) × 1/2 to 10 × 10 ⁻⁶ m / 10 ⁻⁵ = 0.5 m
(1)
It becomes. The reason why the above formula (1) is multiplied by ½ is that there are two concave menisci. The average thickness of the lens determined from the solder filling amount and the diameter of the through hole was about 10 μm, and the lens transmittance of X = ray at E = 10 keV at this thickness was about 40%.

FIG. 2 shows a second embodiment of the present invention. In this embodiment, the X-ray refractive lens according to the present invention obtained in the first embodiment is applied to X-ray CT. Radiated X-rays generated by an undulator installed in SPring-8 (not shown in the figure) were monochromatized to E = 10 keV with a Si111 reflection monochromator not shown in the figure and irradiated on the sample 6. As the sample 6, a porous metal for a metal filter having fine pores was used. The X-ray beam transmitted through the sample 6 passed through the X-ray refractive lens 1 according to the present invention and was incident on the CCD camera 8. The distance from the lens 1 to the CCD camera 8 is L ₂ = 10 m. The distance between the sample 6 and the lens 1 is L ₁ = fL ₂ / (L ₂ −f) = 0.53 m. Therefore, the X-ray transmission image of the sample 6 is enlarged and projected onto the CCD camera 8, and the random enlargement ratio is m = L ₂ / L ₁ = 19. Since the pixel size of the CCD camera used here is 20 × 20 μm ² , the spatial resolution in direct measurement is about 20 μm. However, in this embodiment, the transmission image is enlarged 19 times, so that measurement with spatial resolution = 20 / 19≈1 μm becomes possible. With this arrangement, the sample 6 was rotated around the rotation axis 9 and a three-dimensional image of the fine pores in the sample could be reconstructed by CT image calculation.

  As described above, it has been found that since the X-ray refractive lens unit according to the present invention has a concave surface with a small curvature radius, a single unit can obtain a focal length of 1 m or less. Further, the concave surface formed by the meniscus is a precise spherical surface, and is flat at the atomic level, so that high condensing performance was obtained. The X-ray refractive lens unit according to the present invention generates aberration (spherical aberration) due to the concave surface not being a paraboloid, but is used under the condition that the aberration can be ignored by using light near the optical axis (paraxial light beam). It's easy to do. Furthermore, when heat generation due to high-intensity X-rays becomes a problem, it is excellent in that water cooling is easy.

FIG. 1 is a schematic sectional view of an X-ray refractive lens unit according to the present invention. FIG. 2 is a schematic diagram regarding application of the X-ray refractive lens unit according to the present invention to X-ray CT. FIG. 3A shows a conventional X-ray condenser lens unit, and FIG. 3B shows a compound lens combining the conventional X-ray condenser lens unit as viewed from the end face of the cylinder, and a cross section taken along the line AA. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Refraction lens for X-rays 2 Lens frame material 3 Cylindrical hole 4 Concave meniscus 5 Lens material 6 Sample 7 Monochromatic X-ray 8 CCD camera 9 Rotation center axis 101 Lens unit 102 Lens material (cylindrical beryllium)
103 cylindrical end face 104 spheroidal hole 105 X-ray condenser lens 106 lens case

Claims (8)

A lens frame having a cylindrical hole therethrough, and a concave meniscus formed by melting and solidifying a metal inside the cylindrical hole;
The contact angle at the time of melting of the metal with respect to the material of the lens frame is 45 ° or less,
A material for the lens frame is gold, silver, copper, or brass, and the metal is a solder material. 2. The X-ray refractive lens unit according to claim 1, wherein a radius of curvature of the concave surface of the concave meniscus is 100 μm or less. The X-ray refractive lens unit according to claim 1 or 2, wherein the concave surface of the concave meniscus has a spherical accuracy of 0.1 µm or less.   The X-ray refractive lens unit according to claim 1, wherein the cylindrical hole has a diameter of 1000 μm or less.   The refractive lens unit for X-rays according to any one of claims 1 to 4, wherein a depth of the cylindrical hole is larger than a diameter of the cylindrical hole. A step of placing a lens frame member having a penetrating cylindrical hole in contact with a heating source;
Filling the inside of the cylindrical hole with a lens material having high wettability with respect to the lens frame material, heating and melting,
Cooling and solidifying the concave meniscus formed by the molten lens material at the opening end of the cylindrical hole,
The contact angle at the time of melting of the lens material with respect to the material of the lens frame material is 45 ° or less,
The method of manufacturing a refractive lens for X-rays, wherein a material of the lens frame material is any of gold, silver, copper, or brass, and a material of the lens material is a solder material.   The manufacturing method of the refractive lens for X-rays of Claim 6 whose cooling rate of the said cooling solidification is 10 degrees C / min or less.   The manufacturing method of the refractive lens for X-rays of Claim 6 or 7 which performs the said heat melting and cooling solidification in inert gas.

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