JP2011053096A - Neutron optical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To condense a non-monochromatic neutron beam with a simple structure. <P>SOLUTION: In a neutron condensing element 10, a through-hole 11 shaped like a cone to pass neutrons is formed. One end (the left side) of the through-hole 11 is an opening 111 on an incidence side which lets in a neutron beam, and the other end (the right side) is an opening 112 on an emission side which emits the neutron beam. The contours of both openings 111 and 112 on the incidence and emission sides are circular and the area of the opening 112 on the emission side is smaller than that of the opening 111 on the incidence side. The optical axis 100 of the neutron beam to be condensed passes through the centers of the openings 111 and 112 on the incidence and emission sides. In the neutron condensing element 10, neutrons are scattered on the inside face of the through-hole 11 and the utilization of the broadening of the scattering angle can enhance the strength in the opening 112 on the emission side. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a structure of a neutron optical element capable of focusing (focusing) a neutron beam.

  A technique for condensing parallel light or divergent light in an extremely narrow area using a condensing mirror or lens and obtaining extremely strong intensity is widely used in various fields. The condensing mirror focuses light using reflection of light on the reflecting surface, and the lens focuses light using transmission and refraction of light in the substance. Although it is difficult to compare with visible light or the like, X-rays can be condensed similarly using a condensing mirror, thereby irradiating the sample with intense X-rays in an extremely narrow region. be able to. There is also known a technique for using this to perform highly sensitive elemental analysis. In addition, it is difficult to refract and reflect an electron beam like light or X-rays, but since an electron beam has a charge, it is possible to bend the electron beam trajectory using an electromagnetic field and focus it. is there. Therefore, it is possible to focus an electron beam on a sample in the same manner as light or X-ray, and an apparatus using this is also known.

  On the other hand, a neutron beam is a kind of radiation like an X-ray and an electron beam, but has a weak interaction with a substance and has no electric charge. Accordingly, there is no known lens or mirror that can focus (condensate) the light.

  In recent years, neutron radiography, for example, has come to be used as a technique using neutron beams. In neutron radiography, transmission images of neutrons through a sample can be obtained. However, since neutrons have weak interaction with substances and high transmission power, it is possible to obtain information that cannot be obtained with transmission images of X-rays or visible light. it can. As the neutron source in this case, for example, an experimental nuclear reactor, an accelerator, or the like is used, but it is still necessary to sufficiently increase the intensity of the neutron beam on the sample. Therefore, a technique for condensing neutron beams is required as in the case of visible light, X-rays, electron beams, and the like.

  However, for neutrons, a collimator that determines the direction of the neutron beam is used, but as described above, the neutron beam cannot be collected using a lens or a mirror, and this is collected electromagnetically. It is also difficult to make it. For this reason, in order to focus a neutron beam, the technique different from visible light, an electron beam, etc. is used. As an example, there is a technique described in Patent Document 1, for example. In this technique, a plurality of fiber-like capillaries that allow X-rays to pass through are bundled, and X-rays can be condensed on the emission side, but it is described that neutrons are also used in the same way as X-rays. Yes. Therefore, the structure in which the capillaries are bundled can be used as a neutron lens in a pseudo manner.

  Patent Document 2 describes a neutron optical element having a configuration in which a plurality of openings (apertures) are arranged. In this technique, each diaphragm functions as a collimator that selectively transmits a neutron beam having a specific traveling direction. By optimizing the interval of the collimator according to the energy of the neutron, the neutron beam can be substantially condensed using the curvature of the orbit of the neutron beam due to gravity.

JP 2005-321246 A JP 2005-536757 A

  In the technique described in Patent Document 1, although a neutron beam can be condensed regardless of the energy of neutrons, there is no condensing ability with a single capillary. Therefore, it is important to bundle a plurality of capillaries into a predetermined shape, but the manufacturing process is complicated, and the reliability of the finally obtained structure (pseudo-neutron lens) has also been lowered.

  In the technique described in Patent Document 2, since the orbit of the neutron beam differs depending on the energy of neutrons, it is necessary to adjust the aperture interval according to the energy of neutrons. Therefore, the focusing effect can be obtained only for monochromatic neutron beams. However, neutrons emitted from, for example, an experimental reactor are not monochromatic but have a broad spectrum. It has been difficult to collect neutron beams that are not monochromatic (or forward monochromatic). This situation was the same for neutron optical elements that use reflection and diffraction, since reflection and diffraction are also dependent on the energy of neutrons.

  Therefore, it has been difficult to collect neutron beams having no uniform energy with a simple configuration.

  The present invention has been made in view of such problems, and an object thereof is to provide an invention that solves the above problems.

In order to solve the above problems, the present invention has the following configurations.
The neutron optical element of the present invention is a neutron optical element that causes a neutron beam to be incident from an incident side opening and to be emitted from an emission side opening, and is composed of a neutron scatterer, one end being the incident side opening and the other end Is provided with a through-hole that becomes the exit side opening, and the area of the exit side opening is smaller than the area of the entrance side opening.
In the neutron optical element of the present invention, an inner surface shape of the through hole between the incident side opening and the emission side opening is configured by a straight line on a cross section including the optical axis of the neutron beam. It is characterized by.
In the neutron optical element according to the present invention, the inner shape of the through hole is formed by a part of a conical surface.
In the neutron optical element according to the present invention, the inner shape of the through hole is a part of a polygonal conical surface.
In the neutron optical element of the present invention, the neutron scatterer is mainly composed of an organic polymer material.
In the neutron optical element of the present invention, the organic polymer material is mainly composed of any one of polyimide, polyethylene, polyetheretherketone, polymethyl methacrylate resin, and polyethylene terephthalate.
In the neutron optical element of the present invention, the neutron scatterer has beryllium as a main component.

  Since this invention is comprised as mentioned above, the neutron beam which is not monochromatic can be condensed with a simple structure.

It is the perspective view (a) of the neutron condensing element which concerns on embodiment of this invention, and sectional drawing (b) on an optical axis. It is a figure explaining the condition of the condensing of the neutron beam in the neutron condensing element which concerns on embodiment of this invention.

  Hereinafter, the neutron optical element according to the embodiment of the present invention will be described. Note that although neutron rays are not light, they can be treated as if they behave like light. Therefore, the terms used when the neutron rays are replaced with light rays, such as condensed light, divergent light, and parallel light, are used for convenience. FIG. 1 is a perspective view (a) of a neutron focusing element 10 as an example of this neutron optical element and a cross-sectional view (b) in the AA direction (on the optical axis).

  The neutron condensing element 10 is made of a material (neutron scatterer) having a high ability to scatter neutrons. As this material, an organic material containing a large amount of hydrogen and a material that can easily realize the shape of FIG. 1 are used, such as polyethylene, polyimide, etc., which are organic polymer materials, and beryllium, which is a light metal. .

  In this neutron condensing element 10, a conical through-hole 11 that allows neutrons to pass through is formed. One end (left side) of the through-hole 11 is an incident side opening 111 through which a neutron beam is incident, and the other end (right side) is an emission side opening 112 through which the neutron beam is emitted. The shapes of the incident side opening 111 and the emission side opening 112 are both circular, and the area of the emission side opening 112 is smaller than the area of the incident side opening 111. The optical axis 100 of the focused neutron beam passes through the center of the incident side opening 111 and the center of the emission side opening 112. In the cross section including the optical axis 100 (FIG. 1B), the line connecting these two openings is a straight line. Therefore, the inner surface of the through hole 11 is a part of the conical surface.

  Since the size of the exit side opening 112 is the size of the condensing point (condensation size), the size is appropriately set according to the size or intensity required according to the purpose of use of the neutron beam. It can be about 1 μmφ. The size of the entrance-side opening 111 is appropriately set according to the characteristics of the neutron beam (for example, whether it is divergent light or parallel light) and the neutron beam intensity required at the focal point. It can be about 10 mm to 100 mm. The thickness of the neutron condensing element 10 (the distance between the incident side opening 111 and the emission side opening 112) depends on the size of the emission side opening 112, the size of the incident side opening 111, the light collection efficiency, and the like. The cone-shaped apex angle θ is determined accordingly.

  An example of the traveling direction of the neutron beam when the neutron beam is incident on the neutron condensing element 10 is schematically shown in FIG. Here, it is assumed that the neutron beam 20 is divergent light emitted from a neutron source, and a part of the light is incident on the through hole 11. Here, a path along which the B, C, and D neutron beams 20 passing through the incident side opening 111 travel will be described.

  The neutron beam 20 of B in FIG. 2 is linearly incident on the inner surface 113 in the through hole. Some of the neutrons that have weak interactions with the material enter the neutron scatterer at this incident point, and the neutrons that have entered enter the neutron scatterer or pass through the neutron scatterer. It reaches the outside of the neutron focusing element 10. Neutrons that have not penetrated are reflected or scattered at this incident point. Here, when visible light or the like is incident on the surface of the substance, the ratio of reflection is high, but the ratio of reflection of neutrons on the surface of the substance is extremely low.

When the neutron beam 20 is reflected by the inner surface 113 in the through hole, the incident angle and the emission angle of the neutron beam 20 with respect to the inner surface 113 in the through hole are equal due to the law of conservation of momentum. However, when this is scattered, the scattering angle of a neutron beam having a certain incident angle is not single, but generally has a spread. This scattering angle varies depending on, for example, the state of the inner surface of the through hole 11 and the energy of neutrons. Accordingly, for example, the B neutron beam 20 is scattered in four directions of B ₁ , B ₂ , B ₃ , and B ₄ . Among these, the neutron beam traveling in the direction of B ₄ passes through the emission side opening 112. Neutron rays traveling in the directions of B ₁ , B ₂ , and B ₃ reach, for example, the through hole inner bottom surface 114 and enter the neutron scatterer, or are reflected or scattered at this incident point.

Similarly, when the C neutron beam 20 linearly incident on the inner bottom surface 114 of the through hole is scattered in the directions of C ₁ , C ₂ , C ₃ , and C ₄ , the neutron beam traveling in the direction of C ₄ is emitted. It passes through the side opening 112.

  The D neutron beam 20 traveling on the optical axis 100 passes through the exit-side opening 112 as it is. Alternatively, the neutron beam 20 that passes in the vicinity of the optical axis 100 and travels in a direction in which the angle with the optical axis 100 is small also passes through the emission-side opening 112 in the same manner. This action is similar to a collimator for neutron beams.

Therefore, the neutron beam that passes through the emission-side opening 112 is obtained by adding B ₄ , C _4, etc., which are scattering components, to the D component that is transmitted through a normal collimator. Therefore, when a neutron beam that is diverging light passes through the incident side opening 111, this structure allows neutrons in the emission side opening 112 to be more than when a collimator having the same opening as the emission side opening 112 is used. The line strength can be increased. That is, so-called neutron beams can be collected (focused) to increase the intensity of neutron beams in a narrow range.

  In addition, in FIG. 2, the case where the neutron beam which is a diverging light injects into this neutron condensing element 10 (incident side opening part 111) was demonstrated. However, even if the neutron beam is, for example, parallel light, it is clear that a part of the neutron beam scattered on the inner surface of the through hole 11 reaches the emission side opening 112. Therefore, also in this case, the neutron condensing element 10 has a condensing effect.

  That is, in the neutron condensing element 10, neutrons are scattered on the inner surface of the through-hole 11 and the intensity at the emission-side opening 112 can be increased by utilizing the fact that the scattering angle is wide. It is obvious that this action is realized not only when the inner surface of the through-hole 11 is conical, but also when the area of the exit side opening 112 is smaller than the area of the entrance side opening 111.

The distribution of the scattering angle is dependent on the energy of neutrons, but is similar in that it has a spread, and this is different from the case of reflection with a constant reflection angle. Therefore, for example, although the intensity ratio of B _{1 to} B ₄ may change depending on the energy of neutrons, the situation shown in FIG. 2 occurs independently of the energy of neutrons. Therefore, the neutron beam can be collected by the neutron focusing element 10 regardless of the energy of neutrons. That is, it is possible to collect neutron beams that do not have the same energy.

  Further, for example, the neutron condensing element 10 has a simple shape as shown in FIG. 1 as compared with the elements described in Patent Documents 1 and 2 configured by combining a plurality of components. Therefore, it is possible to collect neutron beams having no uniform energy with a simple configuration.

  On the other hand, for example, if a similar shape is made of metal and the inner surface of the through hole is a mirror surface having an elliptical or parabolic shape, it is well known that this can be used as a condensing mirror. In this case, the shape of the through hole in the cross section on the optical axis is a curve constituting a part of an ellipse or a parabolic shape. Thereby, visible light, X-rays, etc. can be reflected by the inner surface of a through-hole, and it can be made to condense in the condensing point located in an exit side opening part or this rear part. In this case, such a condensing effect is achieved by the property that the incident angle of light and the reflection angle with respect to the reflection surface (the inner surface of the through hole) are equal.

  On the other hand, in this neutron condensing element 10, since the cross-sectional shape of FIG. 1B and FIG. 2 in the through hole 11 is constituted by a straight line, there is no condensing effect due to such reflection. However, since the scattering angle of neutron rays is generally wide, a part of the scattered neutron rays can be guided to the emission side opening 112 even if the neutron ray is not in the shape of an ellipsoid or a paraboloid. Therefore, for example, the neutron beam can be condensed although the light condensing efficiency is lower than that of a condensing mirror that condenses visible light using reflection. On the other hand, there is no known material that can uniformly reflect high-reflectance neutron beams, so it is difficult to obtain a condensing mirror that collects neutron beams using reflection. is there. Similarly, there is no known material that uniformly and effectively transmits and refracts neutron beams having no uniform energy, so it is difficult to obtain a lens that collects neutron beams by refraction.

  A number of machining techniques are known for machining the inner surface of the through-hole into an ellipsoidal or parabolic shape in the condenser mirror. In this case, in order to maintain a high reflectance, this surface polishing technique is important, and it is also required to reduce the surface roughness to, for example, less than the wavelength of the light to be used. In this case, the cost required for processing increases, and it is not easy to maintain high processing accuracy.

  On the other hand, in this neutron condensing element 10, the inner surface of the through-hole 11 has a conical surface shape that is easier to process than an elliptical surface or a parabolic surface. Furthermore, since reflection is not used, it is not required that the surface roughness be as small as that of the condenser mirror. Therefore, this neutron condensing element 10 can be manufactured at low cost.

  In addition, the larger the apex angle θ of the cone, the larger the absolute amount of neutron rays incident from the incident side opening 111. However, in this case, the incident angle at which the neutron beam 20 is incident on the inner surface of the through hole 11 (for example, the inner surface 113 in the through hole and the lower surface 114 in the through hole) increases (becomes perpendicular). Therefore, the scattering angle (distribution) of the neutron beam also changes depending on the setting of θ, and the absolute amount of the scattered neutron beam reaching the emission side opening 112 also differs depending on θ. Since this characteristic varies depending on the material of the neutron scatterer, the average energy of the neutron beam, etc., θ for maximizing the neutron intensity in the exit-side opening 112 varies depending on these settings, and an optimum value is obtained experimentally. be able to.

  In addition, in said example, although the inner surface of the through-hole 11 was made into the shape which becomes a part of conical surface, as long as there exists said effect, another form can also be taken. For example, the inner surface may have a shape that becomes a part of a polygonal pyramid surface (triangular pyramid, quadrangular pyramid, etc.). In this case, since the inner surface is configured by a combination of planes that can be easily processed, the process of forming the through hole 11 can be performed particularly easily and precisely. In this case, the shapes of the entrance-side opening 111 and the exit-side opening 112 are polygons (triangles, quadrangles, etc.) corresponding thereto. In addition, it is clear from the above principle that the polygon at this time is not necessarily a regular polygon (regular triangle, regular square, etc.).

  In addition to the conical surface shape and the polygonal conical surface shape, it is clear that the same effect can be obtained if the shape between the entrance-side opening and the exit-side through hole is a straight line in the cross section on the optical axis. .

  Furthermore, this shape does not necessarily need to be a strict straight line, and a shape that can be easily machined can be used as appropriate. For example, only when the inner surface of the through hole 11 has a simple linear shape on the cross section including the optical axis 100 (when the inner surface of the through hole 11 has a conical shape, a polygonal pyramid shape, or the like). Alternatively, this shape may be a shape combining straight lines. As such a form, for example, a form in which two conical surfaces having different apex angles θ are combined can be considered. Even in such a form, it is easy to collect the neutrons and to form the through holes 11. Therefore, on the cross section including the optical axis 100, the inner surface shape of the through hole 11 is preferably a shape constituted by a straight line. Even if the inner surface of the through-hole 11 is shaped so that the light collecting ability by such reflection cannot be obtained, the neutron condensing element has a light condensing effect on neutrons.

  The neutron scatterer here means a material having a relatively high ability to scatter neutrons. This high ability is generally a material containing a lot of hydrogen atoms having a high ability to scatter neutrons. Among these, as materials that can easily realize the shape shown in FIG. 1, in addition to the above-mentioned organic polymer materials such as polyethylene and polyimide, polyether ethers having excellent wear resistance, impact resistance, and radiation resistance. Ketone (PEEK) and the like are also preferably used. Similarly, polymethyl methacrylate resin or polyethylene terephthalate (PET), which is a kind of polyethylene, can be used as an acrylic resin having excellent mechanical properties. However, it is obvious that other than these can be used similarly. A method other than machining (cutting, polishing) may be used to make these materials into the shape shown in FIG. The same applies to beryllium, which is a light metal. Further, this neutron scatterer does not need to be composed of these materials of 100% purity, and it is sufficient that at least one of these materials is a main component, and as long as the effect of scattering neutrons is achieved, Other substances may be added to these materials. For example, a material useful for stably forming the shaped body of FIG. 1 may be added as appropriate.

  Also, like a normal optical element such as a lens or a collecting mirror, it is possible to obtain a neutron beam having a desired beam size and intensity by using a plurality of these neutron optical elements or a combination of a plurality of types. it is obvious.

DESCRIPTION OF SYMBOLS 10 Neutron condensing element 11 Through-hole 20 Neutron beam 100 Optical axis 111 Incident side opening part 112 Outgoing side opening part 113 Through-hole inner upper surface 114 Through-hole inner lower surface

Claims (7)

A neutron optical element that causes a neutron beam to be incident from an incident side opening and to be emitted from an emission side opening,
Composed of neutron scatterers,
One end has a through hole with the incident side opening and the other end with the emission side opening,
The neutron optical element according to claim 1, wherein an area of the exit side opening is smaller than an area of the entrance side opening.   The inner surface shape of the through hole between the incident side opening and the emission side opening is configured by a straight line on a cross section including the optical axis of the neutron beam. The neutron optical element described.   The neutron optical element according to claim 2, wherein the inner surface shape of the through hole is configured by a part of a conical surface.   4. The neutron optical element according to claim 2, wherein an inner surface shape of the through hole is constituted by a part of a polygonal pyramid surface. 5.   The neutron optical element according to any one of claims 1 to 4, wherein the neutron scatterer includes an organic polymer material as a main component.   6. The neutron optical element according to claim 5, wherein the organic polymer material is mainly composed of any one of polyimide, polyethylene, polyetheretherketone, polymethyl methacrylate resin, and polyethylene terephthalate.   The neutron optical element according to any one of claims 1 to 4, wherein the neutron scatterer contains beryllium as a main component.

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