JP5481152B2 - Neutron microscope and neutron transmission enlarged image forming method - Google Patents

Description

  The present invention relates to a neutron microscope and a neutron transmission enlarged image forming method for providing a high-definition and clear transmission image of a subject, an irradiation structure, and the like using a neutron beam.

  When radiation such as X-rays, γ-rays, and neutrons passes through a substance, absorption and scattering differ depending on the type and shape of the constituent substance. If the transmitted radiation is recorded as an image as a photograph, video, digital file, etc., the damage state, change, filling state, etc. of the substance can be grasped. In general, X-rays are used as a method of diagnosing the internal state of a human body as a radiograph. This method of measuring the internal state without destroying the object or sample to be measured is called radiography or non-destructive radiography.

  There is a microscope as a method for photographing a detailed state of a measurement object. In general, a microscope is a device that visually enlarges a minute object and makes it visible to the naked eye by using an optical or electronic technique.

  A microscope using X-rays has a feature of high spatial resolution because X-rays have a shorter wavelength than visible light. As for a microscope using X-rays, a microscope that irradiates an object with X-rays and detects reflection thereof, and a transmission type are known. In particular, in the transmission type, there is a method in which an X-ray focal point is provided near a sample and is enlarged and detected by an X-ray detector (for example, see Patent Document 1).

  In addition, there is a paper published by the present inventors on the result of enlarging and photographing a 400 nanometer slit with a color image intensifier using a nanofocus X-ray source (see, for example, Non-Patent Document 1). . Also in this technique, the focus size of X-rays is reduced to the nanometer order, the measurement object is set close to the radiation source, and the imaging system is moved far away to increase the resolution.

  Among the types of radiation, a method for nondestructively inspecting the inside of a substance using neutrons instead of X-rays is known. This method is also called neutron radiography or more recently neutron imaging. When neutrons are used, it is possible to observe the behavior of lighter materials than metals such as water, hydrogen, and lithium in metals that cannot be observed when X-rays or γ-rays are used.

  FIG. 4 shows a state of a fountain toy (see FIG. 4A) placed in a tin can when a transmission image is taken with X-rays (see FIG. 4B) and transmitted with neutron rays. It is a photograph which shows the difference with the case where a picture is photoed (refer to Drawing 4 (c)). As shown in FIG. 4B, when X-rays are used, the fountain is not visible, although the motor and battery are visible inside the can. On the other hand, as shown in FIG. 4 (c), when neutrons are used, it can be seen well that the fountain is coming out and the water hits the can wall and drops. In this way, neutron radiography is used in various fields such as the movement of engine lubricating oil, the behavior of water produced by the reaction of hydrogen and oxygen in fuel cells, and the observation of cooling passages in aircraft engine blades. Use is expected.

  From now on, it is said to be a low-carbon society and a hydrogen society, and efforts are being made to develop fuel cells. Among them, it is required to efficiently remove the reaction product water from the battery reaction membrane, and the resolution required for observation is said to be several microns. At present, there is a reflection-type neutron diffraction device capable of photographing with high resolution, but there is no transmission-type neutron microscope capable of observing the inside (not the surface but inside the structural material) as a two-dimensional image.

JP 09-61600 A

Toshiba Review Vol.63 No.2 (2008) pp.15-18 "Nano Inspection Technology Using X-ray Color I.I.TM"

  The wavelength of neutrons is about 0.2 nanometers for thermal neutrons, and it is theoretically possible to magnify and photograph the measurement object as with X-rays. However, as described above, there has been no neutron microscope that uses conventional neutrons and can observe a substance and the state of the structure in a non-destructive manner through a transmission image.

  The present invention has been made in response to the above-described conventional circumstances, and is intended to provide a neutron microscope and a neutron transmission enlarged image forming method capable of observing a neutron using a transmission image and magnifying and observing a substance and a structure inside the structure. It is what.

One aspect of the neutron microscope of the present invention is a neutron microscope that obtains an enlarged neutron transmission image of a subject from neutrons irradiated with neutrons and transmitted through the subject. A neutron image having a neutron input surface for converting converted light into electrons, an electron lens for accelerating and amplifying the converted electrons to diffuse the image, and an output surface for emitting light by the accelerated electrons A first image generation mechanism that includes an intensifier and obtains an enlarged first image; and the light of the first image formed by the first image generation mechanism is converted into electrons, and the converted electrons are accelerated. A second image generation mechanism that outputs as a color image with a plurality of phosphors that emit light in different colors according to the intensity of the accelerated and accelerated electrons, and obtained by the second image generation mechanism An imaging camera for capturing a serial second image, characterized by comprising a.

One aspect of the neutron transmission enlarged image forming method of the present invention is a neutron transmission enlarged image forming method for obtaining an enlarged neutron transmission enlarged image of a subject from neutrons irradiated with neutrons and transmitted through the subject. Neutron input surface that converts charged particles emitted into light and converts the converted light into electrons, an electron lens that accelerates and amplifies the converted electrons and diffuses the image in an enlarged direction, and accelerated electrons A first image generation step for obtaining an enlarged first image using a neutron image intensifier having an output surface that emits light, and converting the light of the first image formed by the first image generation step into electrons Then, the converted electrons are accelerated and amplified, and a second image generation step for outputting as a color image with a plurality of phosphors that emit light in different colors according to the intensity of the accelerated electrons. And flop, characterized by comprising a an imaging step for imaging at the second imaging pickup camera the second image obtained by the step.

  According to the present invention, it is possible to provide a neutron microscope and a neutron transmission magnified image forming method capable of using a neutron and magnifying and observing a substance and a state inside a structure with a transmission image without destruction.

The figure which shows typically the whole schematic structure of the neutron microscope which concerns on one Embodiment of this invention. The figure which shows the structure of a neutron input surface typically. The figure which shows typically the whole schematic structure of the neutron microscope which concerns on 2nd Embodiment of this invention. A photograph showing the difference between radiography using X-rays and radiography using neutrons.

  Hereinafter, embodiments of the neutron microscope and neutron transmission enlarged image forming method of the present invention will be described in detail with reference to the drawings.

  FIG. 1 schematically shows an overall schematic configuration of a neutron microscope 100 according to an embodiment of the present invention. At the first stage of the neutron microscope 100, there is provided an enlarged neutron image intensifier 3 that reacts with the neutron 1 transmitted through the imaging sample 2 and electronically enlarges it into a visible image.

  A magnifying optical system 6 is provided at the subsequent stage of the magnifying neutron image intensifier 3, and a part of the visible image by the magnifying neutron image intensifier 3 is optically magnified. Further, a second-stage optical color image intensifier 7 for optical amplification is provided at the subsequent stage of the magnifying optical system 6, and the weak visible image at the first stage is amplified and output as a color image. An output color image from the second-stage optical color image intensifier 7 is captured by an imaging camera 11 using an optical system 10 and displayed and recorded. The magnifying optical system 6 has a zoom function for changing the magnification factor.

  The first-stage enlarged neutron image intensifier 3 includes a neutron input surface 4 on which the neutron 1 transmitted through the imaging sample 2 is incident. As shown in FIG. 2, the neutron input surface 4 is configured by laminating a reaction film 41, a phosphor layer 42, and a photoelectric conversion film 43 on an aluminum substrate 40.

  Neutrons incident on the neutron input surface 4 react with reactants (specific neutron reactants such as boron, lithium, and gadolinium) in the reaction film 41, and alpha rays, beta rays, internal conversion electrons, Alternatively, the phosphor of the phosphor layer 42 (made of gadolinium oxysulfide or yttrium oxysulfide using cesium iodide, sodium iodide, praseodymium, terbium, or europium as an activator) is emitted with gamma rays. .

  The emitted light is converted into electrons by the photoelectric conversion film 43, and the electrons are electronically amplified by the electron lens 30 shown in FIG. 1, and the output phosphor (praseodymium, terbium, or europium on the output surface 5 is activated. Yttrium oxysulfide or lanthanum oxysulfide) is emitted to form a visible image. As shown in FIG. 1, the area of the output surface 5 is larger than the area of the neutron input surface 4, and the electron lens 30 emits electrons in the direction of enlarging the image from the neutron input surface 4 toward the output surface 5. Spread.

Here, unless the thickness of the reaction film 41 is reduced, the resolution is lowered and the performance as a microscope is lowered. Therefore, in order to reduce the thickness of the reaction film 41 and increase the reaction efficiency with neutrons, it is desirable to use boron, lithium, or gadolinium enriched with highly reactive isotopes. As such an isotope, boron 10 ( ¹⁰ B) in the case of boron, lithium 6 ( ⁶ Li) in the case of lithium, and gadolinium 157 ( ¹⁵⁷ Gd) in the case of gadolinium are suitable.

Furthermore, in order to form these as the reaction film 41, they must be stable compounds. Therefore, it is preferable to use boron carbide (B ₄ C) when boron is used, lithium fluoride (LiF) when lithium is used, and gadolinium oxide (Gd ₂ O ₃ ) when gadolinium is used.

Moreover, the reaction efficiency varies depending on the energy of neutrons. In general, a reaction cross section (generally, the unit is burn [b], expressed as 1b = 1 × 10 ⁻²⁸ m ² ) is an index indicating the probability of reacting with energy. It differs for each element isotope. In the energy region where the energy of neutrons is lower than the region called thermal neutrons of about 0.025 eV (also called cold neutrons), naturally occurring gadolinium (15.7% of gadolinium 157) is more boron 10 The reaction cross-sectional area is about 12 times or more than that of lithium 6 and about 49 times that of lithium 6.

  When gadolinium 157 is concentrated as an isotope, the reaction cross-sectional area is larger by about 63 times or more than the concentrated boron 10 and the reaction efficiency is increased. However, when the energy of neutrons is higher than that of thermal neutrons (extrathermal neutrons, fast neutrons), the reaction cross section of gadolinium decreases rapidly, and the region that resonates with energy (reaction cross section increases or decreases). In contrast, the high neutron energy of fast neutrons is nearly two orders of magnitude smaller than that of boron 10. Therefore, it is necessary to select the thickness and material of the reaction film 41 according to the energy of the neutron to be used and the required resolution.

  Further, in the interaction between the charged particles generated by reaction with neutrons and the phosphor of the phosphor layer 42, as shown in FIG. 2A, boron and lithium react with neutrons to generate α rays. This α ray causes the phosphor to emit light. The distance (generally called the range) which permeate | transmits the inside of this alpha ray substance is short, and is about 4-5 micrometers.

  On the other hand, in the case of gadolinium, as shown in FIG. 2 (b), γ-rays and internal conversion electrons are generated by reacting with neutrons, and high-energy γ-rays escape with little reaction with the phosphor. The internally converted electrons react with the phosphor with a range of about 20 μm. Within this range, the internally converted electrons lose energy and cause the phosphor to emit light.

  Since α rays lose all energy in the phosphor at a short distance compared to the range of internal conversion electrons, strong light emission can be obtained at a short distance. On the other hand, in the case of internal conversion electrons, the longer the distance of the range, the wider the region where the phosphor emits light, which is not better than alpha rays in terms of resolution. This point needs to be considered together with the thickness of the reaction film and the energy of neutrons.

As shown in FIG. 2A, when boron is used as a material, the thickness of the reaction film ( ¹⁰ B ₄ C) 41 is preferably about 4 to 5 μm, and the thickness of the phosphor layer 42 is preferably about 5 μm. . Although the thickness of the phosphor layer 42 may be 5 μm or more, it is necessary to consider diffusion of emitted light. For example, in the case of cesium iodide, a contrivance is made to prevent light diffusion as a needle-like crystal. In this case, the thickness of the phosphor layer 42 may be about 20 μm.

On the other hand, as shown in FIG. 2B, when gadolinium is used as a material, the thickness of the reaction film (Gd ₂ O ₃ ) 41 is preferably about 10 μm (for example, 12 μm) from the viewpoint of reaction efficiency. The thickness of the phosphor layer 42 is preferably about 20 μm. Also in this case, for example, in the case of cesium iodide, the thickness of the phosphor layer 42 may be set to about 50 μm if the device is designed to prevent light diffusion as a needle-like crystal.

  However, in order to increase the resolution, although the reaction efficiency is lowered, it is necessary to reduce the thickness of the reaction film 41 and the thickness of the phosphor layer 42. In order to ultimately increase the resolution, it is desirable to thin the reaction film 41 and the phosphor layer 42 using boron.

  After being converted into electrons by the photoelectric conversion film 43 shown in FIG. 2, the electrons are accelerated by the electron lens 30 shown in FIG. 1 and amplified to cause the phosphor on the output surface 5 to emit light. The size of the phosphor particles on the output surface 5 is preferably about 1 to 3 μm in terms of average particle diameter, and the thickness to be coated is also preferably about 1 to 3 μm.

  The phosphor used for the output surface 5 is selected so that its emission wavelength matches the wavelength spectral sensitivity characteristic of the photoelectric conversion film on the input surface 8 of the optical color image intensifier 7 to be amplified in the next stage. For example, when the wavelength of the photoelectric conversion film is green and the sensitivity is maximum, the emission wavelength of the output surface 5 of the first-stage neutron image intensifier 3 is green. Similarly, when the photoelectric conversion film on the input surface 8 is sensitive to blue, a blue-emitting phosphor is selected, and when the sensitivity is red, a red phosphor is selected.

  The field of view of the output surface 5 of the first stage magnified neutron image intensifier 3 is magnified 100 times on the input surface 8 of the second stage optical color image intensifier 7 by the magnification optical system 6. If the enlarged neutron image intensifier 3 at the stage is enlarged 10 times on the output surface 5 with respect to the neutron input surface 4, it can be enlarged 1000 times as a whole.

  In the second stage optical color image intensifier 7, transparent glass is used for the input surface 8, and a photoelectric conversion film is formed on the inner surface thereof. Light is converted into electrons by the photoelectric conversion film, and the electrons are reduced and irradiated to the color image output surface 9 by the electron lens 70, and the phosphor on the color image output surface 9 emits light in color. The phosphor used for the color image output surface 9 is selected by selecting a plurality of different colors (in this embodiment, red, green, blue (RGB)) having different light emission amounts according to the electron intensity. The width of measurement (dynamic range) can be widened. As such a phosphor, for example, yttrium oxysulfide or gadolinium oxysulfide using europium as an activator can be used.

  Further, the image of the color image output surface 9 is formed by the optical system 10 and imaged by the photographing camera 11 so that it can be displayed and recorded. When the optical system 10 is magnified 10 times, it can be theoretically magnified 10,000 times in combination with the magnification in the previous stage. As the imaging camera 11, a generally used moving image camera, single-lens digital camera, or the like can be used.

  The enlarged neutron image intensifier 3, the enlarged optical system 6, the optical color image intensifier 7, the optical system 10, and the imaging camera 11 are housed in a dark box 12 that has been subjected to anti-vibration measures. In addition, as an anti-vibration measure, it can carry out by installing on the anti-vibration stand generally used. In this case, it is preferable that the subject 2 is also installed on the same vibration isolation table. By taking the anti-vibration measures in this way, a resolution of several microns can be obtained.

  The magnification optical system 6, the optical color image intensifier 7, the optical system 10, and the imaging camera 11 are integrally movable with respect to the magnification neutron image intensifier 3. This movement is adjusted so that the light incident side of the magnifying optical system 6 moves along the curved surface of the output surface 5 of the magnifying neutron image intensifier 3. It is possible to change the position of the output surface 5 to be viewed in an enlarged manner. A precise jig (not shown) for this movement is also housed in the dark box 12 with anti-vibration measures taken.

  In the neutron microscope 100 of FIG. 1, it is difficult to obtain a color visible image on the output surface when the neutron intensity is small only with the first-stage enlarged neutron image intensifier 3. For this reason, the second stage light color image intensifier 7 is used for amplification. However, when the intensity of the neutron is sufficiently strong and the first stage enlarged neutron image intensifier 3 alone can be sufficiently imaged, the color image of the optical color image intensifier 7 on the output surface 5 of the enlarged neutron image intensifier 3. The color luminescent phosphor used for the output surface 9 may be used as an enlarged neutron color image intensifier.

  Next, a neutron microscope 200 according to the second embodiment will be described with reference to FIG. In the configuration of the neutron microscope 100 shown in FIG. 1, when sufficient sensitivity cannot be obtained with the first-stage enlarged neutron image intensifier 3, the enlargement ratio decreases, but the enlarged neutron image intensifier 3 is As shown in FIG. 3, the neutron image intensifier 3a is changed to a type reduced by the electron lens 30. In this case, compared with the case of the neutron microscope 100, the amplification factor can be about 100 times or more. In FIG. 3, the same parts as those in FIG.

  In each image intensifier used in the above embodiment, the field of view can be adjusted by adjusting the acceleration voltage in the electron lens. The field of view of the input surface can be adjusted by considering the field of view (fixed) of the output surface. For example, in the case of the optical color image intensifier 7, when the input surface size is 9 inches in diameter and the color image output surface size is 25 mm in diameter, the input surface size may be changed to 9 inches, 6 inches, and 4.5 inches. it can. Therefore, the enlargement ratio can be increased by 1.5 times or 2 times only by the light color image intensifier 7. On the contrary, in the enlarged neutron image intensifier 3, since the size of the output surface is different from that of the neutron input surface (fixed), when the input surface size is 25 mm in diameter and the output surface size is 9 inches, it is 9 inches. By changing the activation of the electronic lens to 6 inches and 4.5 inches, the reduction ratio can be increased by 1.5 times and 2 times. With these combinations, it is possible to adjust the enlargement ratio by controlling the electronic lens in addition to adjusting the enlargement ratio in the enlargement optical system.

  In each of the above embodiments, one optical color image intensifier 7 is provided in the second stage to amplify it, but it may be multistaged to further increase sensitivity. In this case, the optical color image intensifier 7 is used in the final stage, and the intermediate stage image intensifier is a monochromatic (monochrome) optical image intensifier. At this time, the phosphor to be used for the monochromatic optical image intensifier output surface of the intermediate stage is selected according to the wavelength sensitivity characteristic of the photoelectric conversion film used for the input surface of the subsequent image intensifier. This is the same as the case of selecting the output phosphor of the first-stage enlarged neutron image intensifier 3 described above. In general, the photoelectric conversion film often has high sensitivity in a wavelength range from blue to green. For this reason, it is preferable to select a phosphor that emits light from blue to green. It is also possible to use a micro-channel plate type amplifier instead of the optical image intensifier for intermediate stage optical amplification.

  In addition, this invention is not limited to the said embodiment, Of course, various deformation | transformation are possible. For example, instead of the optical color image intensifier 7, an optical amplifier using a microchannel plate can be used.

  1 ... Neutron, 2 ... Sample, 3 ... Enlarged neutron image intensifier, 4 ... Neutron input surface, 5 ... Output surface, 6 ... Enlarged optical system, 7 ... Optical color image intensifier , 8 ... input surface, 9 ... color image output surface, 10 ... optical system, 11 ... photographing camera, 12 ... dark box, 30, 70 ... electronic lens.

Claims (11)

A neutron microscope that obtains an enlarged neutron transmission image of the subject from neutrons irradiated with neutrons and transmitted through the subject,
A neutron input surface that converts charged particles emitted by reaction with neutrons into light and converts the converted light into electrons, an electron lens that accelerates and amplifies the converted electrons to diffuse the image, and acceleration A first image generating mechanism comprising a neutron image intensifier having an output surface that emits light by the emitted electrons and obtaining an enlarged first image;
A phosphor that converts light of the first image formed by the first image generation mechanism into electrons, accelerates and amplifies the converted electrons, and emits light in a plurality of different colors according to the intensity of the accelerated electrons A second image generation mechanism for outputting as a color image at
An imaging camera that captures the second image obtained by the second image generation mechanism;
A neutron microscope characterized by comprising: The neutron microscope according to claim 1,
The first image generation mechanism includes an enlarged neutron image intensifier that obtains an enlarged image having a larger area of the output surface than the area of the neutron input surface, and an image obtained by the enlarged neutron image intensifier. And a magnifying optical system that further expands. The neutron microscope according to claim 1,
The first image generation mechanism enlarges the image obtained by the neutron image intensifier and the neutron image intensifier that obtains a reduced image that is configured with a reduced area of the output surface than the area of the neutron input surface. A neutron microscope comprising: a magnifying optical system. The neutron microscope according to claim 2 or 3,
The magnifying optical system includes a moving mechanism for selecting an image of a part of the output surface of the first image generating mechanism, and a zoom mechanism for changing a magnification factor. The neutron microscope according to any one of claims 1 to 4,
A neutron microscope characterized in that a phosphor containing yttrium oxysulfide or lanthanum oxysulfide using praseodymium, terbium, or europium as an activator is used on the output surface of the first image generation mechanism. The neutron microscope according to any one of claims 1 to 5,
A phosphor containing yttrium oxysulfide or gadolinium oxysulfide using europium as an activator is used as the phosphor that emits light in a plurality of different colors according to the accelerated electron intensity of the second image generation mechanism. A neutron microscope. The neutron microscope according to any one of claims 1 to 6,
The second image generation mechanism includes:
One or more first amplification mechanisms for converting light into electrons, accelerating and amplifying the converted electrons, and forming a monochromatic image with the accelerated electrons;
The light of the monochromatic image of the first amplifying means is converted into electrons, the converted electrons are accelerated and amplified, and output as a color image with phosphors that emit light in a plurality of different colors according to the intensity of the accelerated electrons. A neutron microscope, comprising: a second amplification mechanism. The neutron microscope according to claim 7,
The neutron microscope, wherein the first amplification mechanism is constituted by a microchannel plate. A neutron microscope according to claim 7 or 8,
The neutron microscope, wherein the second amplification mechanism is composed of an optical color image intensifier. The neutron microscope according to claim 1,
The subject, the first image generation mechanism, the second image generation mechanism, and the imaging camera are provided on a vibration isolation table, and the first image generation mechanism and the second image generation mechanism A neutron microscope characterized in that the imaging camera is provided integrally in a dark box. A neutron transmission enlarged image forming method for obtaining an enlarged neutron transmission enlarged image of the object from neutrons irradiated with neutrons and transmitted through the object,
A neutron input surface that converts charged particles emitted by reaction with neutrons into light and converts the converted light into electrons, an electron lens that accelerates and amplifies the converted electrons to diffuse the image, and acceleration A first image generating step of obtaining an enlarged first image using a neutron image intensifier having an output surface that emits light by the emitted electrons;
A phosphor that converts the light of the first image formed by the first image generation step into electrons, accelerates and amplifies the converted electrons, and emits light in a plurality of different colors according to the intensity of the accelerated electrons A second image generation step of outputting as a color image at
An imaging step of imaging the second image obtained by the second image generation step with an imaging camera;
A neutron transmission enlarged image forming method characterized by comprising: