Neutron position recording device and track image generation method

Abstract

[Problem] To provide a technique capable of visualizing, with high spatial resolution in neutron imaging, the internal structure of an object to be inspected, without performing chemical treatment that is required when a nuclear emulsion is used. [Solution] A neutron position recording device 10 is provided with a conversion film 1 and a fluorescent nuclear track detector 2 in order to generate an image representing the fine structure of an object T to be inspected. When each neutron that has passed through the object T to be inspected is incident, the conversion film 1 converts each neutron into a charged particle. The fluorescent nuclear track detector 2 has a surface 2a facing the conversion film 1, and records, due to the incidence of the charged particle from the conversion film 1, the track of the charged particle corresponding to the position of the neutron.

Description

Neutron position recording device and track image generation method

[0001] This invention relates to a technique for acquiring images of the fine structure (e.g., internal structure or surface structure) of an object under inspection based on neutrons that have passed through the object.

[0002] Neutron imaging is a technique for visualizing the internal structure of an object under inspection. In neutron imaging, a neutron beam is irradiated onto the object under inspection, the neutrons that pass through the object are detected, and an image representing the internal structure of the object is generated based on the detected neutrons.

[0003] In recent years, neutron imaging using fine-grained nuclear emulsion (FGNE) has been developed (for example, see Non-Patent Documents 1 and 2 below). In neutron imaging using nuclear emulsion, the side of the object under test that is irradiated with neutrons is designated as the front side, and the neutron converter and nuclear emulsion are placed on the back side of the object under test in this order from the object side. With this arrangement, neutrons are irradiated onto the object under test from the neutron source. As a result, each neutron that passes through the object under test is incident on the neutron converter. In the neutron converter, the incident neutrons are converted into charged particles, and these charged particles are incident on the nuclear emulsion. As a result, the tracks of each charged particle are recorded on the nuclear emulsion. Based on the tracks of each charged particle recorded on the nuclear emulsion in this way, it is possible to generate an image that represents the internal structure of the object under test with high spatial resolution.

[0004] Japanese Patent No. 5956691 (Title of Invention: Method for Measuring Radiation Dosage Using Fluorescence Imaging with Accuracy Correction)

[0005] Katsuya Hirota et al., “Neutron Imaging Using a Fine-Grained Nuclear Emulsion” Journal of Imaging, Volume 7, Issue 1, 10.3390 / jimaging7010004 Naotaka Naganawa, “Nuclear Emulsion Plate for Low-Energy Neutrons Exhibiting Spatial Resolution of Less Than 100 nm”, Japan Isotope Association, Isotope News [No. 766] December 2019 issue

[0006] However, in order to visualize the tracks recorded in the nuclear emulsion, the nuclear emulsion needs to be chemically treated. Furthermore, the nuclear emulsion cannot be reused after this chemical treatment.

[0007] Therefore, the object of the present invention is to provide a technology that enables the visualization of the internal structure of an object under inspection with high spatial resolution without the need for chemical processing required when using nuclear emulsions in neutron imaging.

[0008] The inventors of this application focused on using a fluorescence nucleus tracking detector (see, for example, Patent Document 1 concerning a radiation dose measurement method), which is conventionally used for dose measurement, to generate images representing the fine structure of an object under inspection. The present invention was made based on this novel idea. That is, it has been newly discovered that the above objective can be achieved by the present invention made based on this idea.

[0009] A neutron position recording device according to one aspect of the present invention is a device for generating an image representing the microstructure of an object under inspection, comprising: a conversion film that converts each neutron that has passed through the object under inspection into a charged particle when incident on the neutron; and a fluorescence nucleus track detector having a surface facing the conversion film, which records the track of the charged particle corresponding to the position of the neutron when the charged particle from the conversion film is incident on the detector.

[0010] A method for generating a track image according to one aspect of the present invention is a method for generating a track image representing the fine structure of an object under inspection using the neutron position recording device described above, comprising: (A) positioning the neutron position recording device such that the surface of the fluorescence nucleus track detector faces the object under inspection from one side of the object under inspection; (B) irradiating the object under inspection with a neutron beam from the other side of the object under inspection, converting each neutron that has passed through the object under inspection into a charged particle using the conversion film, and recording the tracks of the charged particles in the fluorescence nucleus track detector; and (C) irradiating a target range in the fluorescence nucleus track detector with excitation light containing a predetermined wavelength component to generate fluorescence from each track in the target range, and generating the track image based on the fluorescence.

[0011] According to the present invention, the internal structure of an object under inspection can be visualized with high spatial resolution without performing the chemical processing required for neutron imaging using nuclear emulsions. For example, a track image showing the fine structure of the object under inspection can be obtained with a resolution of less than 1 μm (0.887 ± 0.009 μm in the experimental example).

[0012] This is a diagram showing the configuration of a neutron position recording device according to an embodiment of the present invention. It shows the state after suction has been applied to the inside of the protective bag in Figure 1A. This shows an example of the configuration of a track image generation device according to an embodiment of the present invention. This shows another example of the configuration of a track image generation device according to an embodiment of the present invention. This is a flowchart showing the track image generation method according to an embodiment of the present invention. This is an explanatory diagram of an experimental example. This is a track image obtained in the experimental example.

[0013] Embodiments of the present invention will be described based on the drawings. Common parts in each figure are denoted by the same reference numerals, and redundant explanations are omitted.

[0014] (Neutron Position Recording Device) Figure 1A is a diagram showing the configuration of a neutron position recording device 10 according to an embodiment of the present invention. The neutron position recording device 10 is a device that records the position of each neutron that has passed through the object under test T (shown by a dashed line in Figure 1B, described later) when the object under test T is irradiated with neutron beams. The neutron position recording device 10 comprises a conversion film 1, a fluorescence nuclear track detector (FNTD) 2, and a protective bag 3.

[0015] The object under test T may be made of a material that absorbs neutrons. This material may contain elements such as lithium, cadmium, gadolinium, or hydrogen. Such an object under test T may be, but is not limited to, a lithium battery or a semiconductor device containing the above-mentioned material.

[0016] The conversion film 1 is a thin film that converts each neutron that has passed through the object T under test into a charged particle. The conversion film 1 may be a thin film mainly composed of boron. In this case, the conversion film 1 is boron carbide. １０ B ４ It may be a thin film formed of C.

[0017] The conversion film 1 is boron１０ When containing B as the main component, the boron contained in the conversion film 1 １０ As shown in the following reaction formula, B absorbs neutrons incident on the conversion film 1 from the test object T and flies in opposite directions to each other ７ Li atomic nucleus and ４ Two He atomic nuclei (alpha particles) are generated as charged particles. １０ B + n → ７ Li + ４ He In this reaction formula, n represents a neutron. Among the two charged particles generated in this way, one ( ７ Li atomic nucleus or ４ He atomic nucleus) enters the fluorescent nuclear track detector 2, and as a result, the track of the one charged particle is recorded by the fluorescent nuclear track detector 2.

[0018] The fluorescent nuclear track detector 2 has a surface 2a facing the conversion film 1. In the example of FIG. 1A, the conversion film 1 is formed on the surface of a support substrate 4 described later. The conversion film 1 extends along the surface 2a of the fluorescent nuclear track detector 2. The surface 2a of the fluorescent nuclear track detector 2 may be a flat surface (for example, a smooth flat surface). The fluorescent nuclear track detector 2 records the track of the charged particle when the charged particle from the conversion film 1 enters. The track of the charged particle recorded by the fluorescent nuclear track detector 2 indicates the position of the neutron transmitted through the test object T when viewed from a direction perpendicular to the surface 2a of the fluorescent nuclear track detector 2. The direction perpendicular to the surface 2a may coincide with the irradiation direction of the neutron beam to the test object T.

[0019] The fluorescent nuclear track detector 2 may be formed of an aluminum oxide material (Al ２ O ３ : C, Mg) such as alumina doped with carbon and magnesium. As this fluorescent nuclear track detector 2, the FNTD manufactured by Landau Company in the United States can be used.

[0020] The fluorescence nucleus tracking detector 2 may have a thin plate shape. In this case, the thickness of the fluorescence nucleus tracking detector 2 (the dimension in the left-right direction in Figure 1A) may be 0.1 mm or more and less than 1 mm (for example, about 0.5 mm), but is not limited to this range. When viewed from the thickness direction, the fluorescence nucleus tracking detector 2 may have dimensions of, for example, 1 cm or more and 10 cm or less in length and width, but is not limited to this range.

[0021] The conversion film 1 is detachably attached to the fluorescent nucleus tracking detector 2 either directly or via another film (in the example of Figure 1A, via the stabilizing film 5 and protective film 6 described later) so as to face and cover the surface 2a of the fluorescent nucleus tracking detector 2.

[0022] The protective bag 3 houses the main body M of the neutron position recording device 10. The main body M includes a conversion film 1 and a fluorescence nucleus track detector 2. The protective bag 3 may be airtight to the outside. Furthermore, the protective bag 3 may have light-shielding and / or moisture-proof properties. Such a protective bag 3 can seal its interior to the outside while housing the main body M of the neutron position recording device 10 inside.

[0023] The protective bag 3 may be constructed, for example, as shown in Figure 1A, by joining the outer edges of two layers of sheets together to close it, thereby accommodating the main body M of the neutron position recording device 10 inside. The sheets may be formed using an aluminum film that has light-shielding and moisture-proof properties. For example, the protective bag 3 may be made by laminating films made of nylon, polyethylene, aluminum, polyethylene, and black polyethylene in that order from the surface to the inner surface with adhesive in between.

[0024] The conversion film 1 described above may be formed, for example, on a support substrate 4 that constitutes the main body M of the neutron position recording device 10, as shown in Figure 1A. That is, the main body M may have a support substrate 4 for supporting the conversion film 1. The conversion film 1 is formed on the surface of the support substrate 4 (the right-hand side in Figure 1A) and supported by the support substrate 4. The support substrate 4 is made of a neutron-permeable material (for example, silicon). The thickness of the support substrate 4 may be on the order of 0.1 mm (0.1 mm or more and less than 1 mm), but is not limited to this range.

[0025] The thickness of the conversion film 1 may be set to appropriate values ​​for the physical stability of the conversion film 1, the neutron detection efficiency by the neutron position recording device 10, and the imaging resolution. The thickness of the conversion film 1 may be on the order of 100 nm (100 nm or more and less than 1000 nm), or 10 nm or more and 10 μm or less, or 50 nm or more and 1000 nm (1 μm) or less, but is not limited to values ​​within these ranges. The conversion film 1 may be formed, for example, by ion beam sputtering.

[0026] A stabilizing film 5 and a protective film 6 may be formed on the conversion film 1. That is, the main body M of the neutron position recording device 10 may further have a stabilizing film 5 and a protective film 6.

[0027] The stabilizing film 5 is formed on the outer surface of the conversion film 1 (the surface opposite to the support substrate 4). The stabilizing film 5 physically stabilizes the conversion film 1. For example, the stabilizing film 5 prevents contact and friction of the conversion film 1 with external objects. Such a stabilizing film 5 may be formed of nickel carbide (NiC), but is not limited to this. The thickness of the stabilizing film 5 may be on the order of 10 nm (for example, 10 nm or more and less than 100 nm), but is not limited to this range. The stabilizing film 5 may be formed, for example, by ion beam sputtering.

[0028] The protective film 6 is formed on the outer surface of the stabilizing film 5 (the surface opposite to the support substrate 4). The protective film 6 chemically protects the stabilizing film 5 and the fluorescence nucleus tracking detector 2 from each other. For example, when the protective film 6 is attached to the surface 2a of the fluorescence nucleus tracking detector 2, it prevents the fluorescence nucleus tracking detector 2 and the stabilizing film 5 from degrading due to humidity, temperature, or oxygen. Such a protective film 6 may be, but is not limited to, a film formed of carbon C. The thickness of the protective film 6 may be on the order of 10 nm (for example, 10 nm or more and less than 100 nm), but is not limited to this range. The protective film 6 may be formed, for example, by ion beam sputtering.

[0029] The support substrate 4 is attached to the fluorescent nuclear track detector 2 such that a conversion film 1, a stabilization film 5, and a protective film 6 are sandwiched between the support substrate 4 and the fluorescent nuclear track detector 2. For example, the support substrate 4 may be attached to the fluorescent nuclear track detector 2 so that the outer surface of the protective film 6 is in close contact with the surface 2a of the fluorescent nuclear track detector 2. The surface 2a of the fluorescent nuclear track detector 2 may be a polished, smooth, flat surface. This enhances the adhesion of the protective film 6 to the surface 2a.

[0030] The attachment of the support substrate 4 to the fluorescent nuclear track detector 2 may be performed using a protective bag 3 as follows. As shown in FIG. 1A, the support substrate 4 and the fluorescent nuclear track detector 2 are disposed inside the protective bag 3 such that the outer surface of the protective film 6 and the surface 2a of the fluorescent nuclear track detector 2 face each other and come into contact. In this state, the inside of the protective bag 3 is evacuated, and in this evacuated state, the inside of the protective bag 3 is sealed against the outside. For example, the protective bag 3 is sealed using an appropriate vacuum packaging machine. The sealing method may be heat sealing. By such vacuum sealing, as shown in FIG. 1B, the protective bag 3 is shrunk so that the support substrate 4 (conversion film 1) and the fluorescent nuclear track detector 2 are sandwiched between the inner surfaces 3a and 3b of the protective bag 3 that face each other. As a result, due to the inside of the protective bag 3 being in a vacuum state, the support substrate 4 (conversion film 1) and the fluorescent nuclear track detector 2 are sandwiched between the inner surfaces 3a and 3b of the protective bag 3 that face each other. Thereby, the support substrate 4 is attached to the fluorescent nuclear track detector 2. In this state, in the example of FIG. 1B, the protective film 6 is in contact (adhered) with the surface 2a of the fluorescent nuclear track detector 2.

[0031] <Effects of the Neutron Position Recording Device According to the Embodiment> When a neutron beam is irradiated onto the object under test T, each neutron that passes through the object under test T is converted into a charged particle in the conversion film 1, and the tracks of these charged particles are recorded in the fluorescence nucleus track detector 2. The tracks recorded in the fluorescence nucleus track detector 2 indicate the position of the neutrons that passed through the object under test T when viewed from the direction of neutron beam irradiation onto the object under test T. Therefore, based on the tracks recorded in the fluorescence nucleus track detector 2, it is possible to obtain a track image (described later) that shows the fine structure of the object under test T as viewed from the direction of neutron beam irradiation with high precision. For example, as in the experimental example described later, it is possible to obtain a track image with a resolution of less than 1 μm.

[0032] Furthermore, there is no need to chemically treat the fluorescent nucleus track detector 2 in order to obtain a track image that accurately represents the fine structure of the object T under inspection. Also, as described above, the tracks of charged particles are recorded in the fluorescent nucleus track detector 2, and after generating a track image by optically reading the tracks from the fluorescent nucleus track detector 2, the tracks can be erased by irradiating the fluorescent nucleus track detector 2 with laser light of approximately 350 nm. The fluorescent nucleus track detector 2, with the tracks erased in this way, can be reused. In addition, when reused, the track recording performance of the fluorescent nucleus track detector 2 is improved compared to before reuse. Even when using the fluorescent nucleus track detector 2 for the first time, it may contain parts that produce fluorescence, so the fluorescent parts can be removed by irradiating it with laser light of approximately 350 nm before using the fluorescent nucleus track detector 2.

[0033] The conversion film 1 is boron １０ A membrane containing B as the main component (for example, boron carbide) １０ B ４ If it is a C film, the neutron incident on the conversion film 1 is boron １０ Due to B, it is converted into a charged particle with a relatively short range. That is, the neutron is converted into a boron １０ According to B, charged particles with a range of less than 10 μm (for example, He nuclei with a range of 9 μm and particles with a range of 4 μm) ７It is converted into a Li atomic nucleus). In this case, the thickness of the conversion film 1 is made sufficiently small (for example, less than 1 μm, 0.5 μm or less, or less than 0.3 μm), and the distance from the back surface of the conversion film 1 (the surface on the side of the fluorescent nuclear track detector 2) to the surface 2a of the fluorescent nuclear track detector 2 is made sufficiently small (for example, less than 0.5 μm or less than 0.1 μm). Thus, when viewed in the irradiation direction of the neutron beam (the thickness direction of the fluorescent nuclear track detection), the insensitive region between the generation point of each charged particle and the fluorescent nuclear track detector 2 in the vicinity of the surface 2a of the fluorescent nuclear track detector 2 can be shortened. As a result, based on the recorded tracks, it becomes easier to obtain a track image that more clearly represents the fine structure of the test object T.

[0034] (Track Image Generation Device) FIG. 2A is a schematic configuration diagram of a track image generation device 20 according to an embodiment of the present invention. The track image generation device 20 is a device that generates a track image as a fine structure image of the test object T based on the tracks of charged particles recorded in the fluorescent nuclear track detector 2 as described above.

[0035] The track image generation device 20 includes an excitation light source 21, a dichroic mirror 22, a lens optical system 24, a scanning mechanism 23, a relative position adjustment device 25, a control device 26, and an image generation unit 27.

[0036] The excitation light source 21 emits excitation light including a predetermined wavelength component that generates fluorescence (hereinafter also simply referred to as fluorescence) from the tracks of charged particles recorded in the fluorescent nuclear track detector 2. The excitation light of the predetermined wavelength excites the electrons of the atoms in the tracks in the fluorescent nuclear track detector 2, and fluorescence is generated when the electrons are de-excited. The excitation light from the excitation light source 21 may have only the component of the above predetermined wavelength, or may further have other wavelength components in addition to the above predetermined wavelength component. In the present embodiment, the fluorescent nuclear track detector 2 is made of an aluminum oxide material (Al ２ O ３ : C, Mg) doped with carbon and magnesium, and the above predetermined wavelength is about 640 nm. The excitation light source 21 may be, for example, a laser light source that emits excitation light that is excitation light including a predetermined wavelength component.

[0037] The excitation light from the excitation light source 21 is focused into the fluorescence nucleus track detector 2 on the stage 28 via the dichroic mirror 22, the scanning mechanism 23, and the lens optical system 24 (for example, in this order).

[0038] The dichroic mirror 22 reflects the excitation light from the excitation light source 21 toward the fluorescence nucleus track detector 2 on the stage 28. On the other hand, the dichroic mirror 22 transmits the fluorescence generated from the tracks recorded by the fluorescence nucleus track detector 2. That is, the fluorescence generated from the tracks of the fluorescence nucleus track detector 2 passes through the lens optical system 24, the scanning mechanism 23, and the dichroic mirror 22 (for example, in this order) before being incident on the light receiving unit 27b, which will be described later.

[0039] The lens optical system 24 focuses the excitation light from the excitation light source 21 to a focal point. The lens optical system 24 includes an objective lens 24a. The lens optical system 24 may include other lenses not shown. When the focal plane of the lens optical system 24 (hereinafter also simply referred to as the focal plane) is located within the fluorescence nucleus tracking detector 2, the focal plane may be perpendicular to the thickness direction of the fluorescence nucleus tracking detector 2. Here, the fluorescence nucleus tracking detector 2, which is arranged as shown in Figure 2A relative to the lens optical system 24, constitutes the neutron position recording device 10 described above, and the tracks of charged particles are recorded as described above. Note that the support substrate 4 described above may be removed together with the conversion film 1, stabilization film 5, and protective film 6 from the fluorescence nucleus tracking detector 2 arranged as shown in Figure 2A.

[0040] The scanning mechanism 23 moves the focal point of the excitation light on the focal plane of the lens optical system 24. For example, the scanning mechanism 23 may be a two-dimensional galvanometer scanner composed of two mirrors 23a and 23b. Mirror 23a moves the focal point of the excitation light on the focal plane in the X-axis direction, and mirror 23b moves the focal point of the excitation light on the focal plane in the Y-axis direction. Here, the X and Y axes are the coordinate axes of the XYZ coordinate system in Figure 2A, the X-axis direction is to the right in Figure 2A, the Y-axis direction is perpendicular to the plane of Figure 2A, and the Z-axis direction is the thickness direction of the fluorescence nucleus tracking detector 2 (up and down direction in Figure 2A). In the following, (X, Y) means the combination of the X-axis coordinate and the Y-axis coordinate in the XYZ coordinate system of Figure 2A.

[0041] The relative position adjustment device 25 adjusts the relative optical axis position (i.e., the scanning depth described later) between the surface 2a of the fluorescence nucleus tracking detector 2 and the focal plane of the lens optical system 24. For example, the relative position adjustment device 25 adjusts the relative optical axis position by moving the stage 28 on which the fluorescence nucleus tracking detector 2 is installed along the optical axis (Z axis direction). The relative position adjustment device 25 may be composed of a drive device such as a motor or a piezo positioner. The above optical axis position refers to the position of the lens optical system 24 in the optical axis direction. The relative position adjustment device 25 may also be configured to have the above drive device that adjusts the relative optical axis position by moving the objective lens 24a along the optical axis. In this case, the relative position adjustment device 25 may further have an additional drive device (e.g., a motor or piezo positioner) to adjust the optical axis position of other lenses (such as the focusing lens 27d or other lenses not shown) in accordance with this adjustment.

[0042] The control device 26 controls the excitation light source 21, the scanning mechanism 23, and the relative position adjustment device 25. The control device 26 rotates the mirrors 23a and 23b around a predetermined drive axis via a drive device (not shown), thereby moving the focal point of the excitation light in the X and Y directions. The control device 26 also adjusts the relative optical axis position between the surface 2a of the fluorescence nucleus tracking detector 2 and the focal plane of the lens optical system 24 by controlling the relative position adjustment device 25.

[0043] The control device 26 performs the following processes (A) to (C): (A) Controls the relative position adjustment device 25 to position the focal plane at one scanning depth within a local range from the surface 2a of the fluorescence nucleus track detector 2 to a predetermined depth. (B) With the focal plane positioned at one scanning depth via the relative position adjustment device 25 in process (A), controls the excitation light source 21 and the scanning mechanism 23 to scan a two-dimensional scanning range on the focal plane at the focal point of the excitation light. (C) Repeats processes (A) and (B) multiple times, changing the scanning depth in process (A).

[0044] The local area of ​​the above-described process (A) is the range to which the charged particles generated in the conversion film 1 can reach or pass. The predetermined depth may be a value within the range of 3 μm or less.

[0045] In process (C), the number of times processes (A) and (B) are repeated may be two or more, three or more, or five or more. In this case, the number of repetitions may be seven or less, or ten or less, but is not limited to this range. Also, in the repetition of processes (A) and (B), the control device 26 may change the scanning depth by a predetermined amount from the scanning depth in the previous process (A) each time process (B) is completed. This predetermined amount may be a value of 1.0 μm or less. For example, the predetermined amount may be 0.2 μm or more, or 0.4 μm or more, and may be 0.7 μm or less, or 1 μm or less.

[0046] The image generation unit 27 generates a fluorescence image of the scanned range based on the fluorescence generated from the scanned focal point for each processing (B), as follows. Each position showing fluorescence in this fluorescence image corresponds to the path of charged particles emitted from the conversion layer 1. The brightness value of each position (pixel) showing fluorescence in the fluorescence image indicates the intensity of ionization of the charged particles. Therefore, the fluorescence image is an image of the path of charged particles emitted from the conversion layer 1 as viewed from the direction of neutron irradiation onto the object under test T (i.e., the thickness direction of the fluorescence nucleus track detector 2), and may represent the fine structure of the object under test T as a grayscale pattern formed by the transmission and absorption of the neutrons from which the particles originated.

[0047] The image generation unit 27 includes a filter 27a, a light receiving unit 27b, and a data processing unit 27c.

[0048] The filter 27a selectively transmits fluorescence generated from the fluorescence nucleus track detector 2 and transmitted through the dichroic mirror 22. The filter 27a may be configured to not transmit light other than the wavelength of fluorescence.

[0049] The light-receiving unit 27b receives fluorescence generated from the fluorescence nucleus track detector 2 via the filter 27a and outputs an electrical signal (i.e., a brightness value) corresponding to the brightness of the fluorescence to the data processing unit 27c. The light-receiving unit 27b may be, for example, a photomultiplier tube (PMT).

[0050] The image generation unit 27 may further include a focusing lens 27d and a confocal pinhole 27e. The focusing lens 27d focuses the fluorescence from the dichroic mirror 22 onto the confocal pinhole 27e. The confocal pinhole 27e cuts out the fluorescence focused by the focusing lens 27d from light other than the focusing point (focal) of the excitation light in the fluorescence nucleus track detector 2, and selectively allows the fluorescence from the focusing point to pass to the light receiving unit 27b. In this case, the track image generation device 20 may function as a confocal scanning microscope.

[0051] In the above process (B), each time the control device 26 moves the focal point to each position (X, Y) within the scanning range on the focal plane, it outputs position information indicating the position (X, Y) of the focal point to the image generation unit 27. Each time the data processing unit 27c receives position information from the control device 26, it generates pixel data that associates the fluorescence brightness value received by the light receiving unit 27b at the time the position information was received with the position information. In this way, the data processing unit 27c generates pixel data for each position (X, Y) across the entire scanning range, and generates a fluorescence image of the scanning range based on this pixel data. In the fluorescence image, the brightness value of each position (pixel) in the scanning range is the fluorescence brightness value at that position (X, Y). In this way, the image generation unit 27 generates a fluorescence image for each of the multiple (B) processes.

[0052] According to this embodiment, in one example, the data processing unit 27c of the image generation unit 27 generates a track image by superimposing multiple fluorescence images generated for multiple processing steps (B). That is, this track image is an image formed by superimposing multiple fluorescence images on each other, and the brightness value at each position (X, Y) in the track image may correspond to the sum of the brightness values ​​at that position (X, Y) in the multiple fluorescence images. The multiple fluorescence images constituting the track image may include fluorescence images on the surface 2a of the fluorescence nucleus track detector 2 (i.e., fluorescence images when the scanning depth is zero).

[0053] The track image generation device 20 according to this embodiment may function as a confocal scanning microscope as described above, but is not limited thereto. For example, the track image generation device 20 may function as a fluorescence microscope without utilizing the confocal function and scanning function.

[0054] Figure 2B is a schematic diagram of a track image generation device 20 that functions as a fluorescence microscope without confocal and scanning functions. As shown in Figure 2B, this track image generation device 20 may omit the confocal pinhole 27e, scanning mechanism 23, control device 26, focusing lens 27d, and data processing unit 27c described above, and instead be equipped with an imaging lens 27f and an imaging unit 27g. That is, as shown in Figure 2B, the image generation unit 27 may be equipped with an imaging lens 27f, an imaging unit 27g, and the filter 27a described above. The excitation light source 21 focuses and irradiates the target area of ​​the fluorescence nucleus track detector 2 with excitation light, and as a result, the fluorescence generated from the target area passes through the filter 27a and the imaging lens 27f. The imaging lens 27f images the fluorescence from the target area onto the imaging surface of the imaging unit 27g. The imaging unit 27g generates a track image based on the imaged fluorescence. The imaging unit 27g may be configured with, for example, a CCD or CMOS. Furthermore, with respect to the track image generation device 20 described based on Figure 2B, matters not described here may be the same as those in the case of the track image generation device 20 described based on Figure 2A, as long as they do not contradict each other.

[0055] (Track Image Generation Method) Figure 3 is a flowchart showing a track image generation method according to an embodiment of the present invention. This track image generation method is a method for generating a track image representing the fine structure of the object under inspection T using the neutron position recording device 10 described above. This method comprises the following steps S1 to S3.

[0056] In step S1, for example, as shown in Figure 1B, the neutron position recording device 10 is positioned so that the surface 2a of the fluorescence nucleus track detector 2 faces the object under inspection T from one side (the right side in Figure 1B).

[0057] In step S2, with the neutron position recording device 10 positioned in step S1, a neutron beam is irradiated onto the object under inspection T from the other side of the object under inspection T (the left side in Figure 1B). Each neutron that passes through the object under inspection T is converted into a charged particle by the conversion film 1, and the tracks of these charged particles are recorded by the fluorescence nucleus track detector 2. The neutron beam irradiated onto the object under inspection T in step S2 may be a neutron beam shaped by a collimator so that a large number of neutrons from a neutron source (not shown) fly substantially parallel to each other. This neutron beam may have a cross-section narrowed by the collimator. In step S2, the neutron beam (for example, the neutron beam described above) may be irradiated onto the object under inspection T in the thickness direction of the fluorescence nucleus track detector 2.

[0058] In step S3, excitation light containing a predetermined wavelength component is irradiated onto the target area of ​​the fluorescence nucleus track detector 2 where the tracks were recorded in step S2, thereby generating fluorescence from each track in the target area, and a fluorescence image is generated based on the fluorescence. Step S3 comprises steps S31 and S32. Step S3 may be performed by the track image generation device 20 described above based on Figure 2A or Figure 2B.

[0059] In step S31, the fluorescent nucleus track detector 2, whose tracks were recorded in step S2, is removed from the protective bag 3, and the fluorescent nucleus track detector 2 is detached from the support substrate 4 on which the conversion film 1 etc. is formed, and is placed on the stage 28 of the track image generation device 20, for example, as shown in Figure 2A or Figure 2B. The fluorescent nucleus track detector 2 on the stage 28 has its surface 2a facing the side opposite the objective lens 24a.

[0060] <In the case of a confocal scanning microscope> Step S32 may be performed by the above-described track image generation device 20, which functions as a confocal scanning microscope as shown in Figure 2A. In this case, in step S32, the control device 26 performs the above-described processes (A) to (C), and the data processing unit 27c of the image generation unit 27 generates a track image by superimposing multiple fluorescence images as described above. In this case, the above-described target range irradiated with excitation light means multiple scanning ranges with different depths.

[0061] Alternatively, the control device 26 may perform processes (A) and (B) once without performing process (C) described above, and the image generation unit 27 may generate one fluorescence image of the scanning range as a track image representing the fine structure of the object T under inspection.

[0062] <In the case of a fluorescence microscope> Step S32 may be performed by the above-described track image generation device 20 which functions (or is made to function) as a fluorescence microscope as shown in Figure 2B. In this case, in step S32, excitation light containing a predetermined wavelength component is irradiated onto the target range of the fluorescence nucleus track detector 2 by an excitation light source. This causes fluorescence to be generated from each track in the target range, and the imaging unit 27g generates a fluorescence image as a track image representing the fine structure of the object to be inspected, based on the fluorescence incident through the filter 27a and the imaging lens 27f.

[0063] The fluorescence image is an image of the target area irradiated with excitation light. In other words, this fluorescence image is a two-dimensional image of the target area viewed from the side facing the surface 2a of the fluorescence nucleus tracking detector 2 (the direction in which the excitation light is irradiated onto the surface 2a). Therefore, in this fluorescence image, the brightness value of each pixel is the brightness value of the fluorescence at the position (X, Y) in the target area corresponding to that pixel.

[0064] When the track image generation device 20 is used as a fluorescence microscope, the target range irradiated with excitation light in step S32 is the range in which the excitation light is focused and irradiated by the lens optical system 24, and is a minute two-dimensional range when viewed in the direction of irradiation of the excitation light to the fluorescence nucleus track detector 2. This target range may include the surface 2a of the fluorescence nucleus track detector 2 in the irradiation direction, or it may be a range on a virtual cross-section located at a depth within a local range from the surface 2a and perpendicular to the irradiation direction (for example, the local range may be 3 μm or less, 1 μm or less, 0.5 μm or less, or 0.1 μm or less from the surface 2a). In this case, the target range may have a certain thickness in the irradiation direction, and in this case, the thickness may be 1 μm or more and 3 μm or less. Alternatively, the target range may not have substantially any thickness in the irradiation direction, and in this case, the thickness may be less than 1 μm, 0.5 μm or less, or 0.1 μm or less.

[0065] <Effects of the Track Image Generation Method of this Embodiment> According to the track image generation method of this embodiment, a track image representing the fine structure of the object under inspection T can be generated with a high spatial resolution of less than 1 μm based on the fluorescence generated from the tracks recorded by the fluorescence nucleus track detector 2. This track image may be a two-dimensional image, and the dimensions in each direction (vertical and horizontal dimensions) of the track image may be on the order of 10 μm or 100 μm.

[0066] As described above, a fluorescent image can also be generated for each scanning depth within a local range from the surface 2a of the fluorescent nucleus track detector 2 to a predetermined depth, and a track image can be generated by superimposing these fluorescent images. This makes it possible to generate a track image that contains a sufficient amount of information to represent the fine structure of the object under test T, even if the amount of information in a single fluorescent image is small.

[0067] Furthermore, because the localized area is the vicinity of surface 2a, a fluorescence image (track image) is obtained in which the tracks of each charged particle are kept short. Therefore, it becomes possible to obtain a track image that shows the fine structure more clearly.

[0068] (Experimental Example) An experiment was conducted to acquire a track image representing the fine structure of the object under inspection T using the neutron position recording device 10 described above and the track image generation device 20 shown in Figure 2A.

[0069] In this experimental example, a neutron position recording device 10 having a main body M with the following configuration and dimensions was prepared, as shown in Figure 4. As a fluorescence nucleus track detector 2, a carbon and magnesium doped alumina crystal (Al ２ O ３ A fluorescent nucleus tracking detector (C, Mg) was prepared. This fluorescent nucleus tracking detector 2 is a rectangular thin plate with a thickness of 0.5 mm in the left-right direction of Figure 4, a dimension of 8.0 mm in the up-down direction of Figure 4, and a dimension of 4.0 mm in the direction perpendicular to the plane of the paper in Figure 4. In addition, a silicon substrate with a thickness of 0.4 mm was prepared as the support substrate 4. On the surface of this support substrate 4 (the right side of Figure 4), １０ B ４ A conversion film 1 made of C, a stabilizing film 5 made of NiC, and a protective film 6 made of carbon C were formed with thicknesses of 230 nm, 46 nm, and 14 nm, respectively.

[0070] As shown in Figure 4, a test object T with a known microstructure was prepared for the experiment. This test object T has numerous teeth 31 formed as microstructures on a silicon substrate, as shown in Figure 4. These teeth 31 extend parallel to each other in a direction perpendicular to the plane of the paper in Figure 4. These teeth 31 are formed at intervals of approximately 9 μm in the vertical direction of Figure 4. More specifically, each tooth 31 has a width of approximately 5 μm in the vertical direction of Figure 4, and the gap between adjacent teeth 31 in the vertical direction of Figure 4 is approximately 4 μm. Note that the actual shape of each formed tooth 31 differs slightly from the perfect rectangle shown in Figure 4. Also, the actual number of teeth 31 is greater than the number of teeth 31 schematically drawn in Figure 4.

[0071] The object under test T and the neutron position recording device 10, prepared in this manner, were placed close to each other as shown in Figure 4. Then, in Figure 4, a neutron beam with small divergence was irradiated onto the object under test T from left to right. That is, the neutron beam was irradiated onto the object under test T so that a large number of teeth 31 were included within the irradiation range of the neutron beam on the silicon substrate. The divergence of this neutron beam was 0.3 milliradians in the vertical direction of Figure 4 and 10 milliradians in the direction perpendicular to the plane of the paper in Figure 4.

[0072] Of the many neutrons incident on the object T under test, those incident on the teeth 31 are absorbed by the gadolinium forming the teeth 31, but the remaining neutrons pass through the gaps between adjacent teeth 31 and are incident on the conversion film 1. Each neutron incident on the conversion film 1, as described above, acts as a charged particle. ７ Li nucleus and ４ The two charged particles are converted into He nuclei (alpha particles), and one of these two charged particles is incident on the fluorescence nucleus tracking detector 2. As a result, the tracking path of the incident charged particle is recorded in the fluorescence nucleus tracking detector 2.

[0073] Based on the tracks of charged particles recorded in the fluorescence nucleus track detector 2, a track image was generated by the track image generation device 20 shown in Figure 2A. In this experimental example, an excitation light source 21 emitting 640 nm laser light was used to generate fluorescence with a wavelength of 750 nm from the track position within the fluorescence nucleus track detector 2.

[0074] Figure 5 shows the track image generated in this experimental example. In Figure 5, the horizontal direction corresponds to the direction perpendicular to the plane of the paper in Figure 4, and the vertical direction corresponds to the up and down direction in Figure 4. The track image in Figure 5 is a 1024 pixel × 1024 pixel image, where 1024 pixels corresponds to a length of 106.07 μm. Furthermore, the track image in Figure 5 is a superimposed image of fluorescence images with scanning depths of 0 μm, 0.5 μm, 1.0 μm, and 1.5 μm, respectively.

[0075] In the trajectory image of Figure 5, the numerous black areas extending laterally are each teeth 31, and the bright areas extending laterally are the gaps between the teeth 31. The trajectory image of Figure 5 shows the numerous teeth 31 (each tooth with a width of 5 μm) and the gaps between the teeth (each gap with a width of approximately 4 μm) as microstructure. In other words, the trajectory image of Figure 5 accurately represents the microstructure of the object under inspection T.

[0076] Furthermore, the measured resolution of the track image in Figure 5 was 0.887 ± 0.009 μm. Therefore, with the neutron position recording device 10 and track image generation device 20 according to this embodiment, a track image representing the fine structure of the object under inspection T can be obtained with a resolution of less than 1 μm.

[0077] (Application example) The above-mentioned track images can be repeatedly generated by changing the direction of neutron beam irradiation to the object under inspection T. Based on the numerous track images corresponding to each of these irradiation directions, three-dimensional image data representing the three-dimensional microstructure inside the object under inspection T can be generated, for example, by back projection.

[0078] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea of ​​the present invention. For example, the neutron position recording device 10, the track image generation device 20, and the track image generation method according to the embodiments of the present invention do not have to have all of the above-described items, and may have only some of the above-described items.

[0079] Furthermore, to the extent that at least some of the above-mentioned problems can be solved, or to the extent that at least some of the effects described herein can be obtained, one or more of the claims and components described herein can be omitted, or any combination of the claims and components described herein is possible.

[0080] Furthermore, you may adopt any of the following modification examples 1 to 3 individually, or you may adopt any combination of two or more of modification examples 1 to 3. In this case, the points not mentioned below may be the same as those described above.

[0081] (Example of modification 1) The conversion film 1 may be formed directly on the surface 2a of the fluorescence nucleus track detector 2. In this case, in order to generate a track image using the track image generation device 20 described above, the conversion film 1 has a thickness small enough that the excitation light and fluorescence described above can sufficiently pass through the conversion film 1. This thickness may be, for example, 50 nm or less or 30 nm or less, but is not limited to this range, and may be 100 nm or less or 70 nm or less, or in other ranges. When the conversion film 1 is formed directly on the surface 2a of the fluorescence nucleus track detector 2 in this way, the stabilizing film 5, the protective film 6, and the support substrate 4 may be omitted.

[0082] (Example of modification 2) The stabilizing film 5 and the protective film 6 may be omitted. In this case, the support substrate 4 is attached to the fluorescence nucleus tracking detector 2 such that the conversion film 1 is sandwiched between the support substrate 4 and the fluorescence nucleus tracking detector 2. This attachment may be done, for example, using the protective bag 3 as described above.

[0083] (Example of modification 3) The conversion film 1 may be formed of a main component other than boron. This main component may be, for example, lithium. ６ It can be Li. ６ Li converts incident neutrons into charged particles, namely alpha particles and tritium ions. In this case, lithium ６ The conversion film 1, which mainly contains Li, may be formed from lithium fluoride (LiF).

[0084] 1 Conversion film, 2 Fluorescence Nucleus Track Detector (FNTD), 2a Surface, 3 Protective bag, 3a, 3b Inner surface, 4 Support substrate, 5 Stabilization film, 6 Protective film, 10 Neutron position recording device, 20 Track image generation device, 21 Excitation light source, 22 Dichroic mirror, 23 Scanning mechanism, 23a, 23b Mirror, 24 Lens optical system, 24a Objective lens, 25 Relative position adjustment device, 26 Control device, 27 Image generation unit, 27a Filter, 27b Light receiving unit, 27c Data processing unit, 27d Focusing lens, 27e Confocal pinhole, 27f Imaging lens, 27g Imaging unit, 28 Stage, 31 Teeth, M Main body of neutron position recording device, T Tested object

Claims

1. A neutron position recording device for generating an image representing the microstructure of an object under inspection, comprising: a thin-film conversion film that converts each neutron that has passed through the object under inspection into a charged particle upon incidence; and a fluorescence nucleus track detector having a surface facing the conversion film, which records the tracks of the charged particles corresponding to the positions of the neutrons when the charged particles from the conversion film are incident upon it.

2. The neutron position recording device according to claim 1, wherein the conversion membrane is a membrane mainly composed of boron.

3. The conversion membrane is boron carbide １０ B ４ The neutron position recording device according to claim 2, wherein the film is formed of C.

4. A neutron position recording device according to any one of claims 1 to 3, comprising a support substrate on which the conversion film is formed, wherein the support substrate is made of a neutron-permeable material, and the support substrate is attached to the fluorescent nuclear track detector such that the conversion film is positioned between the fluorescent nuclear track detector and the support substrate.

5. The neutron position recording device according to claim 4, wherein the support substrate, the conversion film, and the fluorescence nucleus track detector constitute the main body of the neutron position recording device, and a protective bag is provided to house the main body inside, and the conversion film and the fluorescence nucleus track detector are sandwiched between opposing inner surfaces of the protective bag by the inside of the protective bag being suctioned.

6. The neutron position recording device according to any one of claims 1 to 3, wherein the conversion film is formed on the surface of the fluorescence nucleus track detector.

7. A method for generating a track image representing the fine structure of an object under inspection using a neutron position recording device according to any one of claims 1 to 6, comprising: (S1) positioning the neutron position recording device such that the surface of the fluorescence nucleus track detector faces the object under inspection from one side of the object under inspection; (S2) irradiating the object under inspection with a neutron beam from the other side of the object under inspection, converting each neutron that has passed through the object under inspection into a charged particle using the conversion film, recording the tracks of the charged particles in the fluorescence nucleus track detector; and (S3) irradiating a target range in the fluorescence nucleus track detector with excitation light containing a predetermined wavelength component to generate fluorescence from each track in the target range, and generating the track image based on the fluorescence.

8. The method for generating a track image according to claim 7, wherein the target range is a range on the surface of the fluorescent nucleus track detector, or a range on a virtual cross-section located at a depth within a local range from the surface of the fluorescent nucleus track detector and perpendicular to the irradiation direction of the neutron beam.

9. The method for generating a track image according to claim 7, wherein in (S3), (A) the focal plane of the lens optical system is positioned at a scanning depth within a local range from the surface of the fluorescent nucleus track detector in order to focus the excitation light into the fluorescent nucleus track detector using the lens optical system, (B) the scanning range on the focal plane is scanned at the point of focus of the excitation light, (C) (A) and (B) are repeated in (A) by changing the scanning depth, and (D) each time in (B) a fluorescence image of the scanning range is generated based on the fluorescence generated from the scanned point of focus, and the track image is generated by superimposing a plurality of fluorescence images for a plurality of scanning depths.

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