JP2010096648A - Radiation-into-light transducing element, and radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To acquire a radiation detector which has a high detection sensitivity, with respect to radiation whose permeabilities to substances are high, and can acquire a two-dimensional image with respect to an incident radiation. <P>SOLUTION: This radiation detector 10 includes a radiation-to-light transducing element 20 and an imaging element 30. The radiation-to-light transducing element 20 is constituted by bundling a number of cylindrical fluorescent elements 21. The individual fluorescent elements 21 are arranged, in correspondence with individual pixels 31 in the imaging device 30. In these fluorescent elements 21, cylindrical fluorescent objects 22, made of scintillator materials are set so that the axes (long axes) of the cylinders, are parallel with the direction of incidence of radiation to be detected. On the top surfaces 221 of the fluorescent objects 22 and their side surfaces 222, metal layers 23 are formed. On their undersurfaces 223, metal layers 23 are not formed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiation-to-light conversion element that converts radiation such as X-rays, γ-rays, high-energy electron beams and neutron beams into visible light or ultraviolet light. Moreover, it is related with the radiation detector which detects the two-dimensional image of a radiation using this.

  Many detectors for detecting radiation such as X-rays, γ-rays, electron beams, and neutrons are known. Among them, radiation detectors using scintillators using fluorescent materials are widely used. . In this detector, the scintillator emits visible light and ultraviolet light by absorbing these radiations, and indirectly detects the radiation by detecting these lights with a photodetector such as a photomultiplier tube or CCD. Can be detected. In general, it is difficult to directly detect these radiations with a photomultiplier tube or a photo detector such as a CCD, but here the radiation is converted into visible light or ultraviolet light that can be detected with these photo detectors. It can be detected in the same manner as visible light or ultraviolet light using a photodetector.

  Here, if a two-dimensional image is obtained in addition to simply detecting radiation, the detector is useful in many fields. For example, a technique for obtaining a two-dimensional image of X-rays or γ-rays is important in the medical field, and a technique for obtaining a two-dimensional image of neutrons is important in the field of nuclear power. Therefore, a technique for obtaining a two-dimensional image of radiation using a solid-state imaging device such as a CCD for the above-described photodetector has been developed.

  For this reason, for example, in Patent Document 1, a scintillator panel having a structure in which a scintillator material having a columnar structure is formed on a substrate is attached to the surface of an imaging device (CCD) after a protective film or the like is formed on the surface. A radiation detector (image sensor) of a different form is described. Here, a columnar crystal such as CsI used as an inorganic scintillator material is formed on a substrate by a method such as vapor deposition, and light generated by absorbing radiation is incident on an image sensor and detected. .

  Patent Document 2 describes a radiation detector having a structure in which a large number of optical fibers are arranged corresponding to pixels of an image sensor, and a fluorescent material (scintillator material) is dissolved and integrated in the material of the optical fiber. Has been. In this structure, since the configuration in which the optical fiber and the scintillator are integrated is used, the light generated by the fluorescent material can be guided to the pixels of the image sensor with high efficiency.

  By using such a technique, a radiation detector capable of obtaining a two-dimensional image of radiation was obtained.

JP 2000-356679 A JP-A-8-610

  However, the above radiation detector is required to have a high detection sensitivity for the radiation to be detected at the same time as obtaining a two-dimensional image. In order to sufficiently absorb the radiation to be detected in the scintillator and obtain sufficient light emission, the thickness of the scintillator that can sufficiently absorb this radiation is required. That is, if the scintillator is not sufficiently thick, sufficient light emission intensity cannot be obtained and sufficient detection sensitivity cannot be obtained.

  On the other hand, in the radiation detector described in Patent Document 1, since it is necessary to form a columnar structure scintillator material by vapor deposition or the like, it is difficult to set the thickness to, for example, 1 cm or more. It is. Therefore, it is effective for low energy electron beams and X-rays with low transparency, but it is difficult to detect γ rays and neutrons, which are particularly highly transmissive radiation, with high detection sensitivity.

  On the other hand, in the radiation detector described in Patent Document 2, it is possible to lengthen the optical fiber (thicken the scintillator). However, what is used here is not the scintillator itself but an optical fiber to which a fluorescent material is added. As the amount of the fluorescent material added increases, the emission intensity due to radiation increases, but generally the amount of the fluorescent material that can be added to the optical fiber is limited. Therefore, in this case, it is difficult to obtain sufficient detection sensitivity even when the optical fiber is lengthened.

  Therefore, it has been difficult to obtain a radiation detector that has high detection sensitivity for radiation having high substance permeability and can obtain a two-dimensional image with respect to incident radiation.

  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 radiation-to-light conversion element of the present invention is a radiation-to-light conversion element that converts radiation into visible light or ultraviolet light, and is a columnar scintillator material provided with a major axis direction along the incident direction of the radiation. A plurality of fluorescent elements each having a phosphor made of the above and a metal layer formed on a surface on the incident side of the phosphor are arranged.
The radiation-light conversion element of the present invention is characterized in that in the fluorescent element, a metal layer is formed on a surface other than the surface facing the incident side surface.
In the radiation-light conversion element of the present invention, the scintillator material is a plastic scintillator material.
The radiation detector of the present invention is a radiation detector that detects a two-dimensional image of radiation, an imaging element that detects a two-dimensional image of visible light or ultraviolet light, and a surface on the radiation emission side of the phosphor. And the radiation-light conversion element installed corresponding to the pixels in the imaging element.

  Since the present invention is configured as described above, it is possible to obtain a radiation detector that has high detection sensitivity with respect to radiation having high substance permeability and can obtain a two-dimensional image with respect to incident radiation. it can.

  Hereinafter, a radiation detector that is the best mode for carrying out the present invention will be described. FIG. 1 is a diagram showing an outline of the configuration of this radiation detector. The radiation detector 10 includes a radiation-light conversion element 20 and an imaging element 30. The radiation to be detected is incident on the radiation-to-light conversion element 20 from the upper side in FIG. 1 as indicated by a white arrow, in which the radiation is converted into visible light or ultraviolet light, and this light is converted into light. The image sensor 30 detects. The radiation detected here is arbitrary radiation such as X-ray, γ-ray, electron beam, neutron beam and the like. Although not shown, the radiation passes through the optical system before the radiation enters the radiation-to-light conversion element 20, and the radiation-to-light conversion element 20 is disposed at the image point.

  The image pickup device 30 is a CCD image sensor or a CMOS image sensor, and a plurality of pixels 31 arranged in a two-dimensional manner correspond to photodiodes. Although not shown, a transfer CCD, a selection transistor, etc. Is formed.

  The radiation-light conversion element 20 is configured by bundling a large number of cylindrical fluorescent elements 21. These are fixed by an outer frame (not shown), and each fluorescent element 21 is arranged corresponding to each pixel 31 in the image pickup element 30.

  FIG. 2 shows a top view (a) of each columnar fluorescent element 21 and a cross-sectional view in the AA direction. In this fluorescent element 21, a cylindrical phosphor 22 made of a scintillator material is set so that the axis (long axis) of the cylinder is along the incident direction of radiation to be detected. A metal layer 23 is formed on the upper surface 221 (the surface on the side on which the radiation to be detected is incident) and the side surface 222 of the phosphor 22. The metal layer 23 is not formed on the lower surface 223 (the surface facing the side on which the radiation to be detected is incident or the surface on which the radiation to be detected is emitted). The diameter of the phosphor 22 corresponds to the size of the pixel 31 in the image sensor 30 and can be set to about 1 μm, for example. However, this diameter may be made smaller than each pixel 31 in the image pickup device 30 so that the plurality of fluorescent elements 21 correspond to one pixel 31. When this diameter is made larger than the pixel 31 and a plurality of pixels 31 are set to correspond to one fluorescent element 21, the resolution of the obtained two-dimensional image is not the pixel of the image sensor 30 but this radiation-light. It is determined by the arrangement of the fluorescent elements 21 in the conversion element 20.

  As the material of the phosphor 22, a plastic scintillator material is particularly preferably used. This plastic scintillator material is, for example, a solid plastic obtained by dissolving an organic scintillator material such as anthracene or stilbene, which is a fluorescent material, in a solvent made of styrene and solidifying it. The diameter corresponds to the pixel 31 of the image sensor 30 as described above, but can be, for example, about 1 μm. The length can be arbitrarily set within a range of, for example, 100 μm to several tens of cm as a length that can sufficiently absorb the radiation to be detected.

Further, the material of the metal layer 23 is, for example, aluminum, and it is necessary not to transmit visible light or ultraviolet light in order to suppress crosstalk between pixels, and the thickness thereof is, for example, about 0.1 μm. .

  As shown in FIG. 3, when X-rays, γ-rays, electron beams, and neutron beams (white arrows in FIG. 3) enter these organic scintillator materials, these materials are visible light or ultraviolet light (in the figure). (Thin arrow). In particular, the metal layer 23 is formed on the upper surface 221 of the phosphor 22, but highly transmissive radiation, particularly neutron rays and γ rays, pass through the metal layer 23. Therefore, even if the metal layer 23 is formed on the upper surface 221 of the phosphor 22, this does not reduce the radiation detection sensitivity.

  These lights are emitted from the light emitting point (stars in FIG. 3) to the surrounding direction. However, since the metal layer 23 is formed on the upper surface 221 and the side surface 222 of the phosphor 22, these lights are emitted. When the light reaches the upper surface 221 and the side surface 222, it is reflected, reaches the lower surface 223 where the metal layer is not formed, and is emitted from the lower side in FIG. That is, although the fluorescent element 21 is formed of a material different from that of the optical fiber, the light propagates through the fluorescent element 21 and is emitted from the lower side, and performs the same function as the optical fiber.

  In the case of this configuration, the metal layer 23 formed on the upper surface 221 prevents light from escaping from the upper surface 221 of the fluorescent element 21. In addition, when light passes through the side surface 222 of the fluorescent element 21 and enters the adjacent fluorescent element 21, it causes crosstalk between pixels. This is also caused by forming the metal layer 23 on the side surface 222. It is suppressed.

  Light emitted from the lower surface 223 of the fluorescent element 21 is incident on each pixel 31 of the imaging element 30 immediately below the light. Here, the image pickup device 30 is a CCD image sensor or a CMOS image sensor, and an optical signal from a photodiode serving as the two-dimensionally arranged pixels 31 is read out to the outside. Since each fluorescent element 21 is arranged corresponding to each pixel 31 in the imaging element 30, this light is output to the outside as an optical signal in each pixel 31. Therefore, thereafter, a clear two-dimensional image signal with respect to the incident radiation can be obtained by the same operation as that of the visible light image sensor.

  The manufacturing method of the radiation-light converting element part 20 at this time will be described. First, each cylindrical phosphor 22 injects a liquid obtained by melting an organic scintillator material such as anthracene or stilbene in a solvent made of styrene through pores having the same diameter as the outer diameter of the phosphor 22, It can be obtained by cooling and solidifying. In addition, the same production can be achieved by filling a plate (capillary plate) having a large number of pores with an organic scintillator material or a powdered scintillator material. The phosphor 22 can be made of any scintillator material. From the viewpoint of manufacturing, the above-mentioned plastic scintillator material is particularly preferably used.

  Thereafter, the phosphor 22 is cut into a desired length. This length is the length in the vertical direction in FIG. 2. As described above, when detecting highly transmissive radiation, it is preferable that the phosphor 22 be sufficiently long in the vertical direction.

  The metal layer 23 can be formed on the entire surface of the phosphor 22 that is an insulator, for example, using electroless plating. However, it is necessary to remove the lower surface 223 in FIGS. For this reason, it is preferable to cut the phosphor 22 to a desired length after the formation of the metal layer 23. In addition to electroless plating, the metal layer 23 can also be formed, for example, by vapor deposition.

  Thereafter, the fluorescent element 21 is bundled and fixed. In this case, these may be fixed using an outer frame after fixing them using an adhesive or the like, but if sufficient fixing strength can be obtained without using the outer frame, the outer frame There is no need to use.

  In order for the image sensor to detect emitted light with high efficiency, the distance between the lower surface 223 of the phosphor 22 and the pixel (photodiode) of the image sensor 30 is preferably as small as possible, and is equal to or smaller than the diameter of the phosphor 22. It is preferable that When this interval is large, light leaks from this gap to adjacent pixels, causing crosstalk and a decrease in detection efficiency.

  With the above configuration, the radiation detector 10 can obtain a clear two-dimensional image with respect to incident radiation. In particular, manufacture is possible even when the fluorescent element 21 is lengthened. At this time, the fluorescent element 21 can be formed of a scintillator material having high emission efficiency with respect to radiation, and the generated ultraviolet light or visible light can be incident on the imaging element 30 with high efficiency. Therefore, the absorption in the phosphor 22 can be increased even for γ rays and neutron rays which are particularly highly transmissive radiation, and a clear two-dimensional image can be obtained with high detection sensitivity. Further, when the radiation reaches the image sensor 30 directly without being absorbed in the phosphor 22, it may cause noise in the image sensor 30, but this noise is reduced.

  On the other hand, in the radiation detector described in Patent Document 1, since it is necessary to form the scintillator material by vapor deposition or the like, it is difficult to make the thickness sufficiently thick, for example, 1 cm or more. Met. Therefore, the detection sensitivity for radiation with high transparency is insufficient, and the noise in the image sensor is large, so that it is difficult to obtain a two-dimensional image of radiation with high sensitivity.

  Further, in the radiation detector described in Patent Document 1, a CsI or the like serving as a scintillator is a columnar crystal formed by vapor deposition or the like, and one or a plurality of columnar crystal grains correspond to a pixel of an image sensor. . However, since it is difficult to strictly control the size and arrangement of crystal grains, it is difficult to detect light emission for each pixel with high efficiency. Furthermore, since the light generated in one crystal grain cannot be prevented from entering the adjacent crystal grain, crosstalk between pixels is large.

  On the other hand, in the radiation detector described in Patent Document 2, since the optical fiber corresponds to the pixel of the image sensor, the problem of crosstalk does not occur. However, since it is not a scintillator that absorbs radiation but an optical fiber to which a fluorescent material is added, radiation absorption efficiency and light emission efficiency are low, and high detection sensitivity for incident radiation cannot be obtained.

  In the embodiment of the present invention, the phosphor 22 is composed of a plastic scintillator. However, the present invention is not limited to this, and for example, an inorganic scintillator such as CsI may be used if the same form can be adopted. Is also possible.

  Further, in the fluorescent element 21, the metal layer 23 is formed on the upper surface 221 and the side surface 222. However, the fluorescent elements 21 are bonded to each other by the adhesive layer, and the relationship between the refractive index of the material of the fluorescent element 21 and the refractive index of the adhesive layer. When the light generated by radiation is reflected at the interface between the phosphor 22 and the adhesive layer, it is not necessary to form the metal layer 23 on the side surface 222.

  Furthermore, a CCD or a CMOS image sensor can be used as the image sensor 30, but any image sensor that can detect a two-dimensional light intensity distribution can be used instead.

It is a figure which shows schematic structure of the radiation detector which concerns on embodiment of this invention. It is the top view (a) and sectional drawing (b) which show the structure of the fluorescence element in the radiation-light conversion element which concerns on embodiment of this invention. It is a figure which shows the propagation of the light which generate | occur | produced in the fluorescence element in the radiation-light conversion element which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation detector 20 Radiation-light conversion element 21 Fluorescence element 22 Phosphor 23 Metal layer 30 Image sensor 31 Pixel 221 Upper surface 222 Side surface 223 Lower surface

Claims (4)

A radiation-to-light conversion element for converting radiation into visible light or ultraviolet light,
A plurality of fluorescent elements each including a phosphor made of a columnar scintillator material provided in the long axis direction along the incident direction of the radiation, and a metal layer formed on a surface on the incident side of the phosphor. A radiation-to-light conversion element characterized by being arranged.   2. The radiation-light conversion element according to claim 1, wherein a metal layer is formed on a surface other than the surface facing the incident side surface in the fluorescent element.   The radiation-light conversion element according to claim 1, wherein the scintillator material is a plastic scintillator material. A radiation detector for detecting a two-dimensional image of radiation,
An image sensor for detecting a two-dimensional image of visible light or ultraviolet light;
The radiation-to-light conversion element according to any one of claims 1 to 3, wherein a surface on the emission side of the radiation in the phosphor is disposed corresponding to a pixel in the imaging element.
A radiation detector comprising:

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