Radiation detection element, radiation detection device and radiation image capturing apparatus

Abstract

To provide a radiation direct detection device that uses materials including none of harmful elements such as Cd etc.SOLUTION: The present invention relates to a radiation detection element which comprises a radiation absorption layer and electrodes, wherein the electrodes are positioned on both surfaces of the radiation absorption layer, which comprises a radiation absorption member satisfying (a) to (c). Here, the radiation absorption member (a) has properties of generating electric charges in response to incidence of a radiation, (b) includes a crystal phase of composition shown by formula (1), and (c) comprises a crystallite of 1 mm or larger in short diameter. (1) ABxCy, (where A, B and C are elements constituting the compound: A includes one kind or more of elements selected from the group of K, Rb and Cs, B includes at least Cu, and C includes one kind or more of elements selected from the group of Cl, Br and I; and x and y represent a mol ratio of B and C when A is 1, and are so defined that 1.5≤x≤2.5 and 2.5≤y≤3.5.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radiation detection element, a radiation detection device, and a radiation image pickup apparatus. [Background technology]

[0002] Radiation detection is utilized in various fields such as security, medicine, and resource exploration. For example, by arranging radiation conversion elements (hereinafter sometimes simply referred to as "conversion elements") that convert radiation into an electrical signal in an array and irradiating an object with radiation, when the radiation absorption rate differs depending on the position on the object, an image of the object can be drawn based on the detected dose of each conversion element by utilizing the fact that the amount of radiation incident on each conversion element differs. The main methods for converting radiation into an electrical signal include a method in which a radiation detection element (hereinafter sometimes simply referred to as a "detection element") containing a scintillator and a photoelectric conversion unit is used to convert the radiation into an electromagnetic wave such as visible light by the scintillator, and the electromagnetic wave is then converted into an electrical signal by the photoelectric conversion unit (indirect conversion method), and a method in which the radiation is directly converted into an electrical signal by a conversion element such as a semiconductor (direct conversion method).

[0003] In the indirect conversion method, the electromagnetic waves emitted by the scintillator are emitted in all directions and then scattered within the scintillator. This makes it prone to so-called "crosstalk," in which electromagnetic waves emitted from the scintillator in one detection element are detected by a nearby detection element, and tends to reduce the positional resolution. In contrast, the direct conversion method, for example, places electrodes on both sides of a radiation absorbing layer that converts radiation into electric charges, applies a voltage to one of the electrodes to generate an electric field in the radiation absorbing layer, and then irradiates the layer with radiation. The electric charges generated in the radiation absorbing layer move in the direction of the electric field and reach the other electrode. Here, the accumulation of electric charges in this electrode, or the resulting change in voltage between the electrodes, is extracted as an electric signal to detect radiation. In this way, by directing the charges generated in the radiation absorbing layer in a specific direction, the occurrence of the crosstalk can be suppressed. Therefore, the direct conversion method has better position resolution than the indirect conversion method, but requires a large crystalline element.

[0004] Radiation detection devices using the indirect conversion method include those using halide materials such as CsI, CsI and mixed crystals (Patent Documents 1 and 2). However, the materials in Patent Documents 1 and 2 are all in the form of thin films or needle-like crystals formed by deposition, and their applications are limited to the indirect conversion method, which has the aforementioned crosstalk problem, and no reports have been published on their application to the direct conversion method, which has excellent position resolution, or on the large-sized crystalline elements required for this. As an example of a radiation detection device using the direct conversion method, there have been reported devices that use inorganic compound single crystals such as CdTe and CdZnTe in the radiation absorption layer to detect radiation with high sensitivity (Patent Documents 3 and 4). However, these materials all have the problem that the cost of manufacturing the conversion element is very high and they contain harmful Cd. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2003-147343 A [Patent Document 2] JP 2015-045636 A [Patent Document 3] JP 2016-202901 A [Patent Document 4] JP 2017-096798 A Summary of the Invention [Problem to be solved by the invention]

[0006] In view of the above-mentioned problems with the conventional techniques, an object of the present invention is to provide a radiation direct detection device using materials that do not contain harmful elements such as Cd. [Means for solving the problem]

[0007] As a result of intensive research into the above-mentioned problems, the inventors have discovered that the above-mentioned problems can be solved by using a radiation detection element having a crystalline phase that exhibits a specific composition and a radiation absorbing layer that has high crystallinity, and have thus completed the present invention.

[0008] That is, the present invention relates to the following.

[0009] [1] A radiation detection element comprising a radiation absorbing layer and an electrode, The electrodes are located on both sides of the radiation absorbing layer; The radiation absorbing layer of the radiation detection element comprises a radiation absorbing member that satisfies the following (a) to (c): (a) The property of generating an electric charge in response to incident radiation. (b) Contains a crystalline phase having a composition represented by the following formula (1): (c) Having a single crystallite with a minor axis length of 1 mm or more. A.B. x C y (1) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; x and y respectively represent the molar ratios of B and C when A is taken as 1.0, 1.5≦x≦2.5, 2.5≦y≦3.5 It is.)

[0010] [2] The radiation detection element according to [1], wherein the crystal structure of the crystal phase with the composition represented by formula (1) is an orthorhombic crystal belonging to the space group Cmcm.

[0011] [3] The radiation detection element according to [1] or [2], wherein the radiation absorbing member that satisfies the above (a) to (c) is made of a single crystal.

[0012] [4] Further comprising a capacitor and an electrical signal output section; The capacitor is connected to one of the electrodes of the radiation detection element, The radiation detection element according to any one of [1] to [3], wherein the electric signal output section outputs the charge accumulated in the capacitor as an electric signal.

[0013] [5] The radiation detection element according to any one of [1] to [4], wherein the radiation absorbing layer further comprises another radiation absorbing member, the another radiation absorbing member including a crystalline phase having a composition represented by the following formula (2): A3B z C w (2) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; z and w respectively represent the molar ratios of B and C when A is 3.0, 1.5≦z≦2.5, 4.0≦w≦6.0 It is.)

[0014] [6] The radiation detection element according to [5], wherein the radiation detection layer includes a structure in which the radiation absorbing member satisfying the (a) to (c) and the another radiation absorbing member are laminated together.

[0015] [7] The radiation detection element according to any one of [1] to [6], wherein the radiation absorbing layer is provided, on a part or all of one or more surfaces, with a layer made of a compound containing a monovalent metal element or a divalent metal element and a halogen element.

[0016] [8] A radiation detection device comprising one or more radiation detection elements according to any one of [1] to [7].

[0017] [9] The radiation detection element further includes a capacitor and an electrical signal output unit, The capacitor is connected to one of the electrodes of the radiation detection element, The radiation detection device according to [8], wherein the electrical signal output unit includes a radiation detection element that outputs the charge accumulated in the capacitor as an electrical signal; an image conversion section that converts the signal from the electrical signal output section into an image; Effect of the Invention

[0018] According to the present invention, it is possible to provide a direct radiation detection device using materials that do not contain harmful elements such as Cd. [Brief description of the drawings]

[0019] [Figure 1] 1 is a photograph showing a single crystal CsCu2I3 obtained in Example 1. [Diagram 2] FIG. 2 is a schematic diagram showing a measurement device for measuring a radiation response current of the radiation detection element produced in Example 1. [Diagram 3] 4 is a graph showing the measurement results of the radiation response current density of the radiation detection element produced in Example 1. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, the embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments.

[0021] In one embodiment, the present invention is a radiation detection element comprising a radiation absorbing layer and an electrode, the electrodes being located on both sides of the radiation absorbing layer, and the radiation absorbing layer comprising a radiation absorbing member (hereinafter sometimes referred to as “radiation absorbing member (1)”) that satisfies the following (a) to (c): (a) The property of generating an electric charge in response to incident radiation. (b) Contains a crystalline phase having a composition represented by the following formula (1): (c) Having a single crystallite with a minor axis length of 1 mm or more. A.B.x C y (1) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; x and y respectively represent the molar ratios of B and C when A is taken as 1.0, 1.5≦x≦2.5, 2.5≦y≦3.5 It is.)

[0022] In a specific embodiment of the present invention, the radiation absorbing layer comprises a radiation absorbing member (hereinafter may be referred to as “radiation absorbing member (2)”) different from the radiation absorbing member (1), and the radiation absorbing member (2) includes a crystalline phase having a composition represented by the following formula (2): A3B z C w (2) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; z and w respectively represent the molar ratios of B and C when A is 3.0, 1.5≦z≦2.5, 4.0≦w≦6.0 It is.)

[0023] In a specific embodiment of the present invention, the radiation absorbing layer may have a layer (hereinafter, this layer may be referred to as an "M / X compound layer") composed of a compound containing a monovalent metal element or a divalent metal element and a halogen element (hereinafter, this layer may be referred to as an "M / X compound layer") on a part or all of one or more surfaces. Hereinafter, the radiation detection element in these embodiments may be simply referred to as "the radiation detection element."

[0024] In one embodiment, the radiation detection element further comprises a capacitor and an electrical signal output section, the capacitor being connected to one of the electrodes in the radiation detection element, and the electrical signal output section outputting the charge accumulated in the capacitor as an electrical signal.

[0025] In another embodiment of the present invention, a radiation detection device includes one or more of the radiation detection elements (hereinafter, the radiation detection device in this embodiment may be simply referred to as "the radiation detection device").

[0026] In one embodiment, the present invention is a radiation image capturing apparatus comprising the radiation detection device and an image conversion unit that converts a signal from the electrical signal output unit into an image (hereinafter, the radiation in this embodiment may be simply referred to as a "radiation image capturing apparatus").

[0027] <Radiation detection element> The radiation detection element includes a radiation absorbing layer and electrodes located on both sides of the radiation absorbing layer. The shape of the radiation absorbing layer has two major surfaces, which for the sake of convenience are referred to herein as a first surface and a second surface, respectively. In addition, the electrode located on the first surface side may be referred to as the "first electrode", and the electrode located on the second surface side may be referred to as the "second electrode". For ease of explanation, the electrode to which the voltage is applied is referred to as the "first electrode." That is, the voltage is applied to the first surface. The radiation absorbing layer and the electrodes will be described below.

[0028] <Radiation absorbing layer> The radiation absorbing layer (hereinafter may be simply referred to as "radiation absorbing layer") includes at least the radiation absorbing member (1) which is a substance that generates electric charges upon receiving energy rays such as radiation. The radiation absorbing layer may include the radiation absorbing member (1) and the radiation absorbing member (2). The radiation absorbing member (1) may be of one type or a combination of two or more types. The radiation absorbing member (2) may be of one type or a combination of two or more types. Furthermore, the radiation absorbing member (1) may be used in combination with a substance other than the radiation absorbing member (2), or the radiation absorbing member (2) may be used in combination with the other substance.

[0029] The mode of combination of two or more types of radiation absorbing members or radiation absorbing substances with other substances is not particularly limited, and for example, they may be stacked in the thickness direction connecting the first electrode and the second electrode, or they may be arranged side by side in a plane perpendicular to the thickness direction.

[0030] When the radiation absorbing member (1) and the radiation absorbing member (2) are used, from the viewpoint of improving the characteristics of the radiation detection element, it is preferable to arrange the radiation absorbing member (1)-containing layer and the radiation absorbing member (2)-containing layer in a laminated manner, for example, in the thickness direction connecting the first electrode and the second electrode (hereinafter simply referred to as the "thickness direction").

[0031] Examples of radiation include α-rays, γ-rays, X-rays, and neutron rays, and from the viewpoint of utilization in the fields of medicine and security, X-rays or γ-rays are preferred, and from the viewpoint of versatility in application fields, X-rays are preferred. The charge to be detected is an electron or a hole.

[0032] The radiation absorbing layer is not particularly limited as long as it has a second surface facing the first surface, but from the viewpoint that it is preferable that the electric field intensity generated when a voltage is applied to the first surface is uniform in the radiation absorbing layer, it is preferable that the distance between the first surface and the second surface is equal at least in the region in contact with the first electrode and the second electrode, that is, the first surface and the second surface are parallel surfaces. In addition, the shape of the first surface and the second surface is not particularly limited, and can be a flat surface or a curved surface, for example, a rectangular surface such as a square or a rectangle, a circular surface, a polygonal surface, or a spherical surface. From the viewpoint of ease of device manufacture, a flat surface is preferable, and a rectangular surface is more preferable. In addition, the radiation absorbing layer may be a single layer in which multiple electrodes are arranged in the surface direction, or only a pair of electrodes may be arranged in one layer, and in the latter case, multiple radiation absorbing layers may be arranged in the surface direction. From another aspect, the radiation absorbing layer may be connected between multiple radiation detection elements to form a single layer, or may be independent for each detection element.

[0033] The areas of the first and second surfaces of the radiation absorbing layer are each independently, usually 1 mm 2 More than 4mm, preferably 2 More than 16mm, preferably 16mm 2 The upper limit of the area of ​​the first and second surfaces of the radiation absorbing layer is not particularly limited, but from the viewpoint of the difficulty of manufacturing, it is usually 1000 mm 2 By having the area equal to or larger than the above lower limit, an image of a wider area can be obtained in one imaging operation. The thickness of the radiation absorbing layer is usually 0.5 mm or more, preferably 1 cm or more, more preferably 1.5 cm or more, and even more preferably 2.0 cm or more. There is no particular upper limit to the thickness, but it is usually 50 cm or less, and may be 30 cm or less, 20 cm or less, or 10 cm or less. When the thickness of the radiation absorbing layer is within the above range, the radiation absorption rate can be increased.

[0034] When the radiation absorbing layer contains a radiation absorbing member (1) and a radiation absorbing member (2), the radiation absorbing layer may have one layer each containing radiation absorbing member (1) and one layer containing radiation absorbing member (2), or may have two or more layers of either one or both of them arranged alternately. Usually, the radiation absorbing layer is provided with one layer containing radiation absorbing material (1) and one layer containing radiation absorbing material (2). In this case, the layer containing radiation absorbing material (1) may be on the first electrode side, or the layer containing radiation absorbing material (2) may be on the first electrode side.

[0035] From the viewpoint of uniformity of sensitivity, the radiation absorbing member is preferably crystalline, specifically, it preferably contains single crystallites with a minor axis length of 1 mm or more, and is particularly preferably a single crystal. From another point of view, the length of the minor axis of the crystallite is preferably 1 mm or more, more preferably 5 mm or more. The larger the single crystallite and the fewer defects, the lower the possibility that charges generated by radiation will be trapped, scattered, or absorbed, and the amount of charge reaching the electrode from the single crystallite will increase, resulting in an improved efficiency of conversion from radiation to electric current.

[0036] The crystal structure of the crystalline phase preferably belongs to the orthorhombic system, and more preferably belongs to the space group Cmcm. The crystal structure can be determined by XRD measurement and the Rietveld refinement method using the results.

[0037] The band gap of the radiation absorbing member is preferably as large as possible without exceeding the energy of the radiation, and the lower limit is usually 1.25 eV or more, preferably 1.5 eV or more, more preferably 2.0 eV or more, even more preferably 2.2 eV or more, and particularly preferably 5 eV or more. On the other hand, the upper limit of the band gap of the radiation absorbing member is usually 100 keV or less, preferably 80 keV or less, more preferably 60 keV or less, so long as the applied voltage is not excessive. By having the band gap be equal to or greater than the lower limit, the frequency of thermal carrier generation can be reduced, and the noise of the electric signal generated independently of radiation irradiation can be reduced. In addition, by having the band gap be equal to or less than the upper limit, the energy of the incident radiation can be efficiently absorbed, and the generated charge can be efficiently transported to the electrode, thereby increasing the detection sensitivity.

[0038] The electrical resistance of radiation absorbing materials is usually 10 4 Ωcm or more, preferably 10 6 Ωcm or more, more preferably 10 8 The electrical resistance of the radiation absorbing material is Ωcm or more. By having the electrical resistance of the radiation absorbing material be equal to or higher than the lower limit, leakage current can be reduced and a high signal-to-noise (S / N) ratio can be obtained. There is no particular upper limit for the electrical resistance of the radiation absorbing material, and the higher the electrical resistance, the more insulating the material will be when not excited by radiation, which is preferable.

[0039] The density of radiation absorbing materials is usually 2.0 g / cm 3 or more, preferably 3.0 or more, more preferably 4.0 or more. There is no particular upper limit, and the higher the better. However, it is usually 10 g / cm 3 When the density of the radiation absorbing member is equal to or higher than the lower limit, the radiation absorption efficiency is increased, and high radiation detection sensitivity can be obtained in the radiation detection device.

[0040] The effective atomic number of the radiation absorbing member is usually 40 or more, preferably 50 or more, more preferably 55 or more, and even more preferably 60 or more. There is no particular upper limit, and the higher the better, but it is usually 100 or less. When the effective atomic number of the radiation absorbing member is equal to or greater than the above lower limit, the radiation absorption efficiency is increased, and high radiation detection sensitivity can be obtained in the radiation detection device. The effective atomic number can be determined based on the composition of the radiation absorbing member, with reference to the description in Medical Physics, 39 (2012), p. 1769-1778.

[0041] Hole mobility μ of the radiation absorbing material h and hole lifetime τ h The product μ h τ h is usually 10 -7 cm 2 / V or more, preferably 10 -5 cm 2 / V or more, more preferably 10 -3 cm 2 / V or more, and there is no particular upper limit. The higher the better, but usually it is 10 -1 cm 2 / V or less. The hole mobility μ h and hole lifetime τ h The product μ h τ h By making the product μ h τ h can be determined from the relational equation by performing photoconductivity measurement in which current and voltage are measured while photoexciting (see Journal of Physics of and Chemistry of Solids 1965, Vol. 26, p. 575-578).

[0042] Electron mobility μ of radiation absorbing material e and electron lifetime τ e The product μ e τ e As in the case of the hole, -7 cm 2 / V or more, preferably 10 -5 cm2 / V or more, more preferably 10 -3 cm 2 / V or more. Note that the product of electron mobility and electron lifetime μ e τ e can be determined in a similar manner to that for holes (see above).

[0043] The radiation absorbing layer has a linear transmittance of typically 70% or more, preferably 75% or more, and more preferably 80% or more in a wavelength region longer than 800 nm at a thickness of 1.6 mm. By providing a radiation absorbing layer with such high transmittance, it is possible to provide a radiation detection element and a radiation detection device with improved crystallinity and high absorption efficiency.

[0044] (Radiation absorbing material (1)) The radiation absorbing member (1) contains a crystalline phase having a composition represented by the following formula (1). A.B. x C y (1) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; x and y respectively represent the molar ratios of B and C when A is taken as 1, 1.5≦x≦2.5, 2.5≦y≦3.5 It is.)

[0045] The element A includes at least one of K, Rb, and Cs, and preferably includes Cs. In an embodiment in which A includes Cs, the proportion of Cs in the element A is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, particularly preferably 90 mol % or more, and most preferably 100 mol %. The inclusion of Cs in the A element stabilizes the crystal structure. Furthermore, by removing impurities and reducing crystal distortion, transparent single crystallites can be obtained, preventing scattering of radiation.

[0046] The element B usually contains Cu. The proportion of Cu in the element B is preferably 50 mol % or more, more preferably 70 mol % or more, further preferably 80 mol % or more, particularly preferably 90 mol % or more, and most preferably 100 mol %. The crystal structure is stabilized by including Cu in the B element. Furthermore, by removing impurities and reducing crystal distortion, a transparent single crystal can be obtained, preventing scattering of radiation.

[0047] The C element usually includes at least one of Cl, Br, and I, and preferably includes I. In an embodiment in which the C element includes I, the proportion of I in the C element is preferably 50 mol % or more, more preferably 70 mol % or more, even more preferably 80 mol % or more, particularly preferably 90 mol % or more, and most preferably 100 mol %. The crystal structure is stabilized by including at least one of Cl, Br, and I, preferably I, as the C element. Furthermore, by removing impurities and reducing crystal distortion, a transparent single crystallite can be obtained, and scattering of radiation can be prevented. Furthermore, by including an element with a larger atomic number, the radiation absorption rate of the entire material is improved.

[0048] The above x and y respectively represent the relative molar ratios of B and C when the molar ratio of A in the compound is taken as 1, and each independently represents x is usually 1.5 or more, preferably 1.7 or more, more preferably 1.8 or more, and is usually 2.5 or less, preferably 2.3 or less, more preferably 2.2 or less; y is usually 2.5 or more, preferably 2.7 or more, more preferably 2.8 or more, and is usually 3.5 or less, preferably 3.3 or less, more preferably 3.2 or less. When the content is within the above range, the crystal structure is stabilized and a radiation absorbing layer of uniform quality can be obtained. The composition of the crystalline phase can be measured by conventional methods such as GD-MS and ICP analysis. When the radiation absorbing member (1) contains the crystal phase represented by the above formula (1), radiation can be converted into electric charge without using harmful elements such as Cd and Pb.

[0049] (Radiation absorbing material (2)) The radiation absorbing member (2) contains a crystalline phase having a composition represented by the following formula (2): In one embodiment, the radiation absorbing member (2), like the radiation absorbing member (1), also contains single crystallites having a minor axis length of 1 mm or more, and the crystal structure thereof can belong to an orthorhombic crystal, in particular to the space group Pnma. A3B z C w (2) (In the above formula (1), A, B, and C represent the elements constituting the compound, A comprises one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C comprises one or more elements selected from the group consisting of Cl, Br, and I; z and w respectively represent the molar ratios of B and C when A is 3, 1.5≦z≦2.5, 4.0≦w≦6.0 It is.)

[0050] In formula (2), A, B, and C have the same meanings as A, B, and C in formula (1), respectively, and the preferred ones and the reasons why they are preferable are the same as those described above. As described above, by including the radiation absorbing layer in the radiation absorbing material (2), excellent quantum efficiency can be obtained. From the viewpoint of obtaining such an effect more effectively, A, B, and C in the formula (2) contain Cs, Cu, and I, respectively. More preferably, A, B, and C in the formula (2) each consist of 80 mol % or more of Cs, Cu, and I, respectively. Particularly preferably, A, B, and C each consist of Cs, Cu, and I, respectively.

[0051] The above z and w respectively represent the relative molar ratios of B and C when the molar ratio of A in the compound is 3, and each independently represents z is usually 1.5 or more, preferably 1.7 or more, more preferably 1.8 or more, and is usually 2.5 or less, preferably 2.3 or less, more preferably 2.2 or less; w is usually 4.0 or more, preferably 4.3 or more, more preferably 4.7 or more, and is usually 6.0 or less, preferably 5.7 or less, more preferably 5.3 or less. When z and w are within the above ranges, the crystal structure is stabilized and a radiation absorbing layer of uniform quality can be obtained. As mentioned above, the composition of the crystalline phase can be measured by conventional methods such as GD-MS and ICP analysis. When the radiation absorbing member (2) contains the crystal phase represented by the above formula (2), radiation can be converted into electric charge without using harmful elements such as Cd and Pb.

[0052] To form a radiation absorbing layer having a structure in which such a radiation absorbing material (2) is laminated with the radiation absorbing material (1), for example, in the production of a single crystal of the radiation absorbing material (1) in the examples described below, the crystal growth may be repeated by changing the composition of the precipitation solution.

[0053] (M / X compound layer) In certain embodiments of the present invention, an M / X compound layer may be present on the first and / or second surface of the radiation absorbing layer, between the radiation absorbing layer and the first and / or second electrode.

[0054] The M / X compound constituting the M / X compound layer, i.e., a compound containing a monovalent metal element or a divalent metal element and a halogen element, is preferably a heavy atom iodide from the viewpoint of radiation stopping ability, and is particularly preferably CuI (copper iodide).

[0055] M / X compounds such as CuI have more dispersive valence and conduction bands than radiation absorbing materials (1), and the effective mass of electrons and holes is smaller, which leads to improved current characteristics in radiation detection elements (for example, APL Mater. 7, 2019, Page 111113 reports a comparison of the characteristics of CuI (copper iodide) and CsCu2I3 (cesium copper iodide), which are made of similar materials). By providing such an M / X compound layer at the interface between the electrode and the radiation absorbing layer, carriers generated by radiation absorption can efficiently reach the electrode, providing a radiation detection element with good detection sensitivity.

[0056] The thickness of the M / X compound layer (thickness per layer) is preferably 0.1 mm or more, particularly 0.5 mm or more, from the viewpoint of the detection sensitivity, while it is preferably 30 mm or less, particularly 20 mm or less, from the viewpoint of the radiation detection element characteristics.

[0057] Such an M / X compound layer can be formed on the surface of a radiation absorbing layer, for example, by deposition on an iodide crystal substrate.

[0058] <Electrode> The electrodes (first electrode and second electrode) included in the radiation detection element are usually located on the two main surfaces of the radiation absorbing layer, respectively.

[0059] The material of the electrode is not particularly limited, but a metal having high electrical conductivity can usually be used, for example, Al, W, Ru, Ni, Pd, Cu, Ag, Au, Pt, Pb, Bi, etc. From the viewpoint of preventing diffusion into the radiation absorbing layer in contact with the electrode, it is preferable that the electrode has a property of having a low diffusion coefficient, and for example, Al, W, Ru, Ni, Pd, Cu, Au, Pt, Pb, Bi can be used. From the viewpoint of obtaining a good high-resistance electrical resistivity, the absolute value of the work function of the electrode is preferably larger than the absolute value of the work function of the conduction band of the radiation absorbing layer, and is preferably smaller than the absolute value of the work function of the valence band of the radiation absorbing layer. The work function can be determined by a conventional method.

[0060] This radiation detection element is usually used in a state where a voltage is applied to the first electrode and an electric field is generated between the first electrode and the second electrode. When charges are generated by radiation, either electrons or holes reach each of the two electrodes due to the electric field. Usually, when a negative voltage is applied to the first electrode, holes reach the first electrode and electrons reach the second electrode. It is preferable that the absolute value of the work function of the electrode intended to receive holes is smaller than the absolute value of the work function of the other electrode.

[0061] <Power supply section> The radiation detection element may include a power supply unit for applying a voltage between the electrodes. The power supply unit is connected to the first electrode and applies a voltage to the first electrode. The power supply unit may be connected to an external power source to supply power to the first electrode, or may include a self-power source to supply power to the first electrode. A commonly used power source may be used as the external power source or the self-power source, and may be, for example, a direct current (DC) power source or an alternating current (AC) power source.

[0062] <Voltage converter> The power supply unit may include a voltage converter for adjusting the different voltages applied to the first electrode. The arrangement of the voltage converter is not particularly limited as long as the above-mentioned purpose is achieved, and is usually arranged between the power source and the first electrode. For example, the voltage converter may be directly connected to the power source or may be connected via some kind of circuit. A known voltage converter may be used, for example, a linear regulator or a switching regulator.

[0063] <Electrical signal output section> The radiation detection element may further include an electric signal output section that is connected to any one of the electrodes and outputs the charge accumulated in the electrode as an electric signal. The electrical signal output section may be provided inside the radiation detection element, or an external electrical signal output device may be used. In the radiation detection device including two or more of the radiation detection elements, it is preferable that one electrical signal output section is provided for each of the radiation detection elements, and each electrical signal output section is connected to a corresponding electrode. The electric signal output unit may be a normal one, for example, one including one or more charge storage circuits that secondarily store the charge stored in the electrode, and an electric signal output circuit that outputs the charge stored in the charge storage circuit as an electric signal. The charge storage circuit is not particularly limited, but for example, a capacitor may be used.

[0064] The operation of the electric signal output circuit is preferably capable of performing at least one of the following operations: outputting an electric signal based on the electric charge when the electric charge accumulated in any of the charge accumulation units reaches a threshold value or more; outputting the electric charge accumulated in any of the capacitors as an electric signal at a certain timing; and outputting the electric charge accumulated in any of the capacitors as an electric signal by the operation of an external power source (for example, using a transistor switch, etc.), and a circuit capable of performing these operations can be used. These operations may be performed alone or in combination. In addition, a plurality of some or all of the circuits corresponding to these operations may be provided, and a repetitive structure may be used. By the above operations, the electric charge accumulated in each pixel of the second electrode can be output as an electric signal at a certain threshold value and / or at a certain timing.

[0065] The electric signal output unit may also include an amplifier circuit (such as an amplifier or an integral amplifier circuit) that amplifies the charge or information of the electric signal, a glitch removal circuit such as a sample-and-hold circuit, a ground that can be connected to a circuit that can store electric charge and a switch that switches ON / OFF the connection between the ground and the circuit, a filter circuit (such as a low-pass filter or a high-pass filter) that removes unnecessary low-frequency and high-frequency noise, etc. By appropriately providing these circuits, it is possible to improve the sensitivity, remove noise, remove residual charge after outputting the electric signal, etc., and improve the accuracy of the electric signal.

[0066] When the response current measurement of the present radiation detection element is performed by continuous irradiation with radiation, the current density during radiation exposure is E1 and the current density during non-radiation exposure is E2, and the value of E1 / E2 is usually 5 or more, preferably 8 or more, more preferably 10 or more, even more preferably 15 or more, particularly preferably 20 or more, and especially preferably 30 or more, and there is no particular upper limit, and a higher value is more desirable. For example, ideally, the current density during non-radiation exposure approaches 0, and the value of E1 / E2 approaches infinity.

[0067] When the radiation detection device includes two or more of the radiation detection elements, the two or more radiation detection elements may be arranged in a state where the radiation absorbing elements, each having a radiation absorbing layer and an electrode, are separated from each other, or may share some of the electrodes or radiation absorbing layers. There are no particular limitations as long as the charges generated in the different radiation absorbing elements can be distinguished and position information can be obtained.

[0068] <Other parts> The radiation detection element or the radiation detection device may include other parts, for example, an insulating layer may be provided between the electrode for applying a voltage and the radiation absorbing layer, and a protective layer may be provided on the outside to protect the element or device. Alternatively, an adhesive layer may be provided to enhance adhesion between the layers.

[0069] <Image conversion section> According to another embodiment, the present invention is a radiation imaging apparatus including the radiation detection device and further including an image conversion unit. The image conversion unit creates image data based on the electrical signal output from the radiation detection device. That is, data collection of the signal value of the electrical signal is started, and an energy value is obtained from the signal value of the electrical signal, and position information is obtained from the position of the radiation detection element. Time information can also be obtained from the timing of transmission. Then, by integrating the radiation energy value for each position, an image is constructed according to the radiation absorption rate of the subject in the radiation incidence direction for each position. The output control method of the image signal can be a conventional method, such as a conventional method used in a CMOS image sensor, a CCD image sensor, etc. Incidentally, since the image conversion section processes information of an electrical signal, it is sometimes generally called a signal processing section or an information processing section.

[0070] The radiation imaging apparatus may include an A / D converter between the electrical signal output section and the image conversion section. When the image conversion section processes digital signals, the electrical signals can be appropriately processed by performing A / D conversion.

[0071] This radiation imaging device can be used as a radiation detection device as is, or can be used in devices that detect radiation at spots, such as spatial dosimeters, and can be used for a variety of purposes, such as baggage inspection devices, medical radiation imaging devices, and radiation detection devices for resource exploration.

[0072] <Manufacturing method for radiation absorbing materials> The radiation absorbing member (1) contains a crystalline phase represented by formula (1) and contains single crystallites with a minor axis of 1 mm or more. The radiation absorbing member (2) contains a crystalline phase represented by formula (2), and preferably contains single crystallites with a minor axis of 1 mm or more. The method for producing such a crystalline phase containing single crystallites is not particularly limited. For example, the crystalline phase can be obtained by adding a solvent in which raw materials of each element are mixed so that the molar ratio of each element corresponds to the composition ratio of the compound to be obtained, to prepare a saturated solution, and then growing crystals. The method for growing the crystals is not particularly limited, but an example of the method is the VSA (Vapor Saturation of an Antisolvent) method for growing the crystals.

[0073] An example of a specific manufacturing method is as follows: The raw materials of each element are mixed so that the molar ratio of each element used in the crystal phase is equal to the desired composition, and the mixture is stirred in an environment of 10°C to 80°C until no powder is observed, after which a saturated solution is made with an appropriate solvent, and the remaining powdery solid is filtered through a filter. The temperature during stirring is preferably 20° C. or higher, and preferably 70° C. or lower, more preferably 60° C. or lower. The solvent is not particularly limited, but is preferably one in which the raw materials are dissolved and the target product is appropriately precipitated. For example, when using halides of the elements A and B in the formula (1) or formula (2), a polar solvent such as alcohols can be used to ensure the solubility of the raw materials, and a poor solvent such as acetone can be used to promote the precipitation of the product. The solvent can be appropriately changed or mixed depending on the raw materials and the target product.

[0074] Although the raw materials for each element are not particularly limited, it is preferable to use a compound consisting of any of the elements A, B, and C, since unnecessary elements can be eliminated, and for example, halides of each of A and B are preferable. The purity of the raw materials is preferably as high as possible, and is usually 95% by mole or more, and preferably 99% by mole or more.

[0075] The material of the filter used for filtration is preferably one having low reactivity, and for example, a resin such as polytetrafluoroethylene (PTFE) can be used, but is not limited to this. The pore size of the filter is usually 5.0 μm or less, preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.6 μm or less. There is no particular lower limit, but it is usually 0.1 μm or more.

[0076] After filtration, the filtered solution is subjected to crystal growth by the VSA method (Vapor Saturation of an Antisolvent). That is, the above-mentioned saturated solution is poured into a vial, covered with a perforated film, and then placed in a beaker filled with an appropriate solvent. After that, the top of the beaker is also covered with a film, and then left standing on a hot plate or the like at a temperature of 10°C or higher and 80°C or lower for 50 hours or more, whereby single crystals having a minor axis of 1 mm or more can be obtained. The solvent used here is preferably the same as the solvent used in the saturated solution in order to suppress changes in solubility. Also, for the same reason, the temperature during standing is preferably the same as the temperature of the saturated solution. The film is preferably made of a non-reactive material, and for example, paraffin or the like can be used. The standing time is not particularly limited as long as the crystal phase has sufficiently grown, but it is preferably 50 hours or more, more preferably 100 hours or more. The gentler the crystal growth, the easier it is to obtain crystals with fewer defects, and in that case, more time is required for standing.

Examples

[0077] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

[0078] [Example 1] <Production of CsCu2I3 single crystal> To a mixed solvent having a volume ratio of dimethyl sulfoxide to methanol of 5:2, CsI (purity 99.9%) and CuI (purity 99.999%) manufactured by Sigma-Aldrich were added so that the molar ratio of Cs:Cu:I was 1:2:3, and the mixture was stirred until the raw materials were dissolved to prepare a Cs / Cu / I solution. Acetone was added to this Cs / Cu / I solution, and after stirring until it became sufficiently uniform, it was passed through a 0.45 μm filter to prepare a precipitation solution. A container containing the precipitation solution was placed inside a container containing acetone having a volume 10 times that of the precipitation solution to prepare a crystal growth container. After the crystal growth container was left standing for 6 days, the precipitated crystals were taken out. The diffraction pattern of the obtained crystals was confirmed by XRD (X-ray diffraction measurement) to be a single phase of CsCu2I3. Figure 1 is a photograph of the obtained single crystal CsCu2I3. From Figure 1, it can be seen that the short axis of this single crystal CsCu2I3 is 1 mm.

[0079] <Fabrication of radiation detection element> Using the above crystal plate (CsCu2I3 single crystal), a radiation detection element was fabricated as shown in Figure 2, and its radiation response current was measured. First, electrodes 2 and 4 were formed by evaporating gold to a thickness of 100 nm through a metal mask onto the upper and lower surfaces of the CsCu2I3 single crystal 3, and then gold wires 6A and 6B were joined to the gold electrodes 2 and 4 with silver paste, respectively, to produce a radiation detection element measurement device. The gold wires 6A and 6B were connected to a grounded electrometer 5, and the current value was measured by changing the voltage. The X-ray irradiation device used consisted of a tungsten X-ray target, a tube voltage of 100 kV, and a tube current of 0.5 mA. The dose rate was measured at the measurement position with a dose rate meter, and was found to be 3.52 mGy / s.

[0080] When a voltage was applied to the measurement device in the dark and the current was measured, the current density detected from the measurement device with a voltage of -100 V was 4 μA / cm 2 In addition, when the device was irradiated with X-rays by an X-ray irradiation device while a voltage of -100 V was applied, the current density detected during X-ray irradiation was 5 μA / cm 2 From this, the ratio of the current density during X-ray irradiation to the current density during non-X-ray irradiation (ON / OFF ratio) was calculated to be 1.25. FIG. 3 shows the change in current density over time during current density measurement.

[0081] As described above, according to the present invention, it is possible to provide a radiation direct detection device using materials that do not contain harmful elements such as Cd. [Explanation of symbols]

[0082] 1 Radiation detection element 2. Gold Electrode 3. CsCu2I3 Single Crystal 4. Gold Electrode 5 Electrometer 6A,6B gold wire

Claims

1. A radiation detection element comprising a radiation absorbing layer and an electrode, The electrodes are located on both sides of the radiation absorbing layer; The radiation absorbing layer comprises a radiation absorbing member that satisfies the following (a) to (c): (a) It exhibits the property of generating electric charge in response to the incidence of radiation. (b) Contains a crystalline phase having a composition represented by the following formula (1): (c) Having single crystallites with a minor axis length of 1 mm or more. AB ｘ C ｙ ・・・(1) (In the above formula (1), A, B, and C represent elements constituting the compound, A contains one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C includes one or more elements selected from the group consisting of Cl, Br, and I; x and y respectively represent the molar ratios of B and C when A is taken as 1; 1.5≦x≦2.5, 2.5≦y≦3.5 It is.)

2. 2. The radiation detection element according to claim 1, wherein the crystal structure of the crystal phase having the composition represented by formula (1) is an orthorhombic crystal belonging to the space group Cmcm.

3. 2. The radiation detection element according to claim 1, wherein the radiation absorbing member that satisfies the above conditions (a) to (c) is made of a single crystal.

4. Further, a capacitor and an electrical signal output unit are provided, The capacitor is connected to one of the electrodes of the radiation detection element, The radiation detection element according to claim 1 , wherein the electric signal output section outputs the charge accumulated in the capacitor as an electric signal.

5. The radiation detection element according to claim 1 , wherein the radiation absorbing layer further comprises another radiation absorbing member, the another radiation absorbing member including a crystalline phase having a composition represented by the following formula (2): A ３ B ｚ C ｗ ・・・(2) (In the above formula (1), A, B, and C represent elements constituting the compound, A contains one or more elements selected from the group consisting of K, Rb, and Cs; B contains at least Cu, C includes one or more elements selected from the group consisting of Cl, Br, and I; z and w respectively represent the molar ratios of B and C when A is 3; 1.5≦z≦2.5, 4.0≦w≦6.0 It is.)

6. 6. The radiation detection element according to claim 5, wherein the radiation detection layer has a structure in which the radiation absorbing member satisfying the conditions (a) to (c) and the separate radiation absorbing member are laminated together.

7. The radiation detection element according to claim 1 , wherein the radiation absorbing layer comprises a layer made of a compound containing a monovalent metal element or a divalent metal element and a halogen element on a part or all of one or more surfaces.

8. A radiation detection device comprising one or more radiation detection elements according to any one of claims 1 to 7.

9. The radiation detection element further includes a capacitor and an electrical signal output unit, The capacitor is connected to one of the electrodes of the radiation detection element, The radiation detection device according to claim 8 , wherein the electrical signal output unit includes a radiation detection element that outputs the charge accumulated in the capacitor as an electrical signal; an image conversion section that converts the signal from the electrical signal output section into an image;

Images