Scintillators and Radiation Detectors

Abstract

The present invention addresses the problem of providing a scintillator which has a short fluorescence decay time, and in which fluorescence intensity after a time has elapsed is small when irradiated with radiation, and light-transmitting properties are markedly improved. A scintillator represented by general formula (1), the scintillator including Zr, the content of Zr in the scintillator being 1500 mass ppm or greater, and the scintillator being a block of a sintered compact. (1): QxNyO3z (In formula (1): Q includes at least one divalent metal element, and M includes at least Hf; and x, y, and z each independently satisfy the conditions 0.5 ≤ x ≤ 1.5, 0.5 ≤ y ≤ 1.5, and 0.7 ≤ z ≤ 1.5.)

Description

[Technical Field]

[0001] The present invention relates to a scintillator for use in a scintillation detector for radiation such as gamma rays for use in a high count radiation detection device, for example, a positron emission tomography (PET) device. [Background technology]

[0002] Representative scintillators for detecting radiation include Lu2SiO5 and Ga3Al5O 12 Known compounds include Gd2Si2O7 and Gd2Si2O7. Research and development in this field has attempted to improve the scintillator properties by using the structures of these compounds as a base, substituting atoms of the same group for host atoms, or by co-doping impurity atoms with different valences together with the luminescent center atom (Patent Documents 1 to 3). In recent years, with the widespread use of silicon photomultipliers, there is a demand for scintillators with short fluorescence decay times (DT) in order to improve spatial resolution resulting from temporal resolution. For example, it has been reported that the DT can be reduced to approximately 30 to 40 ns by using a lutetium orthosilicate scintillator doped with Ce (Patent Document 2). Furthermore, hafnate-based scintillators such as SrHfO3 and BaHfO3 have been reported as scintillators that exhibit even shorter DTs (Non-Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5674385 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-56378 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-151535 [Non-patent literature]

[0004] [Non-Patent Document 1] Scintillation Properties of SrHfO3:Ce3+ and BaHfO3:Ce3+Ceramics, EV van Loef, WM Higgins, J. Glodo, C. Brecher, A. Lempicki, V. Venkataramani, WW Moses, SE Derenzo, and KS Shah, IEEE Transactions on Nuclear Science, 54 741-743 (2007) [Non-patent document 2] BaHfO3:Ce sintered ceramic scintillators, A. Grezer, E. Zych, and L. Lepinski, Radiation Measurements 45, 386-388 (2010) Summary of the Invention [Problem to be solved by the invention]

[0005] Previously reported hafnate scintillators have short fluorescence decay times, but multiple components affect the decay curve, and when irradiated with radiation, the remaining fluorescence intensity can be large after a certain period of time (Non-Patent Document 1), and they have low sintering degrees and extremely low light transmittance due to scattering (Non-Patent Document 2).Another problem is that they are very expensive because they use high-purity Hf raw materials. That is, the problem to be solved by the present invention is to provide a scintillator that has a short fluorescence decay time, that when irradiated with radiation, exhibits low fluorescence intensity over time, and has significantly improved light transmittance. Another problem to be solved by the present invention is to provide a production method that solves these problems and that can provide a scintillator that can be produced inexpensively. [Means for solving the problem]

[0006] According to the present invention, the inventors have conducted extensive research in light of the above problems and have found that the above problems can be solved by using a scintillator containing an appropriate amount of Zr, thereby completing the present invention.

[0007] That is, the gist of the present invention includes the following. [1] A scintillator represented by the following general formula (1), which contains Zr, the Zr content in the scintillator being 1500 mass ppm or more, and which is a block of a sintered body. Q x M y O 3z ···(1) (In general formula (1), Q contains at least one divalent metal element, M contains at least Hf, and x, y, and z each independently satisfy 0.5≦x≦1.5, 0.5≦y≦1.5, and 0.7≦z≦1.5.) [2] The scintillator according to [1], wherein the Zr content is 21,000 ppm by mass or less. [3] The scintillator according to [2], wherein the Zr content is 5000 ppm by mass or less. [4] The scintillator according to any one of [1] to [3], wherein the divalent metal element contains one or more elements selected from the group consisting of Ba, Sr, and Ca. [5] The scintillator according to any one of [1] to [4], further comprising, as an activator, one or more elements selected from the group consisting of Ce, Pr, Nd, Eu, Tb, and Yb. [6] The scintillator according to any one of [1] to [5], which has a columnar, flat plate, or curved plate shape and a height of 1 mm or more. [7] The scintillator according to any one of [1] to [6], which has a fluorescence decay time of 30 ns or less. [8] The scintillator according to any one of [1] to [7], wherein the fluorescence decay time is 20 ns or less. [9] The scintillator according to any one of [1] to [8], which has a linear transmittance of 1% or more for light with a wavelength of 390 nm at a thickness of 1.6 mm.

[10] The scintillator according to any one of [1] to [9], which has a linear transmittance of 5% or more for light with a wavelength of 800 nm at a thickness of 1.6 mm.

[11] The scintillator according to any one of [1] to

[10] , wherein when irradiated with gamma rays, the fluorescence intensity is 2% or less 100 ns after the fluorescence intensity reaches its maximum value, with the maximum value being 100%.

[12] A radiation detector comprising the scintillator according to any one of [1] to

[11] .

[13] A radiation inspection device equipped with a radiation detector, The radiation detector is a radiation inspection device including the scintillator according to any one of [1] to

[11] .

[14] A method for manufacturing a scintillator, comprising: a raw material mixing step of mixing the raw materials to obtain a raw material mixture; a synthesis step of heat-treating the raw material mixture to obtain a synthetic powder; The raw material contains HfO2 with a purity of at least 99.0 mol% or less, The scintillator is a scintillator represented by the following general formula (1), and contains Zr, the Zr content in the scintillator being 1500 mass ppm or more, and is a block of a sintered body: How scintillators are manufactured. Q x M y O 3z ···(1) (In general formula (1), Q contains at least one divalent metal element, M contains at least Hf, and x, y, and z each independently satisfy 0.5≦x≦1.5, 0.5≦y≦1.5, and 0.7≦z≦1.5.)

[15] The method for producing a scintillator according to

[14] , wherein the content of Zr in the HfO2 is 1500 mass ppm or more.

[16] a pressure molding step of pressure molding the synthetic powder to obtain a pressure molded body; a firing step of firing the processed molded body to obtain a fired product; The method for producing a scintillator according to

[14] or

[15] , further comprising:

[17] A pressure molding step of pressure molding the synthetic powder to obtain a pressure molded body; a firing step of firing the processed molded body to obtain a fired product; The method for producing a scintillator according to

[14] or

[15] , further comprising, after the firing step, an annealing step of annealing the fired product. [Effects of the Invention]

[0008] The present invention can provide a scintillator that has a short fluorescence decay time, low fluorescence intensity over time when irradiated with radiation, and significantly improved translucency. Furthermore, the present invention can provide a scintillator that has these effects and can be produced inexpensively. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a graph showing linear transmittance curves of the scintillators of Reference Example 1, Examples 2 and 3, and Comparative Example 1. FIG. [Figure 2] FIG. 1 is a diagram showing the fluorescence decay waveform of the scintillator of Reference Example 1. [Figure 3] FIG. 10 is a diagram showing the fluorescence decay waveform of the scintillator of Example 2. [Figure 4] FIG. 10 is a diagram showing the fluorescence decay waveform of the scintillator of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes in detail the embodiments of the present invention, but these descriptions are examples (typical examples) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not deviate from the gist of the invention. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0011] <Scintillator> A scintillator (hereinafter also simply referred to as "scintillator") according to one embodiment of the present invention is a scintillator represented by the following general formula (1), which contains Zr, the Zr content in the scintillator is 1500 by mass, and which is a block of a sintered body. Q x M y O 3z ···(1) (In general formula (1), Q contains at least one divalent metal element, M contains at least Hf, and x, y, and z each independently satisfy 0.5≦x≦1.5, 0.5≦y≦1.5, and 0.7≦z≦1.5.)

[0012] Q in general formula (1) contains at least one divalent metal element. From the viewpoint of obtaining a short fluorescence decay time and improving fluorescence intensity and translucency after irradiation, it preferably contains an alkaline earth metal element, and more preferably contains at least one element selected from the group consisting of Ba, Sr, and Ca. Q may contain one of these elements alone, or two or more of them in any combination and ratio, but it is particularly preferable that it contains Ba from the viewpoint of obtaining a short fluorescence decay time. The total proportion of divalent metal elements in Q is not particularly limited, but from the viewpoint of maintaining an optimal charge balance, it is usually 20 mol% or more, preferably 30 mol% or more, more preferably 40 mol% or more, and even more preferably 50 mol% or more. There is no particular upper limit, and it is usually 100 mol% or less.

[0013] When Q contains one or more elements selected from the group consisting of Ba, Ca, and Sr, the total proportion of Ba, Ca, and Sr in Q is typically 10 mol% or more, preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and most preferably 50 mol% or more. The upper limit is 100 mol% or less. The individual proportions of Ba, Ca, and Sr are not particularly limited, and are typically 0.001 mol% or more and 100 mol% or less of the total proportion, provided that the total does not exceed the above-mentioned total proportion. Only one of Ba, Ca, and Sr may be used, or two or more may be used as main components in any desired proportion. Alternatively, one or two may be used as the main component with trace amounts of other elements added as activators. By appropriately including each element, a desirable fluorescence decay time can be achieved.

[0014] M in general formula (1) is not particularly limited as long as it contains at least Hf, from the viewpoint of reducing the fluorescence decay time and improving the fluorescence intensity and translucency after irradiation. The proportion of Hf in the whole of M is not particularly limited, but is usually 10 mol % or more, preferably 20 mol % or more, more preferably 30 mol % or more, and even more preferably 40 mol % or more, with the upper limit being 100% or less. When M contains a sufficient proportion of Hf, the effective nuclear charge becomes large, and a scintillator with high radiation stopping power can be obtained.

[0015] The scintillator represented by general formula (1) contains Zr as an element other than Q, M, and O from the viewpoints of reducing the fluorescence decay time and improving the fluorescence intensity and translucency after irradiation with radiation. Zr may be present in the scintillator in any form, and may be contained in, for example, either Q or M, or in both Q and M, similar to the activator described below.

[0016] By setting the Zr content in the scintillator to 1500 mass ppm or more, it is possible to achieve a reduction in fluorescence decay time and improvements in fluorescence intensity and translucency after radiation irradiation. Furthermore, the Zr content in the scintillator is preferably 2000 mass ppm or more, more preferably 3000 mass ppm or more, and even more preferably 4000 mass ppm or more. The upper limit is usually 21000 mass ppm or less, preferably 18000 mass ppm or less, more preferably 15000 mass ppm or less, even more preferably 12000 mass ppm or less, particularly preferably 8000 mass ppm or less, and most preferably 5000 mass ppm or less. By setting the Zr content at or above the lower limit, it becomes easy to obtain a scintillator that exhibits good afterglow characteristics and good translucency. Furthermore, by setting the Zr content at or below the upper limit, the afterglow intensity derived from Zr is not too high, and appropriate afterglow characteristics are obtained. The Zr content can be adjusted by controlling the amount of Zr (or Zr compound) that can be added as a raw material. When Zr (or Zr compound) is contained as an impurity in a raw material other than Zr (or Zr compound), it can also be adjusted by selecting the raw material from the perspective of the impurity content. Alternatively, the amount of Zr (or Zr compound) added and the selection of the raw material can be combined. The Zr content in the scintillator is not necessarily the same as the content in all the raw materials that are mixed, and may be concentrated or decreased during the manufacturing process, but as will be shown in the examples that will be described later, the Zr content in the scintillator reflects the Zr content in all the raw materials that are mixed, and increases or decreases according to the Zr content in all the raw materials that are mixed. By appropriately adjusting the ratio of the raw materials, the ratio of each element when mixing the raw materials, the addition of the Zr compound, and the manufacturing method conditions, a scintillator containing Zr within a preferred range can be obtained.

[0017] The scintillator represented by general formula (1) may contain, in addition to Q, M, O, and Zr, another element A (also referred to as "activator element A") as an activator, such as one or more elements selected from the group consisting of Ce, Pr, Nd, Eu, Tb, and Yb, as represented by the following general formula (2). From the viewpoint of obtaining a short fluorescence decay time, Ce is preferably contained. Q x M y O 3z :A···(2) The conditions for Q, M, x, y, and z in the general formula (2) are the same as those in the general formula (1). The activator element A may be present in the scintillator in any form, for example, it may be contained in either Q or M, or it may be contained in both Q and M. The content of the activator element A is not particularly limited. For example, it is typically 1.0 mass% or less, more preferably 0.5 mass% or less, even more preferably 0.2 mass% or less, and may be 0.1 mass% or less, based on the entire scintillator; the amount is not particularly limited. For example, when another element A is contained in Q, the content of the activator element A is typically 0.01 mol% or more and 5 mol% or less, and preferably 0.1 mol% or more and 2 mol% or less, based on the entire Q. When the activator element A is contained in M, the content of the activator element A is typically 0.001 mol% or more and typically 5 mol% or less, preferably 1 mol% or less, more preferably 0.1 mol% or less, based on the entire M. It is preferable that the content be as low as possible. By including an appropriate amount of the above element as an activator, greater fluorescence intensity can be obtained.

[0018] The scintillator represented by general formula (1) may contain Al as an element other than the various elements described above. The Al content in the scintillator is usually 1500 mass ppm or less, preferably 1200 mass ppm or less, more preferably 1000 mass ppm or less, and further preferably 800 mass ppm or less, 500 mass ppm or less, 200 mass ppm or less, or 100 mass ppm or less. There is no particular lower limit for the Al content, and the scintillator may not contain Al, but from the viewpoint of the possibility of Al being contained as an impurity, it is usually 1 mass ppm or more. By having the Al content in the above range, a scintillator exhibiting good translucency can be obtained. Al may be present in the scintillator in any form, and like the above-mentioned activators, it may be contained in, for example, either Q or M, or may be contained in both Q and M. If the Al content in the scintillator is too high, the luminescent properties tend to deteriorate, and the sintered body tends not to have desirable translucency. The Al content can be adjusted by controlling the amount of Al (or Al compound) that can be added as a raw material. When Al (or Al compound) is contained as an impurity in a raw material other than Al (or Al compound), it can also be adjusted by controlling the purity of the raw material. The amount of Al (or Al compound) added and the selection of the raw material can also be combined. Furthermore, the Al content can also be reduced by a general method for removing impurities. Furthermore, since Al may be mixed in from tools and equipment during the manufacturing process or from the surrounding environment, the Al content can be adjusted to a preferred level by avoiding tools and equipment that may contain Al or that have handled Al during the manufacturing process, avoiding environments where Al may be mixed in, or any combination of these.

[0019] The scintillator represented by general formula (1) may contain Mg as an element other than the various elements described above, but the Mg content in the scintillator is 100 mass ppm or less, preferably 90 mass ppm or less, more preferably 80 mass ppm or less, and further preferably 60 mass ppm or less, 40 mass ppm or less, 20 mass ppm or less, or 10 mass ppm or less. There is no particular lower limit for the Mg content, and the scintillator may not contain Mg, but from the viewpoint that Mg may be contained as an impurity, it is usually 1 mass ppm or more. By having the Mg content in the above range, a scintillator exhibiting good translucency can be obtained. Mg may be present in the scintillator in any form, and like the activators described above, it may be contained in either Q or M, or in both Q and M, for example. If the Mg content in the scintillator is too high, the luminescence characteristics tend to deteriorate and the sintered body tends not to have desirable translucency. The Mg content can be adjusted by controlling the amount of Mg (or Mg compound) that can be added as a raw material. When Mg (or Mg compound) is contained as an impurity in a raw material other than Mg (or Mg compound), it can also be adjusted by controlling the purity of the raw material. The amount of Mg (or Mg compound) added and the selection of the raw material can also be combined. Furthermore, the Mg content can also be reduced by a general method for removing impurities. Furthermore, since Mg may be mixed in from tools and equipment during the production process or from the surrounding environment, the preferred Mg content can be adjusted by avoiding tools and equipment that may contain or handle Mg during the production process, avoiding environments where Mg may be mixed in, or any combination of these.

[0020] In general formula (1), x is 0.5≦x≦1.5, preferably 0.7≦x, more preferably 0.9≦x, further preferably x≦1.3, and more preferably x≦1.1, from the viewpoint of reducing the fluorescence decay time and improving the fluorescence intensity and translucency after irradiation. In general formula (1), y satisfies 0.5≦y≦1.5, preferably 0.7≦y, more preferably 0.8≦y, further preferably y≦1.3, and more preferably y≦1.1, from the viewpoint of reducing the fluorescence decay time and improving the fluorescence intensity and translucency after irradiation. In general formula (1), z is 0.7≦z≦1.5, preferably 0.8≦z, more preferably 0.9≦z, and further preferably z≦1.4, more preferably z≦1.3, from the viewpoint of reducing the fluorescence decay time and improving the fluorescence intensity and translucency after irradiation.

[0021] The scintillator represented by general formula (1) may further contain other elements within the range that does not impair the effects of the present invention.

[0022] The method for analyzing the elements contained in the scintillator is not particularly limited, and can be carried out, for example, by a total elemental analysis technique using glow discharge mass spectrometry (GDMS) as described in the examples below.

[0023] The fluorescence decay time of the scintillator is not particularly limited, but can be measured, for example, by the same method and conditions as those for measuring the fluorescence decay time in the Examples described below. When measured by this method, the fluorescence decay time of the scintillator is usually 30 ns or less, preferably 20 ns or less, more preferably 17 ns or less, and even more preferably 15 ns or less.

[0024] The linear transmittance of the scintillator for light with a wavelength of 390 nm is not particularly limited, but is usually 1% or more, preferably 5% or more, preferably 7% or less, and more preferably 6.5% or less, and the linear transmittance of the scintillator for light with a wavelength of 800 nm is not particularly limited, but is usually 5% or more, preferably 40% or more, and more preferably 50% or more. The linear light transmittance (also simply referred to as "light transmittance") can be measured by the method described in the examples below. The preferred range of transmittance described above is preferably satisfied when the scintillator has a thickness of 1.6 mm, for example. When the scintillator has a thickness greater than 1.6 mm, the scintillator is processed to reduce its thickness to 1.6 mm to prepare a target for light transmittance measurement. When the scintillator has a thickness less than 1.6 mm, scintillators are stacked so that the thickness is 1.6 mm or more, and then processed to reduce its thickness to 1.6 mm to prepare a target for light transmittance measurement. This processing can be performed by a known method capable of reducing the thickness of a scintillator. For example, a dicer can be used to cut the scintillator to a thickness slightly thicker than the target thickness. In this case, the cut scintillator is ground using a grinding machine. By finely varying the grit size of the grinding stone used in the grinding process, the scintillator surface can be processed to be flat with minimal irregularities.

[0025] The scintillator is preferably one that is excited by irradiation with ionizing radiation and emits light in the wavelength region of 160 nm to 700 nm, and preferably has an emission peak in the wavelength region of 300 nm to 500 nm. Examples of ionizing radiation include X-rays, gamma rays, alpha rays, and neutron rays.

[0026] When a scintillator is irradiated with gamma rays, the fluorescence intensity 100 ns after the time at which the fluorescence intensity reaches its maximum value is not particularly limited, but is usually 5% or less, preferably 2% or less, more preferably 1.5% or less, and even more preferably 1% or less, with the maximum fluorescence intensity being 100%, and the lower limit is not particularly limited, but is usually 0% or more. In this way, the fluorescence decay is very fast and the fluorescence intensity is sufficiently small after the lapse of a predetermined time, so that a scintillator material that is useful for radiological testing with high time resolution can be provided. The fluorescence intensity can be measured by the method described in the Examples below.

[0027] The form of the scintillator is not particularly limited, and can be appropriately selected according to each use and purpose, and can be, for example, any of the form of powder, single crystal, polycrystal, or sintered body, particularly the form of powder, single crystal, or sintered body.For example, when the scintillator is used in a PET device, it does not need to be a powder, and a block of single crystal or sintered body is preferred, when used in an X-ray CT device, a block of single crystal or sintered body is preferred, and a block of sintered body is particularly preferred, and when used in an X-ray detection film for non-destructive testing, it is preferably used as a film in which the powder is dispersed in a resin sheet.

[0028] When the scintillator is used in the form of a block, its shape is not particularly limited, but it is preferably a shape having a radiation incident surface and a radiation emitting surface, with a certain height between the radiation incident surface and the radiation emitting surface, which are preferably parallel to each other. Furthermore, the shape of the block is preferably a pillar shape, a flat plate shape, or a curved plate shape. The height of the block shape is usually 0.5 mm or more, preferably 1 mm or more, more preferably 3 mm or more, even more preferably 5 mm or more, particularly preferably 10 mm or more, and especially preferably 15 mm or more, and there is no particular upper limit and it can be set appropriately depending on the equipment or device that uses the scintillator, but it is usually 100 mm or less. Note that the "height" in the flat plate shape and curved plate shape means thickness.

[0029] <Scintillator manufacturing method> The method for producing the above-mentioned scintillator (also referred to as "the present production method") is not particularly limited, and examples include a raw material mixing step of weighing and thoroughly mixing raw materials so as to obtain a raw material mixture with the desired composition; and a synthesis step of filling a heat-resistant container with the obtained raw material mixture and heat-treating it at a predetermined temperature in a predetermined atmosphere to obtain a synthetic powder; and preferably further including a pressure-molding step of pressure-molding the obtained synthetic powder to obtain a pressure-molded body; and a firing step of firing the obtained pressure-molded body at a predetermined temperature in a predetermined atmosphere, and processing and washing the fired body as necessary to obtain a sintered body. An example of a method for producing a scintillator will be described below.

[0030] [Raw material preparation process] The method for manufacturing a scintillator may include a step of preparing raw materials (raw material preparation step). The raw materials used are not particularly limited as long as they can be used to manufacture the above-mentioned scintillator, but for example, oxides, halides, inorganic acid salts, etc. of the respective constituent atoms can be used. Regarding Hf, for example, HfO2 can be used as a raw material, and the purity of HfO2 in the raw material is usually 99.999 mol% or less, preferably 99.9 mol% or less, more preferably 99.0 mol% or less, and usually 90 mol% or more. If the purity is too high, sintering may not proceed and the translucency may decrease. Also, if the purity is too low, the decay time of the luminescence will be long, which is undesirable. Furthermore, by using HfO2 of the above purity as a raw material, cheaper raw materials can be used, and a scintillator can be produced inexpensively. Regarding Ba, for example, BaCO3 can be used, and the purity of BaCO3 is usually 90 mol% or more, preferably 99 mol% or more, with no particular upper limit. Regarding Ca, for example, CaCO3 can be used, and the purity of CaCO3 is usually 90 mol% or more, preferably 99 mol% or more, with no particular upper limit. Regarding Sr, for example, SrCO3 can be used, and the purity of SrCO3 is usually 90 mol % or more, preferably 99 mol % or more, with no particular upper limit. For Ce, for example, CeO2, CeI3, Ce2O3, Ce(NO3)3, etc. can be used, and the purity of the raw material is usually 90 mol % or more, preferably 99 mol % or more, with no particular upper limit. Regarding Zr, Zr contained in small amounts as an impurity in raw materials such as HfO2 may be used as is, or a separate Zr compound may be added. The Zr compound is not particularly limited, but examples include ZrO2 and Zr2O3. The Zr content in the HfO2 is not particularly limited, but is typically 100 mass ppm or more, preferably 500 mass ppm or more, more preferably 1000 mass ppm or more, and even more preferably 1500 mass ppm or more, and may be 10 mass% or less, 50,000 mass ppm or less, 30,000 mass ppm or less, 21,000 mass ppm or less, 18,000 mass ppm or less, or 10,000 mass ppm or less. However, when Zr contained as an impurity in a raw material is used, the higher the purity of the raw material, the lower the Zr content tends to be. However, the purity of the raw material and the amount of Zr contained as an impurity are not completely linked, and vary depending on the type of raw material and the manufacturing process. For example, some materials have high purity and a low content of Zr contained as an impurity, while others have high purity and a high content of Zr contained as an impurity. For Al, for example, Al2O3 can be used, and the purity of Al2O3 is usually 90 mol% or more, preferably 99 mol% or more, with no particular upper limit. Furthermore, although trace amounts of Al may be contained as an impurity in raw materials other than Al (or Al compounds), the Al content in each raw material (excluding Al or Al compounds) is usually 1 mass ppm or less to several tens of mass ppm. Therefore, by selecting appropriate raw materials, the Al content in the raw material mixture after mixing the raw materials can be kept sufficiently low. For example, 3MgCO3·Mg(OH)2·3H2O can be used for Mg. The purity of 3MgCO3·Mg(OH)2·3H2O is typically 90 mol% or higher, preferably 99 mol% or higher, with no particular upper limit. While trace amounts of Mg may be contained as an impurity in raw materials other than Mg (or Mg compounds), the Mg content in each raw material (excluding Mg or Mg compounds) is typically 1 mass ppm or less to several mass ppm. By selecting appropriate raw materials, the Mg content in the raw material mixture after mixing the raw materials can be kept sufficiently low.

[0031] [Raw material mixing process] The present production method may include a step of mixing raw materials to obtain a raw material mixture (raw material mixing step). The method of mixing the raw materials is not particularly limited, and commonly used methods can be applied, such as a dry mixing method and a wet mixing method. An example of the dry mixing method is mixing using a ball mill. Examples of the wet mixing method include adding a solvent or dispersion medium such as water to the raw materials, mixing them using a mortar and pestle to form a dispersion solution or slurry, and then drying them by spray drying, heat drying, natural drying, or the like.

[0032] [Synthesis process] The present manufacturing method may include a step of heat-treating the raw material mixture to obtain a synthetic powder (synthesis step), in which the raw material mixture is filled into a heat-resistant container such as a crucible or tray and heat-treated to obtain a synthetic powder. The material of the heat-resistant container is not particularly limited as long as it is a material that has low reactivity with the raw materials, and examples thereof include platinum-based containers such as Pt, Pt / Rh, and Ir. The atmosphere during the heat treatment is not particularly limited, and examples include reducing atmospheres such as a hydrogen atmosphere or a hydrogen-rare gas mixed atmosphere; air; and the like. When the heat treatment is performed in a reducing atmosphere, Mo- or W-based containers can also be used in addition to platinum-based containers.

[0033] The temperature and time of the heat treatment are not particularly limited as long as the above-mentioned scintillator can be obtained, and it is preferable to select a temperature and time that allow the mixed raw materials to react sufficiently, but the heat treatment temperature is usually 900° C. or higher, preferably 1000° C. or higher, and usually 2000° C. or lower, preferably 1800° C. or lower. The synthesis time is usually 1 hour or longer, preferably 3 hours or longer, and usually 50 hours or shorter. The synthesized powder obtained in this synthesis step may be used to obtain a sintered body through the pressure molding step, pre-firing step, firing step, etc., which will be described later, or it may be used as it is as a powder scintillator. Incidentally, by checking whether the composition of the synthetic powder satisfies the preferred range before obtaining a sintered body by the process described below, the composition of the sintered body can be adjusted to fall within the preferred range more reliably.

[0034] The synthesized powder obtained in this synthesis step may be sieved. The mesh size (opening) of the sieve is usually 500 μm or less, preferably 200 μm or less. Sieving eliminates agglomerations of the powder, allowing a scintillator of uniform quality to be obtained.

[0035] [Pressure molding process] The present manufacturing method may include a step of pressure-molding the synthetic powder obtained in the synthesis step to obtain a pressure-molded body (pressure molding step). The method and conditions for pressure molding are not particularly limited, but can be performed, for example, by uniaxial pressure pressing or cold isostatic pressing. The pressure during pressure molding may be, for example, 10 MPa or more, and preferably 30 MPa or more. By performing appropriate pressure molding, voids after sintering are reduced and translucency is improved.

[0036] [Pre-firing process] The present production method may include a step (pre-firing step) of pre-firing the synthetic powder obtained in the synthesis step or the pressure-molded body obtained in the pressure-molding step to obtain a pre-fired product. The temperature, pressure, time, and atmosphere during pre-firing are not particularly limited as long as the scintillator described above can be obtained, but the pre-firing temperature is usually 1200°C or higher, preferably 1300°C or higher, and usually 2000°C or lower, preferably 1800°C or lower. The pre-firing pressure is usually 10 -5 Pa or more, preferably 10 -3 The pre-baking pressure is usually 10 MPa or more, and usually 10 MPa or less, and preferably 2 MPa or less. The pre-baking time is usually 1 hour or more, and preferably 2 hours or more, and usually 50 hours or less. The atmosphere is preferably an inert atmosphere such as an argon atmosphere or a nitrogen atmosphere.

[0037] [Firing process] This manufacturing method may include a step (sintering step) of further heating (sintering) under pressure the synthetic powder obtained in the synthesis step, the pressure-molded body obtained in the pressure-molding step, or the pre-fired product obtained in the pre-fired step to obtain a fired product (sintered body). The pressing method and conditions are not particularly limited, but hot isostatic pressing (HIP) can be used, for example. A hot press treatment may also be performed before firing. The firing conditions are not particularly limited as long as the above-mentioned scintillator is obtained, but the firing temperature is usually 1200°C or higher, preferably 1300°C or higher, and usually 2000°C or lower, preferably 1800°C or lower. The firing pressure is usually 10 MPa or higher, preferably 50 MPa or higher, and usually 300 MPa or lower, preferably 200 MPa or lower. The firing time is usually 0.5 hours or longer, preferably 1 hour or longer, and usually 20 hours or shorter, preferably 10 hours or shorter.

[0038] The atmosphere during firing is not particularly limited as long as the above-mentioned scintillator can be obtained, but it is preferable to carry out firing in an appropriate atmosphere taking into consideration the stability of the materials, reaction vessel, furnace materials, etc. Specific examples of the atmosphere include inert atmospheres such as argon atmosphere and nitrogen atmosphere.

[0039] The firing step may optionally include a pre-treatment step (steps of cleaning, drying, vacuum degassing, etc.), a post-treatment step (steps of cleaning, drying, etc.), etc.

[0040] [Annealing process] In the present manufacturing method, when the scintillator is obtained as a sintered body, the sintered product obtained in the sintering step may be used as the sintered body as is, or the sintered product may be annealed after the sintering step (annealing step) for the purpose of repairing crystal defects. By performing annealing, light absorption due to crystal defects is reduced, and a sintered body with higher light transmittance can be obtained. The conditions for the annealing step, such as temperature, pressure, time, and atmosphere, are not particularly limited as long as the above-mentioned scintillator is obtained, but the annealing temperature is usually 1000°C or higher, preferably 1200°C or higher, and usually 1500°C or lower. The annealing pressure is usually 10 MPa or higher, preferably 20 MPa or higher, and usually 300 MPa or lower, preferably 200 MPa or lower. The annealing time is usually 0.5 hours or longer, preferably 1 hour or longer, and usually 20 hours or shorter, preferably 10 hours or shorter. The atmosphere is preferably an inert atmosphere such as an argon atmosphere or a nitrogen atmosphere.

[0041] [Single crystal growth process] When obtaining a scintillator as a single crystal, for example, the sintered body obtained by the firing step or annealing step can be heated and melted, and the single crystal can be grown from the melt. The container and atmosphere used for growing the single crystal can be selected appropriately from the same perspective as in the production of the sintered body. There are no particular limitations on the method for growing the single crystal, and common methods such as the Czochralski method, Bridgman method, micro-pulling down method, EFG method, and zone melt method can be used. For the purpose of lowering the melting point, a flux method can also be used. When growing a large crystal, the Czochralski method and Bridgman method are preferred.

[0042] The method for obtaining the above-mentioned scintillator as a powder is not particularly limited, and examples thereof include a method in which the synthesized powder obtained in the synthesis step is directly obtained as a powder scintillator, a method in which the sintered body obtained in the firing step or annealing step is pulverized, a method in which the single crystal obtained in the single crystal growth step is pulverized, etc. The pulverization method is not particularly limited.

[0043] <Scintillator Applications> The scintillator can be used in any applications, but is preferably used in a radiation detector, which can be used in fields such as radiology (e.g., positron emission tomography (PET) for medical diagnosis, cosmic ray observation, and underground resource exploration), physics, physiology, chemistry, mineralogy, and petroleum exploration. When used as a radiation detector, the form of the scintillator is not particularly limited, and it can be any of powder, single crystal, and sintered body. The scintillator can be used as a radiation detector by combining it with a photoreceiver. Photoreceivers used in radiation detectors include position-sensitive photomultiplier tubes (PS-PMTs), silicon photomultipliers (Si-PMs), photodiodes (PDs), and avalanche photodiodes (APDs).

[0044] Furthermore, a radiation detector equipped with the above-described scintillator can also be used as a radiation inspection device. Examples of radiation inspection devices equipped with the radiation detector include nondestructive inspection devices such as detectors for nondestructive testing, detectors for resource exploration, and detectors for high-energy physics, as well as diagnostic devices such as medical image processing devices. Examples of medical image processing devices include positron emission tomography (PET) devices, X-ray CT, and SPECT. Furthermore, PET types include two-dimensional PET, three-dimensional PET, time-of-flight (TOF) PET, and depth-of-imaging (DOI) PET. These types can also be used in combination. [Example]

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0046] < reference Example 1> BaCO3 (purity 99.99 mol%), CeO2 (purity 99.99 mol%), and high-purity HfO2 (purity 99.7 mol%, containing Zr as an impurity, with a Zr content of 2800 mass ppm in HfO2) were prepared and mixed so that the molar ratio of Ba:Ce:Hf was 0.99:0.01:1.00 to obtain a powdered raw material mixture. The obtained raw material mixture was heat-treated at 1150°C for 12 hours in an air atmosphere to obtain a synthetic powder (powdered scintillator). The resulting synthetic powder was passed through a sieve with a 106 μm opening to prepare the raw material for the sintered scintillator. The resulting raw material was subjected to uniaxial pressing at 40 MPa for 1 minute and cold isostatic pressing at 170 MPa for 1 minute to obtain a pressed compact. The pressed compact was then pre-fired at 1600°C for 6 hours under a nitrogen flow (1 L / min). Finally, it was fired by hot isostatic pressing (HIP) in a nitrogen atmosphere at 1600°C and 100 MPa for 2 hours to obtain sintered scintillator A with the composition expressed by the general formula (1) above (Table 1).

[0047] <Example 2> High-purity HfO2 (purity 99.7 mol%, containing Zr as an impurity, the Zr content in HfO2 being 2800 mass ppm) was changed to low-purity HfO2 (purity 98 mol%, containing Zr as an impurity, the Zr content in HfO2 being 4000 mass ppm), and the mixture was mixed so as to obtain a scintillator having the Zr content shown in Table 1 below. reference In the same manner as in Example 1, a sintered scintillator B having the composition represented by the above general formula (1) was obtained (Table 1).

[0048] Example 3 High-purity HfO2 (purity 99.7 mol%, containing Zr as an impurity, Zr content in HfO2 2800 mass ppm) was changed to low-purity HfO2 (purity 98.5 mol%, containing Zr as an impurity, Zr content in HfO2 1.8 mass %), and the mixture was mixed to obtain a scintillator with the Zr content shown in Table 1 below. reference In the same manner as in Example 1, a sintered scintillator C having the composition represented by the above general formula (1) was obtained (Table 1).

[0049] <Comparative Example 1> High-purity HfO2 (purity 99.7 mol%, containing Zr as an impurity, Zr content in HfO2 2800 mass ppm) was changed to another high-purity HfO2 (manufactured by Kojundo Chemical Laboratory Co., Ltd.; purity 99.5 mol%, containing Zr as an impurity), and the composition and Zr content were compared according to Table 1 below. except that the mixture was mixed to obtain a sintered substance. reference In the same manner as in Example 1, a sintered scintillator D was obtained (Table 1).

[0050] <Total elemental analysis> The contents (by mass) of Ba, Hf, O, Ce, and Zr in sintered scintillators A to D were measured by glow discharge mass spectrometry (GDMS) using a VG9000 manufactured by VG Elemental under the following measurement conditions. The contents (mass ratios) of Ba, Hf, O, and Ce were converted to molar ratios, and the molar ratios of each element were calculated when Ba + Hf + Ce = 2. The results are shown in Table 1. (Measurement conditions) Discharge gas: High-purity argon (purity 99.9999 mol%) Discharge cell: Mega Cell ·Discharge conditions: 0.8-1kV, 1.6-2mA Detector: O, Y, Ba, Hf: Faraday cup, Other elements:Daly-multiplier Integration time: Faraday cup: 160 msec x 60 points x 1 scan, Daily multiplier: 200 msec x 60 points x 1 scan. Analysis values ​​were calculated as the average of n = 1 to 5.

[0051] <Translucency> The transmittance of sintered scintillators A to D was evaluated using a Hitachi High-Tech Science U-3310. An 8.3mm diameter x 1.6mm thick sample was fixed with transparent tape to a black jig with a 1mm diameter pinhole. The black jig with the sample fixed to it was then placed in close contact with an integrating sphere so that the pinhole was centered on the incident light from the U-3310, and the linear transmittance was measured. The effect of scattering was evaluated using the transmittance at the central emission wavelength of 800nm. The effect of absorption was evaluated using the transmittance at the central emission wavelength of 390nm. reference Example 1 , Example 2 The measurement results of Comparative Examples 1 to 3 are shown in Table 1 and FIG.

[0052] <Fluorescence decay time (DT)> The fluorescence decay time (DT) of sintered scintillators A to D was evaluated. A 1.6 mm thick sample was covered with Teflon tape and then attached to a Hamamatsu Photonics H7195 photomultiplier tube using an Optoseal tape manufactured by Shin-Etsu Chemical Co., Ltd. The sample was irradiated with gamma rays using Cs-137 as an excitation source, and the fluorescence intensity during and after gamma ray irradiation was measured using a Tektronix MSO54 5-BW-1000 oscilloscope. The fluorescence decay time (DT) was calculated based on the fluorescence intensity by fitting with a single exponential function. The maximum fluorescence intensity was defined as 100%, and the percentage of the fluorescence intensity 100 ns after the time at which the fluorescence intensity reached its maximum was calculated. reference Example 1 , Example 2The measurement results for Comparative Example 1 are shown in Table 1. reference Example 1 and Example 2 The measurement results of 1 to 3 are shown in Figures 2 to 4.

[0053] [Table 1]

[0054] As shown in Table 1 and Figure 1, the scintillators of the Examples had higher light transmittance than those of the Comparative Examples. Furthermore, the scintillators of the Examples had a very short DT of 14 to 15 ± 2 ns. Furthermore, when the maximum fluorescence intensity was taken as 100%, the percentage of fluorescence intensity 100 ns after the time at which the fluorescence intensity reached its maximum was 2% or less, indicating that the fluorescence intensity after irradiation with radiation was low. Furthermore, even when inexpensive low-purity HfO2 with a purity of 99.0% or less was used in Examples 2 and 3, the scintillators exhibited excellent characteristics as described above. The scintillators of the Comparative Examples had very low linear transmittance of light in the wavelength ranges of 800 nm and 390 nm, and very low emission intensity, making it impossible to measure the fluorescence intensity and fluorescence decay time during and after irradiation with radiation.

[0055] As described above, the present invention can provide a scintillator that has a short fluorescence decay time, a low fluorescence intensity over time when irradiated with radiation, and significantly improved translucency. Furthermore, the present invention can provide a scintillator that has a short fluorescence decay time, that when irradiated with radiation, exhibits low fluorescence intensity over time, that has significantly improved translucency, and that can be produced inexpensively.

Claims

1. A scintillator represented by the following general formula (1), which also contains Zr, the scintillator being a block of a sintered body having a Zr content of 1500 ppm by mass or more and 5000 ppm by mass or less, and which has a linear transmittance of 5% or more at a thickness of 1.6 mm for light having a wavelength of 390 nm: Q ｘ M ｙ O ３ｚ ・・・(1) (In general formula (1), Q contains at least one divalent metal element, M contains at least Hf; x, y, and z each independently satisfy 0.5≦x≦1.5, 0.5≦y≦1.5, and 0.7≦z≦1.5.)

2. 2. The scintillator of claim 1, wherein the divalent metal element comprises one or more elements selected from the group consisting of Ba, Sr, and Ca.

3. 3. The scintillator according to claim 1, further comprising, as an activator, one or more elements selected from the group consisting of Ce, Pr, Nd, Eu, Tb, and Yb.

4. 4. The scintillator according to claim 1, which has a columnar, flat plate, or curved plate shape and a height of 1 mm or more.

5. 5. The scintillator according to claim 1, wherein the fluorescence decay time is 30 ns or less.

6. 5. The scintillator according to claim 1, wherein the fluorescence decay time is 20 ns or less.

7. 7. The scintillator according to claim 1, wherein the in-line transmittance of light with a wavelength of 800 nm at a thickness of 1.6 mm is 5% or more.

8. 8. The scintillator according to claim 1, wherein, when irradiated with gamma rays, the maximum value of the fluorescence intensity is taken as 100%, and the fluorescence intensity 100 ns after the time when the fluorescence intensity reaches the maximum value is 2% or less.

9. A radiation detector comprising the scintillator according to any one of claims 1 to 8.

10. A radiation inspection device equipped with a radiation detector, A radiation inspection device, wherein the radiation detector comprises the scintillator according to any one of claims 1 to 8.

11. A method for manufacturing a scintillator, comprising: a raw material mixing step of mixing the raw materials to obtain a raw material mixture; a synthesis step of heat-treating the raw material mixture to obtain a synthetic powder; a pressure molding step of pressure molding the synthetic powder to obtain a pressure molded body; The raw material contains HfO with a purity of 99.0 mol% or less. ２ Including, The scintillator is a scintillator represented by the following general formula (1), and contains Zr, the scintillator being a block of a sintered body having a Zr content of 1500 ppm by mass or more and 5000 ppm by mass or less, and having a linear transmittance of 5% or more at a thickness of 1.6 mm for light having a wavelength of 390 nm: How scintillators are manufactured. Q ｘ M ｙ O ３ｚ ・・・(1) (In general formula (1), Q contains at least one divalent metal element, M contains at least Hf; x, y, and z each independently satisfy 0.5≦x≦1.5, 0.5≦y≦1.5, and 0.7≦z≦1.5.)

12. The HfO ２ The method for producing a scintillator according to claim 11 , wherein the Zr content therein is 1500 ppm by mass or more.

13. a firing step of firing the pressure-molded body to obtain a fired product; The method for producing a scintillator according to claim 11 or 12, further comprising:

14. a firing step of firing the pressure-molded body to obtain a fired product; The method for producing a scintillator according to claim 11 or 12, further comprising, after the firing step, an annealing step of annealing the fired product.

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