Scintillator, radiation detector, radiation imaging system, and manufacturing method of scintillator

Abstract

To provide a scintillator for radiation detection, which can suppress deterioration in luminance due to long-time radiation exposure while suppressing burn-in on itself.SOLUTION: A scintillator includes: a plurality of columnar crystals which is arranged on a substrate so as to convert radiation into light; and protective films covering the surfaces of the plurality of columnar crystals. The plurality of columnar crystals contains an activator agent. The protective films contain silica. Decrease in an amount of luminescence after irradiation of the scintillator with the radiation of 1000 gray (Gy) is 35% or less compared to before the irradiation with the radiation.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a scintillator, a radiation detector, a radiation imaging system, and a method for manufacturing a scintillator.

Background Art

[0002] Among flat panel detectors (FPDs) used for X-ray imaging in medical settings and the like, there are those that receive X-rays that have passed through a subject with a scintillator for radiation detection and detect the light emitted by the scintillator with a light receiving element. The scintillator has, for example, a columnar crystal group of an alkali metal halide such as cesium iodide formed on a substrate. A void is formed between each columnar crystal in the columnar crystal group. For example, due to the ratio of the refractive index of cesium iodide (about 1.8) to the refractive index of air (1.0), light is repeatedly totally reflected in the columnar crystal containing high-refractive-index cesium iodide and can be effectively guided to the light receiving element.

[0003] However, since the light emission amount of cesium iodide alone is small, an element called an activator, for example, thallium that can replace a part of cesium which is a cation, may be added. The activator can be introduced into the crystal by vapor-depositing (co-vapor-depositing) a raw material containing thallium such as thallium iodide during the vapor deposition of the alkali metal halide.

[0004] On the other hand, it is known that when irradiated with radiation for a long period of time, the scintillator itself is colored and the light emission amount, that is, the luminance decreases. Such coloring is called the formation of color centers. Patent Document 1 describes a technique for suppressing the formation of color centers by reducing the concentration of the activator.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the concentration of the activator was lowered, the scintillator sometimes suffered from burn-in. An object of the present invention is to provide a scintillator for radiation detection that can suppress burn-in of the scintillator and suppress a decrease in luminance due to long-term radiation irradiation.

Means for Solving the Problems

[0007] To solve the above problems, the scintillator of the present invention is a scintillator having a plurality of columnar crystals disposed on a substrate and converting radiation into light, and a protective film covering the surfaces of the plurality of columnar crystals, wherein the plurality of columnar crystals contain an activator, the protective film contains silica, and the decrease in the amount of light emission after irradiating the scintillator with 1000 Gray (Gy) of radiation is 35% or less with respect to that before the radiation irradiation.

Effects of the Invention

[0008] According to the present invention, it is possible to provide a scintillator for radiation detection that can suppress burn-in of the scintillator and suppress a decrease in luminance due to long-term radiation irradiation.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential for the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are given the same reference numerals, and duplicate explanations are omitted.

[0011] According to the present embodiment, it is possible to reduce the decrease in the light emission amount of the scintillator with respect to the cumulative radiation dose. FIG. 1 is a graph comparing the light emission amounts of the scintillator according to Example 1 to which the present invention described later is applied and the scintillator of Comparative Example 1 to which the present invention is not applied. Here, the decrease in the light emission amount can be obtained as the decrease rate of the following formula. In this graph, the light emission amount before radiation irradiation corresponds to the state before irradiating the radiation for the durability evaluation of the scintillator, and the light emission amount after radiation irradiation corresponds to the state after irradiating the radiation for the durability evaluation.

[0012] (Formula 1) Decrease rate of light emission amount = 1 - (light emission amount after radiation irradiation / light emission amount before radiation irradiation) Here, the radiation irradiation conditions for the durability evaluation are a tube voltage of 130 kV, an additional filter of 1 mm thickness of aluminum, and an irradiation dose rate of 0.1 Gy (gray) / min. Also, the light emission amount measurement conditions conform to RQA5. FIG. 1 plots the decrease rates of the above light emission amounts when the cumulative irradiation dose reaches 100 Gy and 1000 Gy, respectively. In the graph, each measurement point is connected by a straight line and displayed, but it is considered that it is actually a smooth curve. It can be seen that after 100 Gy irradiation, the decrease rate of the light emission amount in Example 1 is suppressed to about half compared to Comparative Example 1. Even after 1000 Gy irradiation, the decrease rate of the light emission amount in Example 1 is smaller than that in Comparative Example 1. Hereinafter, the scintillator according to the present invention will be described in detail.

[0013] (Scintillator) The base material of the scintillator used in the present invention can be selected from alkali metal halide compounds capable of forming columnar crystal groups, such as cesium iodide. To impart sufficient luminescence function to the base material, for example, thallium (Tl) may be used as an activator. If the concentration of thallium used as an activator is low, a kind of burning phenomenon called bright burn may occur in the scintillator. It is known that to suppress this bright burn, the concentration of the activator may be increased. In view of reducing bright burn, the concentration of thallium as the activator is preferably 0.25 mol% or more. The scintillator of the present invention can be formed by general vacuum film-forming means such as vapor deposition.

[0014] According to one aspect of the present invention, as shown in FIGS. 2a and 2b, the entire crystal separation region of the scintillator composed of an aggregate of columnar crystals formed on the substrate is continuously covered with a protective film described later, and the initial layer of the scintillator is partially covered with the protective film.

[0015] Here, the initial layer of the scintillator refers to a layer of fine crystal nuclei formed on the substrate at the initial stage of film formation by selecting the substrate temperature, pressure, and film-forming rate in the vapor deposition process of columnar crystals using cesium iodide as the base material, for example. The initial layer refers to a region with a film thickness ranging from 10 μm to less than several tens of μm, where crystal nuclei are preferentially growing in the <100> orientation at the initial stage of film formation. In this region, the orientation and size of the columnar crystals are not yet completely determined.

[0016] The crystal separation region of the scintillator refers to a region with a film thickness of several tens of μm or more, where film formation further proceeds from the initial layer, the crystal orientation of the columnar crystals is determined to be the <100> orientation, and they grow into columnar crystals of a larger size. In this region, the sizes of the columnar crystals become larger, and each columnar crystal is in a separated state, and voids are formed and maintained between the crystals. If a liquid raw material is used to form the protective film in the voids of the crystal separation region, it is preferable that a continuous protective film can be formed by soaking due to capillary action.

[0017] In the voids of the region where the outer shape of each columnar crystal in the initial layer is unclear, a discontinuous protective film can be formed by partially immersing the liquid raw material for forming the protective film. If most of the voids in the initial layer are filled with the protective film, the light that emits and propagates in the scintillator is scattered and spreads, resulting in a decrease in spatial resolution, which is not preferable. By continuously forming the protective film in the crystal separation region and discontinuously forming the protective film in the initial layer, it may be possible to achieve both the spatial resolution and moisture resistance of the scintillator.

[0018] (Protective film) The liquid raw material of the protective film used in the present invention contains, for example, a polysilazane-based inorganic polymer, which is a silica conversion material containing silicon, nitrogen, and hydrogen including perhydropolysilazane, as a component, and its concentration is adjusted with an organic solvent. The liquid material can be produced by appropriately using a liquid to which various catalysts are added. Depending on the type of raw material selected, heating may be appropriately applied during the hydrolysis reaction or the conversion reaction to silica glass, but it is more preferable to select a raw material in which the reaction occurs at room temperature. If the concentration of the silica conversion material in the liquid raw material of the protective film is less than 0.5% by weight, the continuity of the formed protective film is insufficient and the moisture resistance is insufficient, which is not preferable. Also, if the concentration of the silica conversion material in the liquid raw material of the protective film is greater than 2% by weight, the voids of the columnar crystals are filled with the formed protective film, or before the impregnation of the liquid raw material into the scintillator progresses, the drying of the organic solvent and the silica conversion proceed outside the columnar crystal group of the scintillator. For this reason, cracks occur during the drying of the applied protective film, or the scintillator floats or peels off from the substrate, etc., which is not preferable. If the concentration of the silica conversion material is 0.5% by weight or more and 2% by weight or less, it may be possible to achieve both the spatial resolution and moisture resistance of the scintillator.

[0019] The protective film applicable to the present invention is characterized in that it is formed by using the capillary phenomenon of a liquid raw material. Therefore, as shown in Fig. 2a, the coverage range of the protective film gradually changes from a discontinuous coating state to a continuous coating state from the initial layer toward the crystal separation region. In the crystal separation region where the separation between columnar crystals has sufficiently progressed and the gaps are clear, and even if the side walls of the columnar crystals are coated with the protective film, the gaps between the protective films covering the columnar crystals can be maintained, that is, it is characterized in that it is continuously formed. Thereby, it becomes possible to improve the moisture-proof property without impairing the spatial resolution of the scintillator.

[0020] (Method for forming the protective film) As a method for forming the protective film, by appropriately selecting a method using a liquid such as spin coating, spray coating, dip coating, flow coating, bar coating, etc., for example, compared with the vapor deposition method, it becomes possible to easily obtain a coating of a desired thickness on the columnar crystals. Also, by using a liquid raw material, it becomes easy to supply a large amount of the raw material to the concave portions on the surface of the columnar crystal group in particular, so it is also possible to reduce the surface roughness of the surface unevenness of the columnar crystal surface.

[0021] For example, if the spin coating method is used, since the time for the liquid raw material to be applied to stay at the tip portion of the columnar crystal due to the centrifugal force caused by rotation becomes long, it is easy to form a protective film on the tip portion of the columnar crystal, which is preferable. Also, it is possible to suppress the formation of the protective film between the columnar crystals to the minimum necessary.

[0022] Also, if the spray coating method is used, it becomes possible to equalize the coating amount of the raw material solution on a large-area substrate, or if the dip coating method is used, it becomes possible to supply a large amount of the raw material solution to both sides of the substrate at once. Furthermore, according to the dip coating method, by holding the tip portion of the columnar crystal vertically downward during the application or drying of the raw material solution, it is also possible to suppress the formation of the protective film between the columnar crystals. If necessary, it is also possible to promote the chemical reaction by appropriately performing temperature increase, heating, or humidification to such an extent that the columnar crystal does not deliquesce during the raw material supply, application, and even after film formation.

[0023] When there are abnormal crystal growth parts with large unevenness during scintillator vapor deposition, before the protective film treatment of the present invention, it is advisable to form a very thin film of the scintillator by a vapor phase growth method using a conventional metal alkoxide or the like and perform a coating treatment. After taking measures to suppress the deterioration of characteristics during the next process or the required storage period due to the coating treatment, after reducing the surface roughness of the scintillator (planarization treatment), the protective film formation of the present invention may be carried out. As means for the planarization treatment, in addition to the coating treatment, it is also possible to use a method of applying pressure with a flat plate or a roller, or a method of removing abnormal crystal growth parts. As long as the surface roughness of the scintillator can be reduced, the means are not limited.

[0024] As the order of protective film formation, after film formation, a very thin protective film is formed by coating the scintillator with a metal alkoxide such as ethyl silicate of the prior art. Thereby, measures can be taken to reduce the deterioration of characteristics during the time until the completion of the next process or the storage period, that is, moisture resistance can be maintained. Thereafter, if necessary, a planarization treatment of the abnormal crystal growth part of the scintillator film may be performed, and further, the protective film formation of the present case may be carried out.

[0025] When using spray coating as a means for forming the protective film, by controlling the coating amount on the scintillator surface in terms of wet film thickness, it becomes possible to easily form the protective film of the present invention over a large area.

[0026] The wet film thickness is the film thickness immediately after coating. Assuming W: wet film thickness, G: discharge amount per unit time, L: total nozzle movement distance, S: nozzle scanning speed, d: liquid raw material density, and A: coating area, it can be expressed by the following formula 2.

[0027] (Formula 2) TIFF2025107934000002.tif1948

[0028] For example, when the discharge amount per unit time is 7.2 g / min, the coating time is 2 minutes, the density of the liquid raw material is 0.8 g / cc, and the coating area is 30 cm square, the wet film thickness is 200 μm. Note that the applied liquid raw material quickly penetrates into the scintillator, and during the process of drying the organic solvent, silica conversion occurs and a protective film is formed.

[0029] (Thickness of the protective film) When analyzed by energy dispersive X-ray fluorescence spectroscopy (EDX), the presence of silicon (Si) is confirmed in the crystal separation region and the initial layer of the scintillator on which the protective film is formed. The amount of Si present is the largest at the tip of the columnar crystals in the crystal separation region, followed by the middle part, and there is also a slight amount in the initial layer. The protective film formed on the scintillator is considered to form a regular tetrahedron structure (height 0.216 nm) by the repetition of four oxygens (O) coordinated to silicon (Si) (the bond length of Si-O is 0.162 nm). According to the analysis, the number of molecular layers can be estimated to be approximately 15 to 30 layers. In terms of thickness, it is several nanometers, and the gaps between the protective films covering the scintillator crystals are generally maintained, and gaps are maintained between the crystals. Also, the thickness of the protective film is considered to have sufficient moisture-proof properties.

[0030] (Coating range of the protective film) The coating range of the protective film of the present invention in the film thickness direction of the scintillator will be described below. For example, when forming columnar crystals on a substrate by means such as vapor deposition, since columnar crystals growing from fine-grained crystal nuclei gradually undergo elimination and fusion to form a columnar crystal group, the column diameter of the columnar crystals increases as the film thickness increases. On the other hand, the space between the columns of the columnar crystals is extremely small between fine crystal nuclei, but the separation between the columns progresses with each increase in film thickness and is maintained at a certain interval from a certain film thickness. When the protective film of the present invention is formed in the region at the initial stage of vapor deposition consisting of fine-grained crystal nuclei, the protective film fills the gaps between the columnar crystals and the gaps disappear, causing the light to be guided to scatter and the spatial resolution to decrease.

[0031] (Heat treatment) In this embodiment, after forming the above-described protective film on the surface of the scintillator, heat treatment is performed. The conditions for the heat treatment are such that temperature and time are the main parameters. Since heating is performed after forming the protective film, it is possible to heat in an air atmosphere. Even if heat treatment is performed in the air without controlling the atmosphere gas, no influence on the spatial resolution due to deliquescence is observed. Therefore, it is possible to use an inexpensive commercially available clean oven, hot plate, electric furnace, or the like.

[0032] By the heat treatment of this embodiment, it is possible to suppress a decrease in the amount of light emission due to radiation irradiation, and this is considered as follows. First, by forming the protective film, it is considered that the halide element, which is a constituent element, is difficult to desorb from the surface of the scintillator, and it is also difficult to react with the surface adsorbed elements. By performing heat treatment under such circumstances, it is considered that the crystal arrangement inside the scintillator becomes homogenized and a structure in which defects are difficult to form is obtained. It is presumed that the energy of the heat treatment correlates with the homogenization of the crystal arrangement, and this affects the rate of decrease in the amount of light emission depending on the conditions of the heat treatment.

[0033] (Evaluation) For the evaluation of the size and change of the column diameter of the columnar crystals of the manufactured scintillator, the shape can be observed with, for example, a scanning electron microscope (SEM). Also, the chemical composition of the vapor-deposited film can be evaluated by, for example, fluorescent X-ray analysis, inductively coupled plasma analysis, and the crystallinity can be evaluated by, for example, X-ray diffraction analysis.

[0034] Regarding the formation state of the protective film, for example, elemental mapping evaluation by energy-dispersive X-ray fluorescence spectrometry (EDX) and morphological observation by transmission electron microscope (TEM) are possible. Also, the reflectance of the scintillator can be evaluated using a spectrophotometer.

[0035] For the evaluation of the spatial resolution characteristics, quantitative comparison can be made by measuring the modulation transfer function (MTF). The evaluation of the detective quantum efficiency (DQE) and the evaluation of the light emission amount of the scintillator can be evaluated using various light detectors such as a charge-coupled device (CCD) and a complementary metal-oxide-semiconductor (CMOS), and cameras.

[0036] In addition, when evaluating radiation durability, an X-ray irradiation device used can be an X-ray generator capable of irradiating at an irradiation dose rate of about 0.1 Gy per minute.

[0037] (Radiation detector) As a radiation detector using the scintillator of the present invention, for example, as shown in Fig. 3a, a plurality of columnar crystals 310 are formed on a substrate 305 with an optical sensor on which a photoelectric conversion element is arranged, and are combined with a reflective layer 303 via an adhesive layer 301. Such a configuration may be called a direct type. Alternatively, for example, as shown in Fig. 3b, a plurality of columnar crystals 310 are formed on a substrate 304 provided with a reflective layer 303, and are combined with a substrate 302 with an optical sensor via an adhesive layer 301. Such a configuration may be called an indirect type. Further, in order to adjust the spatial resolution and sensitivity, optical system elements or materials such as a fiber optics plate (FOP) or a light absorption filter may be added between the substrate 302 with an optical sensor on which the photoelectric conversion element is arranged and the scintillator.

[0038] The above-described scintillator and radiation detector can be applied to a radiation detection device, a radiation imaging device, and a radiation imaging system for detecting radiation. Typically, X-rays are used for radiation, but alpha rays, beta rays, etc. may also be used.

[0039] Fig. 6 shows a radiation imaging system which is an example of a usage mode of the radiation detector according to the present embodiment. Radiation 611 generated by a radiation source 610 passes through the chest 621 of a subject 620 such as a patient and enters a radiation detection device 630. The radiation 611 incident on the device 630 contains information on the inside of the body of the patient 620, and the device 630 acquires electrical information corresponding to the radiation 611. This electrical information is converted into a digital signal by an image processor 640 including a signal processing unit, and predetermined signal processing is performed.

[0040] Users such as doctors can observe a radiation image corresponding to this electrical information on, for example, the display 650 in the control room. The user can transfer the radiation image or its data to a remote location by a predetermined communication means 660 and can also observe this radiation image on the display 651 in the doctor's room, which is another location. Further, the user can also record this radiation image or its data on a predetermined recording medium, for example, can record it on the film 671 by the film processor 670.

[0041] Several preferred examples have been shown above, but the present invention is not limited to these, and a part thereof may be modified without departing from the gist of the present invention. In addition, each term described in this specification is merely used for the purpose of explaining the present invention, and it goes without saying that the present invention is not limited to the exact meaning of that term and may include its equivalents.

[0042] Hereinafter, an example of a scintillator to which the present invention is applied and a comparative example of the scintillator will be described.

[0043] <Example 1> In this example, a scintillator having a columnar crystal structure is formed by vapor deposition. As a base material (parent material) to be vapor-deposited, a material supply source filled with cesium iodide, as an activator raw material to be vapor-deposited, a material supply source filled with thallium iodide, and a substrate on which crystals are to be formed were placed in a vacuum vapor deposition apparatus. The substrate used was one in which an aluminum reflection layer with a thickness of 100 nm and silicon dioxide with a thickness of 50 nm were laminated on a glass substrate. After evacuating the inside of the vapor deposition apparatus to 0.01 Pa or less, a current was gradually passed through each material supply source to heat it. When the set temperature was reached, film formation was started by opening a shutter provided between the substrate and the material supply source while rotating the substrate. Note that the substrate temperature was gradually increased from 80°C to 160°C. While checking the state of film formation, when a desired film thickness (200 μm) was formed, the shutter was closed to finish film formation. Thus, columnar crystals mainly composed of cesium iodide were formed on the substrate.

[0044] After cooling the substrate and the material supply source to room temperature, ethyl silicate was immediately brought into contact with the vapor-deposited film by chemical vapor deposition and coated with a protective film. Four substrates vapor-deposited simultaneously in the above steps were prepared. When the concentration of thallium element, which is an activator, was determined using a fluorescent X-ray analyzer for one of them, it was 0.34 mol%.

[0045] Subsequently, after setting one of the above substrates with the vapor-deposited film on a spray coater, a protective film was formed under the condition that the wet film thickness was 100 μm by setting the discharge amount and the scanning speed respectively using a solution raw material containing 1 wt% of perhydropolysilazane in a dibutyl ether solvent.

[0046] Thereafter, after drying the above protective film in an environment of 25°C and 50% humidity, heat treatment was performed using a clean oven. The conditions of the heat treatment were 230°C for 1 hour in an open atmosphere, and after heating, it was naturally cooled in the clean oven.

[0047] The film-forming surface of the vapor-deposited film of the scintillator thus prepared was brought into close contact with a CMOS photodetector via an FOP (Fiber Optic Plate), and radiation conforming to the international standard line quality RQA5 was irradiated from the substrate side to acquire an image and determine the light emission amount. The irradiation dose was 4.8 μGy, and the output value (LSB) of the CMOS photodetector was taken as the light emission amount.

[0048] Next, the substrate with the vapor-deposited film was removed from the CMOS photodetector and a radiation durability evaluation was carried out. The conditions were a tube voltage of 130 kV, an Al-added filter with a thickness of 1 mm, and an irradiation dose rate of 0.1 Gy / min. After irradiation with 100 Gy, it was brought into close contact with the CMOS photodetector again to measure the light emission amount. The measurement conditions were the same RQA5 as the previous measurement and 4.8 μGy. As a result, the light emission amount decreased by 11% compared with that before X-ray durability.

[0049] Similarly, as an additional radiation durability evaluation, after further irradiation with 900 Gy, the light emission amount was measured. As a result, the light emission amount decreased by 27% compared with that before X-ray durability.

[0050] <Comparative Example 1> In Comparative Example 1, up to the formation of a scintillator having a columnar crystal structure with cesium iodide as the base material and thallium iodide as the activator using a vacuum evaporation apparatus was the same as in Example 1. However, the protective film of perhydropolysilazane was not formed thereafter. Also, the heat treatment performed in Example 1 was not performed. In this state, it would deliquesce during the radiation durability evaluation described later, so a 10-μm film of parylene was formed to prepare a sample of Comparative Example 1.

[0051] The film-forming surface of the deposited film thus prepared was brought into close contact with a CMOS photodetector via a FOP (Fiber Optic Plate), and radiation conforming to the international standard line quality RQA5 was irradiated from the substrate side to acquire an image and determine the light emission amount. The irradiation dose was 4.8 μGy, and the output value (LSB) of the CMOS photodetector was taken as the light emission amount.

[0052] Next, the substrate with the deposited film was removed from the CMOS photodetector, and the radiation durability evaluation was performed. The conditions were a tube voltage of 130 kV, an Al-added filter of 1 mm, and an irradiation dose rate of 0.1 Gy / min, which were the same conditions as in Example 1. After irradiation with 100 Gy, it was brought into close contact with the CMOS photodetector again to measure the light emission amount. The measurement conditions were the same RQA5 as in the previous measurement and 4.8 μGy. As a result, the light emission amount decreased by 21% compared to before X-ray durability. This value was approximately twice as large as the 11% decrease in Example 1.

[0053] Similarly, as an additional radiation durability evaluation, after further irradiation with 900 Gy, the light emission amount was measured. As a result, the light emission amount decreased by 38% compared to before X-ray durability. This value was large compared to the 27% decrease in Example 1.

[0054] <Example 2> In Example 2, the heat treatment conditions were different from those of Example 1 described above. The heat treatment conditions were 210 °C for 3 hours in open air, and after heating, it was naturally cooled in a clean oven.

[0055] The film-forming surface of the scintillator vapor deposition film thus formed was brought into close contact with a CMOS photodetector via an FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in Example 1 and Comparative Example 1. As a result, after irradiation with 100 Gy, the light emission amount decreased by 12% compared to before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 35% compared to before radiation durability.

[0056] In this Example 2 as well, it can be seen that the rate of decrease in the light emission amount is small compared to Comparative Example 1. A list of the results of Example 1, Example 2 and Comparative Example 1 above is shown in Table 1.

[0057] (Table 1) TIFF2025107934000003.tif2278

[0058] <Example 3> In this Example 3, a substrate on which a vapor deposition film with a Tl element concentration of 0.25 mol% as an activator was formed was prepared. After setting one of the substrates with the vapor deposition film on a spray coater, a protective film was formed under the condition that the wet film thickness was 100 μm by setting the discharge amount and the scanning speed respectively using a solution raw material containing 1 wt% of perhydropolysilazane in a dibutyl ether solvent.

[0059] Thereafter, after drying the above-mentioned protective film in an environment of 25 °C and 50% humidity, heat treatment was performed using a clean oven. The conditions of the heat treatment were 230 °C for 1 hour in an open atmosphere, and after heating, it was naturally cooled in the clean oven. These heat treatment conditions are common to Example 1.

[0060] The film-forming surface of the vapor deposition film thus formed was brought into close contact with a CMOS photodetector via an FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in the above-mentioned Examples and Comparative Examples. As a result, after irradiation with 100 Gy, the light emission amount decreased by 10% compared to before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 28% compared to before radiation durability.

[0061] <Example 4> In Example 4, the heat treatment conditions are different from those in Example 3. The heat treatment conditions were 230 °C for 0.5 hours in open air, and after heating, it was naturally cooled in a clean oven. The film-forming surface of the vapor-deposited film thus created was adhered to the CMOS photodetector via a FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in the above-described Examples and Comparative Examples.

[0062] As a result, after irradiation with 100 Gy, the light emission amount decreased by 11% compared to before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 34% compared to before radiation durability.

[0063] <Comparative Example 2> In Comparative Example 2, different from Examples 3 and 4, a protective film was not formed with perhydropolysilazane, and heat treatment was not performed either. In this state, it would deliquesce during the radiation durability evaluation described later, so a 10-μm film of parylene was formed to prepare a sample of Comparative Example 2.

[0064] The film-forming surface of the vapor-deposited film thus created was adhered to the CMOS photodetector via a FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in the above-described Examples and Comparative Examples. As a result, after irradiation with 100 Gy, the light emission amount decreased by 22% compared to before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 41% compared to before radiation durability.

[0065] A list of the results of Examples 3 and 4 and Comparative Example 2 above is shown in Table 2. From Table 2, it can be seen that the time as a heat treatment condition affects the reduction rate of the light emission amount. Although the difference in the light emission amount is small after irradiation with 100 Gy, after irradiation with 1000 Gy, the reduction rate of the light emission amount is smaller when the heat treatment time is longer.

[0066] (Table 2) TIFF2025107934000004.tif2277

[0067] <Example 5> In Example 5, a vapor deposition film with a Tl element concentration of 0.71 mol% as an activator was prepared. After setting one substrate with the vapor deposition film on a spray coater, a protective film was formed under the condition that the wet film thickness was 100 μm by setting the discharge amount and the scanning speed respectively using a solution raw material containing 1 wt% of perhydropolysilazane in a dibutyl ether solvent. Then, after drying the above-mentioned protective film in an environment of 25°C and 50% humidity, heat treatment was performed using a clean oven. The heat treatment conditions were 250°C for 1 hour in an open atmosphere, and after heating, it was naturally cooled in the clean oven.

[0068] The film-forming surface of the vapor deposition film thus prepared was brought into close contact with a CMOS photodetector via an FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in the above-mentioned Examples and Comparative Examples. As a result, after irradiation with 100 Gy, the light emission amount decreased by 18% compared with that before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 30% compared with that before radiation durability.

[0069] <Example 6> In Example 6, the heat treatment conditions are different from those in Example 5. The heat treatment conditions were 200°C for 1 hour in an open atmosphere, and after heating, it was naturally cooled in the clean oven. The film-forming surface of the vapor deposition film thus prepared was brought into close contact with a CMOS photodetector via an FOP (Fiber Optic Plate), and radiation durability evaluation was carried out in the same manner as in the above-mentioned Examples and Comparative Examples. As a result, after irradiation with 100 Gy, the light emission amount decreased by 22% compared with that before X-ray durability. Further, after irradiation with 900 Gy, the light emission amount decreased by 35% compared with that before radiation durability.

[0070] <Comparative Example 3> Unlike Example 5 and Example 6, in Comparative Example 3, a protective film was not formed with perhydropolysilazane. Also, no heat treatment was performed. In this state, it would deliquesce during the radiation durability evaluation described later, so a 10-μm film of parylene was formed to prepare a sample of Comparative Example 3. The film-forming surface of the vapor-deposited film thus created was brought into close contact with the CMOS photodetector via an FOP (Fiber Optic Plate), and the radiation durability evaluation was carried out in the same manner as in the above-described Examples and Comparative Examples.

[0071] As a result, after irradiation with 100 Gy, the light emission amount decreased by 29% compared to before X-ray durability. Also, after further irradiation with 900 Gy, the light emission amount decreased by 45% compared to before radiation durability. A list of the results of Example 5, Example 6, and Comparative Example 3 above is shown in Table 3 of Fig. 9. From Table 3, it can be seen that the temperature as a heat treatment condition affects the reduction rate of the light emission amount. Although the difference is small after irradiation with 100 Gy, after irradiation with 1000 Gy, the reduction rate of the light emission amount is smaller when the heat treatment temperature is higher.

[0072] (Table 3) TIFF2025107934000005.tif2377

[0073] Regarding the samples of Example 5 and Comparative Example 3, the reflectance was also measured before radiation durability and after cumulative irradiation with 1000 Gy. The measurement results of the reflectance before radiation durability are shown in Fig. 4. The measurement results of the reflectance after cumulative irradiation with 1000 Gy are shown in Fig. 5. In the graph of Fig. 4, the horizontal axis represents the wavelength and the vertical axis represents the reflectance. The sample of Example 5 has a higher reflectance in the wavelength range of approximately 450 nm or less and a lower reflectance in the wavelength range of 450 nm or more compared to Comparative Example 3.

[0074] From the graph of Fig. 5, even after cumulative irradiation of 1000 Gy, the sample of Example 5 shows a tendency of higher reflectance at approximately 450 nm or less compared to Comparative Example 3. Also, the difference between Example 5 and Comparative Example 3 becomes smaller at 450 nm or more. In particular, in Comparative Example 3, significant decreases in reflectance are observed near wavelengths of 520 nm and 560 nm, but the decreases are smaller in Example 5. This corresponds to the suppression of the decrease rate of the light emission amount described above. From the above results, it was also shown that the radiation durability is improved in this example.

[0075] <Summary of Examples> Regarding the scintillators described in Examples 1 to 6, when compared with the comparative examples, the decrease in luminance between the scintillator after irradiation with 1000 Gy of radiation by heat treatment and the scintillator before radiation irradiation was within 35%. The heat treatment conditions in Examples 1 to 6 had a temperature of 200°C or higher. In Examples 1, 3, and 5, the decrease in luminance was even better at 30% or less, but the heat treatment temperature in these Examples 1, 3, and 5 was 230°C or higher, and the heat treatment time was 1 hour or more. In contrast, in the comparative examples, a decrease in luminance of 38% to 45% was observed. From the above, when the heat treatment temperature was 200°C or higher, the decrease in luminance could be reduced to 35% or less. Preferably, when the heat treatment temperature was 230°C or higher and the heat treatment time was 1 hour or more, the decrease in luminance could be suppressed to 30% or less.

[0076] (Other Embodiments) The disclosure of this specification includes the following scintillator, radiation detector, radiation imaging device, and method for manufacturing a scintillator.

[0077] (Item 1) A plurality of columnar crystals disposed on a substrate for converting radiation into light, A scintillator having a protective film covering the surfaces of the plurality of columnar crystals, wherein The plurality of columnar crystals contain an activator, The protective film contains silica, The scintillator is characterized in that the decrease in the amount of light emission after irradiating the scintillator with 1000 gray (Gy) of radiation is 35% or less with respect to that before the radiation irradiation. (Item 2) The scintillator according to item 1, wherein there is a gap between the protective films covering the plurality of columnar crystals. (Item 3) The scintillator according to item 1 or 2, wherein the plurality of columnar crystals contain cesium iodide as a main component. (Item 4) The scintillator according to any one of items 1 to 3, characterized in that the decrease in the amount of light emission after irradiation with 1000 Gy is 30% or less with respect to that before the radiation irradiation. (Item 5) The scintillator according to any one of items 1 to 4, wherein the activator is thallium and the concentration of the activator is 0.25 mol% or more. (Item 6) A scintillator having a plurality of columnar crystals arranged on a substrate for converting radiation into light, and a protective film covering the surfaces of the plurality of columnar crystals, wherein the plurality of columnar crystals contain an activator, the protective film contains silica, and the scintillator is heat-treated. (Item 7) The scintillator according to item 6, wherein there is a gap between the protective films covering the plurality of columnar crystals. (Item 8) The scintillator according to item 6 or 7, wherein the plurality of columnar crystals contain cesium iodide as a main component. (Item 9) A scintillator according to any one of items 1 to 8, and a photoelectric conversion element for converting light from the scintillator into electric charge, characterized in that the radiation detector has the photoelectric conversion element. (Item 10) The radiation detector according to item 9, A radiation imaging system, comprising a signal processing unit that processes a signal from the radiation detector. (Item 11) A step of forming a plurality of columnar crystals containing an activator on a substrate, A step of forming a protective film containing silica on the surface of the plurality of columnar crystals, A method for manufacturing a scintillator, comprising a step of performing a heat treatment at 200 °C or higher after forming the protective film. (Item 12) The method for manufacturing a scintillator according to Item 11, wherein a gap is formed between the plurality of columnar crystals in a state where the protective film is formed. (Item 13) The method for manufacturing a scintillator according to Item 11 or 12, wherein the plurality of columnar crystals contain cesium iodide as a main component. (Item 14) The method for manufacturing a scintillator according to any one of Items 11 to 13, further comprising a planarization step of forming a film for planarizing the surface of the plurality of columnar crystals, and forming the protective film after the planarization step. (Item 15) The method for manufacturing a scintillator according to any one of Items 11 to 14, wherein the concentration of the silica conversion material contained in the liquid raw material used for forming the protective film is 0.5% by weight or more and 2% by weight or less. (Item 16) The method for manufacturing a scintillator according to any one of Items 11 to 15, wherein the silica conversion material contained in the liquid raw material used for forming the protective film contains a polysilazane-based inorganic polymer. (Item 17) The method for manufacturing a scintillator according to any one of Items 11 to 16, wherein the temperature of the heat treatment is 230 °C or higher and the time of the heat treatment is 1 hour or longer.

[0078] The invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, claims are attached to disclose the scope of the invention.

Description of Symbols

[0079] 100: Substrate, 101: Columnar crystal, 102: Initial layer, 104: Protective film

Claims

1. A scintillator having a plurality of columnar crystals disposed on a substrate for converting radiation into light, and a protective film covering the surfaces of the plurality of columnar crystals, wherein the plurality of columnar crystals contain an activator, the protective film contains silica, the scintillator is characterized in that the decrease in the amount of light emission after irradiating the scintillator with 1000 gray (Gy) of radiation is 35% or less compared to before the radiation irradiation.

2. The scintillator according to claim 1, wherein there is a gap between the protective films covering the plurality of columnar crystals.

3. The scintillator according to claim 1, wherein the plurality of columnar crystals are mainly composed of cesium iodide.

4. The scintillator according to claim 1, wherein the decrease in the amount of light emission after irradiating with 1000 Gy of radiation is 30% or less compared to before the radiation irradiation.

5. The scintillator according to claim 1, wherein the activator is thallium and the concentration of the activator is 0.25 mol% or more.

6. A scintillator having a plurality of columnar crystals disposed on a substrate for converting radiation into light, and a protective film covering the surfaces of the plurality of columnar crystals, wherein the plurality of columnar crystals contain an activator, the protective film contains silica, the scintillator is characterized in that the scintillator has been heat-treated.

7. The scintillator according to claim 6, wherein there is a gap between the protective films covering the plurality of columnar crystals.

8. The scintillator according to claim 6, wherein the plurality of columnar crystals are mainly composed of cesium iodide.

9. A radiation detector comprising the scintillator according to any one of claims 1 to 8, and a photoelectric conversion element for converting light from the scintillator into electric charges.

10. A radiation imaging system comprising the radiation detector according to claim 9, and a signal processing unit for processing a signal from the radiation detector.

11. A method for manufacturing a scintillator, comprising the steps of forming a plurality of columnar crystals containing an activator on a substrate, forming a protective film containing silica on the surfaces of the plurality of columnar crystals, and performing a heat treatment at 200 °C or higher after forming the protective film.

12. The method for manufacturing a scintillator according to claim 11, wherein a gap is formed between the plurality of columnar crystals in a state where the protective film is formed.

13. The method for manufacturing a scintillator according to claim 11, wherein the plurality of columnar crystals contain cesium iodide as a main component.

14. The method for manufacturing a scintillator according to claim 11, further comprising a planarization step of forming a film for planarizing the surfaces of the plurality of columnar crystals, and forming the protective film after the planarization step.

15. The method for manufacturing a scintillator according to claim 11, wherein the concentration of the silica conversion material contained in the liquid raw material used for forming the protective film is 0.5 wt% or more and 2 wt% or less.

16. The method for manufacturing a scintillator according to claim 11, wherein the silica conversion material contained in the liquid raw material used for forming the protective film contains a polysilazane-based inorganic polymer.

17. The method for manufacturing a scintillator according to claim 11, wherein the temperature of the heat treatment is 230 °C or higher and the time of the heat treatment is 1 hour or longer.

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