Dosimeter material, measurement device, and measurement method

Abstract

In the dosimeter material according to the present embodiment, a predetermined amount of nitrogen is added in the diamond.

Description

Dosimeter material, measuring device, and measuring method

[0001] This application claims priority to Japanese Patent Application No. 2023-208775, filed on December 11, 2023, the contents of which are incorporated herein by reference.

[0002] With the diversification of radiation medicine, the optimization of medical exposure, and the progress of space development, there is a demand for highly sensitive and accurate measurement technology for radiation exposure dose in living organisms.

[0003] When a thermoluminescent material is irradiated with radiation, the thermoluminescent phenomenon occurs, causing the material to emit light. The intensity of the thermoluminescence emitted from a thermoluminescent material is proportional to the amount of radiation irradiated to the material. Based on this, a device that calculates the amount of radiation irradiated to a thermoluminescent material by measuring the intensity of the thermoluminescence emitted from the thermoluminescent material is called a thermoluminescent dosimeter. Thermoluminescent materials used in thermoluminescent dosimeters are sometimes called dosimeter materials.

[0004] As described above, the radiation dose irradiated to the dosimeter material can be estimated by measuring the intensity of the fluorescence emitted from the dosimeter material. However, to accurately estimate the radiation dose irradiated to the dosimeter material, it is important that the dosimeter material has high sensitivity to radiation, that the intensity of the fluorescence emitted from the dosimeter material varies, for example, linearly with the radiation dose, and that the radiation dose irradiated to the dosimeter material and the intensity of the fluorescence from the dosimeter material clearly correspond to each other. Furthermore, to accurately estimate the radiation dose irradiated to the dosimeter material, it is important that fading is small and that the accuracy of measuring the intensity of the fluorescence from the dosimeter material and the accuracy of calculating the radiation dose irradiated to the dosimeter material are minimal. Fluorescence emitted from the dosimeter material includes thermofluorescence, photostimulated fluorescence, and radiophotoluminescence.

[0005] For example, Patent Document 1 discloses a dosimeter material containing lanthanum (III) oxide (La ２ O ３ ) and boron oxide (B ２ O ３The lanthanum borate glass disclosed in Patent Document 1 contains cerium halide as a dopant, and exhibits Ce, which is the atomic valence of cerium, in the wavelength range of 200 nm to 300 nm. ３＋ The lanthanum borate glass disclosed in Patent Document 1 allows the dosimeter material to be produced simply, inexpensively and with good reproducibility, and the dosimeter material can be used repeatedly.

[0006] Japanese Patent Application Publication No. 2023-161118

[0007] Conventional dosimeter materials have low absorption efficiencies of irradiated radiation and low sensitivity to radiation, making it difficult to accurately calculate the radiation dose of a living body. Recent dosimeter materials, including the lanthanum borate glass disclosed in Patent Document 1, use materials containing elements with higher atomic numbers than those abundant in living bodies in order to achieve high sensitivity to irradiated radiation. However, because the radiation absorption efficiency of materials with high atomic numbers differs from that of living bodies, even if dosimeter materials containing materials with high atomic numbers are used to measure radiation doses, it is difficult to accurately calculate the radiation dose of a living body, resulting in increased uncertainty in the radiation dose of a living body. In order to accurately calculate radiation doses at a level applicable to calculating radiation doses of a living body, it is necessary to use dosimeter materials with high bioequivalence.

[0008] In view of the above circumstances, the present invention provides a dosimeter material, a measurement device, and a measurement method that are capable of calculating the dose of irradiated radiation with high sensitivity and high accuracy.

[0009] In the dosimeter material according to the present invention, nitrogen is added to the diamond.

[0010] The measurement device according to the present invention comprises a heating element for heating a dosimeter material to 200°C or higher, a light receiving device for detecting light emitted from the heated dosimeter material, and a control device for controlling the temperature of the dosimeter material heated by the heating element, receiving optical information related to the intensity of the light from the light receiving device, and acquiring optical properties of the dosimeter material. The heating element has a brass body. A silver metal layer is provided on the surface of the body facing the dosimeter material.

[0011] The measurement method according to the present invention comprises a first step of irradiating radiation onto a dosimeter material in which a predetermined amount of nitrogen has been added to diamond; a second step of, after the first step, heating the dosimeter material, detecting light emitted from the dosimeter material, and acquiring the optical properties of the dosimeter material; and a third step of, after the second step, heating the dosimeter material at an annealing temperature according to the predetermined amount.

[0012] According to the present invention, it is possible to provide a dosimeter material, a measuring device, and a measuring method that are capable of calculating the dose of irradiated radiation with high sensitivity and high accuracy.

[0013] FIG. 1 is a schematic diagram for explaining the principle of thermoluminescence generation in a thermoluminescent material. FIG. 2 is a schematic diagram of a measurement device according to an embodiment of the present invention. FIG. 3 is a schematic diagram of a thermoluminescence measurement device that can be used in an embodiment of the present invention. FIG. 4 is a graph showing a glow curve obtained in Example 1. FIG. 5 is a graph showing various spectra obtained in Example 2. FIG. 6 is a photograph of a dosimeter material used in Example 3. FIG. 7 is an image of thermoluminescence obtained in Example 3. FIG. 8 is a graph showing the intensity distribution of thermoluminescence obtained in Example 3. FIG. 9 is a schematic diagram of a measurement device used in Example 4. FIG. 10 is a graph showing the optically stimulated luminescence spectrum obtained in Example 4. FIG. 11 is another graph showing the optically stimulated luminescence spectrum obtained in Example 4.

[0014] Hereinafter, thermoluminescence measurement methods and thermoluminescence measurement devices according to embodiments will be described with reference to the drawings. In the following description, components having the same or similar functions will be denoted by the same reference numerals.

[0015] First, the principle of thermoluminescence will be briefly explained. FIG. 1 is a schematic diagram illustrating the principle of thermoluminescence generation in a thermoluminescent material 51. As shown in FIG. 1, when the thermoluminescent material 51 is irradiated with radiation RA, such as X-rays, an electron e in the valence band 61 acquires excitation energy through interaction and moves to the conduction band 63. After the electron e leaves the valence band 61, a hole h is generated. The hole h is captured by a trap center formed by lattice defects in the crystals constituting the thermoluminescent material 51 or lattice distortion due to the active material, and moves to the vicinity of the fluorescence center level LV1. The electron e that has moved to the conduction band 63 is captured by a trap center level LV2 formed by lattice defects in the crystals constituting the thermoluminescent material 51 or lattice distortion due to the active material, and becomes metastable. The fluorescence center level LV1 is sometimes simply referred to as the fluorescence level. The trap center level LV2 is sometimes simply referred to as the trap level.

[0016] When activation energy due to thermal T is externally applied to the thermoluminescent material 51 in a state in which it is irradiated with radiation RA, an electron e moves from the trap center level LV2 to the conduction band 63. When the electron e recombines with a hole in the fluorescence center level LV1, energy corresponding to the level difference between the trap center level LV2 and the fluorescence center level LV1 is emitted as thermoluminescence T L. The light intensity of the thermoluminescent light T L is proportional to the amount of radiation RA irradiated to the thermoluminescent material 51. In other words, by applying thermal T L to the thermoluminescent material 51 irradiated with radiation RA to cause thermoluminescence, and measuring the amount of light emitted by the thermoluminescent material 51, the amount of radiation received by the thermoluminescent material 51 can be calculated.

[0017] In order to use the thermoluminescent substance 51 as a dosimeter material for a thermoluminescent dosimeter and apply thermoluminescence measurement to the measurement of radiation exposure dose in a living body to calculate the radiation exposure dose with high sensitivity and accuracy, a dosimeter material with high bioequivalence is required. Examples of highly bioequivalent elements include carbon (C), nitrogen (N), and oxygen (O). The dosimeter material of this embodiment is the thermoluminescent substance 51, which is composed of diamond consisting of only carbon covalent bonds. Because the dosimeter material of this embodiment is composed of diamond, which is made of carbon with extremely high bioequivalence, it is expected to have the same absorption efficiency for radiation as a living body, excellent radiation resistance, and optical properties. Furthermore, because the refractive index of the dosimeter material of this embodiment is high, the amount of thermoluminescence per unit area of ​​the dosimeter material can be kept approximately constant.

[0018] The diamond of the dosimeter material of this embodiment is doped with a predetermined amount of nitrogen as a dopant.By adding a predetermined amount of nitrogen to diamond, the electron capture power at the trap level of the dosimeter material of this embodiment is strengthened, the electrons at the trap level are stabilized, and fading is effectively suppressed in an environment of less than 200 ° C after the dosimeter material is irradiated with radiation.Fading refers to the low stability of the glow peak temperature and trap level of the dosimeter material, and the number of electrons and holes that should be detected decreases before detection, which affects the measurement accuracy of the thermoluminescence intensity from the dosimeter material and the calculation accuracy of the radiation dose irradiated to the dosimeter material.The predetermined amount of nitrogen will be explained later.

[0019] The dosimeter material of this embodiment is manufactured by heteroepitaxially growing diamond on a substrate by, for example, chemical vapor deposition (CVD) and adding nitrogen during the diamond growth process. The substrate is removed after the formation of the nitrogen-doped diamond is completed. The substrate is, for example, a sapphire substrate.

[0020] Next, a measurement device and a measurement method for a dosimeter material including the dosimeter material of this embodiment, and the thermoluminescence characteristics of the dosimeter material of this embodiment will be described. Figure 2 is a schematic diagram of a thermoluminescence measurement device 100 of this embodiment, and is a plan view of the thermoluminescence measurement device 100. The thermoluminescence measurement device 100 includes a heating element 110, a temperature control device 120, a focusing optical system 130, a light receiving device 140, a control device 150, and a cover 160.

[0021] The heating element 110 includes a metal body 112 and a metal layer 114 covering at least the plate surface 112b of the metal body 112. The metal body 112 is formed into a plate shape with a predetermined thickness and is made of a metal that can be heated by application of a voltage or the like and is resistant to deformation, such as brass. The plate surface 112b is the heat radiation surface of the metal body 112 and is one of the plate surfaces of the plate-shaped metal body 112. The metal layer 114 is made of, for example, silver (Ag). Silver is a preferred material for the metal layer 114 because it reduces the influence of thermal radiation during measurement of thermofluorescence from a dosimeter material S disposed on the metal layer 114 as described below. For example, the metal layer 114 is disposed by silver plating the plate surface 112b of the brass metal body 112.

[0022] The dosimeter material S of this embodiment is formed in a plate shape. The planar shape of the dosimeter material S, i.e., the shape of the dosimeter material S when viewed from a direction perpendicular to the plate surface, is not limited to a specific shape, but may be, for example, a circle or a rectangle. The dosimeter material S is arranged to face the metal layer 114. The surface of the metal layer 114 opposite to the surface that contacts the plate surface 112b of the metal body 112 and one plate surface Sa of the dosimeter material S face each other and are arranged parallel to each other with a gap therebetween.

[0023] The temperature adjustment device 120 is electrically connected to the heating member 110 and can apply an electrical signal, such as a voltage, to the heating member 110. The temperature adjustment device 120 maintains the temperature of the heating member 110 at a desired temperature by starting or stopping the supply of the electrical signal to the heating member 110. The temperature adjustment device 120 is, for example, a programmable thermoregulator.

[0024] The focusing optical system 130 is disposed on the optical path of the thermofluorescence emitted from the other plate surface Sb of the dosimeter material S. The focusing optical system 130 focuses at least a portion of the thermofluorescence, which is emitted radially in all directions from the plate surface Sb of the dosimeter material S around the axis AX, which is perpendicular to the plate surface Sb. The focusing optical system 130 is composed of, for example, biconvex lenses 132, 134, and 136. The number of optical elements constituting the focusing optical system 130 is not limited to a specific number and may be two or less, four or more, or may be set and changed as appropriate. At least one of the biconvex lenses 132, 134, and 136 and the optical elements constituting the focusing optical system 130 may be optical elements other than biconvex lenses, such as plano-convex lenses, meniscus lenses, aspherical lenses, etc.

[0025] The light receiving device 140 is disposed on the optical path of the thermofluorescence collected by the collecting optical system 130, specifically, disposed so that its light receiving surface substantially overlaps the collecting position on the axis AX of the thermofluorescence collected by the collecting optical system 130. The light receiving device 140 receives the thermofluorescence emitted from the dosimeter material S and collected by the collecting optical system 130, and detects the intensity of the thermofluorescence or the amount of light or number of photons correlated with the intensity. The light receiving device 140 is preferably capable of detecting weak light and has high sensitivity, and is, for example, a photon counter or a photon counting head.

[0026] The control device 150 is communicatively connected to each of the temperature adjustment device 120 and the light receiving device 140. The control device 150 transmits and receives signals to and from the temperature adjustment device 120 to acquire information on the temperature of the heating element 110. The control device 150 receives an electrical signal from the light receiving device 140 and calculates the intensity of thermofluorescence emitted from the dosimeter material S from the received electrical signal. The control device 150 obtains a correspondence relationship between the temperature of the dosimeter material S and the intensity of thermofluorescence from the dosimeter material S based on the information on physical quantities acquired from the temperature adjustment device 120 and the light receiving device 140. Specifically, the control device 150 is a processor incorporating a program that calculates and organizes the correspondence relationship between the temperature of the dosimeter material S and the intensity of thermofluorescence from the dosimeter material S from the information on physical quantities acquired from the temperature adjustment device 120 and the light receiving device 140. The control device 150 is, for example, a computer incorporating the aforementioned processor.

[0027] The cover 160 is disposed to surround the heating member 110, the dosimeter material S, the light-collecting optical system 130, and the light-receiving device 140, and blocks light from entering from outside. The cover 160 is formed in a box shape using a material such as a black plate-like member or cloth, for example.

[0028] The light receiving device 140 may receive thermoluminescence emitted from the dosimeter material S and collected by the collecting optical system 130, and detect spectral information of the fluorescence. In this case, the light receiving device 140 is preferably capable of detecting weak light, has high sensitivity, and has high wavelength resolution, for example, preferably has wavelength resolution of 1 nm or less. The light receiving device 140 is configured, for example, by combining a spectrometer or spectrometer such as an optical filter or diffraction grating with an imaging camera such as a CMOS (Complementary Metal Oxide Semiconductor) camera and a photomultiplier tube.

[0029] 3 is a schematic diagram of the thermoluminescence measurement device 200 used in this embodiment, and is a schematic diagram of the thermoluminescence measurement device 200 viewed from the side. The thermoluminescence measurement device 200 is an apparatus capable of measuring the two-dimensional distribution of thermoluminescence emitted from a dosimeter material S. As shown in FIG. 3 , the thermoluminescence measurement device 200 includes a support base 250, a heat shielding member 240, a heat absorption filter 230, an optical lens 220, an imaging camera 210, and a cover 260. The support base 250, the heat shielding member 240, the heat absorption filter 230, the optical lens 220, and the dosimeter material S are housed in a box-shaped cover 260.

[0030] The support base 250 has a plurality of legs 252, a fixed base 251, a movable base 254, and a plurality of rod-shaped members 256. The legs 252 extend vertically from the bottom surface of the cover 260 toward an installation surface (not shown) on which the thermoluminescence measurement apparatus 200 is installed. The fixed base 251 is provided at the upper ends of the plurality of legs 252 and is a plate-shaped member having a plate surface that is approximately parallel to the horizontal plane. The legs 252 and the fixed base 251 are made of, for example, brass, stainless steel, or the like.

[0031] The plurality of rod-shaped members 256 extend vertically from the upper plate surface of the fixed base 251. In order to enable the plurality of rod-shaped members 256 to support the plate-shaped dosimeter material S, for example, three or more rod-shaped members 256 are arranged in an area overlapping the dosimeter material S in a planar view. The dosimeter material S is supported on the upper ends of the plurality of rod-shaped members 256 via plate-shaped members 258 made of ceramic.

[0032] The movable stage 254 is disposed above the fixed stage 251 so as to overlap with the fixed stage 251 in a plan view. A plurality of rod-shaped members 256 penetrate the movable stage 254. The movable stage 254 is movable between positions P1 and P2 in the vertical direction, and is disposed so as to be able to move up and down relative to the fixed stage 251 and move closer to or farther away from the dosimeter material S. The movable stage 254 is connected to a power source (not shown) and is heated as appropriate. With this configuration, the temperature of the dosimeter material S can be easily managed and controlled.

[0033] The heat-shielding member 240 is disposed above the movable stage 254 at position P1 and is disposed parallel to the horizontal plane. The heat-shielding member 240 shields the heat generated when the movable stage 254 heats the plate-shaped member 258 and the dosimeter material S below, preventing the heat from being transmitted upward. The heat-shielding member 240 is formed of a material that at least blocks heat, but may be formed of a material that is not translucent or has low translucency to various types of light, including thermofluorescence emitted from the dosimeter material S. For this reason, a translucent quartz member 242 is provided in the heat-shielding member 240 in an area through which the various types of light from the dosimeter material S pass.

[0034] The heat absorption filter 230 and the optical lens 220 are disposed on the optical path of the thermofluorescence emitted from the dosimeter material S, and are disposed above the heat shielding member 240. Specifically, the heat absorption filter 230 and the optical lens 220 are installed in an opening formed in the upper surface of the cover 260 above the heat shielding member 240, and are disposed so as to overlap with the quartz member 242 in a plan view. The optical lens 220 collects the thermofluorescence emitted from the dosimeter material S. The heat absorption filter 230 is disposed on the incident surface of the optical lens 220.

[0035] The imaging camera 210 is disposed on the optical path of the thermofluorescence emitted from the dosimeter material S and collected by the optical lens 220. Specifically, the imaging camera 210 is disposed above the cover 260 with its light receiving unit facing an opening formed on the top surface of the cover 260. The imaging camera 210 receives the thermofluorescence emitted from the dosimeter material S and emitted from the optical lens 220, and acquires the two-dimensional intensity distribution of the thermofluorescence along a horizontal plane. The imaging camera 210 outputs the two-dimensional intensity distribution of the thermofluorescence from the dosimeter material S as an image to a display unit (not shown) or a display device (not shown) connected to the imaging camera 210. The imaging camera 210 is, for example, a CMOS camera.

[0036] The cover 260 is formed in a box shape as described above, and blocks light from entering from the outside. The cover 260 is formed of, for example, a black plate-like member or a material such as cloth.

[0037] The dosimeter material S of this embodiment described above is a material in which nitrogen is added to diamond.

[0038] The dosimeter material S of this embodiment is composed of carbon and nitrogen, which have very high bioequivalence. The dosimeter material S of this embodiment is mainly composed of diamond, a carbon crystal, with a predetermined amount of nitrogen added to the diamond. The dosimeter material S of this embodiment has an absorption efficiency for irradiated radiation closer to that of a living body and excellent radiation resistance than conventional dosimeter materials. It is believed that the nitrogen added to the diamond contributes to improving the electron capture power at the capture level. Therefore, the dosimeter material S of this embodiment generates almost no glow peak at temperatures below 200°C, while obtaining a clear glow peak at temperatures above 200°C, and achieving optical properties including thermoluminescence with high sensitivity and precision. Furthermore, by annealing the dosimeter material S according to the predetermined amount of nitrogen added to the diamond, the reproducibility of the properties of the dosimeter material S is improved compared to conventional dosimeter materials. In the dosimeter material S of this embodiment, the predetermined amount of nitrogen added to the diamond is related to, for example, the temperature when annealing the dosimeter material S, and depends on the conditions of optical measurement including thermoluminescence measurement. As an example, if the nitrogen content of diamond is 1.0, the dose of radiation irradiated to a living body can be measured. Therefore, by using the dosimeter material S of this embodiment, the dose of radiation irradiated to the living body can be calculated with high sensitivity and accuracy at a level where the dose can be measured.

[0039] Conventional dosimeter materials have unstable trap levels and large fading when measuring optical properties at temperatures below 200°C. Therefore, in practice, conventional dosimeter materials are sometimes preheated to temperatures above 200°C, for example, 240°C, and then thermoluminescence measurement or other optical measurements are performed. If conventional dosimeter materials are not preheated, fading correction is required, but fading correction is difficult and impractical. However, as described above, the dosimeter material S of this embodiment has stable trap levels and small fading, so the conventional preheating of the dosimeter material and fading correction are unnecessary, thereby reducing the complexity of conventional optical property measurements.

[0040] The thermoluminescence measuring device (measuring device) 100 of this embodiment includes a heating element 110, a light receiving device 140, and a control device 150. The heating element 110 heats the dosimeter material S of this embodiment to at least 200°C. The light receiving device 140 detects thermoluminescence (light) emitted from the dosimeter material S. The control device 150 controls the temperature of the dosimeter material S heated by the heating element 110, receives optical information related to the intensity of the thermoluminescence from the light receiving device 140 as an electrical signal, and acquires optical characteristics of the dosimeter material S, such as a glow curve and various spectra. The heating element 110 is connected to the control device 150 and has a metal body (main body) 112 made of brass. A metal layer 114 made of silver is provided on a plate surface (surface) 112b of the metal body 112 facing the dosimeter material S.

[0041] In the thermoluminescence measurement apparatus 100 of this embodiment, the control device 150 calculates and acquires, as optical information, for example, a correspondence relationship between the temperature of the dosimeter material S and the intensity of thermoluminescence, thereby obtaining a glow curve of the dosimeter material S. It can also calculate and acquire a correspondence relationship between the wavelengths of various types of light from the dosimeter material S and the intensity of each wavelength, thereby obtaining various optical spectra of the dosimeter material S. In the thermoluminescence measurement apparatus 100 of this embodiment, the metal layer 114 is provided on the plate surface 112b of the metal body 112 of the heating element 110, thereby effectively suppressing the effects of thermal radiation. According to the thermoluminescence measurement apparatus 100 of this embodiment, the thermoluminescence spectrum of the dosimeter material S is not affected by the thermal radiation of the heating element 110 in a wavelength band near the peak wavelength of the thermoluminescence spectrum of the dosimeter material S after irradiation with radiation, and therefore optical characteristics such as the thermoluminescence glow curve and spectrum of the dosimeter material S can be measured with high sensitivity and accuracy.

[0042] In the thermoluminescence measurement apparatus 100 of this embodiment, the control device 150 heats the dosimeter material S to a temperature of 700° C. or higher by the heating element 110. For example, the control device 150 controls an electrical signal supplied to the heating element 110, thereby heating the heating element 110 so that the dosimeter material S reaches a temperature of 700° C. or higher.

[0043] In the thermoluminescence measurement apparatus 100 of this embodiment, for example, the thermoluminescence spectrum of the dosimeter material S after irradiation with radiation at a temperature of 700° C. or higher is not significantly affected by the thermal radiation of the heating element 110, so that optical characteristics such as the thermoluminescence glow curve and spectrum of the dosimeter material S can be measured with high sensitivity and accuracy even at high temperatures of 700° C. or higher. If the heating element 110 is made of aluminum (Al), the peak wavelength of the thermal radiation of the heating element 110 and the peak wavelength of the thermoluminescence of the dosimeter material S are close to each other, and the thermoluminescence spectrum of the dosimeter material S is affected by the thermal radiation of the heating element 110. As a result, the signal-to-noise ratio during measurement of the thermoluminescence spectrum of the dosimeter material S is significantly reduced, and in some cases the thermoluminescence spectrum cannot be detected.

[0044] In the thermoluminescence measuring apparatus 100 of this embodiment, in order to measure the optical properties including the thermoluminescence spectrum of the dosimeter material S with high sensitivity and accuracy, a heat-absorbing filter (not shown) may be disposed on the optical path of the thermoluminescence emitted from the dosimeter material S. Furthermore, the heating member 110 may be covered with a member made of quartz.

[0045] The thermoluminescence measuring device 100 of this embodiment is useful and effective for the optical measurement of the dosimeter material S of this embodiment as described above, and in the optical measurement of dosimeter materials including the dosimeter material S of this embodiment and conventional dosimeter materials, the thermoluminescence measuring device 100 effectively suppresses the effects of thermal radiation and is widely applicable to the optical measurement of dosimeter materials.

[0046] The measurement method of this embodiment is a method for measuring the optical properties, including the thermoluminescence properties, of a dosimeter material S, and comprises at least steps 1 to 3. In step 1, radiation is irradiated onto the dosimeter material S, which has been doped with a predetermined amount of nitrogen in diamond. In step 2, which is performed after step 1, the dosimeter material S is heated, and various types of light (light), including thermoluminescence, emitted from the dosimeter material S are detected to obtain the optical properties of the dosimeter material. In step 3, which is performed after step 2, the dosimeter material S is heated at an annealing temperature corresponding to the predetermined amount of nitrogen doped in the diamond.

[0047] In the measurement method of this embodiment, the dosimeter material S, which has been irradiated with radiation in the first step and has emitted various types of light including thermoluminescence in the second step, is appropriately annealed in the third step to release the radiation energy remaining in the dosimeter material S. Specifically, in the third step, the dosimeter material S is heated at an annealing temperature corresponding to a predetermined amount of nitrogen, thereby releasing and removing electrons that remained in the trap levels of the dosimeter material S after the second step. Therefore, it is possible to prevent optical characteristics of the dosimeter material S measured in the next second step from including optical characteristics resulting from electrons that remained in the trap levels after the previous second step. Therefore, the measurement method of this embodiment makes it possible to calculate the dose of radiation irradiated to a living body with high sensitivity and precision, and with good reproducibility regardless of the number of times it has been used, at a level at which the dose of radiation irradiated to the living body can be measured.

[0048] The preferred embodiments of the present invention have been described above. The present invention is not limited to the above-described embodiments. The present invention can be modified within the scope of the spirit of the present invention as defined in the claims.

[0049] For example, the dosimeter material S of the above-described embodiment may be placed in the thermoluminescence measurement device 100 and optically excited to obtain the optically stimulated luminescence (OSL) or radiophotoluminescence (RPL) characteristics of the dosimeter material S. In this case, an optical excitation device (not shown) is required.

[0050] The dosimeter material S, thermoluminescence measurement device 100, and measurement method of the above-described embodiment may be used for environmental radiation monitoring in natural environments that are highly relevant to living organisms.

[0051] Next, examples of the present invention will be described. Note that the present invention is not limited to the parameters used or set in the following examples.

[0052] Example 1 Figure 4 shows an example of a glow curve of dosimeter material S measured using the thermoluminescence measurement device 100. A photon counting head was used as the light receiving device 140. In this example, dosimeter material S-A, in which 1.0 ppm of nitrogen was added to diamond, and dosimeter material S-B, in which 3.0 ppb of nitrogen was added to diamond, were used. Each of dosimeter materials S-A and S-B was irradiated with 10 Gy of X-rays.

[0053] The dosimeter material S-A used in the first measurement was designated as dosimeter material S-A1, and the dosimeter material S-A1 was placed in the thermoluminescence measurement device 100. The heating element 110 was changed at a rate of 0.1°C / s within a temperature range from room temperature of approximately 20°C to a high temperature of less than 500°C, and the intensity of thermoluminescence from the dosimeter S-A1 relative to the temperature of the dosimeter material S-A1 was measured. As shown in Figure 4, by using the thermoluminescence measurement device 100, a clear glow peak at approximately 385°C was obtained for the dosimeter material S-A1.

[0054] When measuring thermoluminescence from dosimeter material S including dosimeter material S-A1 multiple times, annealing is performed on dosimeter material S. Annealing is performed to release the radiation energy remaining in dosimeter material S after the previous measurement. In the annealing treatment in Example 1, dosimeter material S-A1 was heated to 600°C, which is equal to or higher than the glow peak temperature, immediately before the next measurement after the initial measurement, to release the radiation energy remaining in dosimeter material S-A1 after the initial measurement.

[0055] Dosimeter material S-A after the 600°C annealing treatment was designated as dosimeter material S-A2. Dosimeter material S-A2 was placed in thermoluminescence measurement apparatus 100, and heating element 110 was changed within a temperature range from room temperature of approximately 20°C to a high temperature below 500°C, and the intensity of thermoluminescence from dosimeter S-A2 was measured relative to the temperature of dosimeter material S-A2. As shown in Figure 4, by using thermoluminescence measurement apparatus 100, clear glow peaks at approximately 250°C, 308°C, and 400°C were obtained for dosimeter material S-A2. The measurements were then repeated several times, and the clear glow peaks at approximately 250°C, 308°C, and 400°C shown in Figure 4 were obtained with good reproducibility.

[0056] In both dosimeter materials S-A1 and S-A2, clear glow peaks were obtained at temperatures above 200°C, and it was confirmed that fading was well suppressed within the temperature range of 20°C or higher and less than 200°C.

[0057] Next, the dosimeter material S-B for the first measurement was placed in the thermoluminescence measurement device 100, and the heating element 110 was changed within a temperature range from room temperature of approximately 20°C to a high temperature of less than 500°C, and the intensity of thermoluminescence from the dosimeter S-B was measured relative to the temperature of the dosimeter material S-B. As shown in Figure 4, by using the thermoluminescence measurement device 100, a weaker glow peak was obtained at approximately 225°C for the dosimeter material S-B compared to the dosimeter materials S-A1 and S-A2.

[0058] The amount of nitrogen in dosimeter material S-A in Example 1 is 1.0 ppm, which is an example of the predetermined amount of nitrogen contained in dosimeter material S of this embodiment. 600°C, which is set in the annealing treatment of dosimeter material S-A, is an example of an annealing temperature corresponding to the predetermined amount of nitrogen in the measurement method of this embodiment. The predetermined amount of nitrogen contained in dosimeter material S of this embodiment is not limited to 1.0 ppm, and can be appropriately set depending on the measurement conditions and environment of the optical properties of dosimeter material S. The annealing temperature in the measurement method of this embodiment is not limited to 600°C, and is appropriately set in accordance with the predetermined amount of nitrogen contained in dosimeter material S, for example, so that the energy of radiation remaining in dosimeter material S after the previous measurement is released.

[0059] 5 shows examples of various spectra of the dosimeter material S similar to that of Example 1 measured using the thermoluminescence measurement device 100. A spectrometer having sensitivity in the visible wavelength range was used as the light receiving device 140. In this example, dosimeter material S-A, in which 1.0 ppm of nitrogen was added to diamond, was used.

[0060] As shown in FIG. 5, a scintillation spectrum having a peak at a wavelength near 650 nm, a photoluminescence (PL) spectrum having a peak at a wavelength near 690 nm, and a thermoluminescence (TL) spectrum having peaks at wavelengths near 700 nm and 900 nm were obtained.

[0061] The glow curve and thermoluminescence characteristics of diamond have been reported previously (see, for example, Physica Status Solidi (A) Applications and Materials Science. 2018 21; 215 (22): 1800246, etc.), but the glow peak was measured at a temperature below 200 ° C. In addition, in the previous report, it was confirmed that the characteristics exhibited were unstable because the dosimeter material contained levels at which the sensitivity to the radiation irradiated thereto decreased and levels at which the sensitivity increased over the measurement time. As shown in Examples 1 and 2, the dosimeter material of this embodiment does not exhibit a glow peak in the temperature range below 200 ° C., but exhibits a stable and reproducible glow curve and various spectra in the temperature range of 200 ° C. or higher. The properties of the dosimeter material of this embodiment, in which a predetermined amount of nitrogen, for example 1.0 ppm, is added to diamond, differ from those previously reported and were discovered through extensive research by the inventors. By using the dosimeter material and thermoluminescence measurement device 100 of this embodiment, the dose of irradiated radiation can be calculated with higher sensitivity and accuracy than conventional methods.

[0062] Example 3 The two-dimensional distribution of thermoluminescence from dosimeter material S was measured using thermoluminescence measurement device 200. In this example, dosimeter material S-A, which was a diamond doped with 1.0 ppm of nitrogen and had a size of 20 mm x 20 mm in plan view, was used as dosimeter material S. Figure 6 is a photograph of dosimeter material S-A used in Example 3. As shown in Figure 6, X-rays were irradiated at 10 Gy or more to only one region R1, with the diagonal line of dosimeter material S-A as the boundary, and the other region R2 was not irradiated with X-rays.

[0063] Fig. 7 is an example of an image of thermofluorescence from dosimeter material S-A measured using thermofluorescence measurement device 200. Fig. 8 is a graph showing the intensity distribution of thermofluorescence at position d1-d2 shown in Fig. 7. Note that in Fig. 8, in the area of ​​high thermofluorescence intensity, the intensity decreases with increasing distance from the 300 pixel position representing the center of dosimeter material S-A. This is because the distance between the light receiving position of imaging camera 210 and the position on the surface of dosimeter material S-A that emits thermofluorescence changes on the surface of dosimeter material S-A.

[0064] 7 and 8, in dosimeter material SA, substantially uniform thermoluminescence was detected from both the region R1 irradiated with X-rays and the region R2 not irradiated with X-rays. From the results of Example 3, it was confirmed that the dosimeter material S of this embodiment can uniformize the amount of thermoluminescence per unit area.

[0065] From the results obtained in the examples described above, it was confirmed that the dosimeter material S, the thermoluminescence measurement devices 100 and 200, and the measurement method described in the above embodiments can calculate the dose of irradiated radiation with high sensitivity and high accuracy.

[0066] Example 4 As described above, two types of dosimeter materials S-A-Hi and S-A-Lo, which have different crystallinity from each other, were prepared for the dosimeter material S-A. The two types of dosimeter materials S-A-Hi and S-A-Lo may be collectively referred to simply as dosimeter material S or dosimeter material S-A. The crystallinity of S-A-Hi is relatively higher than that of dosimeter material S-A-Lo.

[0067] 9 is a schematic diagram of a measurement apparatus 300 used in Example 4. As shown in Fig. 9 , the measurement apparatus 300 includes an X-ray generation source 310, a box-shaped cover 262, a movable stage 254, a support table 250 including a plurality of legs 252, a cooling fan 320, a temperature controller 350, a fan controller 360, a stage controller 370, a white light source 400 such as a xenon lamp, optical filters 402 and 412, a fiber bundle 404, a collimating lens 414, an optical fiber 416, a light receiving device 140 such as a spectroscope, and a control device 150.

[0068] In the measurement device 300, the dosimeter material S is placed on a movable stage 254 via a plate-like member 330 and supported by a support stage 250. The support stage 250 can be raised and lowered under the control of the control device 150 via a stage controller 370. X-rays generated from the X-ray generation source 310 are irradiated toward the dosimeter material S below. White light in the visible wavelength range emitted from the white light source 400 passes through an optical filter 402 and enters a fiber bundle 404 as light in a predetermined wavelength range, and is then irradiated onto the dosimeter material S. The spectrum emitted from the dosimeter material S passes through an optical filter 412, is collimated by a collimating lens 414, enters an optical fiber 416, and is transmitted to the light receiving device 140 by the optical fiber 416.

[0069] The light receiving device 140 is appropriately selected depending on the type of spectrum from the dosimeter material S to be measured, and may be, for example, a photomultiplier tube when measuring the glow curve of a thermoluminescence spectrum or PL or OSL, or a multi-channel spectrometer when measuring various spectra including a thermoluminescence spectrum. The cover 262 blocks light from the outside and X-rays from the inside.

[0070] The control device 150 is electrically connected by wire or wirelessly to each of the X-ray generation source 310, the white light source 400, the temperature controller 350, the fan controller 360, the stage controller 370, and the light receiving device 140. The control device 150 drives each of the devices electrically connected as described above, and adjusts and controls the output from each device, depending on the conditions during measurement.

[0071] FIG. 10 is a graph showing the OSL intensity measured using the measurement device 300 versus the dose of X-rays, i.e., radiation, irradiated onto dosimeter materials S-A-Hi and S-A-Lo. In this measurement, both dosimeter materials S-A-Hi and S-A-Lo were irradiated with X-rays at a dose represented by the horizontal axis of FIG. 10 , and then irradiated with light of a wavelength of 450 nm for 5 minutes. As shown in FIG. 10 , for both dosimeter materials S-A-Hi and S-A-Lo, the OSL intensity was approximately proportional to the dose of radiation irradiated onto the dosimeter material S. When the same dose of X-rays was irradiated, the OSL intensity from dosimeter material S-A-Lo was greater than the OSL intensity from dosimeter material S-A-Hi and was approximately three times the OSL intensity from dosimeter material S-A-Hi. From the results of this measurement, it was confirmed that the dose of irradiated radiation can be calculated with high sensitivity and precision using dosimeter materials SA-Hi and SA-Lo, and that the crystallinity of dosimeter material S can affect sensitivity.

[0072] In addition, when the wavelength of the optical stimulus is 450 nm, the PL and OSL emitted from each of the dosimeter materials S-A-Hi and S-A-Lo overlap each other, so in order to calculate the OSL measurement value, it is necessary to subtract the measurement value corresponding to PL from the actual measurement value obtained by the light receiving device 140, etc. When the wavelength of the optical stimulus is 450 nm, if the dosimeter material S-A is irradiated with radiation at a certain dose, the OSL intensity is measured, and then the next dose is irradiated with radiation without annealing the dosimeter material S-A, and the OSL intensity is measured, the relative OSK intensity, i.e., sensitivity, is improved. If the dosimeter material S-A is annealed after irradiating with radiation at a certain dose and measuring the OSL intensity, the relative OSK intensity, i.e., sensitivity, is restored.

[0073] 11 is a graph different from FIG. 10 , showing the OSL intensity measured versus the dose of X-rays, i.e., radiation, irradiated onto the dosimeter material S-A-Lo using the measurement device 300. In this measurement, the dosimeter material S-A-Lo was irradiated with X-rays at a dose represented by the horizontal axis of FIG. 11 , followed by irradiating with light of 850 nm wavelength for 5 minutes. As shown in FIG. 11 , when the wavelength of the optical stimulus was changed from 450 nm in the above measurement to 850 nm, the OSL intensity emitted from the dosimeter material S-A-Lo was approximately proportional to the dose of radiation irradiated onto the dosimeter material S-A-Lo when the dose of radiation irradiated onto the dosimeter material S-A-Lo was high, around 10 Gy, preferably several tens of Gy. When the same dose of X-rays was irradiated, the OSL intensity emitted from the dosimeter material S-A-Lo when the wavelength of the optical stimulus was 850 nm was lower than the OSL intensity emitted from the dosimeter material S-A-Lo when the wavelength of the optical stimulus was 450 nm. From the results of this measurement, it was confirmed that the dosimeter material S-A-Lo can calculate the radiation dose with high sensitivity and high accuracy, and can be particularly suitably applied to measuring and calculating the radiation dose when the dose of radiation irradiated to the dosimeter material S-A-Lo is a high dose of about several tens of Gy.

[0074] When the wavelength of the optical stimulus is 850 nm, the PL and OSL emitted from the dosimeter material SA-Lo do not overlap with each other, making it easier to measure the OSL than when the wavelength of the optical stimulus is 450 nm.

[0075] Note that, since the dosimeter materials S-A-Hi and S-A-Lo generate glow peaks in the high-temperature range of approximately 300°C to 400°C, the influence of thermal radiation from the plate-like member 330 on which the dosimeter material S is placed and the moving stage 254 must be considered during measurement, and this must be separated from the actual measured values. In the above-mentioned measurements, the temperature of the dosimeter material S and its vicinity during irradiation with radiation and visible light was set to 40°C. The PL and OSL emitted from the dosimeter materials S-A-Hi and S-A-Lo each contain diamond-derived TL as background, and this must be separated from the actual measured values. As a result of various measurements performed using the measurement device 300, as described above, for the dosimeter materials S-A-Hi and S-A-Lo, when the wavelength of the optical stimulus was, for example, 450 nm, a correlation was observed between the radiation dose of 1 Gy to 100 Gy irradiated to the dosimeter material S-A and the measured thermofluorescence intensity or OSL intensity. It was also confirmed that dosimeter material SA has favorable fading characteristics for use as an OSL dosimeter. The sensitivity of thermoluminescence and OSL of dosimeter material SA is thought to correspond to the product of the number of luminescence centers, such as so-called NV centers, and the number of captured electrons.

[0076] From the measurement results of Example 4, it was confirmed that in order to optimize the luminescence center of the dosimeter material S and the electron capture state, it is effective to irradiate with a high dose of radiation, for example, several tens of Gy or more, or to irradiate with light having a wavelength of, for example, 450 nm.

[0077] Furthermore, when dosimeter material S-B was irradiated with a dose of X-rays and then irradiated with light of 450 nm wavelength for 5 minutes, almost no thermofluorescence or OSL was observed, although PL was detected and the PL intensity remained approximately constant immediately after irradiation.

[0078] REFERENCE SIGNS LIST 100 Thermoluminescence measuring device (measuring device) 110 Heating member 112 Metal body (body) 112b Plate surface (surface) 114 Metal layer 140 Light receiving device 150 Control device S Dosimeter material

Claims

1. A dosimeter material in which nitrogen is added to diamond.

2. A measuring device comprising: a heating member for heating a dosimeter material to 200°C or higher; a light receiving device for detecting light emitted from the heated dosimeter material; and a control device for controlling the temperature of the dosimeter material heated by the heating member, receiving optical information relating to the intensity of the light from the light receiving device, and acquiring the optical characteristics of the dosimeter material, wherein the heating member has a main body made of brass, and a metal layer made of silver is provided on the surface of the main body facing the dosimeter material.

3. The measuring device according to claim 2, wherein the control device heats the dosimeter material to a temperature of 700° C. or higher by the heating member.

4. A measurement method comprising: a first step of irradiating radiation onto a dosimeter material in which a predetermined amount of nitrogen has been added to diamond; a second step of, after the first step, heating the dosimeter material, detecting light emitted from the dosimeter material, and acquiring optical properties of the dosimeter material; and a third step of, after the second step, heating the dosimeter material at an annealing temperature corresponding to the predetermined amount.

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