Radiation detection device, radiation detection method, radioactive particulate matter detection device

Abstract

To obtain a radiation detection device that can discriminate between beta rays and gamma rays. [Solution] First, the measurement result (detection result) of the radiation detector 10 within a certain period of time is obtained (S11: measurement step), and this result is stored in the memory unit. Multiple detection patterns are recognized as a continuum of pixels in which light emission is detected (S13: detection pattern recognition step). First, one detection pattern is selected, and the energy absorbed in this detection pattern is calculated from the sum of the outputs (pulse heights) of the pixels included in it (S14). The analysis unit 31 determines whether this detection pattern was formed by alpha rays, beta rays, or gamma rays from this energy and the feature quantities (spread, hardness, eccentricity) calculated from the detection pattern as described above (S15: identification step).

Description

Technical Field

[0001] The present invention relates to a radiation detection device that discriminates and detects the types of radiation, a radiation detection method, and a radioactive particle detection device that detects radioactive particles that emit radiation.

Background Art

[0002] In an environment contaminated with radioactive substances, a dust monitor (radioactive particle detection device) that indirectly measures the spatial density of radioactive particles is used by sucking the radioactive particles and adsorbing them onto a filter paper or the like, and then recognizing the density thereof. The configuration of such a dust monitor is described in, for example, Patent Document 1. The dust monitor includes a suction device for adsorbing particles onto a filter paper and a radiation detector that detects radiation emitted from the filter paper in a state where the particles are adsorbed.

[0003] Here, the most important nuclide to be monitored is the nuclide that emits α-rays, which is the most significant cause of internal exposure. In addition to this, it is also required that nuclides that emit β-rays can be recognized as well. For this reason, in the dust monitor, a radiation detector that can distinguish (discriminate) and detect α-rays and β-rays is used. Examples of such a radiation detector include those that combine a scintillator and a photomultiplier tube. Alternatively, it is also possible to use a combination of two types of dust monitors, one dedicated to α-rays and the other dedicated to β-rays.

[0004] Such a dust monitor is placed in the environment to be measured, and in that state, the radiation on the filter paper is measured by the radiation detector. Thereby, the spatial concentration of radioactive particles in real time can be recognized.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] For example, in nuclear reactor facilities slated for decommissioning, it is important to recognize the spatial concentration of radioactive particles using dust monitors like the one described above. However, when performing this measurement in real time, high doses of gamma rays are often present in such environments. In this case, since gamma rays have higher penetrating power than alpha and beta rays, radiation detectors also detect gamma rays present in the environment, making it difficult to eliminate the influence of these gamma rays. Alternatively, in such cases, it became necessary to install thick lead plates around the sample to shield against gamma rays and eliminate their influence, which resulted in a larger overall device and made it difficult to install it in the desired measurement environment.

[0007] Therefore, a technology was desired in radiation detectors that could discriminate gamma rays when detecting alpha rays and beta rays (especially beta rays). It was also desired to use this technology to obtain a more accurate radioactive particle detection device.

[0008] This invention has been made in view of the above-mentioned problems, and aims to provide an invention that solves the above-mentioned problems. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following configuration. The present invention relates to a radiation detection device that detects radiation incident on the detection surface of a radiation detector and discriminates and detects the radiation according to its type, wherein the radiation detector comprises a detection surface on which a plurality of detection elements, each of which detects the radiation, are arranged in an array, and each detection element is configured to produce an output corresponding to the absorption of the radiation's energy, and the device comprises an analysis unit that recognizes a detection pattern, which is a combination of a plurality of adjacent detection elements that produced the output for a single incident of radiation, from the detection result which is the output for each detection element, and discriminates between beta rays and gamma rays as the radiation types that generated the detection pattern based on feature quantities calculated from the two-dimensional shape of the recognized detection pattern. The feature quantity may be the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the first reference pattern, which is a pattern composed of the detection elements and containing the detection pattern. The feature quantity may be the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the second reference pattern, which is a pattern obtained when the detection pattern is enveloped by the detection elements. The aforementioned feature may be the eccentricity of the ellipse when the detection pattern is approximated by an ellipse. The analysis unit may discriminate alpha rays as the radiation type that generated the detection pattern based on the sum of the energies obtained by the detection elements that constitute the detection pattern. The analysis unit may obtain the detection results in a time series and recognize the radiation detected between the first and second time points by comparing the first detection result obtained at the first time point with the detection result obtained at the second time point, which is later than the first time point. The radiation detector may be a position-sensing semiconductor detector, or a detector that detects light emission caused by the incidence of radiation on a plate-shaped scintillator. The present invention relates to a radiation detection method for detecting radiation incident on the detection surface of a radiation detector and discriminating and detecting the radiation according to its type, wherein the radiation detector comprises a detection surface on which a plurality of detection elements, each of which detects the radiation, are arranged in an array, and each detection element is configured to produce an output corresponding to the absorption of the energy of the radiation, and comprises a detection pattern recognition step of recognizing a detection pattern which is a combination of a plurality of adjacent detection elements that produced the output when a single radiation was incident, based on the detection result which is the output of each detection element, and an identification step of discriminating between beta rays and gamma rays as the radiation types that generated the detection pattern based on feature quantities calculated from the two-dimensional shape of the recognized detection pattern. As the feature quantity, the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the first reference pattern, which is a pattern composed of the detection elements and containing the detection pattern, may be used. As the feature quantity, the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the second reference pattern, which is a pattern obtained when the detection pattern is enveloped by the detection elements, may be used. As the aforementioned feature quantity, the eccentricity of the ellipse obtained by approximating the detection pattern with an ellipse may be used. In the identification step, alpha rays may be discriminated as the radiation type that generated the detection pattern based on the sum of the energies obtained by the detection elements constituting the detection pattern. The present invention relates to a radioactive particulate matter detection device for detecting radioactive particulate matter suspended in the air and emitting alpha or beta rays, comprising: a thin plate-shaped filter body having a mesh-like structure; a suction device that captures the radioactive particulate matter present in the atmosphere by sucking in the atmosphere near the main surface of the filter body; and a radiation detection device having a detection surface positioned in close proximity to and opposite to the filter body from which the radioactive particulate matter has been captured, wherein the radioactive particulate matter is detected from the radiation recognized by the detection surface. A measuring cartridge may be used, in which a radiation detector holder to which the radiation detector is mounted and a sample holder to which the filter body is mounted are detachably coupled. Alternatively, a detection device body may be used in which the measuring cartridge is detachably mounted to a housing to which a suction device for sucking up the filter body is fixed. [Effects of the Invention]

[0010] As described above, the present invention provides a radiation detection device that can discriminate against gamma rays when detecting beta rays. Using this, a more accurate radioactive particle detection device can be obtained. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the configuration of a radioactive particulate matter detection device using a radiation detection device according to an embodiment of the present invention. [Figure 2] This figure schematically shows the configuration of the detection unit in a radiation detection device according to an embodiment of the present invention. [Figure 3] This is a real-world example of a binarized detection result. [Figure 4] This is an example of an energy histogram for the entire detection result. [Figure 5] This is an example showing three types of feature quantities of the detection pattern used in the radiation detection method according to an embodiment of the present invention. [Figure 6] This flowchart shows a radiation detection method according to an embodiment of the present invention. [Figure 7] This flowchart shows an example of the identification step in a radiation detection method according to an embodiment of the present invention. [Figure 8] This figure shows the actual detection results with the judgment results added. [Figure 9] This figure shows an overview of the configuration of the detection device body used in the radioactive particle detection device according to an embodiment of the present invention. [Figure 10] This is a cross-sectional view showing the configuration of the measuring cartridge used in the detection device body.

Embodiments for Carrying Out the Invention

[0012] When the radiation detection device according to an embodiment of the present invention is used in a dust monitor (radioactive fine particle detection device), it can detect radiation emitted from radioactive nuclides in fine particles adsorbed on a measurement sample such as filter paper. At this time, as radiation types, particularly β-rays and γ-rays can be discriminated and detected. Therefore, even in the presence of a high dose of γ-rays, β-rays can be discriminated and recognized. Furthermore, since α-rays can also be discriminated and recognized, radioactive fine particles emitting α-rays and radioactive fine particles emitting β-rays can be appropriately detected even in an environment with a high γ-ray dose. Here, for the recognition of fine particles and the discrimination of these radiations, a position detection type radiation detector capable of obtaining outputs from radiation detection for each pixel arranged in a two-dimensional array is used.

[0013] FIG. 1 is a diagram showing the configuration when this radiation detection device 2 is used in the radioactive fine particle detection device 1. Here, as in the conventional dust monitor, the entire main surface (the lower surface in the figure) of a thin plate-shaped sample (filter paper: filter housing) 100 having a fine mesh-like structure is sucked by a suction device 20, so that fine particles in the environment are captured by the sample 100. Radiation emitted from radioactive nuclides contained in these fine particles is detected by the radiation detection device 2. The radiation detection device 2 includes a radiation detector 10 that directly detects radiation, and an analysis device 30 that analyzes the detection result and determines whether the detected radiation is α-ray, β-ray, or γ-ray.

[0014] In FIG. 1, the analysis device 30, which is a computer, recognizes radioactive fine particles captured by the sample 100 from the detection result of the radiation detector 10. Here, for this purpose, an analysis unit 31 that performs analysis described later, a storage unit 32 that is a hard disk or non-volatile memory for storing data for analysis, and a display unit 33 that is a display for displaying mapping results and the like are provided. Although a memory or the like for temporarily storing data during analysis is also provided, its description is omitted.

[0015] Figure 2 schematically shows the configuration of the detection unit 11 into which radiation is incident in the radiation detector 10. For convenience, the top-bottom relationship is reversed compared to Figure 1, and the radiation is shown as incident from above. The radiation detector 10 is a semiconductor detector made of silicon (semiconductor). Generally, in a semiconductor detector, incident radiation imparts energy to the semiconductor, generating electron-hole pairs, and these electron-hole pairs are extracted as an electrical output (pulse output). In this detection unit 11, a detection surface 11A on which two-dimensionally arranged detection elements P are provided is used, and the above output is obtained for each detection element P. The detection unit 11 is made of silicon with a thickness of about 300 μm and is configured to obtain the above output for each detection element P. The detection elements P mainly function as pixels in the detection results described later. This configuration is similar to that of a commonly known two-dimensional position detection type semiconductor detector, so a detailed explanation is omitted.

[0016] When a single radiation particle (alpha, beta, or gamma ray) is incident on the detection surface 11A, the radiation particle loses energy and is absorbed within the detection unit 11 (semiconductor), or it passes through the detection unit 11. If the radiation particle passes through multiple detection elements P, pulse outputs are obtained from multiple detection elements P with a single incident of radiation particle. The arrangement pattern (detection pattern) of these multiple detection elements P corresponds to the shape of the radiation particle's trajectory when the detection results in the radiation detection unit 11 are represented as a two-dimensional image with each detection element P as a pixel. The thickness of the detection unit 11 is set to approximately 50 μm to 2000 μm (particularly preferably 100 μm to 500 μm) so that such a detection pattern is clearly visible. If the thickness is too thin, the probability of beta rays passing through the detection unit 11 increases, making it difficult to recognize the elongated detection pattern of beta rays described later. On the other hand, if the thickness is too thick, the absorption efficiency of gamma rays increases, making it difficult to distinguish between beta rays and alpha rays based on the detection pattern described later.

[0017] Here, the circumstances under which radiation imparts energy to a semiconductor differ depending on the type of radiation. In a semiconductor, alpha rays are absorbed after imparting most of their energy over a short distance, resulting in a point-like track within the semiconductor. Therefore, the detection pattern described above is also point-like.

[0018] In contrast, beta rays impart small amounts of energy over a certain distance, gradually gaining energy and losing it before being absorbed, resulting in a longer detection pattern. During this process, beta rays are scattered, so their propagation direction is generally not straight. Therefore, the aforementioned detection pattern is curved.

[0019] Furthermore, because gamma rays have very high penetrating power, they do not continuously transfer energy in semiconductors like beta rays, resulting in longer sections where they pass straight through. Also, unlike beta rays, the direction of propagation of gamma rays does not change significantly during this process. For this reason, the detection pattern of gamma rays is smaller and more like a point than that of alpha rays, or shorter and more like a straight line than that of beta rays.

[0020] Furthermore, as described above, the output of the semiconductor detector is obtained as a pulse output signal intensity corresponding to the number of electron-hole pairs. In the radiation detector 10 described above, this signal intensity is obtained for each detection element P, and this signal intensity corresponds to the energy imparted by the radiation particle to the semiconductor at that pixel. Therefore, if such outputs are obtained at multiple detection elements P (corresponding to the detection pattern described above) due to the incidence of a single radiation particle, the sum of the signal intensities of each detection element P corresponds to the energy imparted by the radiation particle to the detection unit 11 (semiconductor) at the time of detection.

[0021] Generally, the energy of alpha rays originating from nuclear materials is often around 4 MeV to 6 MeV. In reality, even if these alpha rays are generated on the sample 100, they lose energy in the air and within the sample 100 before reaching the detection surface 11A, so they enter the detection unit 10A with a lower energy. However, as mentioned above, the energy imparted by beta rays (absorbed by the semiconductor) is often lower than the energy of the alpha rays in this case. Also, as mentioned above, gamma rays tend to pass through the detection unit 11 more easily, so the energy imparted within a single detection element P is small. For this reason, the energy absorbed due to alpha rays (signal intensity) is higher than that caused by beta rays and gamma rays.

[0022] Therefore, alpha rays, beta rays, and gamma rays can be distinguished from the signal intensity obtained from the pixels (detection elements P) in the detection pattern. Furthermore, beta rays and gamma rays can be discriminated from the aforementioned detection pattern. This makes it possible to discriminate between alpha rays, beta rays, and gamma rays. The specific methods for these discriminations will be described later.

[0023] Various types of radiation detectors can be used as the above-mentioned radiation detector 10, as long as they can perform similar detection. For example, as semiconductors constituting the semiconductor detector, in addition to silicon (Si), germanium (Ge), diamond, thallium bromide (TlBr), silicon carbide (SiC), cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe), etc. may be used. Alternatively, a detector using a scintillator may be used instead of a semiconductor detector. In this case, a two-dimensional photodetector (position-sensitive photomultiplier tube) can be attached in close contact to a plate-shaped scintillator and used in the same manner. In this case, the amount of light emitted per pixel (the number of photons generated in the region of the scintillator corresponding to the pixel) is used in correspondence with the electron-hole pairs, and each light emission is recognized by the two-dimensional photodetector as a pulse output signal intensity, and this signal intensity corresponds to the energy as described above. In this case, the plate-shaped scintillator corresponds to the detection unit, and it is particularly preferable to shield the area between pixels to suppress crosstalk between pixels.

[0024] Figure 3 shows the measurement of sample 100, in which numerous thorium-containing particles that serve as alpha and beta ray sources were captured, with the gamma ray source being... 137 This is a two-dimensional detection result showing the output of each pixel within a certain period of time obtained by measuring under a gamma-ray background of 10 mSv / h or more with Cs in close proximity to the radiation detector 10. Each side is 14 mm, which is the same size as the sample 100 and the detection unit 11. In reality, the signal intensity of each pixel (detection element P) is an analog value with various values, but here, a threshold is set for the detected signal intensity, and pixels with an output above this threshold are displayed in white, and pixels with an output below this threshold are displayed in black, thus binarizing the image. By appropriately selecting this threshold, each detection pattern becomes clear as shown here. This result can be displayed on the display unit 33 in Figure 1, which allows for the determination of the appropriateness of the threshold for this binarization.

[0025] As shown here, the incidence of a single radiation particle (alpha, beta, or gamma ray) is recognized as a single detection pattern (a group of pixels), and it is clear that the shape of the detection pattern can be mainly classified into linear patterns and near-point patterns.

[0026] Furthermore, Figure 4 shows a histogram (spectrum) of the energy (keV) for each detection of radiation particles as described above, for the entire result. Here, a distribution on the low-energy side and a distribution on the higher-energy side with a lower frequency are observed. As mentioned above, the former corresponds to beta rays and gamma rays, and the latter corresponds to alpha rays. Therefore, the energy threshold for determining these (energy threshold) can be set to, for example, around 2 MeV. In other words, radiation particles detected at energies of 2 MeV or higher are alpha rays, meaning that detection patterns recognized as having such energies can be presumed to be caused by fine particles emitting alpha rays.

[0027] Next, we will explain the discrimination between beta rays and gamma rays based on the detection patterns described above. As mentioned above, the detection pattern caused by beta rays is curved, while the detection pattern caused by gamma rays is point-like or a straight line shorter than that of beta rays. Therefore, as a feature quantity to numerically evaluate the shape of this detection pattern, we define a numerical value that represents the degree of difference between this detection pattern and the point-like and straight-line shapes, and it becomes possible to distinguish between beta rays and gamma rays using this feature quantity. Here, as examples of feature quantities to evaluate the shape characteristics of this detection pattern, we can use "spread," "hardness," and "eccentricity," which will be explained below.

[0028] Figure 5 is a diagram illustrating this definition and example in detail. Here, each pixel is square, and pixels that have been binarized as described above and detected are shown in color. In each detection pattern, the pixels are continuous, and each pixel has adjacent pixels. Therefore, the analysis unit 31 can easily recognize such detection patterns.

[0029] Figure 5(a) shows five examples of "spread". "Spread" is defined as "number of pixels occupying the detection pattern (colored pixels in the figure)" / "number of pixels occupying the smallest rectangular pattern (first reference pattern) that includes the entire detection pattern". In Figure 5(a), the first reference pattern corresponding to each detection pattern is composed of 3 × 3 pixels in (1), (3), and (4) (number of pixels horizontally) × (number of pixels vertically), 5 × 1 in (2), and 4 × 4 in (5). Therefore, the "spread" is 9 / 9 = 1 in (1), 5 / 5 = 1 in (2), 5 / 9 in (3), 5 / 9 in (4), and 8 / 16 = 1 / 2 in (5). The more concentrated the pixels are in the detection pattern, the larger the "spread" becomes. "Spread" is a parameter that expresses the degree of concentration of pixels in one place, so for example, if the detection pattern is point-like or linear, it will be large (close to 1), and if it is curved, it will be small (close to 0). Therefore, the "spread" is smaller in the case of beta rays than in the case of gamma rays. The relationship between beta rays and alpha rays shows a similar trend.

[0030] Figure 5(b) shows five examples of "hardness". "Hardness" is defined as "number of pixels occupying the detection pattern" / "number of pixels occupying the pattern obtained when the detection pattern is enveloped in a convex envelope (second reference pattern)". Here, a convex envelope, as illustrated in Figure 5(b), encloses all the detected pixels in the detection pattern, and is designed so that the total length of the envelope is the shortest possible. The "number of pixels occupying the detection pattern" is the same as in the case of "spread", and each detection pattern is shown in color on the left side of Figure 5(b). On the other hand, the corresponding second reference pattern is shown as a dashed line corresponding to a rope on the left side of Figure 5(b), and as colored pixels to the right of it. In (1) and (2), the detection pattern and the second reference pattern are equal, so the "hardness" is 9 / 9 and 5 / 5, respectively, which is 1 in both cases. Also, in (3), the second reference pattern includes one pixel in the upper center that does not constitute the detection pattern, so the "hardness" is 6 / 7 (<1). In (4), the second reference pattern includes the two pixels in the upper center that do not constitute the detection pattern, so the "hardness" is 5 / 7 (<1). In (5), the second reference pattern includes the second pixel from the upper left to the right and the second pixel from the bottom that do not constitute the detection pattern, so the "hardness" is 6 / 7 (<1). For this reason, like "spread", the "hardness" is large (closer to 1) if the detection pattern is point-like or linear, and small (closer to 0) if it is curved. For this reason, the "hardness" is also smaller in the case of beta rays than in the case of gamma rays. The relationship between beta rays and alpha rays shows a similar trend.

[0031] For example, the detection patterns for the rectangular shape (1) and the cross shape (a shape diverging from a single point) (3) in "spread" and the rectangular shape (1) and cross shape (2) in "hardness" are identical in shape. From these results, it can be seen that there is no difference between the rectangular shape and the cross shape in "hardness" (both are 1), whereas there is a difference between the rectangular shape and the cross shape in "spread" (rectangular shape: 1, cross shape: 5 / 9). Also, the detection patterns for (4) in "spread" and (4) in "hardness" are identical in shape (U-shape), but while spread is 5 / 9, hardness is 5 / 7, and the difference from the aforementioned rectangular shape (both are 1) is greater for "spread". Therefore, both "spread" and "hardness" are numerical representations of the degree of difference from the point-like shape of the detection pattern, but which is more effective for the actual detection pattern will be confirmed by experiment. As will be described later, these can actually be used in combination.

[0032] Figure 5(c) shows five examples of "eccentricity". "Eccentricity" is defined as "the eccentricity of the ellipse when the detection pattern is approximated by this ellipse". This ellipse can be obtained, for example, as an ellipse with the same second moment as the detection pattern. In case (1), this ellipse is actually a circle, so the "eccentricity" is 0. In cases (2) and (3), the number of pixels in the vertical direction is 1 (the smallest unit), and in reality, this ellipse is a line segment with a short side length of 0, so the "eccentricity" is 1. In cases (4) and (5), according to the above definition, the "eccentricity" is 0.7 and 0.8, respectively. "Eccentricity" is a parameter that expresses whether the detection pattern is elongated (closer to 0 if it is close to a point or a circle, and closer to 1 if it is elongated) in the range of 0 to 1. In other words, "eccentricity" is a parameter that expresses whether the detection pattern is elongated along a specific direction. For this reason, the "eccentricity" is smaller in the case of beta rays than in the case of gamma rays. Furthermore, as mentioned above, alpha rays often exhibit a point-like detection pattern, resulting in the smallest "eccentricity" compared to beta and gamma rays.

[0033] As described above, in the detection pattern of beta rays, "a long detection pattern" corresponds to "a large eccentricity," and "a curved detection pattern" corresponds to "small spread and stiffness." Therefore, by using the magnitude relationship between the detection pattern and the threshold for "spread" (spread threshold), the threshold for "stiffness" (stiffness threshold), and the threshold for "eccentricity" (eccentricity threshold), it is possible to determine whether this detection pattern is caused by beta rays or gamma rays. The same applies to discrimination from alpha rays.

[0034] Figure 6 is a flowchart of an example of the operation performed by the analysis unit 31. In this operation, first, the measurement result (detection result) of the radiation detector 10 within a certain period of time is obtained (S11: measurement step), and this result is stored in the storage unit 32 in Figure 1. The analysis unit 31 then binarizes the light emission intensity (signal intensity) recognized for each pixel as described above, based on its relationship to a threshold (S12). This threshold is set appropriately so that the detection pattern becomes clear, as shown in Figure 3. As a result, multiple detection patterns are recognized as a continuum (or individual pixels) of pixels in which light emission is detected (S13: detection pattern recognition step). The following analysis is performed on each recognized detection pattern.

[0035] Here, first, one detection pattern is selected, and the energy absorbed in this detection pattern is calculated from the sum of the outputs (pulse heights) of the pixels included in it (S14). The analysis unit 31 determines whether this detection pattern was formed by alpha rays, beta rays, or gamma rays, based on this energy and the feature quantities (spread, hardness, eccentricity) calculated from the detection pattern as described above (S15: identification step). This determination is repeated until it is performed for all recognized detection patterns (S16: Yes). As a result, the type of radiation (whether it corresponds to alpha rays, beta rays, or gamma rays) is recognized for all detection patterns. This determination result is stored in the memory unit 32 (S17).

[0036] In the identification process (S15), the accuracy of identifying radiation types can be increased by combining the above-mentioned feature quantities and energy-based determinations in a way that best matches the experimental results. Figure 7 shows an example of the specific contents of this identification process, which yielded a high accuracy rate.

[0037] In Figure 7, the first step is identification by "spread" (S21). If the "spread" is below the spread threshold (S21: Yes), then identification by "hardness" (S22) is performed. If the "hardness" is below the hardness threshold (S22: Yes), then the detection pattern is determined to be caused by beta rays (S23). If it is greater than the hardness threshold (S22: No), then the detection pattern is determined to be caused by gamma rays (S24).

[0038] If the "spread" is greater than the spread threshold (S21: No), identification by energy (S25) is performed. If the energy is greater than the energy threshold set for energy (energy threshold) (S25: No), this detection pattern is determined to be caused by alpha rays (S26). If the energy is less than or equal to the energy threshold (S25: Yes), identification by eccentricity (S27) is performed. If the eccentricity is less than or equal to the eccentricity threshold (S27: Yes), this detection pattern is determined to be caused by gamma rays (S24). If it is greater than the eccentricity threshold (S27: No), it is determined to be caused by beta rays (S23).

[0039] In this flowchart, a ray is identified as a β-ray (S23) when its "spread" is small (S21: Yes) and its "hardness" is small (S22: Yes) (these are considered the first case), as well as when its "spread" is large (S21: No), its energy is small (S25: Yes), and its eccentricity is large (S27: No) (these are considered the second case). A ray is identified as a γ-ray (S24) when its "spread" is small (S21: Yes) and its "hardness" is large (S22: No) (these are considered the third case), as well as when its "spread" is large (S21: No), its energy is small (S25: Yes), and its eccentricity is small (S27: Yes) (these are considered the fourth case). In the example shown in Figure 3, the accuracy rate for identifying α-rays, β-rays, and γ-rays based on these results was over 99%.

[0040] Figure 8 shows the results of identifying alpha, beta, and gamma rays (indicated as ○-α, ○-β, ○-γ: ○ is a number) by applying the identification process shown in Figure 7 to the results in Figure 3, with an energy threshold of 2 MeV for identifying alpha rays, a spreading threshold of 0.66 (or less) for identifying beta rays, a hardness threshold of 0.94 (or less), and an eccentricity threshold of 0.99 (or more).

[0041] Under the aforementioned measurement conditions, the detected alpha rays and gamma rays are detected by placing the edge of a piece of paper between the sample 100 and the detection surface 11A, respectively. 137 By separating Cs, the effect is significantly reduced. This allows us to determine the validity of this result, and according to this, the accuracy of discriminating between beta rays and gamma rays was over 99% when gamma rays were at background levels (approximately 0.0005 mSv / h to 10 mSv / h; the same applies hereafter), and over 96% even when gamma rays were at 10 mSv / h.

[0042] The numbers enclosed in the dotted rectangles in Figure 7 indicate the number of detection patterns assigned to each step when the total number of detection patterns recognized in the embodiment was 199969. From these results, for the determination of beta rays (S23), the contribution of the first case (when the "spread" is small (S21:Yes)) is large at 55200, while the contribution of the second case (when the "spread" is large (S21:No)) is small at 1125. On the other hand, for the determination of gamma rays (S24), the contribution of the fourth case (when the "spread" is large (S21:No)) is large at 140727, while the contribution of the third case (when the "spread" is small (S21:Yes)) is small at 2887.

[0043] Therefore, among the above features, the most effective feature for distinguishing between beta rays and gamma rays is "spread," and by adding determinations based on energy, stiffness, and eccentricity, this determination can be made with high accuracy. For this reason, the above determination may be made using only "spread" and energy, in which case the processing speed of the analysis unit 31 can be made particularly high, or the configuration of the analysis unit 31 can be simplified (cost reduced). In this case, step S22 in Figure 7 can be omitted and steps S21 (:Yes) and S23 can be connected (equivalent to always setting S22:Yes), and step S27 can be omitted and steps S25 and S24 can be connected (equivalent to always setting S27:Yes).

[0044] Furthermore, in the operation shown in Figure 7, energy was used for the recognition of alpha rays (S25). However, for alpha rays as well, other feature quantities besides those shown in Figure 5 may be defined and used for their recognition. In this case, for example, as shown in Figure 8, the detection pattern caused by alpha rays will be in the form of large clumps. Accordingly, the number of pixels constituting the detection pattern, for example, can also be introduced as a feature quantity and used for determination. That is, it is possible to distinguish between alpha rays, beta rays, and gamma rays using only the detection pattern. However, it is generally easy to recognize energy in radiation detectors, and as shown in Figure 4, the distinction between alpha rays, beta rays, and gamma rays using this method can be performed with high accuracy. For this reason, using energy to distinguish alpha rays as described in Figure 7 is particularly effective.

[0045] Furthermore, in the aforementioned radioactive particle detection device, it is particularly important to distinguish between alpha and beta rays. In this process, gamma rays were detected as described above in order to reduce the influence of gamma rays, which interfere with the recognition of alpha and beta rays. In this case, selectively reducing the detection efficiency of gamma rays in the radiation detection device is also effective.

[0046] For example, in the measurement of radiation detector 10, the output when radiation is detected once is obtained as a pulse output. However, since the waveform of this pulse output differs between beta rays and gamma rays, it is possible to discriminate between them using the characteristics of the waveform (e.g., decay time in the pulse), making it difficult to detect gamma rays. In actual measurements, the time course of the concentration of radioactive material in the atmosphere is measured by repeating measurements at predetermined time intervals (window time). By shortening this window time (for example, setting it to 0.1 seconds in the case of 10 mSv / h), it is possible to reduce the number of gamma ray detections even in high-dose environments, enabling highly accurate discrimination of radiation types.

[0047] In the radioactive particle detection device 1 described above, since it can detect particles on the sample 100 that emit alpha and beta rays while reducing the effects of gamma rays, a thick structure for shielding against gamma rays is unnecessary. Therefore, the structure of the device can be simplified, made lighter, and its convenience can be improved. The configuration that enhances this convenience will be described below.

[0048] Figure 9 shows a front view (a) and side perspective views ((b)(c)) of the detection device body (dust monitor body) 5, which integrates all components except the analysis device 30 (computer) shown in Figure 1. The side perspective views ((b)(c)) correspond to the directions shown in Figure 1. Here, the x, y, and z directions are defined as shown, with the negative x-direction being forward and the positive x-direction being backward, and the positive z-direction being upward and the negative z-direction being downward. The analysis device 30 in Figure 1 can be a separate unit from this detection device body and can be electrically connected to it.

[0049] In the detection device body 5, the suction device 20 is fixed to the lower side of the housing 40, and as shown in Figure 9(a), the housing 40 is provided with an intake port 40A on the upper front side and an exhaust port 40B on the lower side. As the suction device 20, a type using a well-known double counter-rotating fan is particularly preferred from the viewpoint of weight reduction, and its flow rate is, for example, about 16 L / min. In this case, it is also easy to move the detection device body 5 to the environment to be measured. On the other hand, in Figure 9, a measurement cartridge 50 is used in which the radiation detector 10 and the sample 100 etc. shown in Figure 1 are integrated and fixed, and the measurement cartridge 50 is detachable from the housing 40 from the rear side. Figure 9(b) shows the form when the measurement cartridge 50 is attached to the housing 40 and measurement is performed, and Figure 9(c) shows the form when the measurement cartridge 50 is attached to or detached.

[0050] Figure 10(a) is a cross-sectional view taken near the center in the y-direction, corresponding to the direction shown in Figures 9(b) and (c) which illustrate the structure of the measuring cartridge 50. The measuring cartridge 50 is composed of a radiation detector holder 60, to which the radiation detector 10 is fixed at the top, and a sample holder 70, to which the sample (filter body) 100 is fixed at the bottom. Figures 10(b) and (c) are cross-sectional views of the radiation detector holder 60 and the sample holder 70, respectively.

[0051] As shown in Figure 10(a), the radiation detector holder 60 and the sample holder 70 are configured such that when they are combined, the radiation detector 10 (detection surface 11A) and the sample 100 are in close proximity and facing each other. In particular, the sample holder 70 is configured such that the sample 100 is sucked in from below by the suction device 20 and air is drawn in from the negative x-direction side.

[0052] As shown in Figure 10(b), in the radiation detector holder 60, the detection surface 11A of the radiation detector 10 is fixed to the main body 61 of the radiation detector holder 60, which is the main component of the holder, so that it faces downwards. In this case, the detection surface 11A is covered with a light-shielding film 62 to block visible light, which is a noise component during radiation detection. The light-shielding film 62 can be any material that blocks visible light but allows the radiation to be detected (especially alpha rays and gamma rays) to pass through, and can prevent contamination by radioactive particles. For example, it can be made of a resin material (about 2 μm thick) with a thin metal film (for example, aluminum about 50 nm thick) deposited on it.

[0053] As shown in Figure 10(c), in the sample holding section 70, the sample 100 is fixed to the main body 71 of the sample holding section, which constitutes the section, with the sample 100 on the upper side. A protective film 72 is attached to the upper side of the sample 100 so as to cover the sample 100 from above, with a gap formed between the film and the sample 100. The protective film 72 can be made of any material that has high radiation transmittance and can prevent contamination by radioactive particles, for example, a thin resin material (for example, about 4 μm thick). In addition, the sample holding section body 71 has a sample holding section side intake port 71A that communicates with the aforementioned intake port 40A formed at the front, and a suction opening 71B for suction by the suction device 20 is formed on the lower side of the sample 100. The protective film 72 is fixed to the sample holding section body 71 on its lower side, except where the sample holding section side intake port 71A is located.

[0054] By drawing air through the suction opening 71B with the suction device 20, outside air is introduced from the air intake 40A into the narrow space between the protective film 72 and the sample 100 through the air intake 71A on the sample holding side. This allows airborne particles to be adsorbed onto the sample 100. At this time, by providing the protective film 72, adhesion of particles to the radiation detector 10 (light-shielding film 62, etc.) is suppressed, and the radiation emitted from the radioactive particles adsorbed on the sample 100 can be recognized more accurately.

[0055] As shown in Figure 10(a), when combining the radiation detector holder 60 and the sample holder 70, the positional relationship between the two can be properly maintained by fitting together the protrusions and recesses provided on the radiation detector holder body 61 and the sample holder body 71. Therefore, the reproducibility of measurements in the radiation detector 10 can be maintained at a high level. In this case, as mentioned above, the light-shielding film 62 and the protective film 72 are also effective.

[0056] Furthermore, by preparing multiple sample holder units 71 with the sample 100 already loaded, more efficient measurements are possible compared to simply replacing only the sample 100. This reduces the time the operator spends in the measurement environment and thus reduces the operator's radiation exposure. Also, as mentioned above, if radioactive particles adhere to the radiation detector 10 (such as the light-shielding film 62), subsequent measurements will not be accurate. However, with the above configuration, measurements can be easily resumed by replacing the radiation detector holder unit 60.

[0057] In other words, by using the measurement cartridge 50 (radiation detector holder 60, sample holder 70) as described above, measurements can be performed efficiently. This makes it possible to analyze radioactive particles in the air in real time with high accuracy. Performing such real-time, high-accuracy analysis leads to the rapid detection of radioactive material concentrations in the air, and therefore contributes to reducing the radiation exposure of workers. Using a measurement cartridge 50 of this type allows for high-accuracy measurement of alpha and beta rays even in the presence of gamma rays, as described above, and is possible because it eliminates the need to provide a shielding material near the sample 100 to shield against gamma rays.

[0058] The above has been described based on embodiments of the present invention. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in the combination of these components, and that such modifications also fall within the scope of the present invention. [Explanation of Symbols]

[0059] 1. Radioactive particulate matter detection device 2. Radiation detection device 5. Detection device main unit 10. Radiation detectors 11 Detection Unit 11A Detection surface 20 Suction device 30 Analyzer 31 Analysis Department 32 Storage section 33 Display section 40 enclosures 40A air intake 40B Exhaust port 50 measuring cartridges 60 Radiation detector holder 61 Radiation detector holding unit body 62 Light-shielding film 70 Sample holding section 71A Sample holding section side air intake 71B Suction opening 71 Sample holding unit body 72 Protective film 100 samples (filter paper: filter body) P detection element

Claims

1. A radiation detection device that detects radiation incident on the detection surface of a radiation detector and discriminates and detects the radiation according to its type, The radiation detector comprises a detection surface in which a plurality of detection elements, each of which detects the radiation, are arranged in an array, and is configured such that an output is obtained for each detection element due to the absorption of the radiation's energy. From the detection results, which are the outputs for each detection element, a detection pattern is recognized, which is a combination of multiple adjacent detection elements from which the output was obtained when a single radiation was incident. A radiation detection device characterized by comprising an analysis unit that discriminates between beta rays and gamma rays as the radiation types that generated the detection pattern, based on feature quantities calculated from the two-dimensional shape of the recognized detection pattern.

2. The radiation detection device according to claim 1, characterized in that the feature quantity used is the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting a first reference pattern, which is a pattern composed of the detection elements and containing the detection pattern.

3. The radiation detection device according to claim 1 or 2, characterized in that the feature quantity used is the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the second reference pattern, which is a pattern obtained when the detection pattern is convexly enveloped by the detection elements.

4. The radiation detection device according to claim 1 or 2, characterized in that the eccentricity of the ellipse when the detection pattern is approximated by an ellipse is used as the feature quantity.

5. The radiation detection device according to claim 1 or 2, characterized in that the analysis unit discriminates alpha rays as the radiation type that generated the detection pattern based on the sum of the energies obtained by the detection elements constituting the detection pattern.

6. The radiation detection device according to claim 1 or 2, characterized in that the analysis unit obtains the detection results in a time series and recognizes the radiation detected between the first time and the second time by comparing the first detection result obtained at the first time with the detection result obtained at the second time, which is later than the first time.

7. The radiation detection device according to claim 1 or 2, characterized in that the radiation detector is a position-sensing semiconductor detector or a detector that detects light emission due to the incidence of radiation in a plate-shaped scintillator.

8. A radiation detection method that detects radiation incident on the detection surface of a radiation detector and discriminates and detects the radiation according to its type, The radiation detector comprises a detection surface in which a plurality of detection elements, each of which detects the radiation, are arranged in an array, and is configured such that an output is obtained for each detection element due to the absorption of the radiation's energy. A detection pattern recognition step involves recognizing a detection pattern which is a combination of multiple adjacent detection elements from which the output was obtained when a single radiation was incident, based on the detection result which is the output for each detection element. A discrimination step in which beta rays and gamma rays are distinguished as the radiation types that generated the detection pattern, based on the feature quantities calculated from the two-dimensional shape of the recognized detection pattern, A radiation detection method characterized by comprising the following:

9. The radiation detection method according to claim 8, characterized in that the feature quantity used is the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting a first reference pattern, which is a pattern composed of the detection elements and containing the detection pattern.

10. The radiation detection method according to claim 8 or 9, characterized in that the feature quantity used is the ratio of the number of detection elements constituting the detection pattern to the number of detection elements constituting the second reference pattern, which is a pattern obtained when the detection pattern is convexly enveloped by the detection elements.

11. The radiation detection method according to claim 8 or 9, characterized in that the eccentricity of the ellipse when the detection pattern is approximated by an ellipse is used as the feature quantity.

12. The radiation detection method according to claim 8 or 9, characterized in that, in the identification step, alpha rays are discriminated as the radiation type that generated the detection pattern from the sum of the energies obtained by the detection elements constituting the detection pattern.

13. A radioactive particulate matter detection device for detecting radioactive particulate matter suspended in the air that emits alpha or beta rays, A thin, plate-shaped filter body having a mesh-like structure, A suction device that captures radioactive particles present in the air by drawing in air near the main surface of the filter body, A radiation detection device according to claim 1 or 2, comprising the detection surface positioned in close proximity to and opposite to the filter body in which the radioactive particles are captured, It is equipped with, A radioactive particle detection device characterized by detecting radioactive particles from radiation recognized on the detection surface.

14. A measuring cartridge is used, in which a radiation detector holder to which the aforementioned radiation detector is attached and a sample holder to which the aforementioned filter body is attached are detachably connected. The radioactive particulate matter detection device according to claim 13, characterized in that a detection device body is used in which the measuring cartridge is detachably attached to a housing on which a suction device for sucking up the filter body is fixed.

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