JP5925009B2 - Radiation measurement system - Google Patents

Description

  The present invention relates to a radiation measurement system, and more particularly to a radiation measurement system for investigating radioactive contamination inside an object such as soil.

  A conventional general survey meter includes a portable detection probe and a main body having a display and a calculation unit (Patent Document 1). FIG. 13 shows an example of the detection probe. In the detection probe 10, a cylindrical scintillator member 12, a photomultiplier tube (PMT) 14, an electronic circuit 16, and the like are accommodated. In the detection probe 10, a GM tube, a semiconductor detector, or the like may be provided as a radiation detector. FIG. 14 shows another example of the detection probe. In the detection probe 18, a flat scintillator member 22, a photomultiplier tube 26, an electronic circuit 28 and the like are accommodated. When the light emitted from the scintillator member 22 reaches the light receiving surface of the photomultiplier tube 26 through the light guide space 24, the light is converted into an electric signal in the photomultiplier tube 26.

  When investigating the radioactive contamination of the object, the detection probe as described above is brought close to the surface of the object, and in this state, the radiation emerging from the surface of the object is detected. Examples of the radiation measured by the survey meter include γ-rays (X-rays), β-rays, α-rays, etc. In particular, when investigating the degree of radioactive contamination in the environment, γ-rays are measured.

  As is well known, the transmission power of γ-rays (X-rays) is generally very large, and a general detection probe detects γ-rays flying from the entire periphery (FIGS. 13 and 14). Even if the detection probe is brought close to the surface of the object, γ rays from other than the object are also detected. For example, when soil, rivers, air, natural objects, artificial structures, etc. are widely contaminated due to an accident at a nuclear power plant or the like, it is not easy to investigate only soil contamination. For example, even if you make a hole in the soil and insert a detection probe there to detect gamma rays, in addition to gamma rays from radioactive materials contained in the soil, gamma rays from radioactive materials present in the atmosphere together. It is because it will be detected. Similar problems arise when investigating radioactive contamination of seas and rivers.

  It is possible to collect a part of soil or the like, take the sample home, and investigate the radioactive material contained in the sample using a large radiation measurement device equipped with a shielding room. However, in that case, a considerable time is required until the measurement result is obtained. It is necessary to obtain measurement results on site for identification of contamination sources and investigation of contamination areas.

  Patent Document 2 discloses a detection probe including a collimator (shielding member). The detection probe is used by being arranged outside the object. Patent Document 3 discloses a radiation measuring apparatus having a shielding member having a plurality of holes and a plurality of radiation detectors arranged in the plurality of holes. Patent Documents 1-3 do not disclose a technique for measuring radiation by inserting a detector into an object such as a solid or a liquid. In Patent Document 4, radiation having a container containing a liquid mixture of a liquid sample and a liquid scintillator, a photodetector for detecting light emitted from the container, and a guard detector provided so as to surround them. A detection device (liquid scintillation counter) is disclosed.

JP 2007-170935 A JP 2002-214353 A JP 2002-6053 A JP-A-10-227866

  An object of the present invention is to provide a radiation measuring apparatus capable of measuring radiation with high accuracy inside an object such as soil. Alternatively, an object of the present invention is to make it possible to exclude or reduce the influence of radiation flying from the outside in measuring internal contamination of an object such as soil. Alternatively, an object of the present invention is to enable measurement of internal contamination at a plurality of depth positions in an object such as soil.

(1) Preferably, the radiation measurement system is inserted in the depth direction from the surface of an object such as soil, and an insertion unit including a detection unit that detects radiation inside the object, and a signal from the detection unit A signal processing unit for processing the external radiation that has entered the inside of the object from the outside through the surface of the object, and the target radiation to be measured inside the object. A main detector and a first sub-detector having a spatial relationship for distinction and measurement, wherein the signal processing unit includes the main detection signal output from the main detector and the first sub-detector. Based on the first sub detection signal output from the directional characteristic forming process, the signal component of the target radiation is extracted while removing or reducing the signal component of the extraneous radiation. To run includes a directional characteristic formation unit.

  According to the above configuration, the insertion unit is inserted from the surface of the object into the object, and radiation (preferably γ rays) is detected by the detection unit inside the object. The detection unit includes at least a main detector and a first sub-detector, which are arranged with a predetermined spatial relationship. The predetermined spatial relationship is defined as the difference between external radiation (or radiation that is not to be measured) that has entered the object from the outside through the surface of the object and target radiation that is to be measured within the object. It is for measuring separately. For example, extraneous radiation that is a non-measurement target is simultaneously detected by both the main detector and the first sub-detector, and the target radiation is detected individually, that is, non-simultaneously by the main detector and the first sub-detector. In order to achieve this, the first sub-detector is arranged so as to cover or hide the main detector on the side from which the external radiation enters as viewed from the main detector. In this case, it is desirable to apply non-coincidence counting processing (pulse exclusion processing) using the first sub detection signal as a reference signal for the main detection signal as the directivity pattern formation processing. In other configurations, extraneous radiation that is not to be measured is detected individually or non-simultaneously in the main detector and the first sub-detector, and the target radiation is detected simultaneously in both the main detector and the first sub-detector. In order to do so, the first sub-detector is arranged so as to surround the main detector on the side where the target radiation enters as viewed from the main detector. In this case, it is desirable to apply a coincidence counting process using the first sub detection signal as a reference signal with respect to the main detection signal as the directivity forming process. The above two methods may be combined. Other methods may be adopted. In any case, a combination of the spatial arrangement of a plurality of detectors and a process using the relationship between the plurality of detection signals produces a desired directivity characteristic for the entire detection unit, that is, a detection signal component of the target radiation. It is desirable to be able to take out

  The signal processing unit includes a directivity characteristic forming unit that executes directivity characteristic forming processing using at least the main detection signal and the first sub detection signal. The directivity characteristic forming process corresponds to a process of excluding or reducing signal components corresponding to external radiation and extracting signal components corresponding to target radiation. By subsequent signal processing, a directivity characteristic (intra-object directivity characteristic) that matches the measurement purpose can be generated in the detection unit. Thereby, it becomes possible to obtain a measurement result indicating the internal dose of the object itself, the radioactivity in the object, the degree of contamination inside the object, and the like. In that case, since it is hard to be influenced by the radiation from the outside, the measurement accuracy can be improved.

(2) The object is soil (ground), water (sea, lake, river, pool, etc.), artificial structure (concrete block, waste, etc.), tree, and the like. In general, the above-described configuration can be applied when the concentration of radioactive material, contamination, dose, etc. in an object is a problem. By the directivity forming process, at least radiation from the outside world is removed or reduced. In that case, a downward hemispherical sensitivity characteristic may be formed. Desirably, a planar directivity characteristic orthogonal to the depth direction is formed. By using such directivity, it is possible to perform dose measurement for a specific depth without much influence from other depths. A planar directivity characteristic may be formed over a 360-degree azimuth range around the detector, or only in a specific azimuth range. According to the latter, the measurement which limited depth and direction can be performed. Desired directivity can be formed by changing the configuration of each detector or the spatial relationship of a plurality of detectors. A cover may be placed on the outside of the insertion unit so as not to cause radioactive contamination in the insertion unit itself. Prior to the insertion of the insertion unit, a hole may be formed in the object, and the insertion unit may be inserted there. The insertion unit may be formed as a result by arranging the insertion unit in the depression generated in the object and filling the periphery thereof. It is also possible to investigate the radioactive contamination of groundwater by letting the detector reach a considerable depth in the soil. The detector is preferably a scintillator detector. Extraction of the signal from the detector is performed by wire or wireless. The insertion unit is preferably configured as a waterproof / dustproof type. When a scintillator detector is used as the detector, the spatial relationship between the plurality of detectors can be regarded as the spatial relationship between the plurality of scintillator members that are sensitive parts.

(3) Preferably, the first sub-detector is provided on the surface side of the main detector, and the directivity pattern forming process is a first non-coincidence for the main detection signal based on the first sub-detection signal. Includes processing. According to this configuration, for example, extraneous radiation passes through the first sub-detector and reaches the main detector. On the other hand, radiation coming from the horizontal direction reaches the main detector directly without passing through the first sub-detector. When the second sub-detector is not provided below the main detector, radiation from below the main detector also reaches the main detector directly. That is, extraneous radiation coming from above the main detector is simultaneously detected by the main detector and the sub-detector, while target radiation is detected by the main detector without passing through the sub-detector. It is possible to exclude the extraneous radiation component in the main detection signal by utilizing such a difference in conditions.

  Preferably, the detection unit includes a second sub-detector provided on a side opposite to the surface side of the main detector, and the directivity forming process is performed on the main detection signal based on the second sub-detection signal. A second non-coincidence process is included. According to this configuration, radiation coming from both the upper side and the lower side of the main detector can be excluded from the measurement target. Accordingly, the detection unit has a horizontal directivity characteristic orthogonal to the depth direction. That means planar directivity.

  Preferably, a moving mechanism for moving the detection unit in the depth direction is provided. By using this moving mechanism, radiation can be measured at a desired depth without affecting or reducing the influence of extraneous radiation. Preferably, the control unit controls the position of the detection unit in the depth direction by controlling the moving mechanism, and the depth and dose based on a plurality of radiation detection data acquired by changing the position of the detection unit. A graph creation unit for creating a graph showing the relationship between

  Preferably, the insertion unit includes a hollow member that is a member extending in the depth direction and made of a material that transmits radiation, and the detection unit is separated from the object in an internal space of the hollow member. Is provided. According to this hollow member, the detection unit can be prevented from being contaminated and protected.

  Preferably, the insertion unit includes a plurality of detection units arranged in the depth direction, and radiation is measured at a plurality of depth positions by the plurality of detection units. According to this configuration, dose measurement and the like can be performed simultaneously at a plurality of depth positions.

  Preferably, the first sub-detector is provided around the horizontal direction of the main detector, and the directivity pattern forming process is a coincidence process based on the main detection signal and the first sub-detection signal. According to this configuration, the target radiation is detected simultaneously by both the main detector and the first sub-detector. On the other hand, extraneous radiation is detected individually and non-simultaneously in the main detector and the first sub-detector. It is possible to extract the signal component of the target radiation using such a difference in conditions. By adjusting the form of the first sub-detector, the directivity characteristics (directivity angle, directivity direction, detection orientation range, etc.) of the detection unit can be freely set. In the configuration using this coincidence method, the target radiation is detected by transmitting one of the main detector and the first sub-detector and then detecting the other, so that attenuation during transmission becomes a problem. It is desirable to adopt a configuration based on the non-coincidence counting method. Note that it is possible to combine the two methods, and it is also possible to combine a shielding member (collimator).

  Preferably, an insertion unit including a detection unit that is inserted in a depth direction from the surface of an object such as soil and detects radiation inside the object; a signal processing unit that processes a signal from the detection unit; And the detection unit includes a detector array composed of n (where n is 4 or more) detectors arranged in the depth direction for detecting radiation, and the signal processing unit includes the detector array , Based on the detection result of the i-1 th detector and the detection result of the i + 1 th detector, with respect to the detection result of the i (where 2 ≦ i ≦ n−1) th detector Perform non-coincidence processing. According to this configuration, the main detector, the upper sub-detector (first sub-detector), and the lower sub-detector (second sub-detector) are configured in units of three adjacent scintillators. Except for the upper end and the lower end, each scintillator selectively exhibits a plurality of functions depending on the detection depth.

  Preferably, the object is soil, and a support mechanism for supporting the insertion unit with respect to the soil is provided. Preferably, the object is water, and a support mechanism for supporting the insertion unit with respect to the water is provided.

  Desirably, the radiation measurement method includes forming a hole from the surface of the object, inserting a plurality of detectors into the hole, and a plurality of depth positions inside the hole. Detecting the radiation using the plurality of detectors; and processing the plurality of signals obtained by detecting the radiation using the plurality of detectors at the plurality of depth positions. A signal processing step for extracting a target signal component corresponding to radiation emitted from a radioactive substance in the inside, and a graph showing a relationship between depth and dose based on a plurality of target signal components corresponding to the plurality of depth positions Generating. The holes can be formed manually or using a special machine. Desirably, a decontamination range determination method for determining a depth range of decontamination work performed on the soil based on the graph is provided. In addition, as a diversion example of the above-described configuration, measurement of the surface of an object using horizontal directivity and measurement at every height in the air can be considered.

  According to the present invention, radiation can be measured with high accuracy inside an object such as soil. Or according to this invention, the influence of the radiation which flies from the external field can be excluded or reduced in measuring the internal pollution of objects, such as soil. Alternatively, according to the present invention, internal contamination can be measured at a plurality of depth positions in an object such as soil.

It is a figure which shows the structural example of the soil survey system which concerns on this invention. It is an enlarged view of the detection unit shown in FIG. It is a figure which shows the structural example of the directional characteristic formation part shown in FIG. It is a figure which shows an example of dose distribution. It is a figure which shows the other structural example of a detection unit. It is a figure which shows the structural example at the time of applying a coincidence method. It is a figure which shows the other structural example of the soil survey system which concerns on this invention. It is a figure which shows the other example of dose distribution. It is a figure which shows the further another structural example of the soil survey system which concerns on this invention. It is a figure which shows the system configuration example using wireless communication. It is a figure which shows an example of the radiation measurement with respect to a natural ground. It is a figure which shows the structural example of the underwater survey system which concerns on this invention. It is a figure which shows an example of a general detection probe. It is a figure which shows the other example of a general detection probe.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows an example of a radiation measurement system according to the present invention. This system is a soil survey system for investigating radioactive contamination within soil or ground.

  The soil survey system includes a measuring device 30 and a control device 32. The measuring device 30 is installed in a measuring place (usually outdoors) such as a schoolyard. The control device 32 is configured as a personal computer or a dedicated device. Although the control apparatus 32 may be arrange | positioned near the measuring apparatus 30, both may be arrange | positioned separately. The measuring device 30 may be connected to the control device 32 via a network or a communication line.

  The measuring device 30 will be described. The measuring device 30 includes an insertion unit 34 as an insertion body, a support unit 36 as a measurement base, and the like. In the example shown in FIG. 1, the insertion unit 34 has a cylindrical shape extending in the depth direction. The insertion unit 34 is inserted from a soil surface 39 into a hole 38 formed by excavation. The hole 38 is formed manually or using a machine. The insertion unit 34 itself may have a function like a drill. The outer diameter of the insertion unit 34 is, for example, 10-15 cm, and the overall length is 1-3 m. The portion above the surface 39 (upper end portion) of the insertion unit 34 is, for example, several tens of centimeters. The form of the insertion unit 34 is appropriately determined according to the purpose and the like. A small-diameter shape can be adopted, and the size can be reduced. For example, an insertion unit that is inserted deep into the ground may be configured.

  The support unit 36 is installed on the surface (ground) 39 and supports the insertion unit 34. The support unit 36 functions as a pedestal. It has a support base (horizontal plate) 44, legs 46 and the like. The support base 44 also functions as a lid for the detection unit 34. A reel 48 is rotatably provided through the support base 44. It rotates by a driving force from a driving unit 52 such as a motor. A wire 50 is wound around the reel 48. The wire 50 is led into the detection unit 34 through the support base 44, and the lower end thereof is connected to the measurement unit 42. The measurement unit 42 is suspended by a wire. Cables (signal lines, power cables, etc.) extending from the measurement unit 42 are guided to the control device 32 through a support base. A wireless system may be adopted instead of the wired system shown in FIG. The depth detector 54 detects the position (depth) of the detection unit 42 directly or indirectly. As the depth detector 54, one that detects the amount of movement of the wire 50 may be used, or a distance sensor that measures the distance from the support base 44 to the detection unit 42 may be used. The operation of the drive unit 52 is controlled by the control device 32, and the output signal of the depth detector 54 is sent to the control device 32. The depth position of the detection unit 42 may be set manually instead of the drive unit 52.

  In the present embodiment, a reel 52 and a wire 50 are provided as a moving mechanism. As an alternative moving mechanism, a mechanism using a rack and a pinion, a mechanism using a belt drive system, a mechanism using an oil pressure, a mechanism using a rod, and the like can be used. The insertion unit 34 is usually inserted in a direction perpendicular to the surface 39. However, it may be inserted in an oblique direction.

  The insertion unit 34 includes a cylindrical guide member 40 and a detection unit 42 provided therein so as to be movable up and down. The guide member 40 is made of a material that transmits radiation (gamma rays in the present embodiment) (not much attenuated), such as resin or aluminum. The thickness may be reduced as long as a certain structural strength can be obtained. The guide member 40 exhibits a function of separating the soil as the target object and the detection unit 42 therein. That is, functions such as prevention of contamination of the detection unit 42 and protection of the detection unit are exhibited. The guide member 40 may be covered with a cover made of a transparent film or the like. This is to prevent contamination of the insertion unit 34.

  The detection unit 42 constitutes a movable body, and moves up and down in the internal space 40 </ b> A of the guide member 40. The detection unit 42 can be installed at an arbitrary depth, and radiation can be measured at that depth. It is also possible to measure radiation while moving the detection unit 42 upward or downward at a constant speed.

  In the present embodiment, the detection unit 42 includes a main detector 56, an upper sub detector (first sub detector) 58, a lower sub detector (second sub detector) 60, and a hollow case 70. As a result of the directivity forming process for the output signals of the main detector 56, the upper sub-detector 58 and the lower sub-detector 60, a horizontal directivity 68 is generated electronically in the detection unit 42. It is a directional characteristic that spreads in a planar shape in the horizontal direction, and the main sensitivity direction is all directions in the horizontal direction. However, it may be configured to measure only a certain azimuth range. The size and direction of the range can be variably set.

  FIG. 2 shows an enlarged view of the detection unit. The detection unit 42 includes the main detector 56, the upper sub detector 58, and the lower sub detector 60 as described above. Each of the upper sub detector 58 and the lower sub detector 60 functions as a guard detector. The main detector 56 includes a scintillator member 250 having a circular shape or a disk shape disposed at the center of the detection unit 42, and a photomultiplier tube (PMT) 252 that converts light generated therein into an electric signal. . The scintillator member 250 is a sensitive part to radiation. The light receiving surface of the photomultiplier tube 252 is directed downward, and the light receiving surface is in close contact with the upper surface of the scintillator member 250. You may arrange | position a light guide member between both. When radiation enters the scintillator member 250, light is generated there, and the light reaches the light receiving surface and is converted into an electrical signal. The photomultiplier tube 252 is disposed on the central axis of the detection unit 42. The scintillator member 250 is configured as, for example, a NaI scintillator, like the other scintillator members. You may be comprised with another material. The photomultiplier tube 252 generally has a cylindrical shape.

  The upper sub detector 58 includes a disc-shaped scintillator member 254 and a photomultiplier tube 256. The scintillator member 254 has a shape that extends in the horizontal direction so as to cover the entire scintillator member 250. The diameter of the scintillator member 254 is larger than the diameter of the scintillator member 250. A ring-shaped groove (opening) 66 is formed by the difference in diameter between the two. The light receiving surface of the photomultiplier tube 252 is in close contact with the upper surface of the scintillator member 254. You may arrange | position a light guide member between both. The photomultiplier tube 256 is provided at a position shifted from the central axis of the detection unit. However, the installation position is arbitrary. What is necessary is just to determine suitably considering a weight balance, installation space, etc. In the vertical direction (depth direction), the thickness of the scintillator member 254 is smaller than the thickness of the scintillator member 250. However, each thickness may be set based on detection sensitivity and other conditions. Since the scintillator member 254 spreads in the horizontal direction, most of the radiation that reaches the scintillator member 250 from above passes through the scintillator 254. As described above, the radiation detected by the two scintillator members 254 and 250 is not the object of measurement, and the detected component is removed by the non-coincidence processing described later in the signal processing stage.

  The lower sub-detector 60 is provided below the scintillator member 250 and includes a scintillator member 258 and a photomultiplier tube 260. The scintillator member 258 has the same form as the scintillator member 254 described above. However, both forms may be different. The light receiving surface of the photomultiplier tube 260 faces upward, and is in close contact with the lower surface of the scintillator member 258. The scintillator member 258 spreads horizontally so as to conceal it from below on the lower side of the scintillator member 250, and most of the radiation that reaches the scintillator member 250 from below passes through the scintillator member 258. The radiation is not subject to measurement and can be identified by simultaneous detection with scintillators 258 and 260.

  Radiation that enters the scintillator member 250 from the horizontal direction does not pass through the scintillator members 254 and 258 and is not detected by them. That is, it is possible to measure such radiation to be measured separately from other radiation. Although radiation is also incident on the scintillator members 254 and 258 from the horizontal direction, it is not a counting target in the non-coincidence processing described later. Therefore, by appropriately setting the spatial relationship between the scintillator member 250 and the scintillator member 254, the removal range of radiation flying from above can be adjusted, and similarly, the spatial relationship between the scintillator member 250 and the scintillator member 258 is appropriately set. Thereby, the removal range of the radiation which flies from the bottom can be adjusted. In other words, the horizontal directivity characteristic of the detection unit is determined by the spatial relationship between the three.

  The main detector 56, the upper sub detector 58 and the lower sub detector 60 are accommodated in a case 70. The case 70 is composed of a member having radiation transparency, and is composed of, for example, a resin. Since the outer surface of the case 70 and the inner surface of the guide member 40 are in contact with each other, it is desirable to reduce the friction between them. It is also possible to inject insulating oil or the like into the interior 40A. In each of the scintillator members 250, 254, and 258, light shielding films 262 and 264 are provided in portions that need to be shielded except for the portion where the light receiving surface of the photomultiplier tube is in close contact. The case 70 also has a light shielding structure.

  In the present embodiment, the horizontal directivity characteristic as shown in the figure is formed, so that it is possible to measure the radiation contamination of the soil at the installation depth of the detection unit 42 (more precisely, the scintillator member) with high accuracy. That is, the position resolution is good in the depth direction. It is also possible to use an electronic circuit that replaces the photomultiplier tube.

  Returning to FIG. 1, the control device 32 will be described. The signal processing circuit 72 is a circuit for processing output pulses from the three photomultiplier tubes included in the three detectors 56, 58, and 60, and includes an amplifier, a wave height discriminator, a directivity characteristic forming unit 73, and the like. ing. A configuration example of the directivity forming unit 73 is shown in FIG. The directivity forming unit 73 includes two non-simultaneous counting circuits 73A and 73B. The non-coincidence circuit 73A is a gate processing circuit that excludes pulses input simultaneously with pulses output from the upper sub-detector from pulses output from the main detector and outputs other pulses. . The non-simultaneous counting circuit 73B is a gate processing circuit that excludes pulses input simultaneously with pulses output from the lower sub-detector from pulses output from the main detector and outputs other pulses. is there. That is, when radiation coming from above the detection unit is detected by the upper sub-detector and the main detector, pulses are output from both detectors at the same time, and the pulses are excluded from the counting target. When radiation coming from below the detection unit is detected by the lower sub-detector and the main detector, pulses are output simultaneously from both detectors, and the pulses are excluded from the counting target. Therefore, only the pulses that are not excluded from the pulse train from the main detector are output from the signal processing circuit. The pulse to be counted corresponds to the radiation that reaches the scintillator member of the main detector directly from the horizontal direction without passing through another scintillator member. As a result, a horizontal directivity characteristic with the main sensitivity direction directed in the horizontal direction in the detection unit is generated. Such directivity is useful in measuring the dose at each depth.

In FIG. 1, the arithmetic unit 74 has a counter, counts the pulses output from the signal processing circuit 72, and specifically measures the count number (cpm) per fixed time. The count value is converted into a dose or converted into a radioactive substance concentration. The computing unit 74 may be configured as a multi-channel analyzer. The display unit is composed of a liquid crystal display or the like, and a graph described later is displayed on the display screen. Examples of the display unit of measurement results include dose rate (μSv / h), counting rate (cpm or min ⁻¹ ), radioactivity surface density (Bq / cm ² ), and the like. The control unit 78 performs operation control of each component included in the control device 32. The driving unit 52 is controlled, and a signal from the depth detector 54 is referred to at that time. The battery 79 supplies power to the entire system. It is also possible to employ a configuration that operates using electric power from a general power source. The high voltage source 80 generates a high voltage necessary for the operation of the three photomultiplier tubes included in the three detectors. Reference numeral 82 indicates three power signals and three detection signals.

  An input unit 84 is connected to the control unit 78. When the measurement depth is designated by the user using the input unit 84, the control unit 78 performs control to position the detection unit 42 at the designated depth. Further, when the scan mode is selected, control is performed to continuously perform measurement while moving the detection unit 42 upward or downward at a constant speed. In that case, the time constant for the signal moving average processing is adaptively set according to the scanning speed, that is, the ascending / descending speed. When the measurement is continuously performed while moving the detection unit 42, the control unit 78 generates a graph shown in FIG. In FIG. 4, the horizontal axis represents the dose, and the vertical axis represents the depth. As shown in this graph 85, the dose varies according to the depth, and from which depth range to which decontamination should be performed can be accurately determined.

  Next, an operation example of the system shown in FIG. 1 will be described. First, a hole 38 having a predetermined depth is formed in a school yard or the like. The inner diameter of the hole 38 is set so that the insertion unit 34 can be inserted. The guide member 40 is inserted into the hole 38, and the support unit 36 is installed on the surface (ground) 39. At the same time, the detection unit 42 is arranged in a suspended state in the guide member 40. When the preparation is completed and the depth to be measured is designated using the input unit 84, the control unit 78 controls the operation of the driving unit 52, and the detection unit 42 is positioned at the designated depth. In that case, feedback control based on the output of the depth detector 54 is executed as necessary. After the detection unit 42 is positioned, radiation measurement is performed there for a predetermined time. Thereby, dose data at a specified depth can be obtained. When the user selects the scan mode, the control unit 78 moves the detection unit 42 at a low speed over a certain depth range. Thereby, dose data can be obtained for each depth. If they are plotted, the dose graph shown in FIG. 4 can be created. Such measurement work is performed at a plurality of points as necessary.

  According to the said structure, the radiation from the radioactive substance contained in the inside of the soil as a target object can be detected with a sufficient precision, In that case, the radiation which approachs through the surface 39 from the air And radiation coming from deeper points in the ground can be excluded from the measurement target. Therefore, the measurement accuracy of the target radiation can be increased. However, if the lower sub-detector 60 is removed, a downward hemispherical detection sensitivity characteristic can be generated, and radiation can be detected throughout the soil. In this case, it can also be said that the in-object directional characteristic is formed. A small camera for monitoring the installation status of the detection unit 42 may be provided.

  FIG. 5 shows another configuration example of the detection unit. The detector unit 266 includes a main detector 268 and a sub detector 270. The main detector 268 includes a scintillator member 272 having a cubic shape, and a photomultiplier tube 274 that detects light generated there. The sub detector 270 includes an upper scintillator member 274, a lower scintillator member 276, and a photomultiplier tube 278. A light guide member 280 between the upper scintillator member 274 and the lower scintillator member 276 and around the horizontal direction of the scintillator member 272 is provided with little radiation attenuation. A light-shielding film 282 is provided so that light crosstalk does not occur between the two detectors 268 and 270. In the configuration shown in FIG. 5, when radiation is incident on the scintillator member 272 and light is generated, it is detected by the photomultiplier tube 274. When radiation is incident on the upper scintillator member 274 and light is generated, the light reaches the photomultiplier tube 278 via the light guide member 280 and the lower scintillator member 276 and is detected. Light generated by radiation incident on the lower scintillator member 276 is also detected by the photomultiplier tube 278. According to the configuration shown in FIG. 5, the light generated by the upper scintillator member 274 and the lower scintillator member 276 can be detected by the single photomultiplier tube 278, so that the configuration can be simplified. A single photomultiplier tube may be arranged on the upper side instead of the lower side. Although the photomultiplier tube 278 is embedded in the lower scintillator member 276, it may be disposed outside the lower scintillator member 276. When the detection unit 266 shown in FIG. 3 is used, counting of radiation coming from above and below can be excluded by using a single non-coincidence circuit in the directivity forming unit.

  FIG. 6 shows still another configuration example of the detection unit. The detection unit includes a main detector 290 and a sub detector 292. The main detector 290 includes a columnar scintillator member 293 disposed on the central axis, and a photomultiplier tube 294 that detects light generated there. The sub-detector 292 includes a ring-shaped scintillator member 295 and a photomultiplier tube 296 that detects light generated there. The scintillator member 295 is configured to surround the scintillator member 293 on the outer side in the horizontal direction. Radiation from above and radiation from below directly reach the scintillator member 293, while radiation coming from the horizontal direction when viewed from the scintillator member 293 passes through the scintillator member 295 and then reaches the scintillator member 293. . That is, only radiation coming from the horizontal direction is detected twice. Therefore, it is possible to distinguish a detection pulse of radiation from a specific direction from other detection pulses by utilizing such a difference in conditions. That is, of the pulse train output from the main detector 290, only the pulses generated simultaneously from the pulses output from the sub detector are counted. Since radiation coming from other directions does not enter the two detectors simultaneously, it is excluded from the object of counting. The coincidence counting circuit 298 shown in the figure is provided in the directivity forming section in the signal processing circuit. Although the photomultiplier tube 296 is arranged in a sideways posture, it can be arranged in an upright state.

  FIG. 8 shows another configuration example of the soil survey system. The soil survey system includes a measuring device 100 and a control device 102. The measuring apparatus 100 includes an insertion unit 106 and a support unit 104. The insertion unit 106 is inserted into soil, and has a guide member 108 as a sheath. The guide member 108 is a hollow cylindrical member made of a member that transmits radiation. Inside, a detector unit row 110 comprising a plurality of detection units 110a-110e aligned in the vertical direction is provided. Each of the detection units 110a to 110e has the configuration shown in FIG. The control device 102 includes a plurality of signal processing circuits 112A provided corresponding to the plurality of detection units 110a to 110e. Each signal processing circuit 112A has the configuration shown in FIG. That is, two non-simultaneous counting circuits are provided. Thereby, a horizontal directivity characteristic is generated in each of the detection units 110a to 110e. The calculation unit 116 performs counting for each of the detection units 110a to 110e, thereby calculating a plurality of doses corresponding to a plurality of depths. A dose graph 128 shown in FIG. 7 represents this as a graph. It is a bar graph. A plurality of high voltage sources 120A are provided corresponding to the plurality of detection units 110a to 110e. However, a high voltage may be applied to the three photomultiplier tubes included in the individual detection units 110a to 110e using a single high voltage source. In addition to the above, the control device 102 includes a control unit 124, an input unit 126, a display unit 118, a battery 122, and the like. According to the system shown in FIG. 8, radiation can be detected simultaneously at a plurality of different depths in the plurality of detection units 110a to 110e. Therefore, it is not necessary to provide an elevating mechanism for the detection unit.

  FIG. 9 shows still another configuration example of the soil survey system. The soil survey system includes a measuring device 300 and a computing device 302. The measuring device 304 comprises an insertion unit 304, which has a plurality of detectors 305a-305f. Each detector 305a-305f includes scintillator members 306a-306f and photomultiplier tubes 308a-308f. The plurality of scintillator members 306a to 306f have the same form as each other, and specifically have a columnar shape or a disk shape. They are aligned in the depth direction, in other words, stacked in the depth direction. On the other hand, the control device 302 is provided with a signal processing circuit, which includes a plurality of non-simultaneous counting circuits 310-1 to 310-5. The plurality of non-simultaneous counting circuits 310-1 to 310-5 execute non-simultaneous counting processing in units of three vertically adjacent detectors (detector sets).

  Specifically, when the number of detectors aligned in the depth direction is n (where n is an integer of 4 or more), n−1 non-simultaneous counting circuits are provided. For the detection pulse of the i (where 2 ≦ i ≦ n−1) -th detector, the non-coincidence processing is executed using the detection pulse of the i−1-th detector, and the i + 1-th detection The non-coincidence processing is executed using the detector detection pulse. Thereby, a horizontal directivity characteristic is generated in the i-th detector. That is, the horizontal directivity characteristics can be independently generated in the individual detectors from the second detector to the (n-1) th detector. In FIG. 9, signal processing circuits other than the non-simultaneous counting circuit are not shown. Even in this configuration, the dose can be individually measured at a plurality of depths without providing an elevating mechanism. In addition, the third to n-2th detectors simultaneously function as the main detector, the upper sub-detector, and the lower sub-detector, and the second and n-1th detectors are the main detectors. Since the two functions of the detector and the sub-detector are performed simultaneously, the configuration of the measuring device can be simplified. The first and nth detection units function as sub-detectors.

  FIG. 10 shows a modification of the system shown in FIG. However, the measuring apparatus 130 includes the detection unit shown in FIG. In this system, wireless communication is performed between the measurement device 130 and the control device 132. The measuring device 130 has an insertion unit that is inserted into the object, which has a detection unit that is movable in the depth direction. The detection unit has a main detector 134 and a sub-detector 136. The main detector 134 has a scintillator member 138 and a photomultiplier tube 140, and the sub-detector 136 has a scintillator member 142 and a photomultiplier tube 144. The scintillator member 142 surrounds the scintillator member 138 except for the horizontal direction of the scintillator member 138. The measuring device 130 has a signal processing circuit 152, which has a directivity forming unit 153. The directivity characteristic forming unit 153 executes non-coincidence processing using the output pulse of the sub-detector with respect to the output pulse of the main detector. The signal processing circuit 152 calculates the count rate or dose, and the data is transmitted to the control unit 132 via the communication units 154 and 156. The high voltage source 146 applies a high voltage to the photomultiplier tubes 140 and 144. The measuring device 130 includes a battery 150. According to this configuration, since the signal can be exchanged between the measuring device 130 and the control device 132 by wireless communication, the handling property is improved.

  FIG. 11 shows the measurement for natural ground 158. A hole is formed by excavating the slope of the natural ground 158, and the guide member 162 is inserted therein. The detection unit 164 is inserted into the interior 160. The detection unit 164 is attached to the tip of the rod (竿) 168, and the depth position of the detection unit 164 can be variably set by varying the depth of the rod 168 in the depth direction. The rod 168 is operated by a driving mechanism or is operated by a user. In this configuration, the detection unit is inserted in a direction different from the direction of gravity. Even in such a case, radiation can be measured at each depth position in the insertion direction. The detection unit 164 has directivity in the horizontal direction orthogonal to the depth direction. Therefore, in order to satisfactorily block radiation from the outside, it is desirable to insert the insertion unit in a direction approximately perpendicular to the slope of the natural ground 158. However, you may make it provide the mechanism which can change directivity characteristics according to a measurement place and a measurement direction.

  FIG. 12 shows a configuration example of the underwater survey system. This system measures radiation in water in the sea, etc., and effectively detects radiation from radioactive substances existing in water by shielding radiation from the outside (in the air). . The underwater survey system shown in FIG. 12 includes a measuring device 170 and a computing device. The arithmetic device has the same function as the arithmetic device 74 shown in FIG.

  The measuring device 170 has a floating body 174. It floats on the surface (sea surface) 178 of the sea 176. It may be fixedly installed. The floating body 174 includes a balloon or a floating bag. A support plate 182 is installed on the base 180 of the floating body 174, and the insertion unit is held by the support plate 182. The insertion unit has a hollow guide member 192 having a cylindrical shape. A weight 194 for lowering the center of gravity and stabilizing the posture of the insertion unit is provided on the inner bottom surface. The guide member 192 is made of a radiation transmitting material, has an airtight structure, and seawater does not enter the inside thereof. However, it is possible to configure so that seawater is taken into the interior.

  A detection unit 190 is provided inside the guide member 192 so as to be movable up and down. The detection unit 190 has basically the same structure as the detection unit shown in FIG. That is, it comprises a main detector, an upper sub-detector and a lower sub-detector. The installation depth of the detection unit 190 is variable depending on the winding amount of the wire 186 by the reel 184. Signals from the three photomultiplier tubes are sent to the communication circuit via the cable 188 and converted into radio signals. It is transmitted from the antenna 210 to the control device as radio waves. Reference numeral 212 denotes a support.

  According to this configuration, the dose can be measured at a designated depth position in the sea. A dose graph can be formed by measuring the dose while moving the detection unit 190 in the depth direction. In each measurement, radiation coming from the air is shielded, and radiation from a radioactive substance existing at a specific depth can be accurately measured. It is also possible to adopt another configuration in place of the measurement unit shown in FIG.

  30 measurement device, 32 control device, 34 measurement unit, 36 support unit, 42 measurement unit, 56 main detector, 58 upper sub-detector, 60 lower sub-detector, 73 directivity forming unit.

Claims (12)

An insertion unit including a detection unit that is inserted in a depth direction from the surface of an object such as soil and detects radiation inside the object;
A signal processing unit for processing a signal from the detection unit;
Including
The detection unit is a spatial unit for distinguishing and measuring extraneous radiation that has entered the inside of the target object from the outside through the surface of the target object and target radiation to be measured inside the target object. the main detector having a relationship includes a first sub-detector and the second sub-detector,
The signal processing unit includes a main detection signal output from the main detector , a first sub detection signal output from the first sub detector, and a second sub detection output from the second sub detector. a signal, based on, viewing including the directional characteristics forming unit to perform the directional pattern forming process of extracting a signal component of said target radiation removing or reduced while the signal component of the foreign radiation,
The main detector has a main scintillator member that is a disc-like scintillator member having a horizontal direction as a radial direction when the depth direction is a vertical direction,
The first sub-detector is a disc-shaped scintillator member that is provided on an upper side that is one side of the main scintillator member in the vertical direction and covers the entire main scintillator member from the upper side thereof, and is arranged in the horizontal direction. Having a first sub-scintillator member that is wider than the main scintillator member;
The second sub-detector is a scintillator member that is provided on a lower side that is the other side of the main scintillator member in the vertical direction, and that conceals the entire main scintillator member from the lower side thereof. Having a second sub-scintillator member that is wider than the main scintillator member;
The detection unit has a horizontal directivity characteristic over 360 degrees in the horizontal direction;
A radiation measurement system characterized by that. The system of claim 1, wherein
A ring-shaped opening is formed between the first sub scintillator member and the second sub scintillator member around the horizontal direction of the main scintillator member.
A radiation measurement system characterized by that. The system of claim 1 , wherein
The main detector has a main photodetector that detects light generated by the main scintillator member and outputs the main detection signal,
The first sub-detector includes a first sub-detector that detects light generated by the first sub-scintillator member and outputs the first sub-detection signal.
The second sub-detector has a second sub-detector that detects light generated by the second sub-scintillator member and outputs the second sub-detection signal.
A radiation measurement system characterized by that. The system of claim 1 , wherein
The main detector has a main photodetector that detects light generated by the main scintillator member and outputs the main detection signal,
Sub-light detection that detects light generated by the first sub-scintillator member and outputs the first sub-detection signal , detects light generated by the second sub-scintillator member and outputs the second sub-detection signal A vessel was provided,
A radiation measurement system characterized by that. The system of claim 1 , wherein
A moving mechanism for moving the detection unit in the depth direction is provided,
A radiation measurement system characterized by that. The system of claim 5, wherein
A control unit for controlling the position of the detection unit in the depth direction by controlling the moving mechanism;
A graph creation unit that creates a graph showing a relationship between depth and dose based on a plurality of radiation detection data acquired by varying the position of the detection unit;
A radiation measurement system comprising: The system of claim 5, wherein
The insertion unit includes a hollow member made of a material that is a member that extends in the depth direction and transmits radiation,
The detection unit is provided while being separated from the object in the internal space of the hollow member,
A radiation measurement system characterized by that. The system of claim 7 , wherein
The detection unit has a case containing the main detector, the first sub-detector, and the second sub-detector.
A radiation measurement system characterized by that. The system of claim 1 , wherein
The object is soil;
A support mechanism for supporting the insertion unit with respect to the soil was provided,
A radiation measurement system characterized by that. The system of claim 1 , wherein
The object is water;
A support mechanism for supporting the insertion unit with respect to the water is provided;
A radiation measurement system characterized by that. A formation process for forming a hole from the surface of the target soil ,
Inserting a detection unit into the hole;
Performing radiation detection using the detection unit at a plurality of depth positions inside the hole;
The target signal component corresponding to the target radiation emitted from the radioactive substance in the soil , which is the target object , by processing a plurality of signals obtained by detecting the radiation using the detection unit at the plurality of depth positions A signal processing step of extracting
Generating a graph indicating a relationship between depth and dose based on a plurality of target signal components corresponding to the plurality of depth positions;
Only including,
The detection unit includes a main detector having a spatial relationship for distinguishing and measuring extraneous radiation that has entered the soil from the outside through the surface of the soil and the target radiation, and a first sub-detection And a second sub-detector,
In the signal processing step, a main detection signal output from the main detector, a first sub detection signal output from the first sub detector, and a second sub detection output from the second sub detector. Based on the signal, a directional characteristic forming process for extracting the target signal component of the target radiation while removing or reducing the signal component of the extraneous radiation is performed,
The main detector has a main scintillator member that is a disc-like scintillator member that spreads in a horizontal direction when the depth direction is a vertical direction,
The first sub-detector is a disc-shaped scintillator member that is provided on an upper side that is one side of the main scintillator member in the vertical direction and covers the entire main scintillator member from the upper side thereof, and is arranged in the horizontal direction. Having a first sub-scintillator member that is wider than the main scintillator member;
The second sub-detector is a scintillator member that is provided on a lower side that is the other side of the main scintillator member in the vertical direction, and that conceals the entire main scintillator member from the lower side thereof. Having a second sub-scintillator member that is wider than the main scintillator member;
The detection unit has a horizontal directivity characteristic over 360 degrees in the horizontal direction;
The radiation measuring method characterized by the above-mentioned. A decontamination range determination method, comprising: determining a depth range of decontamination work performed on the soil based on the graph obtained by the radiation measurement method according to claim 11 .

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