JP6042627B2 - 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. 12 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. 13 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, the light is converted into an electric signal in the photomultiplier tube 26.

  When investigating radioactive contamination of an object, the detection probe as described above is brought close to the surface of the object, and in this state, radiation emitted 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. 12 and 13). 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 γ rays, in addition to γ rays from radioactive substances contained in the soil, γ rays from radioactive substances present in the atmosphere are also detected. Because it will do. 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. In any case, Patent Documents 1-3 do not disclose a technique for measuring radiation by inserting a detector into an object.

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

  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 includes an insertion unit that is inserted into the interior of a target object such as soil, the insertion unit including a detector that detects radiation in the target object, Provided at least on the surface side of the object in the periphery of the detector, and shields the radiation flying from the outside through the surface of the object into the object and entering the object in the object. And a shielding member that generates an in-object directional characteristic in the detector so that radiation from the existing radioactive material is detected.

  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 detector inside the object. At that time, the shielding member causes the in-object directivity characteristic to the detector. In other words, the shielding member acts to shield or reduce radiation (non-target radiation) flying from the outside to the inside of the target object and to detect radiation (target radiation) from the radioactive substance existing inside the target object. . 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, measurement accuracy can be improved because it is not easily affected by radiation from the outside.

(2) Target objects are soil (ground), water (sea, lake, river, pool, etc.), artificial structures (concrete blocks, waste, etc.), trees, 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. The shielding body shields at least radiation from the outside, and in that case, a downward hemispherical sensitivity characteristic may be formed. Desirably, a planar directivity pattern is formed. Using such directivity, dose measurement can be performed for a specific depth. The planar directivity may be formed over 360 degrees around the detector, or may be formed only in a specific azimuth range. According to the latter, the measurement which limited depth and direction can be performed. It is desirable to form a slit (opening) that exhibits a collimating action in the shielding member. In that case, you may comprise so that the height, width | variety, direction, etc. of a slit can be varied. 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 a scintillator detector, a GM tube, a semiconductor detector or the like. Extraction of the signal from the detector is performed by wire or wireless. The insertion unit is preferably configured as a waterproof / dustproof type.

(3) Preferably, the shielding member has a one-side portion provided on a surface side of the object within the periphery of the detector, and a surface side of the object within the periphery of the detector. And the other side portion provided on the opposite side, and the shielding member generates a directivity characteristic in which the main sensitivity direction is directed in a direction orthogonal to the depth direction as the in-object directivity characteristic of the detector.

  According to the above configuration, the shielding action is exhibited by the one side portion on one side (surface side) of the detector, and the shielding action is exhibited by the other side portion on the other side (opposite to the surface side) of the detector. Is done. As a result, a directivity characteristic in which the main sensitivity direction is directed in a direction orthogonal to the depth direction is generated as the in-object directivity characteristic of the detector. It is preferably a planar directivity. When the insertion unit is inserted in the vertical direction, the planar directivity can be referred to as horizontal directivity. In that case, the spread in the vertical direction in the directivity is defined by the distance and the length of the gap formed between the one side portion and the other side portion. When configuring a small shielding container that accommodates the detector, the upper part functions as the one side part, and the lower part functions as the other side part. The lower portion may be configured to be removable. When configuring a large shielding container that accommodates the detector, the upper side functions as one side part, and the lower side as the other side part, based on the depth at which the detector is currently located. Function.

  Preferably, the shielding member has a slit provided between the one side portion and the other side portion, and the detector detects radiation passing through the slit. The slit functions as a collimator. The slit may be a simple cavity or may be filled with a member that does not attenuate the radiation so much. The slit may be divided into a plurality of slit elements by a plurality of columns connecting the one side portion and the other side portion.

  Preferably, the detector and the shielding member constitute a movable body, and a moving mechanism for moving the movable body in the depth direction is provided. According to this configuration, the detector can be positioned at a specified depth or a fixed depth, and radiation can be measured there. It is also possible to measure radiation while moving the detector continuously or stepwise. As a moving mechanism, a mechanism using a wire (rope), a mechanism using a rack and a pinion, a mechanism using hydraulic pressure, a mechanism for inserting and removing a rod, and the like can be provided. It is desirable to provide a sensor for detecting the position of the movable body. In that case, for example, the momentum of the wire may be detected, or a distance sensor may be used.

  Preferably, a control unit that controls the position of the movable body in the depth direction by controlling the moving mechanism, and a depth based on a plurality of radiation detection data acquired by varying the position of the movable body. And a graph creation unit for creating a graph showing a relationship with the dose. According to this configuration, it is possible to measure radiation at a plurality of depth positions and express a dose change according to the depth change as a graph. Based on this, it is possible to easily specify to what depth the contaminated soil should be removed from the surface or dug up.

  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 movable body is separated from the object by an internal space of the hollow member. Is provided. According to this configuration, it is possible to prevent the problem that the object directly contacts the detector and the shielding member that configure the movable body. When the shielding member is made of lead, it is possible to prevent lead contamination on the object.

  Preferably, the shielding member has a hollow shape extending in the depth direction, the shielding member has a plurality of slits at a plurality of different depths, and each of the slits points in the object of the detector. As a characteristic, a directivity characteristic in which the main sensitivity direction is directed in a direction orthogonal to the depth direction is generated. According to this configuration, a plurality of slits are formed in the shielding member, and radiation can be measured at each depth using these slits. It is desirable to determine the distance between the slits and the shape of the slits so that no radiation crosstalk occurs between the slits.

  Preferably, the detector includes a moving mechanism that moves the detector in the depth direction inside the shielding member, and the detector is positioned with respect to a slit selected from the plurality of slits. In this method, radiation is detected at a specified depth by changing the correspondence between the detector and the slit.

  Preferably, a plurality of detectors are provided in the shielding member corresponding to the plurality of slits. According to this configuration, a moving mechanism is not required, and radiation can be measured simultaneously at a plurality of depths.

  Preferably, the insertion unit includes a hollow member made of a material that transmits radiation in the depth direction, and the shielding member is separated from the object in the hollow member. Provided. The hollow member is made of, for example, a resin or a light density metal (aluminum or the like).

  Preferably, the object is soil, and a support mechanism for supporting the insertion unit with respect to the soil is provided. The object is water, and a support mechanism that supports the insertion unit with respect to the water is provided. In this case, floating is preferably used.

(4) Preferably, the radiation measurement method includes forming a hole from the surface of the object, inserting a radiation detector into the hole, and a plurality of depths inside the hole. A step of detecting radiation by the detector at a position, and a step of generating a graph showing a relationship between depth and dose based on data obtained by detection of radiation at the plurality of depth positions. Including. When forming the hole, a tool such as a screw is used. The hole may be formed manually or a heavy machine may be used. The graph is configured as a curve graph or a bar graph, for example. Other expression forms may be employed. If the dose is measured for each depth at a plurality of geographical points, it is possible to perform three-dimensional dose mapping in the formation. Preferably, the decontamination method includes a step of determining a depth range of decontamination work performed on the soil based on the graph. 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 a figure which shows an example of dose distribution. It is sectional drawing which shows the other structural example of a detection unit. FIG. 4 is a perspective view of the detector assembly shown in FIG. 3. It is a figure which shows the other structural example of a detector assembly. 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 structural example of an array type | mold detector unit. 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. A portion (upper end portion) above the surface 29 in 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 insertion 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 insertion unit 34 through the support base 44, and the lower end thereof is connected to the detection unit 42. The detection unit 42 is suspended by a wire. Cables (signal lines, power cables, etc.) extending from the detection 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 (in the present embodiment, γ-rays) (not exactly attenuated accurately), for example, 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. Reference numeral 42A indicates the detection unit at the uppermost position, and reference numeral 42B indicates the detection unit at the lowermost position.

  The detection unit 42 includes a scintillator member 58, a shielding member 62 that wraps around the scintillator member 58, a hollow case 70 provided on the outside thereof, and the like. The scintillator member 58 is configured as, for example, a NaI scintillator. In this embodiment, the scintillator member 58 has a disk shape or a columnar shape. Similarly, the shielding member 62 has a cylindrical shape, and the case 70 is the same. The shielding member 62 is made of lead, for example, and exhibits an action of shielding (or attenuating) γ rays. The shielding member 62 is provided so as to surround the scintillator member 58 as a detector. However, a circular slit 66 exists around the horizontal direction when viewed from the scintillator member 58. The slit 66 functions as a collimator. Thus, the side peripheral surface of the scintillator member 58 becomes a radiation incident surface. One side (upper side) of the slit 66 is the upper part 62A, and the other side (lower side) of the slit 66 is the lower part 62B. The upper portion 62A and the lower portion 62B are separated with a slit 66 therebetween. However, a member for connecting the two may be provided in the slit 66. You may make it provide the support | pillar which consists of a shielding material or another material for every fixed direction in the slit 66. FIG. The shielding member 62 is configured as a member having a thickness of, for example, 2.5 cm around the scintillator member 58.

  A photomultiplier tube (PMT) 60 is provided above the scintillator member 58. It is arranged in a storage chamber formed in the upper part 62A. The shielding member 62 as a whole surrounds the entire periphery of the detection mechanism except for the slit 66 portion. You may make it put a filler in the inside of the shielding member 62. FIG. Since the photomultiplier tube 60 is arranged inside the shielding member 62 and an electronic circuit such as a preamplifier can be arranged in the shielding member 62, it is hardly affected by electromagnetic noise or the like. 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.

  The slit 66 is formed over an azimuth range of 360 degrees around the central axis of the scintillator member 58. The slit 66 has a certain height. Thereby, planar directivity characteristics (sensitivity characteristics) as indicated by reference numeral 68 can be obtained. It can also be called horizontal directivity. In this characteristic, the main sensitivity direction is the horizontal direction. The center point of the scintillator member 58 as a detector coincides with the intermediate height of the slit 66. The slit may be formed only in a specific azimuth range around the central axis of the scintillator member 58. According to this, it is possible to limit the directivity characteristics in the azimuth direction. The range may be variable, and the height of the slit 66 may be variable. According to these configurations, the directivity can be freely adjusted. In the present embodiment, since the horizontal directivity characteristic as shown in the figure is formed, 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 58, with high accuracy. That is, the position resolution is good in the depth direction.

  The upper side of the scintillator member 58 is covered with an upper portion 62A, thereby preventing or reducing the radiation that has entered the soil from the outside (in the air) through the surface 39 and reaching the scintillator member. This makes it possible to discriminate and detect radiation emitted from radioactive materials in the soil. A lower portion 62B exists below the scintillator member 58, thereby preventing or reducing radiation from deeper in the soil from reaching the scintillator member. That is, a horizontal directivity characteristic is formed, and radiation coming from the periphery in the horizontal direction when viewed from the scintillator member 58 can be selectively detected. Increasing the length of the slit (the length in the radial direction) can increase the collimating effect. The photomultiplier tube 60 is disposed with its lower surface, which is the light receiving surface, facing the upper surface of the scintillator member 58. There may be a light guide member between them. It is also possible to use an electronic circuit instead of the photomultiplier tube. It is desirable to provide a shielding film in a region other than the joint surface of the scintillator member 58 or to make the case 70 a light shielding structure so that extraneous light does not reach the photomultiplier tube 60 inadvertently. Since the guide member 40 is basically a dark room, it is advantageous in terms of extraneous light noise. The output signal of the photomultiplier tube 60 is sent to the control device 32 via a predetermined electronic circuit. A high voltage is applied to the photomultiplier tube 60 by the control device 32. Instead of the scintillator member 58, a known sensor such as a semiconductor detector or a GM tube may be provided.

Next, the control device 32 will be described. The signal processing circuit 72 is a circuit that processes output pulses from the photomultiplier tube 60, and includes an amplifier, a pulse height discriminator, and the like. The output pulse of the signal processing circuit 72 is input to the calculation unit 74. It has a counter and measures the count (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. Measurement result display units include dose rate (μSv / h), count rate (cpm or min ^-1 ),
And the radioactivity surface density (Bq / cm ² ). 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 photomultiplier tube 60. Reference numeral 82 denotes a power signal and a detection signal.

  In the present embodiment, 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. 2, 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. This provides dose data for each depth. If they are plotted, the dose graph shown in FIG. 2 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 shielded. Therefore, the measurement accuracy of the target radiation can be increased. However, if the lower portion 62B 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. 3 shows another configuration example of the detection unit. The detection unit 86 has a hollow case 88 having a cylindrical shape, and a detector assembly 89 is accommodated therein. The detector assembly 89 includes a scintillator member 90, a photomultiplier tube 98, and two shielding plates 92 and 94. A scintillator member 90 is sandwiched between two shielding plates 92 and 94, and a sandwich structure is employed. The upper shielding member 92 has a through hole 92 </ b> A in the center portion, and the tip of the photomultiplier tube 98 is inserted therein. The light receiving surface of the photomultiplier tube 98 is in close contact with the upper surface of the scintillator member 90. As a result, the light generated in the scintillator member 90 is taken into the photomultiplier tube 98, where the light is converted into an electrical signal. The shielding plates 92 and 94 each have a thickness of, for example, 2.5 cm. The scintillator member 90 has a disk shape, and its thickness 106 is, for example, several centimeters. The diameter 104 is about 10 cm, for example. The diameter of the shielding plates 92 and 94 is larger than the diameter 104, and a ring-shaped gap 102 is formed in the horizontal direction between them, thereby forming a ring-shaped slit 107. The slit 107 functions as a collimator, and a planar directivity characteristic, that is, a horizontal directivity characteristic 100 is generated in the scintillator member 90. In this configuration, the case 88 may have a light shielding structure.

  By appropriately variably setting the thickness 106 of the scintillator member 90 and the size of the gap 102, desired directivity can be generated. If the lower shielding plate 94 is removed, a downward hemispherical directivity characteristic can be formed. In that case, it is desirable to arrange the photomultiplier tube below the scintillator member 90. According to this, since the through hole 92A can be eliminated, radiation from above can be effectively shielded. However, since the scintillator member 90 has a flat shape spreading in the horizontal direction, the scintillator member 90 is more sensitive to radiation from the horizontal direction, whereas radiation from the vertical direction is used. Sensitivity to is reduced. Such a flat shape and the slit 107 combine to generate a sharp horizontal directivity characteristic. Instead of the scintillator member 90, a plurality of semiconductor sensors may be arranged side by side in the horizontal direction. FIG. 4 shows a perspective view of the detector assembly 89 shown in FIG.

  FIG. 5 shows another configuration example of the detector assembly. The detector assembly 108 has a disc-shaped scintillator member 110 that is sandwiched between two shielding plates 112 and 114. A notch extending in the vertical direction is formed at the end of the shielding plate 112, and the light guide member 118 is inserted therein. The lower part of the light guide member 118 is in close contact with the side surface of the scintillator member 110, and the upper part of the light guide member 118 is in close contact with the light receiving surface of the photomultiplier tube 116 in the lying position. When radiation enters the scintillator member 110, light is generated there, and the light is guided to the photomultiplier tube 116 via the light guide member 118. There, the light is converted into an electrical signal. Instead of the photomultiplier tube 116, an electronic circuit having the same function may be provided. It is also possible to use an optical fiber as the light guide member.

  FIG. 6 shows another configuration example of the soil survey system. The same components as those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. The soil survey system includes a measuring device 120 and a control device 32.

  The measuring device 120 includes an insertion unit 121 and a support unit 36. The insertion unit 121 is inserted into soil, and has a guide member 122 as a sheath. The guide member 122 is a hollow cylindrical member made of a member that transmits radiation. Inside, a shielding container 124 extending in the depth direction is provided. The shielding container 124 is made of a radioactive shielding material such as lead, and has a hollow cylindrical shape. That is, it is composed of a cylindrical side plate, a ceiling plate and a bottom plate. The upper part protrudes upward from the soil surface. The thickness of the shielding container 124 is, for example, 2.5 cm, and the inner diameter thereof is, for example, 10 cm. The shielding container 124 includes a slit row 134 including a plurality of slits 134a to 134 arranged at a predetermined interval in the depth direction. The first slit 134a is formed at a surface grazing depth D1. The second through sixth slits are formed at a depth of D2-D6, respectively. Each slit is a ring-shaped gap, and each slit generates a horizontal directivity characteristic in the scintillator member when the scintillator member is positioned at a corresponding position. In FIG. 6, the detection unit 126 is positioned at the position of the depth D4, and at this time, the fourth slit functions, thereby generating the horizontal directivity characteristic 138. It is a directional characteristic with the main sensitivity direction as the horizontal direction.

  The detection unit 126 is provided so as to be movable up and down in the internal space of the shielding container 124, and specifically is suspended by a wire 50. Therefore, by driving the wire 50, the detection unit 126 can be positioned at a depth position selected from among a plurality of depth positions (D1-D6). The control device 32 sets the depth position based on the output signal of the depth detector 54. The detection unit 126 has a case 132 in which a scintillator member 128 and a photomultiplier tube 130 are arranged. Since the detection unit 126 does not have a shielding member as shown in FIG. 1, its raising / lowering drive is relatively easy. However, since the shielding container 124 is a fairly heavy structure, it is desirable to install the shielding container 124 using a heavy machine. The dose graph 139 shown in FIG. 7 can be generated by measuring radiation at a plurality of depth positions by the system shown in FIG. The graph 139 is a bar graph.

  FIG. 8 shows still another configuration example of the soil survey system. The measurement unit 140 includes a cylindrical guide member 122 extending in the depth direction and a cylindrical shielding container 124. The shielding container 124 has a slit row 134. A plurality of detectors 142a-142f (detector array 142) are provided corresponding to the plurality of slits 134a-134f constituting the same. In this configuration, radiation can be measured simultaneously using a plurality of detectors 142a-142f at a plurality of depth positions. A plurality of detection signals output from the plurality of detectors 142a to 142 are processed in parallel by the signal processing circuit 72A. The high voltage source 80A applies a high voltage to each of the plurality of detectors 142a to 142f.

  FIG. 9 shows a modification of the system shown in FIG. Wireless communication is performed between the measuring device 144 and the control device 32. The measuring device 144 includes a scintillator member 145 and a photomultiplier tube 146, and a high voltage from a high voltage source 148 is applied to the photomultiplier tube 146. It is operated by the battery 150. Those configurations may be arranged in the measurement unit. The output signal of the photomultiplier tube 146 is processed by the signal processing circuit 152, and the processed signal is transmitted to the control device 32 via the communication unit 154 and the communication unit 156. The signal is processed by the calculation unit 74. A control signal from the control unit 78 is also sent to the measuring device 144 via the communication unit 156 and the communication unit 154.

  FIG. 10 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 includes a scintillator member 166, which has a planar directivity characteristic orthogonal to the depth direction, as described above. 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. 11 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. 11 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 of the sea 176 (sea surface). 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 has a scintillator member 196, a shielding member 200, and a case 208, and a part of the shielding member 200 is a slit 192. This functions as a collimator, and a horizontal directivity characteristic as indicated by reference numeral 206 is formed.

  The installation depth of the detection unit 190 is variable depending on the winding amount of the wire 186 by the reel 184. The signal from the photomultiplier tube 198 is sent to the communication circuit via the cable 188 and converted into a radio signal. 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 in the scintillator member 196, radiation from a radioactive material existing in the sea, particularly a radioactive material having a depth similar to the depth of the scintillator member 196 (γ Line) can be detected with high accuracy. Instead of the measurement unit shown in FIG. 11, it is possible to provide the measurement unit shown in FIG. 6 or FIG.

  30 measurement device, 32 control device, 34 detection unit, 36 support unit, 42 measurement unit, 58 scintillator member.

Claims (12)

A hollow member that is inserted from the surface of an object such as soil into the inside thereof and extends in the depth direction, and is made of a material that transmits radiation;
An insertion unit as a movable body provided while being separated from the object in the internal space of the hollow member;
Including
The insertion unit is
A detector for detecting radiation from the object;
One side portion provided on one side which is the surface side of the object in the periphery of the detector, and the other side which is the opposite side to the surface side of the object in the periphery of the detector A shielding member that generates a directivity characteristic in which a main sensitivity direction is directed in a direction orthogonal to the depth direction, as a directivity characteristic of the detector,
A movable body case that contains the detector and the shielding member and is configured to transmit radiation;
A radiation measurement system comprising: The system of claim 1, wherein
The detector includes a scintillator member having a disk shape,
The detector includes a photodetector that is provided on one side or the other side of the scintillator member and detects light generated by the scintillator member.
A radiation measurement system characterized by that. The system of claim 1, wherein
The insertion unit is inserted in a direction perpendicular to the surface of the object;
Before SL-oriented characteristic is horizontal directional characteristics,
A radiation measurement system characterized by that. The system of claim 1, wherein
The shielding member has a slit provided between the one side portion and the other side portion;
The detector detects radiation passing through the slit;
A radiation measurement system characterized by that. The system of claim 1, wherein
A moving mechanism for moving the movable body 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 movable body in the depth direction by controlling the moving mechanism;
A graph creating 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 movable body;
A radiation measurement system comprising: The system of claim 2, wherein
The one wherein in the side portion and the other side portion scintillator member is sandwiched, the sandwich structure by which they are constituted,
A radiation measurement system characterized by that. The system of claim 2, wherein
The movable body case has a light shielding structure;
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 mechanism for supporting the insertion unit with respect to the water and having a floating body that floats on the water is provided.
A radiation measurement system characterized by that. A formation process for forming a hole in the vertical direction from the surface of the soil as an object,
Providing a hollow member made of a material that transmits radiation in the hole;
Inserting a movable body having a radiation detector into the hollow member;
Detecting radiation by the radiation detector at a plurality of depth positions inside the hollow member; and
Generating a graph indicating a relationship between depth and dose based on data obtained by detection of radiation at the plurality of depth positions;
Including
The movable body is
One side portion provided on one side that is the surface side of the object within the periphery of the radiation detector, and the other side that is opposite to the surface side of the object within the periphery of the radiation detector A shielding member that produces a directivity characteristic in which a main sensitivity direction is directed in a direction orthogonal to the depth direction, as a directivity characteristic of the radiation detector,
A movable body case that contains the radiation detector and the shielding member and is configured by a member that transmits radiation;
A radiation measurement method comprising:   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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