JP2014112066A - Radiation source detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a direction in which a radiation source is located, using a portable radiation meter.SOLUTION: A screen 200, in which a probe P is inserted, is placed on a table 400 in the upright position. The table 400 is rotated intermittently and a dose of radiation is measured in every direction. The dose of radiation in every direction in each height is measured while shortening a linear dimension of a support 402.

Description

  The present invention relates generally to measurement of radiation contamination, and more particularly to a radiation source detection method that is convenient for searching for spotted radiation sources.

  The accident at the Fukushima nuclear power generation facility caused by the March 2011 Tohoku-Pacific Ocean Earthquake and Tsunami (Great East Japan Earthquake) has resulted in continuing to release a large amount of radioactive material into the environment. Yes.

  Decontamination work has begun in earnest along with the reconstruction work in the disaster area. Before starting the decontamination work, it is efficient to identify the contaminated areas and spots and proceed with the decontamination work using an optimal decontamination method. If decontamination is difficult, it is necessary to consider an appropriate construction method to shield the contamination source.

  A radiation meter is used to determine the contamination status. Various types of radiation measuring instruments are available. For example, an available portable radiation measuring instrument equipped with a probe is exemplified by the trade names “Multi Radiation Monitor”, “NaI Scintillation Survey Meter”, “GM Pancake Probe” (sold by Toyo Medic Co., Ltd.), “Survey Meter Probe” (LUDLUM). “RadEye-B20” manufactured and sold by Seiko EG & G Co., Ltd. can be obtained as a portable multipurpose survey meter having a rectangular box-shaped detector as another form.

  When measuring the radiation dose using a radiation measuring device, it is preferable to shield the surroundings of the radiation measuring device in order to avoid the influence of the surroundings. The applicant of the present application has proposed a shield suitable for surrounding the radiation measuring instrument (Patent Document 1). By shielding the detection part of currently available radiation measuring instruments, it is possible to pinpoint the radioactive contamination state without being affected by the surroundings. Moreover, the effect of decontamination can be grasped by measuring the radiation dose using a shield before and after construction of decontamination work.

JP 2012-159517 A

  After performing decontamination work, the decontamination effect expected before decontamination may not be obtained. That is, the results may not be obtained despite the expectation that decontamination would reduce the radiation dose to this extent. One possible cause for this is the presence of a radiation source (typically a hot spot) in the vicinity.

  Obtaining a clue as to such a possibility that a radiation source exists and where it exists is important for improving the accuracy of the subsequent countermeasures.

  An object of the present invention is to provide a radiation source detection method capable of finding an orientation in which a radiation source is located using a portable radiation measuring instrument.

  It is a further object of the present invention to provide a radiation source detection method capable of specifying a location where a radiation source exists using a portable radiation measuring instrument.

The above technical problem is, according to one aspect of the present invention,
A shielding step of shielding the detection unit with a radiation shield that surrounds the detection unit of the portable radiation measuring instrument and includes a radiation passage window provided facing a part of the detection unit;
A rotating step of rotating the radiation shield;
This is achieved by providing a radiation source detection method comprising measuring a radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield.

  By providing a radiation passage window in the radiation shield surrounding the detection part of the portable radiation measurement device, the radiation measurement device reacts to the radiation that has entered through the radiation passage window. It is known that radiation has straightness. Therefore, when the radiation source is in the direction facing the radiation passage window of the shield, the radiation measuring device indicates a high radiation dose. On the other hand, when there is no radiation source in the direction in which the radiation passage window of the shield is directed, the radiation measuring device indicates a low radiation dose.

  By using this characteristic, it is possible to know in which direction the radiation source exists by measuring the radiation dose at multiple rotational positions spaced in the rotational direction while rotating the radiation shield. it can.

The above technical problem is, according to another aspect of the invention,
A shielding step of shielding the detection unit with a radiation shield that surrounds the detection unit of the portable radiation measuring instrument and includes a radiation passage window provided facing a part of the detection unit;
A first rotation step of positioning the radiation shield at a first point and rotating the radiation shield;
A first measurement step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the first point;
A first direction specifying step for obtaining a first direction having the highest radiation dose measured in the first measuring step; a second rotating step for positioning the radiation shield at a second point and rotating the radiation shield;
A second measuring step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the second point;
A second direction specifying step for obtaining a second direction having the highest radiation dose measured in the second measuring step; a third rotating step for positioning the radiation shield at a third point and rotating the radiation shield;
A third measurement step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the third point;
A third direction specifying step for obtaining a third direction having the highest radiation dose measured in the third measurement step;
This is achieved by providing a radiation source detection method including a radiation source position specifying step for obtaining a radiation source position where the first direction, the second direction, and the third direction intersect each other.

  Other objects and advantages of the present invention will become apparent from the detailed description of the preferred embodiments described below.

It is a figure for explaining the example which measures the radiation dose of a road joint or a crack, for example by combining with the shield of the 1st reference example, and a cylindrical shield main part. It is a top view of the shield of the 1st reference example. It is a perspective view of the shield of the 1st reference example. It is the figure which opened and closed the radiation passage window of the shield of the 1st reference example, and was a figure which carried out the section of the door for adjusting the opening. It is the side view illustrated in the state which combined the shielding body of the 1st reference example, and the cylindrical shielding main body. For example, it is sectional drawing for demonstrating the state which installs in the joint part of a road and measures the radiation dose of a joint. For example, it is a figure for demonstrating operation which installs the shield of the 1st reference example in the joint part of a road, operates a door, and adjusts the opening degree of a radiation passage window. It is a figure for demonstrating measuring the radiation dose of the joint of a road simply, for example by using the shielding body of a 1st reference example. It is a perspective view of the shield of the 2nd reference example. It is a side view of the shield of the 2nd reference example. It is a top view of the shield of the 2nd reference example. FIG. 12 is a cross-sectional view of the shielding body of the second reference example, and is a cross-sectional view taken along line X12-X12 of FIG. It is a figure for demonstrating the example which detects the radiation intrusion through the clearance gap between a vertical wall, a floor | bed, and a ceiling which prescribe | regulates indoor space, and a joint using the shield of a 2nd reference example, and measures the radiation dose. It is sectional drawing of the site | part pointed by the arrow X14 of FIG. It is sectional drawing of the site | part pointed by the arrow X15 of FIG. It is a figure for demonstrating an example of the table which can be used effectively for the measurement of the radiation dose using the shield of the 2nd reference example. It is a figure for demonstrating the 1st Example which is an application example of the table shown in FIG. It is the figure which looked at the example of use illustrated in FIG. 16 from the top. It is a figure for demonstrating the other example of the example of application of the table shown in FIG. It is the figure which looked at the example of use illustrated in FIG. 19 from the top. It is a side view of the modification of the shield of the 2nd reference example. It is a top view of the modification shown in FIG. It is a figure for demonstrating the 2nd Example which discovers a hot spot by a three-point measuring method using a 2nd reference example and its modification.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

First reference example (FIGS. 1 to 8) :
The portable radiation shield 100 of the first reference example is typically used as an auxiliary tool for measuring a radiation dose in a narrow gap on a lateral surface such as a road joint, a crack, and a ground crack. More specifically, it is suitably used in combination with the cylindrical shielding body 2 (see FIG. 1 attached to the present specification) opened downward as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2012-159517) described above. The Since the cylindrical-shaped shielding main body 2 is disclosed in detail in Patent Document 1, the detailed description of the shielding main body 2 is omitted by using the description of Patent Document 1 in this specification, and only the outline thereof is described. .

  Referring to FIGS. 1, 5, and 6, the shielding main body 2 has a shielding material S surrounded by an outer skin 4 (FIG. 6) made of a stainless steel plate, and lead is adopted as the shielding material S. . The shield body 2 can be carried with its handle 6 in hand, and is placed in a radiation measurement place, and a cylindrical probe P of a portable radiation measuring instrument is inserted into the shield body 2 so as to surround the probe P. It is possible to measure the radiation dose in a state where is shielded. The outer shape (circular cross section) of the shield body 2 shown in the drawing is merely an example, and the cross section shape of the shield body 2 is arbitrary, and may be, for example, a polygon. The shielding body 2 provided with the handle 6 has a lid 8 having an opening into which the cylindrical probe P can be inserted. With the lid 8 removed, the detection unit in the rectangular box shape of the portable multipurpose survey meter is provided. It is possible to adopt a usage form in which the detector is placed on the shield body 2 or the detector of the radiation measuring instrument having a pancake-shaped detector is placed on the shield body 2.

  The shield 100 of the first reference example is used in a state where it is laid under the cylindrical shield body 2 described above, as best seen in FIG. Therefore, when the shielding body 100 of the first reference example is referred to as a “shielding tray”, the shielding tray 100 includes a flat disk-shaped main body 102 and a vertical extension extending upward to the outer peripheral edge of the disk-shaped main body 102. And a flange 104. The diameter of the disc-shaped main body 102 is substantially the same as the diameter of the cylindrical shielding main body 2 described above. When the cylindrical shielding body 2 is placed on the shielding tray 100, the lower end portion of the cylindrical shielding body 2 is loosely fitted to the vertical flange 104, so that the relative relationship between the cylindrical shielding body 2 and the shielding tray 100 is relative. Positioning is performed. In the illustrated example, the vertical flange 104 is continuous in the circumferential direction, but may be constituted by a plurality of vertical flanges spaced in the circumferential direction.

  Referring to FIGS. 2 and 3, the disc-shaped main body 102 of the shielding tray 100 has a rectangular opening 106 having a shape cut out in the radial direction, and this opening 106 is formed laterally from the outer peripheral edge of the disc-shaped main body 102. It is open to. As best seen from FIG. 6, the disk-shaped main body 102 is filled with a shielding material S in the inner space of the outer skin 102 a made of a stainless steel plate. A typical example of the radiation shielding material S is lead. It may be filled with molten lead or small lead particles. When filling small lead grains, a gap between adjacent lead grains may be filled with a fluid shielding material (for example, water).

  Referring to FIGS. 1 and 2, a sliding door 108 having a rectangular shape in a plan view is disposed in the aforementioned rectangular opening 106 of the disk-shaped main body 102, and the rectangular opening 106 and the sliding type are adjusted by adjusting the position of the door 108. The width of the slit SL defined by the door 108, that is, the opening of the radiation passage window can be adjusted steplessly. Of course, a configuration in which the width of the slit SL, that is, the opening of the radiation passage window is adjusted stepwise may be employed. The door 108 can be fully closed. With the door 108 fully closed, the shielding main body 2 becomes a bottomed shielding body having a bottom wall by placing the shielding main body 2 thereon.

  A plate 102b for supporting the sliding door 108 is fixed to the bottom of the outer peripheral portion of the rectangular opening 106 (FIG. 3). The sliding door 108 has a flat rectangular body 108a complementary to the opening 106 and a handle plate 108b extending obliquely upward from one end of the rectangular body 108a. An operation opening 108c through which a finger can be inserted is formed at the outer end. The outer skin of the rectangular main body 108a and the handle plate 108b of the sliding door 108 are made of stainless steel plate, and the outer skin of the rectangular main body 108a is filled with the radiation shielding material S (FIG. 4). A typical example of the radiation shielding material S is lead. The space surrounded by the outer skin of the stainless steel plate may be filled with molten lead or may be filled with small lead particles. When filling small lead grains, a gap between adjacent lead grains may be filled with a fluid shielding material (for example, water).

  A typical application example of the shielding tray 100 of the first reference example will be described with reference to FIGS. 1, 6, and 7. In the figure, a reference symbol Op indicates a gap on a horizontal surface such as a crack formed on a road joint or a concrete floor. The shield 100 is placed in the gap Op. By operating the door 108 of the shielding tray 100 to adjust the width of the slit SL defined by the rectangular opening 106 of the shielding body 100 and the door 108, the longitudinal direction of the slit SL and the gap Op are aligned (FIG. 7). . The slit SL constitutes a radiation passage window that allows radiation to enter. Next, as shown in FIG. 1, the cylindrical shielding body 2 is placed on the shielding tray 100. And the probe P is inserted in the shielding main body 2 (FIG. 6), and a radiation dose is measured. As a result, the radiation dose in the gap Op such as a crack formed on a road joint or a concrete floor surface can be measured while the probe P is shielded from surrounding radiation.

  With reference to FIG. 8, the most preferable embodiment of the radiation measurement of the gap Op such as a crack formed on a road joint or a concrete floor will be described. FIG. 8I shows a gap Op such as a road joint. Although not shown in FIG. 8, in order to confirm the shielding effect of the cylindrical shielding body 2 in the field, first, without using the cylindrical shielding body 2 and the shielding tray 100, the radiation dose in the gap Op portion. Was measured with an unshielded probe P. This is referred to as “background radiation dose (dose equivalence rate) in an unshielded state”, and the measured value is referred to as “measured value A”. A relatively large lead plate (shielding board) was laid on the road including the gap Op, and the probe P was inserted into the cylindrical shielding body 2 placed thereon to measure the radiation dose. This is called “background radiation dose (dose equivalence rate) in a completely shielded state”, and the measured value is referred to as “measured value B”. This “background radiation dose (dose equivalence rate) in a completely shielded state” can also be measured by fully closing the door 108 of the shield tray 100.

  "Background radiation dose in the unshielded state (dose equivalent rate)" (measured value "A") and "Background radiation dose in the completely shielded state (dose equivalent rate)" (measured value) With “B”), the shielding performance of the cylindrical shielding body 2 can be known. Specifically, the formula: {1- (B / A)} is the shielding rate of the cylindrical shielding body 2. When the shielding effect of the cylindrical shielding body 2 is high, the shielding rate of the cylindrical shielding body 2 is approximately “1”.

  Referring to (I) of FIG. 8, the cylindrical shielding body 2 is placed on the gap Op without using the shielding tray 100, and the probe P is inserted into the cylindrical shielding body 2 so that the gap Op is set. Measure the radiation dose. This is called “joint surface radiation dose (dose equivalence rate)”, and the measured value is referred to as “measured value C”.

  Next, a shielding material, specifically, a rectangular parallelepiped lead block 20 is inserted into the gap Op. A plurality of types of lead blocks 20 having different thicknesses are prepared, and lead blocks 20 having thicknesses suitable for the width of the gap Op at the site are inserted ((II) in FIG. 8). Next, as shown in (III) of FIG. 8, the radiation dose is measured by placing the cylindrical shielding body 2 at a position facing the lead block 20 without using the shielding tray 100. This is referred to as “surface radiation dose (dose equivalent rate) of the gap Op in a state where it is shielded by the lead block 20”, and the measured value is referred to as “measured value D”.

Next, the lead block 20 is taken out from the gap Op, the shielding tray 100 is placed on the gap Op without the lead block 20, and the width of the slit SL of the shielding tray 100 is adjusted to match the width of the gap Op. Next, the cylindrical shielding body 2 is placed on the shielding tray 100, and the probe P is inserted into the cylindrical shielding body 2 to measure the radiation dose. This is called “surface radiation dose of the joint using a shielding tray (dose equivalence rate)”, and the measured value is referred to as “measured value E”.

  When the shielding rate of the cylindrical shielding body 2 can be regarded as approximately “1”, the measured value B means the background radiation dose (dose equivalence rate). On the other hand, the measured value C is the radiation dose in the gap Op, and the measured value D is a value obtained by shielding the gap Op with the lead block 20. Therefore, it can be said that the radiation dose (dose equivalence rate) obtained by the formula: C−D + B is the radiation dose in the gap Op.

  If the value (C−D + B) is equal to the measured value E when the shielding tray 100 is used, the shielding tray 100 is used, and a value F (F) obtained by subtracting the background radiation dose from the measured value. = EB) means the original radiation dose of the gap Op.

When actually tested in a radioactively contaminated area, the measured values were as follows.
(a) Measured value A: 1.272 μSv / h;
(b) Measured value B: 0.098 μSv / h;
(c) Measured value C: 0.603 μSv / h;
(d) Measured value D: 0.448 μSv / h;
(e) Measured value E: 0.235 μSv / h.

  Obtaining the above measurement results, the shielding performance of the portable cylindrical shielding body 2 used was 92.27%. It should be noted that the portable radiation measuring instrument can be considered to have a satisfactory shielding performance, taking into account that the allowable error is about 8%.

  Next, when (C−D + B) is calculated, a value of 0.253 μSv / h can be obtained. That is, CD−B = 0.253. The value 0.253 and the measured value E value 0.235 are approximate values. Based on this, it can be concluded that the use of the shielding tray 100 makes it easy to obtain the original radiation dose of the gap Op.

  In the measurement of the gap Op using the portable shielding tool of the combination of the shielding main body 2 and the shielding tray 100 having high shielding efficiency, the work at the site is sufficient in two steps. That is, first, a relatively large lead plate (shielding board) is laid on the road including the gap Op, and the probe P is inserted into the cylindrical shielding body 2 placed thereon to measure the radiation dose. To do. That is, the “background radiation dose (dose equivalence rate) in a completely shielded state” is measured (measurement value B). Next, the radiation dose is measured using a shielding tool that is a combination of the shielding main body 2 and the shielding tray 100. That is, the “surface radiation dose (dose equivalence rate) of the joint using the shielding tray” is measured (measurement value E). Then, the original radiation dose of the gap Op is obtained by calculation based on the formula: (EB).

  Before and after performing the decontamination work on the gap Op, the effect of the decontamination work can be presented numerically by obtaining the radiation dose of the gap Op using a shielding tool of a combination of the shielding main body 2 and the shielding tray 100. . Similarly, when the gap Op is decontaminated or is shielded by filling the gap Op with an appropriate shielding material, the shielding main body 2 and the shielding tray 100 are not included before and after the shielding material is filled. By using a shielding tool in combination with, the radiation dose in the gap Op can be obtained and the effect of the shielding work can be presented numerically.

  The shielding body 100 of the first reference example is separate from the cylindrical shielding body 2 and is used in combination as necessary. Instead, the shielding body 100 and the cylindrical shielding body 2 are integrated. It may have a different structure. That is, a bottom wall that closes the lower end of the cylindrical shielding body 2 that opens downward may be provided, and the above-described slit SL, that is, a radiation passage window may be provided on the bottom wall. Also in this modified example, a door for adjusting the width of the slit SL may be provided.

  The radiation measurement accompanied by the shielding by the combination of the shielding body 100 and the cylindrical shielding body 2 of the first reference example can also be applied to the measurement of the radiation that enters the room through a crack in the floor surface of the room, for example. Moreover, it is applicable also to the measurement of the radiation dose of the crack (crack) of the outer wall of a building. When measuring the amount of radiation in a vertical surface such as a wall or a gap, the shielding tray 100 may be fixed to the wall using an adhesive tape or the like.

Second Reference Example (FIGS. 9 to 22) :
The portable radiation shield 200 of the second reference example is typically used to detect where a radiation intrusion into a room occurs and to measure the amount of radiation entering the room. Referring to FIG. 9, shield body 200 of the second reference example has shield body 202 having an elongated cylindrical outer shape, but the outer contour may be arbitrary and may be polygonal in cross section. As in the first reference example, the main body 202 is filled with a shielding material (lead) S in a space surrounded by the outer skin of a stainless steel plate (FIG. 12), and has a shielding function. As best seen from FIG. 12, one end (lower end in FIG. 9) of the shield 200 is closed, while the other end (upper end in FIG. 9) of the shield 200 is open. The probe P described above can be inserted into the shield 200 through the opening 204 at the other end.

  A handle H is fixed to an intermediate portion in the longitudinal direction of the elongated cylindrical shielding body 202, and the handle H is arranged in parallel with the body 202. The shield 200 can be handled by holding the handle H with one hand.

  In the portable radiation shield 200 of the second reference example, an elongated slit SL is formed in the peripheral wall in the vicinity of the closed end face 206 of the shield main body 202, and this slit SL is formed at one end of the main body 202 (the lower end of FIG. 9). ) In the longitudinal direction, and constitutes a radiation passage window that allows invasion of radiation. The length dimension of the slit SL is set to a value that matches the height dimension of the radiation detection region of the probe P.

  Referring to FIG. 9, guide plates 210 and 212 are provided at one end and the other end of the cylindrical main body 202. The pair of guide plates 210 and 212 includes a first guide edge 210a (212a) that extends straight, and a second guide edge 210b (212b) that extends in parallel with the first guide edge 210a (212a). And a third guide edge 210c (212c) orthogonal to the first and second guide edges 210a (212a) and 210b (212b), and two portions where these intersect each other are the first and second Further, linear corner edges 210d (212d) and 210e (212e), which are notched straight at an angle of 45 ° with respect to the guide edges 210a (212a) and 210b (212b), are further provided. The above-described slit SL is disposed at a position corresponding to one corner edge 210e (212e).

  In this regard, referring to FIG. 11, which is a plan view of the cylindrical body 202, two perpendicular lines passing through the center O of the cylindrical body 202, which are perpendicular to two reference edges 210 b and 210 c adjacent to each other. The crossing angle is 90 °, but the slit SL is positioned on the center line L extending in the radial direction from the center O at an angle (45 °) that halves the crossing angle. As a preferred embodiment, as shown in FIGS. 9 and 10, a mark 214 (a line in this reference example) indicating the position of the slit SL may be provided on the cylindrical main body 202 and / or the guide plates 210 and 212.

  The radiation shield 200 of the second reference example is designed so that it can be suitably applied to a radiation measuring instrument including the cylindrical probe P described above. The shield 200 of the second reference example employs a configuration in which the guide plates 210 and 212 are provided at the end of the shield body 202, but may be provided on the peripheral wall of the shield body 202 or the outer shape of the cylindrical body 202. You may employ | adopt the same shape as the guide plates 210 and 212 mentioned above as a shape. Further, it is needless to say that the radiation shield 200 of the second reference example can be changed in design in order to be applied to other types of radiation measuring devices. If the measuring device main body and the detector are radiation measuring devices having separate structures, a shape in which the detector can be inserted may be employed as in the shield 200 of the second reference example. If the measuring instrument main body and the detector are a radiation measuring instrument having an integral structure, a shape in which the measuring instrument can be inserted or the detecting portion of the measuring instrument can face the slit SL may be adopted.

  13 to 20 show specific application examples of the radiation shield 200 of the second reference example. In the figure, reference numeral 300 indicates an indoor space. This indoor space 300 is defined by a vertical wall material 302 (typically a vertical wall board), a floor 304 and a ceiling 308 (FIG. 17). The part indicated by the arrow X14 in FIG. 13 and FIG. 14 show a state in which the slit SL faces the boundary between the column 306 and the vertical wall board 302 and the radiation intrusion from this boundary is measured. At this time, as best seen from FIG. 14, the side edges 210 b (212 b) and 210 c (212 c) of the guide plate 210 (212) of the shield 200 are brought into contact with the pillar 306 and the vertical wall board 302. Thus, the slit SL can be directed to the boundary between the column 306 and the vertical wall board 302. And the penetration | invasion of the radiation in the longitudinal direction whole region of the boundary of the pillar 306 and the vertical wall board 302 can be measured by moving the shielding body 200 which accommodated the probe P to an up-down direction.

  The part indicated by the arrow X15 in FIG. 13 and FIG. 15 show a state in which the slit SL faces the boundary between the lower end edge of the vertical wall board 302 and the floor 304 and the radiation intrusion from this boundary is measured. . At this time, as best understood from FIG. 15, the guide edges 210 b (212 b) and 210 c (212 c) of the guide plate 210 (212) of the shield 200 that extend perpendicularly to each other are connected to the vertical wall board 302 and the floor 304. By making contact, the slit SL can be directed to the boundary between the vertical wall board 302 and the floor 304. Then, by moving the shield 200 containing the probe P in the lateral direction along the floor 304, it is possible to measure radiation intrusion in the entire longitudinal direction of the boundary between the floor 304 and the vertical wall board 302. The gap between the upper end of the vertical wall board 302 and the ceiling 308 may be measured in the same manner. Since the guide edges 210b (212b) and 210c (212c) of the guide plate 210 (212) perpendicular to each other are measured in contact with the vertical wall board 302 and the floor 304, the vertical wall board 302 and the floor 304 and the probe are measured. The separation distance (measurement distance) from P can be made constant.

  The operator holding the shield 200 with one hand and moving it up and down causes fatigue as the number of times increases. In order to reduce this work, it is preferable to prepare the table 400 of FIG. A preferred table 400 will be described with reference to FIG. The table 400 includes a column 402 extending vertically, a plurality of legs 404 (four legs 404 in this reference example) provided at the lower end of the column 402 and extending in the radial direction, and a horizontal provided at the upper end of the column 402. The support column 402 is extendable and contractable. Preferably, the support column 402 can be expanded and contracted stepwise at a predetermined pitch, that is, at equal intervals. Of course, the length dimension of the column 402 may be adjusted steplessly.

  The horizontal plate 406 is preferably rotatable 360 °. Further, it is preferable to provide a lock means 410 for fixing the rotational position of the horizontal plate 406. The horizontal plate 406 may be rotated steplessly, or a latch mechanism that temporarily fixes the rotational position at every predetermined angle may be provided. Further, the plurality of legs 404 can be folded upward with the base end as the center according to the storage or measurement location of the table 400, and a caster 408 is provided at the tip of each leg 404. preferable.

  FIG. 17 is a diagram showing a state in which radiation intrusion at the corners between the vertical wall boards 302 and 302 is measured using the shield 200 placed on the horizontal plate 406 of the table 400, and FIG. 18 is a plan view. FIG. The shield 200 into which the probe P is inserted has a horizontal plate 406 (table) with a slit SL, which is a window allowing radiation intrusion, facing down and an end opening 204 through which a cord extending from the probe P passes up. 400).

  The radiation measurement operation using the table 400 is as follows. That is, by measuring the radiation dose at each height position from a high position to a low position while shortening the length dimension of the support column 402 step by step, each measurement height position and the height position are measured without a measure. There is an advantage that it is easy to associate and record the radiation dose in the recording. Of course, since it is not necessary to lift the shield 200 by hand, it is needless to say that the burden on the operator can be reduced. Of course, the radiation dose may be measured at each height position from a low position to a high position while increasing the length of the support column 402 stepwise.

  FIG. 19 is a diagram showing a state in which the radiation intrusion is measured at the joint portion between the vertical wall boards 302, 302 arranged side by side using the shield 200 placed vertically on the horizontal plate 406 of the table 400. FIG. 20 is a plan view. As best understood from FIG. 20, the slit SL is aligned between the vertical wall boards 302 and 302 by bringing the corner edge 210e (212e) of the guide plate 210 (212) of the shield 200 into contact with the vertical wall board 302. Can be directed to the eyes. Also in this case, by measuring the radiation dose while gradually shortening the length dimension of the support column 402, the measurement height position and the radiation dose at each height position can be easily recorded and shielded without a measure. Since there is no need to lift the body 200 by hand, the burden on the operator can be reduced. Since the corner edge 210e (212e) of the guide plate 210 (212) of the shield 200 is measured in contact with the vertical wall board 302, the separation distance (measurement distance) between the vertical wall board 302 and the probe P is measured. Can be constant.

  In the measurement of the joint portion between the upper edge of the vertical wall board 302 and the ceiling 308, the probe P is inserted into the shield 200 with the shield 200 placed horizontally on the horizontal plate 406 of the table 400. Measurement work.

  As can be understood from the application example described above, an existing measuring instrument is used to detect radiation intrusion from a joint of the vertical wall board 302, the floor 304, and the ceiling 308 that divides the space 300, for example, from a crack in the vertical wall board 302 or the floor 304. And can be measured with the probe P shielded. For example, when a board 300 having a radiation shielding function is installed on the wall surface, floor and / or ceiling instead of decontamination to create a shielded space 300, shielding is performed against the joints and corners of the shielding board after the construction. By measuring the radiation dose through the slit SL which is a radiation passage window of the body 200, it is possible to find out whether the shielding board is installed properly or where the installation is defective.

First embodiment :
As an embodiment of the present invention, for example, at the center of the indoor space 300, the shield 200 in which the probe P is inserted is placed on the table 400 in an upright state, and the table 400 is rotated intermittently to thereby reduce the radiation dose in each direction. In addition, by measuring the radiation dose in each direction at each height position while shortening the length dimension of the support column 402, radiation enters the indoor space 300 from which direction and at which height position. The radiation dose at the problematic location may be measured by the method described with reference to FIG.

  As a modified example, the shield 200 into which the probe P is inserted is placed on the table 400 in a laid state, and the shield 200 is intermittently rotated around the horizontal axis so that the radiation dose in each direction in the vertical plane. May be measured.

  21 and 22 show a modification 250 of the shield 200 of the second reference example. In the description of the shielding main body 250 of this modification, the same elements as those included in the shielding body 200 of the second reference example are denoted by the same reference numerals, and the description thereof is omitted. The characteristic part will be described. FIG. 21 is a side view of a modified shielding main body 250, and FIG. 22 is a plan view thereof. The shielding main body 250 of the modification includes an opening / closing lid 252 having a shielding function. As with the main body 202, the open / close lid 252 employs a configuration in which a space surrounded by a stainless steel plate outer shell is filled with a shielding material (typical example: lead).

  The open / close lid 252 includes an opening 254 through which a cord extending from the probe P inserted into the main body 202 (a cord connected to the measuring instrument main body) can pass. The opening 254 is opened laterally from the periphery of the opening / closing lid 252. The opening / closing lid 252 is most preferably connected to the end of the main body 202 by a hinge 256.

Second Example (FIG. 23) :
In the first embodiment, the application example in the indoor space 300 has been mainly described. However, for example, the shields 200 and 250 can be used to detect the orientation of a contamination source (hot spot) even outdoors. In the decontamination target area where decontamination work is performed, it may be desired to investigate from which direction strong radiation comes. To explain this requirement in detail, there is a case where the effect of decontamination is not seen as expected even after completion of the decontamination work, that is, the radiation dose does not decrease as much as expected. In this case, there may be a hot spot in the neighborhood. The orientation in which the hot spot exists is useful for finding a hot spot (radioactive contamination source) by conducting an environmental survey in that orientation and measuring the radiation dose. Of course, if a hot spot (contamination source) is found, the decontamination effect can be further enhanced by decontaminating the hot spot.

  The shields 200 and 250 provided with the slits SL can be used for the above-described outdoor requirements. As a specific method, typically, the horizontal plate 406 of the table 400 is set to a predetermined height, the shield 200 or 250 having the probe P inserted thereon is placed on the horizontal plate 406, and the horizontal plate is gradually added. The radiation dose may be measured while rotating 406.

  FIG. 23 is a diagram for explaining a method of finding a hot spot HS using a three-point measurement method. For example, at the point A, the above-described method is used to find an azimuth with a high radiation dose from all directions, and at the next point B, a azimuth with a high radiation dose is found similarly. By measuring at the points A and B, it is possible to know an approximate point of the hot spot HS. Most preferably, an accurate point of the hot spot HS can be known by measuring a direction with a high radiation dose at the point C.

P Radiation measuring instrument probe (detector)
200 radiation shielding body 202 shielding body 206 closed end face SL slit (radiation passage window)
400 tables (rotary table with adjustable height)

Claims (7)

A shielding step of shielding the detection unit with a radiation shield that surrounds the detection unit of the portable radiation measuring instrument and includes a radiation passage window provided facing a part of the detection unit;
A rotating step of rotating the radiation shield;
And a measuring step of measuring a radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield.   The radiation source detection method according to claim 1, wherein the rotation step is performed by rotating the radiation shield on a horizontal plane.   The radiation source detection method according to claim 1, wherein the rotation step is performed by rotating the radiation shield on a vertical plane. A shielding step of shielding the detection unit with a radiation shield that surrounds the detection unit of the portable radiation measuring instrument and includes a radiation passage window provided facing a part of the detection unit;
A placing step of placing the radiation shield on a rotary table;
A rotating step of rotating the radiation shield by rotating the rotating table;
A radiation source detection method comprising: a measurement step of intermittently stopping rotation of the rotary table and measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield.   The radiation source detection method according to claim 4, further comprising a step of changing a height level of the rotary table. A shielding step of shielding the detection unit with a radiation shield that surrounds the detection unit of the portable radiation measuring instrument and includes a radiation passage window provided facing a part of the detection unit;
A first rotation step of positioning the radiation shield at a first point and rotating the radiation shield;
A first measurement step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the first point;
A first direction specifying step for obtaining a first direction having the highest radiation dose measured in the first measuring step; a second rotating step for positioning the radiation shield at a second point and rotating the radiation shield;
A second measuring step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the second point;
A second direction specifying step for obtaining a second direction having the highest radiation dose measured in the second measuring step; a third rotating step for positioning the radiation shield at a third point and rotating the radiation shield;
A third measurement step of measuring radiation dose at a plurality of rotational positions spaced in the rotational direction of the radiation shield at the third point;
A third direction specifying step for obtaining a third direction having the highest radiation dose measured in the third measurement step;
A radiation source detection method comprising: a radiation source position specifying step for obtaining a radiation source position where the first direction, the second direction, and the third direction intersect each other. The detection part of the portable radiation measuring instrument has a cylindrical shape,
The radiation shield has a cylindrical shape with a bottom that can receive the cylindrical detection unit,
The radiation passing window is composed of a slit formed in a side wall of the cylindrical radiation shield,
The radiation source detection method according to claim 1, wherein the slit extends in a longitudinal direction of the radiation shield.

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