JP2015155834A - Whole body counter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a whole body counter capable of obtaining an excellent sensitivity distribution that can cover the hip and the femoral region.

SOLUTION: A chair 30 is provided in a measuring room. A subject seated in the chair 30 is subjected to internal exposure measurement. A first measuring unit 40 is provided in rear of a backrest surface and a second measuring unit 42 is provided below a seat surface. The measuring units 40 and 42 include scintillator members 50, 54; and a photomultiplier detecting light generated in the scintillator members 50, 54, respectively. Since not only the first measuring unit 40 but also the second measuring unit 42 is provided, a combined sensitivity distribution 70 that can cover even the hip and the femoral region can be obtained. It is thereby possible to measure gamma-rays from radionuclides that may be easily accumulated in muscles with high sensitivity.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a whole body counter, and more particularly to a whole body counter that measures radiation emitted from a subject sitting on a chair.

  The whole body counter is a radiation measurement device that is installed in a nuclear power plant, an exposure inspection organization, and the like, and measures radiation emitted from a subject, particularly γ-rays, for managing internal exposure of the subject. There are known a whole body counter for measuring a subject in a supine posture, a whole body counter for measuring a subject in a standing posture, and a whole body counter for measuring a subject in a sitting posture ( For example, see Patent Documents 1 to 4.)

  In the latter hall body counter, a chair is installed in a measurement chamber surrounded by a radiation shielding member. A measurement unit is arranged on the back side (back side) of the chair. The measurement unit is typically composed of a scintillator member and a photomultiplier tube. The scintillator member has, for example, a shape extending in the vertical direction with a substantially parallel relationship with the backrest surface or the spine of the subject. A photomultiplier tube is joined to the upper end surface or the lower end surface. In such a configuration, the center of the sensitivity distribution of the scintillator member is at the center position of the trunk of the subject or a position slightly closer to the chest in the abdomen.

JP-A-9-101370 JP-A-9-281242 Japanese Patent Laid-Open No. 11-30668 JP 2004-37395 A JP 2000-196077 A

It is said that when radioactive substances such as ¹³⁴ Cs and ¹³⁷ Cs are ingested by the human body, they are absorbed by the internal organs, and at least a part of them is accumulated in the muscle. Muscles are also present in the upper limbs, chest and abdomen, but there are relatively many in particular in the buttocks and thighs. They are distributed below the intermediate height in the sitting position on the chair.

  Therefore, when measuring γ-rays from radioactive substances that are abundant in muscles (and built-in), a sensitivity distribution centering on the lower abdomen of the subject sitting in the chair is generated, or up to the thigh It is desirable to configure the detection unit so that a sufficiently covered sensitivity distribution is generated. However, such sensitivity distribution is not realized in the conventional whole body counter.

  Patent Document 5 discloses disposing a radiation detector below the seat surface of a chair. However, the configuration is to measure the whole trunk with a single radiation detector. No other radiation detector is provided on the back side of the subject. In the first place, the configuration disclosed in Patent Document 5 is for both the measurement of a subject and the measurement of a sample such as food, and the detector faces upward so that the latter measurement can also be performed. .

  An object of the present invention is to make a sensitivity distribution over a wide range centering on the lower abdomen of a subject sitting on a chair in a whole body counter. Alternatively, an object of the present invention is to measure with high sensitivity radiation from radioactive substances that are likely to accumulate in muscle.

  The whole body counter according to the present invention is a chair having a backrest surface and a seating surface, and a measurement unit provided behind the subject sitting on the chair, and extends vertically along the backrest surface. A first measurement unit including the first radiation detector, and a measurement unit provided below the subject sitting on the chair, wherein the second measurement unit extends in the front-rear direction along the seating surface. And a second measurement unit including a radiation detector.

  According to the above configuration, the first measurement unit is provided behind the subject in the sitting position, and the second measurement unit is provided below the subject. It is possible to obtain a composite sensitivity distribution that covers the thigh. That is, since the first measurement unit has the first radiation measuring instrument extending in the vertical direction along the backrest surface (desirably parallel to the backrest surface as an inclined surface), the first measurement unit has a wide spine direction. It is possible to obtain a first sensitivity distribution over a range. Depending on the length and installation position of the first radiation detector, it is generally difficult to sufficiently cover the buttock by the first sensitivity distribution, or for that purpose, the first radiation detector is used which is considerably long. This causes another problem of cost increase. Even if the length of the first radiation detector is increased, it is difficult to obtain a sensitivity distribution that sufficiently covers the thigh extending forward. On the other hand, the second radiation detector extends in the front-rear direction along the seating surface (preferably parallel to the seating surface as a slope), and thereby the second sensitivity over a wide range in the femoral direction. A distribution can be obtained. It leads to an improvement in sensitivity to the entire lower limb in a flexed posture. According to the present invention, it is possible to obtain a combined sensitivity distribution composed of the two sensitivity distributions as described above. That is, the first detection unit and the second detection unit have an approximately L-shaped arrangement when viewed from the side of the subject, and the two sensitivity distributions thereof are approximately orthogonal. As a result, sensitivity peaks or sensitivity peaks are likely to occur on the inside (small angle side) of the L-shape corresponding to the position of the lower abdomen. Therefore, since it is possible to measure the internal exposure of the buttocks and thighs with high accuracy, it is possible to efficiently detect the radiation from the radionuclide that easily accumulates in the muscle. Desirably, relatively good sensitivity can be obtained over a wide range from the thigh to the chest or from the tip of the foot to the top of the head.

  Preferably, the first measurement unit includes a first scintillator member as the first radiation detector, and a first photodetector for detecting light generated by the first scintillator member. The second measurement unit includes a second scintillator member as the second radiation detector, and a second photodetector that detects light generated by the second scintillator member. The first scintillator member has a central axis that is substantially parallel to the central axis of the spine or trunk, and the second scintillator member has a central axis that is substantially parallel to the central axis of the femur or thigh. Although it is possible to arrange a plurality of scintillator members in the left-right direction, it is more advantageous in terms of cost to arrange one scintillator member in the center in the left-right direction, and such a configuration is sufficient in the left-right direction. Sensitivity can be obtained.

  Preferably, the first photodetector is provided on the upper end side of the first scintillator member, and the second photodetector is provided on the rear end side of the second scintillator member. If the first photodetector is provided on the upper end side of the first scintillator member, physical interference between the first photodetector and the second measurement unit can be avoided. That is, even when the second photodetector is arranged on the rear end side of the second scintillator member, it does not collide with the first photodetector. If the second photodetector is provided on the rear end side of the second scintillator member, the second scintillator member can be disposed further forward. Thereby, the sensitivity with respect to the front side of a thigh and a lower knee part can be improved.

  Desirably, a rear end portion of the second scintillator member is located in the vicinity of a position immediately below a lower end portion of the first scintillator member. In the case where a gap is generated between the first scintillator member and the rear end portion of the second scintillator member, the rear end portion of the second scintillator member extends to a position directly below the first scintillator member. It is possible to reduce detection omission of radiation. That is, the second scintillator member may be made longer in order to reduce radiation detection omission, but in that case, there is a problem of cost increase. It is desirable to extend the rear end portion of the second scintillator member to a position just below. From the viewpoint that the length of the thigh is shorter than the length of the spine, the above arrangement is reasonable.

  Preferably, the first measurement unit and the second measurement unit have the same configuration. When this configuration is employed, the first scintillator member and the second scintillator member are configured in the same form, that is, configured with the same length, and thus it is particularly desirable to employ the above arrangement relationship. In addition, although it is also possible to bend each scintillator member, in that case, the problem of manufacturing difficulty and a cost increase tends to arise. Therefore, generally, a scintillator member extending linearly is used.

  A thyroid measurement unit may be further arranged inside the measurement room in which the chair is installed, and local measurement may be performed on the thyroid simultaneously with the measurement by the first and second measurement units. The thyroid measurement unit may be configured to be removable so that the thyroid gland can be measured outside the measurement chamber. In that case, measurement by the first and second measurement units may be performed on the subject inside the measurement chamber, and at the same time, measurement on the thyroid gland may be performed on the subject outside the measurement chamber.

  ADVANTAGE OF THE INVENTION According to this invention, in a whole body counter, the sensitivity distribution over a wide range centering on the lower abdominal part in the subject sitting on the chair can be obtained. Or according to this invention, the radiation from the radioactive substance which is easy to accumulate | store in a muscle can be measured with high sensitivity.

It is a 1st perspective view which shows suitable embodiment of the whole body counter which concerns on this invention. It is a 2nd perspective view of a whole body counter. It is a horizontal sectional view of a whole body counter. It is sectional drawing showing the cross section shown by IV in FIG. It is a figure which shows a 1st measurement unit and a 2nd measurement unit. It is a figure which shows a synthetic | combination sensitivity distribution typically. It is a figure which shows the thyroid measurement in a measurement chamber. It is a figure which shows the thyroid measurement outside a measurement room.

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

  FIG. 1 shows a preferred embodiment of a whole body counter according to the present invention, and FIG. 1 is a first perspective view thereof. This whole body counter is a radiation measurement device that is installed in a nuclear power plant, an exposure inspection organization, and the like and measures radiation from a subject. The whole body counter is used particularly when inspecting internal exposure.

  In FIG. 1, the hall body counter 10 has a measurement chamber 12 surrounded by a radiation shielding member, and a chair on which a subject sits is installed in the measurement chamber 12. This will be described later.

  An enclosure 14, a ceiling plate 18, and a bottom plate 16 are provided around the measurement chamber 12. They constitute a shield. They are configured to include a radiation shielding member such as lead, thereby blocking extraneous radiation such as cosmic rays. In this embodiment, the enclosure 14 includes a left side wall 14A, a corner wall 14B, a front wall 14C, a right side wall 14D, a rear wall 14E, and a partition wall 14F. A window opening 22 is formed in the upper part of the rear wall 14D. Specifically, the window opening 22 constitutes a passage that opens the upper portion of the chair. A window opening 24 having a triangular shape is provided on the upper portion of the partition wall 14F as shown in the figure. A radiation shielding member is provided over the entire partition wall 14 </ b> F, and a space that does not need to be shielded forms a triangular shape in the illustrated example, which forms a window opening 24.

  An inlet opening (entrance / exit opening) 20 is formed between the partition wall 14F and the left side wall 14A. The subject enters the measurement chamber 12 from the outside through the entrance opening 20. Note that the X direction is the front-rear direction, the Y direction is the left-right direction, and the Z direction is the vertical direction, with the subject in the sitting position as a reference.

  FIG. 2 shows a second perspective view of the whole body counter. FIG. 2 particularly shows the right side wall 28B of the whole body counter. An attachment bar 26 is provided at an intermediate position there. The mounting bar 26 is a pole extending in the vertical direction, and both ends thereof are fixed to the right side wall 14D by a pair of holding members. A thyroid measurement unit 28B, which will be described later, is detachably attached to the attachment bar 26. The whole body counter has a single thyroid measurement unit. In each figure, the thyroid measurement unit arranged outside the measurement chamber is indicated by reference numeral 28B. A thyroid measurement unit arranged in the measurement chamber is indicated by reference numeral 28A. Both 28A and 28B are the same.

  FIG. 3 shows a horizontal section of the whole body counter. FIG. 3 shows a cross section of the enclosure 14. A radiation shielding member 36 is provided inside each wall. Incidentally, the code | symbol 38 has shown the radiation shielding member provided in the inside of a partition wall. A chair 30 is provided in the measurement chamber 12. A display 34 is provided in front of the chair 30. Reference numeral 32 represents a route when approaching the chair 30 from the outside. With such a winding path, it is possible to effectively block the external radiation from the entrance 20.

  4 shows a vertical cross section at the position indicated by IV in FIG. In the present embodiment, the whole body counter has a chair 30, the first measurement unit 40 is provided behind the subject sitting on the chair 30, and the second body is located below the subject sitting on the chair 30. A measurement unit 42 is provided. Side frames are provided on the right and left sides of the chair 30, respectively, and a plurality of metal fittings are provided therein. Reference numeral 45 denotes a side frame cover. These metal fittings hook the belt. When the phantom is installed in the chair 30 instead of the human body and the whole body counter is calibrated, the phantom is fixed on the chair 30 by the belt. In that case, a plurality of metal fittings for supporting the belt are used. Usually, these metal fittings are covered with a cover 45. Reference numeral 47 indicates an object sensor unit. In actual calibration, a plurality of phantoms having a box shape are used, and they are stacked on a chair.

  FIG. 5 shows the first measurement unit 40 and the second measurement unit 42. The subject 31 is seated on the chair 30. The chair 30 has a backrest surface 44, which is a surface extending in the up-down direction, and is slightly tilted backward and inclined. A cushion 44 </ b> A is provided on the backrest surface 44. A lower part of the backrest surface 44 is a waistrest surface 46. The waist contact surface 46 is an upright surface, and a cushion 46 </ b> A is provided on the waist contact surface 46. The chair 30 has a seat surface 48. The seat surface 48 is a substantially horizontal surface extending in the front-rear direction, and more specifically, a slope that is slightly higher in the front. A cushion 48 </ b> A is provided on the seat surface 48. A vertical surface is formed downward from the front end of the seat surface 48.

  In the present embodiment, the first measurement unit 40 includes a scintillator member 50 and a photomultiplier tube 52. The scintillator member 50 is composed of a NaI scintillator in this embodiment. The scintillator member 50 has a prismatic form, which has a form extending in the vertical direction parallel to the backrest surface 44. The scintillator member 50 is surrounded by an aluminum case. A photomultiplier tube 52 is provided with the light receiving surface bonded to the upper end surface of the scintillator member 50. The photomultiplier tube 52 is a photodetector. When γ-rays emitted from the subject 31 reach the scintillator member 50, light emission occurs there, and the light is detected in the photomultiplier tube 52, specifically, the light is converted into an electric pulse. The first measurement unit 40 is provided at the center position in the left-right direction on the backrest surface 44.

  The second measurement unit 42 has the same configuration as the first measurement unit 40 in the present embodiment. That is, the first measurement unit 40 and the second measurement unit 42 are configured using two identical measurement units. Specifically, the second measurement unit 42 includes a scintillator member 54 and a photomultiplier tube 56. The scintillator member 54 has a form extending in the front-rear direction parallel to the seating surface 48, and specifically has a prismatic form. The scintillator member is provided at the center position in the left-right direction. The scintillator members 50 and 54 may have a cylindrical shape, for example.

  In the state where the subject 31 is seated on the chair 30, the back surface of the subject 31 will hit the backrest surface 44, and the rear side of the buttocks will be close to or hit the hip resting surface 46. The lower surface and the lower surface of the thigh will contact the seating surface 48. In the present embodiment, handrails are provided on the right and left sides of the chair 30. In FIG. 5, the right and left arms of the subject are placed on their handrails.

  The composite sensitivity distribution will be described with reference to FIG. In FIG. 6, the scintillator member 50 in the first measurement unit 40 is schematically shown, and similarly, the scintillator member 54 in the second measurement unit 42 is schematically shown. In the present embodiment, the central axis 58 of the scintillator member 50 is parallel to the backrest surface 44 extending in the vertical direction of the chair 30. Reference numeral 60 denotes an orthogonal axis that is orthogonal to an intermediate position of the central axis 58 in the scintillator member 50. The orthogonal axis 60 belongs to the XZ plane. With such an arrangement of the scintillator member 50, a sensitivity distribution 66 is obtained. That is, a sensitivity distribution 66 having a substantially symmetric form about the orthogonal axis 60 is obtained. Here, the sensitivity distribution 66 represents the strength of sensitivity by the distance from the central axis 58. In the sensitivity distribution 66, the sensitivity is higher in the central portion. However, the sensitivity distribution 66 is schematically or conceptually represented for explaining the invention.

  Conventionally, radiation has been measured using the sensitivity distribution 66 as described above for the entire subject, and there has been a problem that radiation from the buttocks and thighs cannot always be measured with high sensitivity. On the other hand, in the present embodiment, since the second measurement unit 42 is provided, it is possible to obtain the combined sensitivity distribution 70. Specifically, the scintillator member 54 in the second measurement unit 42 has a central axis 62. Its central axis 62 is approximately parallel to the seating surface 48. Reference numeral 64 denotes a vertical axis that crosses the center of the scintillator member 54 in the direction of the central axis 62. According to the second measurement unit 42, a sensitivity distribution 68 that is symmetric about the vertical axis 64 is generated. Sensitivity is high at the center of the sensitivity distribution 68.

  According to the sensitivity distribution 68, the detection sensitivity for the subject's buttocks, thighs, and lower limbs can be increased. A composite sensitivity distribution 70 is a combination of the sensitivity distribution 66 and the sensitivity distribution 68. This combined sensitivity distribution 70 causes the greatest sensitivity in the lower abdomen or the buttocks of the subject. Alternatively, good sensitivity can be obtained from the thigh to the entire chest. Alternatively, good sensitivity can be obtained from the toes of the foot to the entire top of the head. When viewed from the right or left side of the subject, the two scintillator members 50 and 54 have an approximately L-shaped arrangement, in other words, the two sensitivity distributions 66 and 68 are approximately orthogonal. Therefore, a large sensitivity is obtained at a portion where the two sensitivity distributions 66 and 68 overlap, and such a portion is the lower abdomen or the buttocks. As described above, since there is a tendency that specific radionuclides are likely to be accumulated in the hips and thighs where there are relatively many muscles, the synthetic sensitivity distribution 70 as described above is used when measuring radiation from such radionuclides. Works effectively.

  In general, immediately after ingestion of the radionuclide, it is exclusively present in the internal organs. According to the said structure, it is also possible to detect the nuclide which exists in such an internal organ with high sensitivity. Since there is a tendency for specific radionuclides to collect in the thyroid gland, a thyroid measurement unit is provided for this as described above.

  In order to obtain good sensitivity over a wider range in the direction along the spine, it is conceivable to increase the length of the scintillator member 50. In this case, however, a problem of cost increase occurs. Therefore, the length of the scintillator member 50 cannot be increased freely. As a result, a gap is inevitably generated between the scintillator member 50 and the scintillator member 54, and the problem of radiation detection omission there is likely to occur. Become. On the other hand, in the present embodiment, the back end of the scintillator member 54 extends to a position immediately below the lower end of the scintillator member 50, that is, the back end 54 </ b> A extends further to the back than the position indicated by the line 66. Even if the two scintillator members are spaced from each other, the radiation detection leakage is configured to be as small as possible.

  In this embodiment, the photomultiplier tube is joined to the upper end surface of the scintillator member 50, and the problem that it physically interferes with the second measurement unit is avoided. In the second measurement unit 42, since the photomultiplier tube is joined to the rear end surface of the scintillator member 54, there is an advantage that the front end portion 54B of the scintillator member 54 can be extended as far forward as possible. This makes it possible to obtain good sensitivity for the front and lower knees in the thigh.

  As described above, since two measurement units having the same configuration are provided with the specific arrangement as described above, there is an advantage that more efficient measurement can be realized while avoiding an increase in cost.

  FIG. 7 shows the thyroid measurement in the measurement chamber. The subject 31 sits on the chair 30 and the thyroid gland of the subject 31 is measured by the thyroid measurement unit 28A. The thyroid measurement unit 28A includes a scintillator member 72 and a photomultiplier tube 74 constituting a detector, and the detector is supported by an arm mechanism 76. The arm mechanism 76 is supported by an elevating mechanism 78. The thyroid gland can be measured simultaneously with the measurement by the two measurement units 40 and 42.

  FIG. 8 shows the thyroid measurement outside the measurement room. A portable chair 80 is installed outside the measurement room, and the subject 82 sits on the chair 80. The thyroid gland in the subject 82 is measured using such a thyroid measurement unit 28B. In that case, the detector and arm mechanism 76 are removed from the measurement chamber and attached to the mounting bar 26. Even in such a case, the thyroid gland measurement can be performed on the subject outside the measurement chamber simultaneously with the measurement of the subject inside the measurement chamber.

  As described above, according to the whole body counter according to the present embodiment, it is possible to obtain a good combined sensitivity distribution that covers the buttocks and thighs. As a result, it is possible to measure a specific radionuclide that is likely to accumulate in muscle with high sensitivity.

10 Hall body counter, 12 Measurement room, 30 Chair, 31 Subject, 40 First measurement unit, 42 Second measurement unit, 70 Composite sensitivity distribution.

Claims (5)

A chair having a back surface and a seat surface;
A measurement unit provided behind the subject sitting on the chair, the first measurement unit comprising a first radiation detector extending vertically along the backrest surface;
A measurement unit provided below the subject sitting on the chair, the second measurement unit comprising a second radiation detector extending in the front-rear direction along the seat surface;
A hall-body counter characterized by including. The whole body counter according to claim 1,
The first measurement unit includes a first scintillator member as the first radiation detector, and a first photodetector for detecting light generated by the first scintillator member,
The second measurement unit includes a second scintillator member as the second radiation detector, and a second photodetector for detecting light generated by the second scintillator member.
A whole body counter. The whole body counter according to claim 2,
The first photodetector is provided on the upper end side of the first scintillator member,
The second photodetector is provided on the rear end side of the second scintillator member,
A whole body counter. In the whole body counter according to claim 3,
A rear end portion of the second scintillator member is located in the vicinity of a lower end portion of the first scintillator member;
A whole body counter. The whole body counter according to claim 2,
The first measurement unit and the second measurement unit have the same configuration.
A whole body counter.

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