JP2018119791A - Radiation measurement apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a β-ray incident window deformation in an ionization chamber for detecting γ ray and β ray when a pressure difference occurs between an internal space and an external space.SOLUTION: A β-ray incident window 18 is composed of a window member 32 and a conductive layer 30C formed on an inner surface thereof. A ventilation port 34 is formed in the window member 32, and the ventilation port 34 is closed by a porous membrane 20 as a selectively permeable member. The porous membrane 20 allows air to pass while preventing the passage of water. As a result, a pressure P1 in an internal space of a container 14 becomes equal to a pressure P0 in an external space, so that deformation of the β-ray incident window 18 is prevented.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a radiation measuring apparatus, and more particularly to the structure of an ionization chamber.

  Various types of radiation detection methods are known. The ionization chamber method is a method of detecting radiation using an ionization chamber. A portable survey meter equipped with an ionization chamber, a fixed installation type area monitor equipped with an ionization chamber, a dust monitor, and the like have been put into practical use. An ionization chamber capable of measuring γ rays (including X-rays) and β rays is also known. In such an ionization chamber, a part of the container is constituted by a film-like member having β-ray permeability, and the member functions as a β-ray incident window. At the time of γ-ray measurement, the β-ray incident window is covered with a lid, and at the time of β-ray measurement, the lid is removed. In the ionization chamber, a high voltage is applied between the container electrode and the collector electrode. The interior is usually an airtight space.

JP-A-8-146140

  In the case of an ionization chamber having a β-ray entrance window, the β-ray entrance window is deformed by a pressure difference between the pressure in the internal space (internal pressure) and the pressure in the external space (atmospheric pressure). This causes problems such as breakage of the β-ray incident window and peeling or breakage of the conductive layer formed on the inner surface of the β-ray incident window. Even if the conductive layer does not peel off, there is a problem that the electrical characteristics of the ionization chamber change due to the spatial change between the conductive layer and the collector electrode.

On the other hand, it is possible to remove the β-ray incident window and adopt an open type configuration. However, in such a configuration, intrusion of foreign matters, particularly intrusion of water droplets or the like becomes a problem. Since a high voltage is applied between the container electrode and the collector electrode constituting the ionization chamber, it is important to prevent a decrease in insulation, such as generation of a leak current in the insulator. The above-described problems can be pointed out not only in an ionization chamber having a β-ray incident window but also in an ionization chamber in which all or a part of the casing is made of a deformable material.

  Patent Document 1 discloses an ionization chamber used in thickness measurement. Part of the ionization chamber container constitutes an entrance window, which is constituted by a metal foil. A porous body is provided in front of the metal foil. This is to prevent the metal foil from being damaged by suppressing the outward swelling of the metal foil. Each hole formed in the porous body has a size large enough to allow a droplet or the like to pass through. In addition, realization of an ionization chamber type survey meter capable of specifying a locally contaminated portion is desired.

  An object of the present invention is to eliminate a pressure difference between the inside and outside of an ionization chamber while preventing deterioration of insulation in the ionization chamber. Alternatively, an object of the present invention is to realize an ionization chamber excellent in functionality.

  The radiation measuring apparatus according to the present invention is a hollow ionization chamber and a member that is provided in the ionization chamber and partitions the internal space and the external space of the ionization chamber, allows air to pass therethrough, and allows water to enter. And a selectively permeable member to be restricted.

  In the above configuration, the ionization chamber is provided with a selective transmission member so as to partition the internal space and the external space. Since the permselective member allows the passage of air, the pressure in the internal space is the same as the pressure in the external space. Thereby, the deformation | transformation of the member (container) surrounding the interior space and generation | occurrence | production of the problem resulting from the deformation | transformation can be prevented. Since the permselective member has a waterproof function that restricts the entry of water, it is possible to avoid a decrease in insulation caused by the entry of water droplets, fine water particles, or the like inside the ionization chamber. The permselective member also prevents foreign substances such as dust from entering the internal space.

  In the embodiment, the ionization chamber includes a container that defines the internal space, the container includes a vent hole that allows the internal space and the external space to communicate with each other, and the selective transmission member blocks the vent hole. Is a porous member. The porous member has a large number of micropores, and desired permselectivity is exhibited by adjusting the size of each micropore. The size of each micropore is determined so as to pass air and not allow water as a liquid to pass. As a modification, it is conceivable to use a member having air permeability and water repellency instead of the porous member. When the container includes a housing and a radiation incident window, the vent is provided in one or both of the housing and the radiation incident window. When providing a vent hole in the radiation entrance window, it is desirable to close the vent hole with a flexible porous film. The radiation incident window is, for example, a β ray incident window or an α ray incident window.

  In an embodiment, the ionization chamber has a conductive layer formed on the inner surface of the container, and all or part of the inner surface of the porous member is exposed to the internal space. When the casing of the ionization chamber is formed of an insulating member, a conductive layer is formed on the inner surface of the casing, and the conductive layer functions as a peripheral electrode surrounding the collector electrode. The conductive layer may be configured as a coating film. It is a region where all or part of the inner surface of the porous member is exposed to the internal space, that is, a region where no conductive layer is formed. The intrinsic function of the porous member is exhibited in the exposed region.

  In the embodiment, the radiation measuring apparatus is an apparatus capable of measuring γ-rays and β-rays, the container includes a β-ray incident window, and the β-ray incident window is a window member and a conductive layer formed on an inner surface thereof. And a high-sensitivity region having the vent and the porous member, and the β-ray attenuation action in the high-sensitivity region is smaller than the β-ray attenuation effect in the normal-sensitivity region. . According to this configuration, for example, when a point contamination source exists on the surface of the object, when the ionization chamber is scanned while bringing the β incident window close to the surface of the object, a point when the high sensitivity region approaches the front of the point contamination source. The measured value becomes maximum. It becomes possible to specify the position of the point contamination source from the change in the measured value. In the embodiment, the vent is formed in the center of the window member.

  In the embodiment, a means for identifying the high sensitivity region is provided on the outer surface of the β-ray incident window. According to this configuration, it is possible to visually identify the high sensitivity region. Examples of the process for identification include marker printing, coloring process, and the like. When the material constituting the window member and the material constituting the porous member have different colors, the difference in color functions as an identification means.

  The radiation measurement apparatus according to the embodiment further includes a structure provided adjacent to the ionization chamber, a power supply circuit disposed inside the structure and supplying a high voltage to the ionization chamber, An electrometer circuit disposed inside the structure and observing an ionization current from the ionization chamber, wherein all or a part of the inside of the structure is an airtight space having the power supply circuit and the electrometer circuit. is there. The power supply circuit includes at least one of an electronic circuit, a wiring, an electrode end, and the like constituting the power supply. Still other configurations may be accommodated in the airtight space. According to the airtight space, water does not enter, and condensation can be prevented while maintaining a low humidity state or a dry state. The radiation measurement apparatus can be configured as a portable apparatus such as a survey meter or a fixed installation apparatus such as an area monitor or a dust monitor.

  According to the present invention, in the ionization chamber, the pressure difference between the inside and outside of the ionization chamber can be eliminated while preventing deterioration of the insulating property, so that problems such as container breakage due to the pressure difference do not occur. Alternatively, according to the present invention, a highly practical ionization chamber having excellent functionality can be provided.

1 is a first perspective view showing a first embodiment of a radiation measuring apparatus according to the present invention. FIG. 5 is a second perspective view showing the first embodiment. It is a 3rd perspective view which shows 1st Embodiment. 1 is a schematic cross-sectional view of a first embodiment. It is a figure which shows the deformation | transformation of the beta ray incident window which originates in a pressure difference. 1 is a cross-sectional view of a first embodiment. It is a figure which shows the function of a porous membrane. It is a figure which shows 2nd Embodiment. It is a figure which shows 3rd Embodiment. It is a figure which shows 4th Embodiment. It is a figure which shows 5th Embodiment. It is a figure which shows 6th Embodiment. It is a figure which shows 7th Embodiment.

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

  FIG. 1 shows a first embodiment of a radiation measuring apparatus according to the present invention. This radiation measurement apparatus is a portable radiation measurement apparatus that detects radiation in the environment, radiation from an object, and the like, and specifically, an ionization chamber type survey meter. The radiation to be detected is γ rays (including X-rays) and β rays. Other radiation may be detected.

  In FIG. 1, the survey meter has a detection unit 10 as an ionization chamber and a measurement unit 12 connected to the detection unit 10. The measurement unit 12 is an enlarged portion that is connected to one end of the detection unit 10. The measurement unit 12 includes a display unit and an operation unit. From the viewpoint of visibility and operability, the display surface (and operation surface) of the measurement unit 12 is not orthogonal to the central axis (cylindrical axis) of the detection unit 10 and is configured as an inclined surface. An arithmetic circuit, a display circuit, a control circuit, a power circuit, a battery (battery), and the like are provided inside the measurement unit 12.

  The detection unit 10 includes a container 14 that surrounds the internal space, that is, defines the internal space. The container 14 functions as a partition that partitions the internal space and the external space. The container 14 has a cylindrical shape, and includes a housing 16 and a β-ray incident window 18. The transmission power of γ rays is large, and the γ rays easily pass through the container 14 and reach the internal space. On the other hand, the transmittance of β rays is small. At the time of detecting β-rays, the cap shown later is removed, and a state where the β-ray incident window 18 is exposed is formed. The β-ray incident window 18 is brought close to the object surface, and β-rays are detected in this state.

  In the first embodiment, a vent hole is formed at the center of the β-ray incident window 18, and the vent hole is closed by a porous film 20 as a selective transmission member. The porous membrane 20 is a sheet-like member made of a material that allows passage of air and prevents passage of moisture. That is, the porous membrane 20 has both air permeability and waterproofness. This makes it possible to naturally balance the pressure in the internal space with the pressure in the external space while preventing raindrops and the like from entering the internal space of the container 14. Thereby, the deformation | transformation of the beta ray detection window resulting from a pressure difference and the various problems accompanying the deformation | transformation are eliminated.

  FIG. 2 shows a state at the time of γ-ray measurement. The β-ray incident window in the detection unit 10 is covered with a cap 22. The cap 22 is made of a resin or the like that shields β rays, and is made of the same material and the same thickness as the housing, for example.

  FIG. 3 shows the measuring unit 12. The measurement unit 12 includes an operation unit 24 and a display unit 26. The operation unit 24 has a plurality of buttons. The display unit 26 is configured by an LCD or the like. The display unit 26 displays a dose equivalent rate (Sv / h), an integrated dose (Sv), and the like as measurement results.

  FIG. 4 is a schematic cross-sectional view of the survey meter. As already described, the survey meter includes the detection unit 10 and the measurement unit 12 that constitute an ionization chamber. The detection unit 10 includes a cylindrical container 14, and the container 14 includes a housing 16 and a β-ray incident window 18. The housing 16 is made of an insulating resin, and includes a cylindrical wall 16A and a bottom wall 16B. Examples of the resin include ABS resin. The thickness is 3 mm, for example. A rod-shaped collector electrode 28 is disposed inside the container 14. The collector electrode 28 is fixed to the bottom wall 16 </ b> B via an insulating member 36.

  The β-ray incident window 18 has a window member 32, and a vent hole 34 is formed at the center thereof. The window member 32 is made of, for example, a polycarbonate sheet, and has a diameter of, for example, 8 cm and a thickness of, for example, 0.1 mm. The conductive layer 30 includes a portion 30A formed on the inner surface of the cylindrical wall 16A, a portion 30B formed on the inner surface of the bottom wall 16B, and a portion 30C formed on the inner surface of the window member 32 (hereinafter referred to as “conductive layer 30C”). Also). The thickness of the conductive layer 30 is, for example, 5 μm. In the embodiment, the conductive layer 30 is a coating film, which is made of a material containing an adhesive and carbon. The conductive layer 30 surrounds the entire internal space, which functions as a surrounding electrode. A high voltage is applied between the conductive layer 30 and the collector electrode 28. Reference numeral 38 represents a terminal member for electrical connection to the conductive layer 30.

  The vent 34 is covered with a porous membrane 20 as a selectively permeable member. The vent 34 is, for example, circular, and its diameter is determined within a range of several mm to several cm, for example, 5 mm. The porous membrane 20 is circular, and its diameter is slightly larger than the diameter of the vent hole 34. For example, when the diameter of the vent hole 34 is 5 mm and the width of the surrounding ring-shaped adhesion region is 2 mm, the diameter of the porous film 20 is 9 mm. Airtightness is ensured in the bonded area. As described above, the porous film 20 is fixed to the outside of the window member 32 by the adhesive. The adhesive layer and the conductive layer are not formed on the inner surface of the porous film 20, specifically, the portion facing the vent hole 34, and the portion is an exposed region and faces the internal space.

  The porous film 20 is made of a porous resin, for example, a tetrafluoroethylene resin. The thickness is, for example, 0.1 mm. A number of micropores are formed in the porous film 20. The diameter of the individual holes is for example in the range from 0.1 to 10 μm, preferably 0.6 μm. The pore size is determined so that oxygen molecules and nitrogen molecules can pass, and water fine particles cannot pass. Incidentally, the size of water fine particles as a liquid is, for example, 100 to 3000 μm.

  Each of the numerical values given above is an example. The permselectivity can be adjusted by adjusting the pore diameter, area, thickness and the like of the porous membrane 20. In the case where water vapor passes through the porous film 20 in the same manner as oxygen molecules, nitrogen molecules, etc., and condensation in the container 14 becomes a problem, means such as introduction of a dehumidifying agent may be employed.

  Since the vent hole 34 was formed in the container 14 and was closed with the porous membrane 20, that is, the porous membrane 20 was provided so as to partition the internal space and the external space. Can prevent pressure difference. That is, the pressure P1 in the inner space is always naturally the same as the pressure P0 in the outer space. Since the deformation of the β-ray incident window 18 due to the pressure difference is prevented, the conventional damage to the β-ray incident window, the damage or peeling of the conductive layer formed on the back surface thereof, and the electric power accompanying the distortion of the conductive layer Problems such as changes in mechanical characteristics will not occur.

  Since the porous film 20 has waterproofness, intrusion of raindrops, fog particles, and the like into the internal space is prevented. This can prevent problems such as a decrease in insulation. Further, the porous film 20 can prevent foreign matter from entering. In the region where the vent 34 is provided, the β-ray attenuation is smaller than in other regions. That is, the β-ray sensitivity in that region is higher than the β-ray sensitivity in other regions. A mark may be attached to the center of the β-ray incident window 18 so that the presence of the porous film 20 or the position of a highly sensitive region can be specified from the outside. Or when the color of the outer surface of the window member 32 and the color of the outer surface of the porous membrane 20 differ, the boundary line of two area | regions functions as an identification means.

  The entire region of the β-ray entrance window 18 is indicated by reference numeral 50. The entire area 50 includes a normal sensitivity area 54 and a high sensitivity area 52. The high sensitivity region 52 is, for example, a circular region, and the normal sensitivity region 54 is an annular region existing around the high sensitivity region 52. Here, a narrow adhesive region is ignored. Strictly speaking, this region is a relatively low sensitivity region when viewed relatively. The normal sensitivity region 54 is a region where the window member 32 and the conductive layer 30C are provided. They all attenuate beta rays. The high sensitivity region 52 is a region where the vent hole 34 is present, and is a region where only the porous film 20 is provided. Even in this case, the β-rays are attenuated, but the degree is smaller than that in the normal sensitivity region.

  During γ-ray measurement, γ-rays flying into the detection unit 10 are detected in a state where the β-ray incident window 18 is covered with a cap. Specifically, the gas molecules are ionized by the incoming γ rays, and electrons and ions are generated. Due to the electric field between the collecting electrode 28 and the surrounding electrode (conductive layer 30), electrons are usually attracted to and collected by the collecting electrode 28 and detected as electric charges. At the time of detecting β-rays, the cap is removed to form an exposed state of the β-ray incident window 18, and β-rays passing through and reaching the internal space are detected by the same mechanism as described above. γ-rays are also detected during β-ray detection, but the net β-ray detection value can be obtained by subtracting the γ-ray detection value obtained with the cap attached from the detection value as the background value. It is.

  The β ray attenuation degree in the high sensitivity region 52 is smaller than the β ray attenuation degree in the normal sensitivity region 54. Therefore, when a point-like β-ray source (contaminated spot) exists on the surface of the object, from the detection value peak in the process of scanning the survey meter while bringing the β-ray incident window close to the object surface, It is possible to specify the position of the β-ray source.

  At one end of the detection unit 10, a measurement unit 12 is provided as a hollow structure. The measurement unit 12 includes a display unit 26. An electronic circuit board 44 is provided therein. In addition, a battery chamber for storing a battery is provided inside. In order to apply a high voltage between the base end of the collector electrode 28 and the base end of the terminal 38, a high voltage circuit including a terminal, a wiring, and a power supply component is provided inside the measurement unit 12. In addition, an electrometer circuit for measuring and observing a minute ionization current from the ionization chamber is provided therein. In order to prevent a decrease in insulation in the high voltage circuit and the electrometer circuit, it is necessary to prevent water from entering these circuits and dew condensation in the circuit components. It is configured as an airtight space. The entire internal space may be configured as an airtight space, or the portion 42A including the circuit group or the main part thereof may be configured as an airtight space. The inside of the measurement unit 12 and the inside of the detection unit 10 do not communicate with each other, and an airtight partition wall exists between them. When forming the airtight space, a seal member such as an O-ring is provided at the member joint as necessary. The electronic circuit board 44 is provided with an arithmetic circuit, a control circuit, and the like. A power supply component may be mounted there.

  FIG. 5 shows a comparative example (conventional example). The inside of the container is an airtight space, and the window member 53 is not provided with a vent hole. When a difference occurs between the pressure P0 in the external space and the pressure P1 in the internal space, the window member 53 is deformed as indicated by reference numerals 53A and 53B. However, in FIG. 5, the deformation is exaggerated. Due to this deformation, the end of the window member 53 is damaged, or the conductive layer formed on the inner surface thereof is peeled off.

  FIG. 6 shows a β-ray incident window in the first embodiment. As shown, the window member 32 is actually very thin and easily deformed. A vent hole is formed in the window member 32 and is closed by the porous film 20. Reference numeral 56 indicates the formation range of the vent holes, and reference numeral 55 indicates the formation range of the porous film 20. Since the porous membrane 20 exhibits a pressure balancing action, the window member 32 is not deformed.

  FIG. 7 schematically shows the operation of the porous membrane 20 in the first embodiment. As already described, the conductive layer 30 is formed on the inner surface of the window member 32. A vent hole 34 is formed at the center of the window member 32 and is covered with the porous film 20. The porous membrane 20 allows air to pass in both directions, but prevents water from entering from the outside. That is, it has selective permeability. The porous membrane 20 is made of a material that transmits β rays. As a constituent material of the porous film 20, it is desirable to use a material having a β-ray attenuation coefficient smaller than that of the constituent material of the window member 32.

  FIG. 8 shows a second embodiment. In the second embodiment, the porous membrane 60 is bonded and fixed inside the window member 32. A conductive layer 62 is formed around the porous film 60. Even with such a configuration, the same effect as the first embodiment can be obtained. It is also possible to arrange a porous member so as to fill the vent hole 58.

  FIG. 9 shows a third embodiment. In the third embodiment, the window member is composed of a porous film 64. An electrode layer 68 is provided at a portion other than the central portion 66 of the inner surface. The central portion 66 is not provided with an electrode layer. The central portion 66 effectively functions as a vent. In the third embodiment, since the central portion cannot be visually recognized from the outside, an annular mark 70 is provided on the outer surface of the porous film 64 as a means for identifying it. The mark 70 is configured as a coating film, for example. Coloring treatment may be applied to the central portion of the outer surface of the porous membrane 64. Or in order to avoid the air permeability fall accompanying a coloring process, you may color-process except a center part.

  FIG. 10 shows a fourth embodiment. FIG. 10 shows the inner surface of the β-ray incident window 72. A plurality of vent holes 74 are formed in the window member, and the plurality of vent holes 74 are closed by a plurality of porous films 76. According to the fourth embodiment, it is difficult to identify the contamination source, but the β-ray detection sensitivity can be increased.

  FIG. 11 shows a fifth embodiment. FIG. 11 shows the inner surface of the β-ray incident window 78. The entire window member is composed of a porous film. An electrode layer 80 having a lattice pattern is formed on the inner surface of the window member. According to the fifth embodiment, the β-ray detection sensitivity can be further increased.

  FIG. 12 shows a sixth embodiment. The detection unit 81 includes a container 82, which includes a β-ray incident window 86 and a housing 84. The β-ray incident window 86 is not provided with a ventilation structure, and the casing 84 is provided with a ventilation structure. Specifically, a vent hole 88 is formed on the lower side of the casing 84, and the vent hole 88 is closed with the porous film 90 on the inner surface side of the casing 84. Also in the sixth embodiment, the pressure difference can be eliminated and the deformation of the β-ray incident window 86 can be prevented. Further, according to the sixth embodiment, the sensitivity is made uniform over the entire β-ray incident window 86. The vent 88 becomes a high-sensitivity region for β-rays, and the periphery thereof becomes a shield for β-rays. Therefore, a second β-ray detection structure with a small detection field of view is realized on the lower side of the container 82. If it is not desired to function it, it may be covered with a non-hermetic cap or the like.

  FIG. 13 shows a seventh embodiment. In the seventh embodiment, the detection unit 92 is provided with a plurality of ventilation structures 94 and 96. The ventilation structure 94 includes a relatively large ventilation hole 98 and a relatively large porous membrane 100 that closes the ventilation hole 98. The ventilation structure 96 includes a relatively small vent 102 and a relatively small porous member 104 that closes the vent 102. The individual ventilation structures 94 and 96 function as β-ray detection structures. The two β-ray detection structures have different detection visual field sizes, and it is possible to select a β-ray detection structure to be brought close to the surface of the object depending on the situation. A cap may be attached to a β-ray detection structure that is not used. Three or more opening structures may be provided.

  In any of the first to seventh embodiments, deformation of the β-ray incident window can be prevented, and water and foreign matter can be prevented from entering the ionization chamber. In addition, all of the first to seventh embodiments are highly functional from the viewpoint of β-ray detection.

  A hard porous member may be used instead of the porous film. Moreover, you may utilize other members (water-repellent sheet etc.) provided with air permeability and waterproofness instead of the porous membrane. In any case, the generation of a pressure difference can be prevented by providing a selective transmission member in a part of the ionization chamber. You may apply the said ventilation structure to the ionization chamber apparatus different from a survey meter.

DESCRIPTION OF SYMBOLS 10 Detection part (ionization chamber), 12 Measurement part, 14 Container, 16 Housing | casing, 18 (beta) ray entrance window, 20 Porous membrane (selective transmission member), 28 Collector electrode, 30 Conductive layer, 34 Ventilation hole.

Claims (7)

A hollow ionization chamber,
A selectively permeable member that is provided in the ionization chamber, partitions the internal space and the external space of the ionization chamber, allows air to pass therethrough, and restricts water entry;
A radiation measuring apparatus comprising: The apparatus of claim 1.
The ionization chamber has a container defining the internal space;
The container has a vent for communicating the internal space and the external space,
The permselective member is a porous member provided to close the vent.
A radiation measuring apparatus characterized by that. The apparatus of claim 2.
The ionization chamber has a conductive layer formed on the inner surface of the container,
All or part of the inner surface of the porous member is exposed in the internal space,
A radiation measuring apparatus characterized by that. The apparatus of claim 2.
The radiation measurement device is a device capable of measuring γ rays and β rays,
The container includes a β-ray incident window;
The β-ray incident window is
A normal sensitivity region having a window member and a conductive layer formed on the inner surface thereof;
A highly sensitive region having the vent and the porous member;
Have
The β-ray attenuation action in the high sensitivity region is smaller than the β-ray attenuation action in the normal sensitivity region,
A radiation measuring apparatus characterized by that. The apparatus of claim 4.
The vent is formed in the center of the window member,
A radiation measuring apparatus characterized by that. The apparatus of claim 4.
Means for identifying the high sensitivity region is provided on the outer surface of the radiation incident window,
A radiation measuring apparatus characterized by that. The apparatus of claim 1.
A structure provided adjacent to the ionization chamber;
A power supply circuit disposed inside the structure and supplying a high voltage to the ionization chamber;
An electrometer circuit disposed inside the structure for observing an ionization current from the ionization chamber;
Including
All or part of the inside of the structure is an airtight space including the power supply circuit and the electrometer circuit.
A radiation measuring apparatus characterized by that.

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