JP2017068901A - Ionization chamber for radiation measurement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce measurement error due to charging in an ionization chamber for radiation measurement.SOLUTION: An ionization chamber for radiation measurement includes: a container 28 having an opening provided therein; a lid part 18 which is attachable to and detachable from the container 28 and covers the opening when mounted on the container 28; a β-ray transmission film 30 which blocks the opening and whose transmission characteristics for radiation are different from those of the container 28 and the lid part 18; an antistatic layer 56 provided on the outer surface of the lid part 18; a current collector electrode 32 whose one portion is located in the container 28; and an electrode layer 34 provided on the inner surface of the container 28 and the inner surface of the β-ray transmission film 30.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an ionization chamber for radiation measurement, and more particularly to improvement of characteristics of an ionization chamber.

  Some radiation measuring instruments that measure radiation such as β-rays and γ-rays are equipped with an ionization chamber filled with a gas. When radiation enters the ionization chamber, the gas in the ionization chamber is ionized by the radiation. The radiation measuring device measures a radiation dose based on an electric current caused by electrons or cations collected from an ionized gas to an electrode in an ionization chamber. In general, a current due to electrons having excellent mobility is measured.

  Patent Document 1 below describes an ionization chamber for radiation measurement. The ionization chamber is provided with an aluminum filter that covers the ionization chamber. The filter changes the energy characteristic of γ rays incident on the ionization chamber (characteristic indicating the detection sensitivity of radiation with respect to the energy of γ rays). Patent Document 1 describes an ionization chamber in which a through hole that transmits β rays is provided in a container body. When gamma rays are measured, the through hole is covered with a lid that is detachable from the container body. Since the container body and the lid block β rays, detection of β rays is hindered. On the other hand, when measuring radiation including γ rays and β rays, the lid is removed from the container body. Accordingly, since β rays pass through the through-hole, radiation including γ rays and β rays is measured.

Japanese Patent Laid-Open No. 4-4549

  In a radiation measuring instrument using an ionization chamber, when an charged object is brought close to the ionization chamber or a dielectric is rubbed against the outer surface of the ionization chamber, the ionization chamber is charged, and an electric charge that causes an error in the measured value appears on the internal electrode. Sometimes. This may cause an error in the radiation measurement.

  An object of the present invention is to reduce measurement errors due to charging of an ionization chamber for radiation measurement.

  The present invention provides a container provided with an opening, a lid that is detachably attached to the container, covers the opening when attached to the container, closes the opening, and has a radiation transmission characteristic with respect to the container and A transmissive member different from the lid part, an antistatic layer provided on the outer surface of the lid part, and an electron collecting structure for collecting electrons from the ionized gas in the container are provided.

  In the present invention, an antistatic layer is provided on the outer surface of the lid that is detachable from the container. For the antistatic layer, for example, a material that has conductivity and a uniform distribution of accumulated charges is used. By imparting conductivity, the amount of electric charge charged in the ionization chamber for radiation measurement due to friction is reduced. In addition, since the distribution of charges accumulated in the antistatic layer becomes uniform, the possibility that charges are accumulated locally is reduced. As a result, of the electrons collected by the electron collecting structure, electric charges that cause an error in the measured value are reduced. The electron collecting structure is constituted by, for example, a collector electrode that is partially or entirely located in the container, and an electrode layer provided on the inner surface of the container and the inner surface of the transmission member.

  Preferably, an antistatic layer is provided on the outer surface of the transmissive member.

  In the present invention, an antistatic layer is provided on the outer surface of the transmission member. As a result, even when the lid is removed, the effect of reducing the amount of charge charged in the radiation measurement ionization chamber and the effect of reducing the possibility of local charge accumulation are obtained. . As a result, of the electrons collected by the electron collecting structure, electric charges that cause an error in the measured value are reduced.

  Preferably, an antistatic layer is provided on the outer surface of the container.

  In the present invention, an antistatic layer is provided on the outer surface of the container. This enhances the effect of reducing the measurement error.

  Preferably, the container and the lid attenuate β rays, and the transmitting member transmits β rays.

  According to the present invention, it is possible to make γ-rays enter the radiation measurement ionization chamber and selectively measure the dose of the γ-rays.

  Desirably, the antistatic layer provided on the outer surface of the lid is formed of a conductive material.

  Desirably, the antistatic layer provided on the outer surface of the lid portion is formed of a surfactant.

  According to the present invention, it is possible to reduce measurement value errors due to charging of an ionization chamber for radiation measurement.

It is a perspective view of the radiation measuring instrument which concerns on embodiment of this invention. It is a perspective view of the radiation measuring instrument which concerns on embodiment of this invention. It is a figure which shows typically the axial direction cross section of an ionization chamber. It is a figure which shows typically the axial direction cross section of an ionization chamber.

  FIG. 1 is a perspective view of a radiation measuring instrument 10 according to an embodiment of the present invention. The radiation measuring instrument 10 includes an ionization chamber 12 and a measurement unit 14. The ionization chamber 12 is filled with air. The ionization chamber 12 has a structure for collecting electrons from the air ionized by the radiation incident on the ionization chamber 12. The measurement unit 14 measures the radiation dose based on electrons collected from the ionized air. The front panel 20 of the measurement unit 14 is provided with a display unit 22, and the measurement result is displayed on the display unit 22. An operation button 24 is provided on the front panel 20 and is operated by the user during measurement. The radiation measuring instrument 10 may be used as a portable measuring instrument. In FIG. 1, xyz coordinates are defined such that the direction from the front panel 20 of the radiation measuring instrument 10 toward the rear is the z-axis positive direction, the left direction toward the front panel 20 is the x-axis positive direction, and the upward direction is the y-axis positive direction. Is defined.

  FIG. 2 shows a perspective view when the radiation measuring instrument 10 is viewed from the rear. The ionization chamber 12 includes an ionization chamber main body 16 and a lid 18. The ionization chamber main body portion 16 has a hollow, substantially cylindrical shape, and the lid portion 18 is detachably attached to an opening at the rear of the ionization chamber main body portion 16.

  The ionization chamber main body 16 and the lid 18 are formed of a material that attenuates and blocks α rays and β rays and transmits γ rays. As will be described later, the opening of the ionization chamber body 16 that appears by removing the lid 18 is provided with a β-ray transmission film as a transmission member that seals the air in the ionization chamber body 16 and transmits β-rays. It has been. When measuring γ-rays, the lid 18 is attached to the ionization chamber body 16 and the measurement is performed with the β-rays blocked. On the other hand, when measuring radiation including γ rays and β rays, the lid 18 is removed from the ionization chamber body 16 and the measurement is performed in a state where the γ rays and β rays are incident on the inside of the ionization chamber 12.

  FIG. 3 schematically shows an axial cross section of the ionization chamber 12. Further, a measurement circuit 26, a high voltage generation circuit 27, and a display unit 22 included in the measurement unit are schematically shown in the lower right of the ionization chamber 12. The ionization chamber body 16 includes a container 28, a β-ray transmissive film 30, a collecting electrode 32, an electrode layer 34, a collecting electrode support member 36, an electrode layer terminal 38, a terminal support member 40, and an antistatic layer 42.

  The container 28 forming the ionization chamber body 16 is formed of an insulator such as plastic resin. In the example shown in FIG. 3, the container 28 is formed in a substantially cylindrical shape, but the container 28 may have a polygonal cylindrical shape. The container 28 includes a cylindrical side wall 44 and an end wall 46 provided at one end of the cylindrical side wall 44 (one end on the z-axis negative direction side). The other end of the cylindrical side wall 44 is opened to form an opening. The cylindrical side wall 44 and the end wall 46 have a thickness that sufficiently attenuates and blocks β rays. Instead of a structure in which one end of the cylindrical side wall 44 is closed and the other end is opened as described above, a wall may be provided at the other end, and the opening may be provided by partially removing the wall. Good.

  The opening is blocked by the β-ray transmissive film 30. The β-ray transmissive film 30 is formed of, for example, a plastic resin such as polyethylene terephthalate. The β-ray transmissive film 30 is different from the container 28 and the lid portion 18 in the radiation transmission characteristic. The container 28 and the lid 18 block α rays and β rays and transmit γ rays, whereas the β ray transmitting film 30 blocks α rays and transmits β rays and γ rays.

  A collector electrode fixing hole 48 is provided in the end wall 46 of the container 28. A collector electrode support member 36 formed of an insulator such as plastic resin is inserted into the collector electrode fixing hole 48. The collector electrode 32 extending in the z-axis direction passes through the collector electrode support member 36. The collector electrode 32 is supported by the collector electrode support member 36 in the container 28, and is fixed to the container 28 via the collector electrode support member 36 so as to reach the outside from the inside of the container 28. Further, the collector electrode support member 36 closes the gap between the collector electrode 32 and the end wall 46 and seals the air in the container 28. The collector electrode 32 is connected to the measurement circuit 26 outside the container 28. In addition to fixing the collecting electrode 32 to the container 28 so as to extend from the inside of the container 28 to the outside, the entire collecting electrode 32 is accommodated in the container 28, and the conducting wire connected to the collecting electrode 32 is pulled out from the container 28. It may be connected to the measurement circuit 26.

  A terminal fixing hole 50 is further provided in the end wall 46 of the container 28. A terminal support member 40 formed of an insulator such as plastic resin is attached to the terminal fixing hole 50. The electrode layer terminal 38 extending in the z-axis direction passes through the terminal support member 40. The electrode layer terminal 38 is supported by the terminal support member 40 in the container 28, and is fixed to the container 28 via the terminal support member 40 so as to reach the outside from the inside of the container 28. Further, the terminal support member 40 closes the gap between the electrode layer terminal 38 and the end wall 46 and seals the air in the container 28. The electrode layer terminal 38 is connected to the high voltage generation circuit 27 outside the container 28.

  An electrode layer 34 formed of a conductive material such as carbon is provided on the inner surface of the container 28 and the inner surface of the β-ray transmissive film 30. As a material for forming the electrode layer 34, a material that has a smaller influence on the energy characteristics of the radiation that passes through the electrode layer 34 than the metal may be used. The electrode layer terminal 38 contacts the electrode layer 34 in the container 28 and is electrically connected to the electrode layer 34.

  An antistatic layer 42 is provided on the outer surface of the container 28 and the outer surface of the β-ray transmitting film 30. The antistatic layer 42 is formed of, for example, a conductive material such as metal or carbon. When the antistatic layer 42 is formed of a metal, nickel, aluminum, copper, or the like may be used. Further, the antistatic layer 42 may be formed of a surfactant. A surfactant is a material having both a hydrophilic group and a hydrophobic group in the molecular structure. The surfactant is moistened by the action of the hydrophilic group and has increased conductivity. The antistatic layer 42 may be formed by applying a conductive paint or a surfactant to the outer surface of the container 28 and the β-ray transmitting film 30. The antistatic layer 42 formed on the outer surface of the container 28 and the antistatic layer 42 formed on the outer surface of the β-ray transmissive film 30 may be electrically connected.

  The air inside the container 28 is sealed in the container 28 by the β-ray transmissive film 30, the collecting electrode support member 36 and the terminal support member 40.

  The lid 18 includes a lid plate 52 facing in the positive z-axis direction and a lid side wall 54 surrounding the edge of the lid plate 52. The lid plate 52 and the lid side wall 54 are formed of an insulator such as a plastic resin, for example. The lid plate 52 and the lid side wall 54 have a thickness that sufficiently attenuates and blocks β rays. An antistatic layer 56 similar to the antistatic layer 42 provided on the outer surface of the ionization chamber body 16 is provided on the outer surface of the lid portion 18. When the lid 18 is attached to the ionization chamber body 16, the opening of the ionization chamber body 16 is covered by the lid 18. At this time, when the antistatic layer 56 provided on the outer surface of the lid 18 and the antistatic layer 42 provided on the outer surface of the ionization chamber body 16 are conductive, these antistatic layers are electrically connected. Also good. The lid 18 may be detachable from the ionization chamber body 16 by a hook mechanism. In this case, a protrusion is provided on the side surface of the lid portion 18, and a hook component extending to the side surface of the lid portion 18 is fixed to the side surface of the ionization chamber main body portion 16. The hook component is made of, for example, a J-shaped metal. A structure having the same function as this may be formed by resin processing of the side surface of the ionization chamber body 16 and the lid 18. The lid 18 is fixed to the ionization chamber main body 16 by hooking the projection from the side surface of the ionization chamber main body 16 with a hook part, and the lid 18 is removed from the ionization chamber main body 16 by releasing the hook part from the projection. It becomes possible. Moreover, it may replace with such a structure and may employ | adopt the structure which provided the protrusion in the side surface of the ionization chamber main-body part 16, and provided the hook components in the side surface of the cover part 18. FIG.

  The γ-rays are transmitted through the container 28, the β-ray transmitting film 30, the antistatic layer 42 and the electrode layer 34 constituting the ionization chamber main body 16. In addition, the γ rays are transmitted through the lid plate 52, the lid side wall 54, and the antistatic layer 56 constituting the lid portion 18.

  As shown in FIG. 4, the lid 18 and the ionization chamber body 16 may have a structure in which the lid 18 is fitted to the ionization chamber body 16 with an appropriate frictional force. In this example, a cylindrical lid attaching portion 58 having a diameter smaller than that of the open end is provided along the edge of the open end of the container 28. The inner surface of the lid side wall 54 is in contact with the antistatic layer 42 on the outer surface of the lid attachment portion 58 with a frictional force that allows the lid portion 18 to be detachably attached to the ionization chamber body portion 16.

  The lid 18 may be detachable from the ionization chamber body 16 by a screw mechanism. In this case, a screw thread or a screw groove is formed on the outer surface of the lid attaching portion 58. On the other hand, a screw groove or a thread is formed on the inner surface of the lid side wall 54. By rotating the lid 18, the lid 18 is detachable from the ionization chamber body 16.

  The operation of the radiation measuring instrument will be described with reference to FIG. The high voltage generation circuit 27 applies a DC voltage with the collector electrode 32 side being positive between the collector electrode 32 and the electrode layer terminal 38. As a result, the collector electrode 32 has a high potential with respect to the electrode layer 34, and an electric field is generated between the collector electrode 32 and the electrode layer 34.

  When the gamma ray measurement is performed, the lid 18 is attached to the ionization chamber body 16. Since the ionization chamber body 16 and the lid 18 block β rays, the inside of the ionization chamber 12 is shielded from β rays, and γ rays are measured. When γ rays are incident on the ionization chamber, the air in the ionization chamber 12 is ionized by the γ rays. Electrons are collected on the collector electrode 32 by the electric field generated between the collector electrode 32 and the electrode layer 34. As a result, a current flows through the collector electrode 32. The measurement circuit 26 obtains the dose of γ rays based on the current flowing through the collector electrode 32 and displays the γ dose on the display unit 22.

  When measuring radiation containing γ rays and β rays, the lid 18 is removed from the ionization chamber body 16. Gamma rays enter the ionization chamber 12 from all directions of the ionization chamber 12. β-rays enter the ionization chamber 12 from the antistatic layer 42, the β-ray transmission film 30, and the electrode layer 34 provided in the opening of the ionization chamber body 16. Radiation including γ rays and β rays is measured by the same principle as that of γ rays.

  As described above, the antistatic layer 42 and the antistatic layer 56 are provided on the ionization chamber body 16 and the lid 18. When these antistatic layers are formed of a conductive material, triboelectric charge is less likely to occur, and the amount of charge charged in the ionization chamber 12 is reduced. Further, even if dielectric polarization occurs in the container 28, the β-ray transmissive film 30, the lid plate 52, and the lid side wall 54, the charge distribution in the antistatic layer becomes uniform, and charges may be accumulated locally. Becomes lower. As a result, of the electrons collected at the collector electrode 32, the electrons that cause the measurement value error are reduced, and the measurement value error is reduced. In addition, when the antistatic layer is formed of a surfactant, the antistatic layer is moistened by the action of the hydrophilic group to increase the conductivity. Therefore, the same effect as when the antistatic layer is formed of a conductive material can be obtained.

  In the conventional ionization chamber, when the measured value fluctuates due to an error due to charging, it is difficult to correctly measure the actual radiation dose. According to the present invention, since the error included in the measurement value is reduced, the radiation dose can be accurately measured.

DESCRIPTION OF SYMBOLS 10 Radiation measuring instrument, 12 Ionization chamber, 14 Measurement part, 16 Ionization chamber main-body part, 18 Lid part, 20 Front panel, 22 Display part, 24 Operation button, 26 Measurement circuit, 27 High voltage generation circuit, 28 Container, 30 Beta ray Transmission film, 32 collector electrode, 34 electrode layer, 36 collector electrode support member, 38 electrode layer terminal, 40 terminal support member, 42, 56 antistatic layer, 44 cylindrical side wall, 46 end wall, 48 collector electrode fixing hole, 50 Terminal fixing hole, 52 lid plate, 54 lid side wall, 58 lid mounting part.

Claims (6)

A container provided with an opening;
A lid that is detachable from the container and covers the opening when attached to the container;
A transparent member that closes the opening and has a radiation transmission characteristic different from the container and the lid;
An antistatic layer provided on the outer surface of the lid, and
An electron collection structure for collecting electrons from the ionized gas in the container;
An ionization chamber for radiation measurement, comprising: The ionization chamber for radiation measurement according to claim 1,
An ionization chamber for radiation measurement, comprising an antistatic layer provided on the outer surface of the transmission member. In the ionization chamber for radiation measurement according to claim 1 or 2,
An ionization chamber for radiation measurement, comprising an antistatic layer provided on the outer surface of the container. The ionization chamber for radiation measurement according to any one of claims 1 to 3,
An ionization chamber for radiation measurement, wherein the container and the lid part attenuate β rays, and the transmitting member transmits β rays. The ionization chamber for radiation measurement according to any one of claims 1 to 4,
An ionization chamber for radiation measurement, wherein the antistatic layer provided on the outer surface of the lid portion is formed of a conductive material. The ionization chamber for radiation measurement according to any one of claims 1 to 4,
An ionization chamber for radiation measurement, wherein the antistatic layer provided on the outer surface of the lid portion is formed of a surfactant.

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