JP2676974B2 - 1 ▲ cm ▼ Ionization chamber for deep dose equivalent detection - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aerial ionization chamber which is filled with air and detects radiation and outputs a radiation detection signal corresponding to the detection result, and more particularly, a correction process for the radiation detection signal. This radiation detection signal is 1 cm of radiation without adding
Regarding the ionization chamber that represents the deep dose equivalent (hereinafter, this dose equivalent may be referred to as H1cm).

[Prior art]

FIG. 7 is a longitudinal sectional view of a main part of a conventional pneumatic ionization chamber 1. In the figure, 2 is a bottomed cylindrical container body made of polycarbonate resin having a carbon-based conductive film 3 provided on its inner surface, 4
Is a columnar collector having a carbon-based conductive film 5 provided on the entire surface except one end face 4a, and 6 has one end fixed to the end face 4a and electrically connected to the conductive film 5 by means not shown. A disk-shaped first member having a high electrical insulation property in which a pin-shaped output terminal 7 is airtightly provided so as to support the collector electrode 4 in a fixed manner. 2, the first member 6 and the open end of the main body 2 are fixedly coupled so as to be coaxial with the main body 2, and the ionization chamber container 9 as an airtight container is formed together with the member 6 and the main body 2. It is the annular second member made of synthetic resin so as to be formed. Reference numeral 10 is a pin-shaped high-voltage terminal that is provided in an airtight manner at the open end of the container body 2. In this case, the terminal 10 is electrically connected to the conductive film 3 by means not shown, and the ionization chamber The container 9 is filled with air 11. Thus, the pneumatic ionization chamber 1 described above is composed of the above-mentioned components. Since the ionization chamber 1 is configured as described above, radiation
When 12 penetrates the container body 2 and enters the container 9, the radiation 11 ionizes the air 11. Therefore, if a voltage is applied between the terminals 7 and 10 at this time, the radiation is generated between the terminals 7 and 10. An ionization current having a current value I corresponding to the irradiation dose rate A of 12 flows, and in the case of the ionization chamber 1, the energy E of the radiation 12 of the radiation detection sensitivity S of the ionization chamber 1 defined by I / A = S. (Hereinafter, this dependency may be referred to as the radiation detection sensitivity vs. radiation energy characteristic of the ionization chamber 1 or the energy characteristic of the ionization chamber 1 or the energy characteristic of the detection sensitivity S, etc.). When represented by relative sensitivity D based on [MeV], the characteristic line 13 shown in FIG. 8 is obtained (hereinafter, the relationship between relative sensitivity D and E is also referred to as energy characteristic). . Although not shown in FIG. 8, the characteristic line 13 has a flat characteristic as compared with other radiation detectors such as a GM tube and a scintillation detector, and therefore the ionization chamber 1 In the calibration of the characteristic line 13 prior to the measurement of the irradiation dose rate A using this ionization chamber, the number of calibration points of the energy E is smaller than that of the other radiation detectors described above. There are advantages.

[Problems to be solved by the invention]

The ionization chamber 1 has the energy characteristics as described above, but the radiation detection signal that detects and outputs the radiation 12 is 1 cm deep dose equivalent H1 cm
The appearance of a radiation detector having the energy characteristic shown by the characteristic line 14 in FIG. 4 (hereinafter, this energy characteristic may be referred to as the reference energy characteristic or the H1cm characteristic) is required. In this case,
As can be seen by comparing FIG. 8 and FIG. 4, characteristic lines 13 and 14
Is clearly different. Therefore, when trying to detect H1cm of the radiation 12 using the ionization chamber 1,
First, it is necessary to obtain the energy E of the radiation 12 and then to perform a correction calculation on the radiation detection signal according to the energy E. Therefore, the above-mentioned ionization chamber 1 cannot easily detect H1cm. There will be. Then, again, since the ionization chamber 1 is configured as described above and the ionization chamber container 9 is formed of the members 2, 6 and 8 each having a relatively large thickness, the radiation 12 is a β ray. In some cases, it is almost impossible for this β-ray to enter the container 9. Therefore, if the ionization chamber 1 needs to be provided with another radiation detector when β-ray detection is required, the radiation 12 is emitted. There is also a problem in that it is not easy to use when including γ rays and β rays. The object of the present invention is that the energy characteristic of the pneumatic ionization chamber is H1.
The aim is to obtain a pneumatic ionization chamber that can easily detect H1cm by making it as close as possible to the cm characteristic. By doing so, it is also possible to detect both β rays and γ rays in the same ionization chamber, and obtain a convenient H1cm detection required ionization chamber for detection of radiation including β rays and γ rays. Especially.

[Means for solving the problem]

To achieve the above object, according to the present invention, a carbon-based conductive film is provided on at least a part of the inner surface and at least a part of the outer surface or at least a portion between the outer surface and the inner surface and surrounding the inner surface. An ionization chamber container made of a synthetic resin in which a metal filter that absorbs low-energy radiation is partially provided and filled with air, and an ionization chamber container that is arranged in the ionization chamber container and is included in at least a part of the surface of the electrode body. A film-shaped first conductive region made of a nickel synthetic resin or pure nickel is formed, and a film-shaped second conductive region made of a carbon-containing synthetic resin is formed on the rest of the surface except the first conductive region. Radiation detection that includes an electrode and directly penetrates the ionization chamber container at a position where the film is provided and that is incident on the ionization chamber container at a depth of 1 cm. Signal from the collector electrode, the ratio of the inner volume of the ionization chamber container to the area of the surface of the collector electrode occupied by the first conductive region, the nickel content of the nickel-containing synthetic resin, and the filter. The ionization chamber for 1 cm deep dose equivalent detection is configured by setting the material and thickness of the ionization chamber, and in the above ionization chamber for 1 cm deep dose equivalent detection, a part of the ionization chamber container is A synthetic resin film body, which is disposed so as to face the inside of the container and has a carbon-based conductive film formed on one surface facing the inside, and the other side of the film body is covered with the film body. And a metal filter formed by an inner surface or an outer surface or a synthetic resin lid provided between the inner surface and the outer surface.
An ionization chamber for 1 cm deep dose equivalent detection is constructed.

[Operation]

With the above structure, the γ-rays as the radiation transmitted through the ionization chamber container ionize the air in the container, and the γ-rays transmitted through the container are incident on the nickel in the first conductive region of the collector electrode. Since the electrons knocked out from this nickel further ionize the air in the ionization chamber container, the value of the radiation detection signal generally becomes larger than that in the conventional ionization chamber in which the first conductive region is not provided in the collector electrode,
Moreover, the low energy γ-rays that pass through this filter and enter the ionization chamber container are absorbed by the filter, so the value of the radiation detection signal becomes small in the low energy region of the radiation incident on the ionization chamber container. And in the end,
Since the energy characteristic of the ionization chamber is similar to the H1cm characteristic, an ionization chamber that can easily detect H1cm of radiation will be obtained. Then, again, with the above configuration,
By keeping the thickness of the wire easily permeable,
It is clear that the ionization chamber for β-ray detection can be obtained immediately by removing the lid from the support mechanism of the membrane body, and the ionization chamber for H1cm detection of γ rays can be obtained immediately by attaching the lid to the support mechanism of the membrane body. It is clear that the ionization chamber for H1cm detection is easy to use when detecting radiation including β rays and γ rays.

【Example】

FIG. 1 shows an ionization chamber for detecting H1cm as one embodiment of the present invention.
15 is a vertical cross-sectional view of the main part, where the difference from FIG. 7 of this drawing is
An aluminum filter 16 having a thickness t [mm] is provided on each outer surface of the bottom portion 2a and the side wall of the bottomed cylindrical container body 2 and the other end surface of the collecting electrode 4 is provided. A synthetic resin conductive paint containing 90% [%] or more of nickel in a portion having an area B [cm ² ] consisting of 4b and a cylindrical part of the side surface of the side surface of the collector electrode 4 which is continuous with the end surface 4b. The carbon-based conductive film made of carbon-containing synthetic resin provided on the surface of the collecting electrode 4 except the area B on the surface of the collecting electrode 4.
It is formed so as to be electrically connected to 25. The reason why the ionization chamber 15 is configured as described above will be described below. That is, in FIG. 2, the internal product is 650 [c
m ³ ], which has an ionization chamber container 9 of FIG. 1 and has a structure in which the filter 16 is removed from the ionization chamber 15 of FIG. 1, and the area B is changed as shown in FIG. In the experimental result explanatory diagram of the inventor who measured the energy characteristic of the box, each characteristic line of a, b, and c in FIG. 2 is a representative within the range of the area B shown corresponding to each characteristic line. It is a characteristic line. In addition, FIG. 3 shows the same configuration as the ionization chamber 15 shown in FIG. 1 by providing the filter 16 made of aluminum in the ionization chamber without a filter having the energy characteristic shown by the characteristic line B shown in FIG. In the ionization chamber with a filter, the above-mentioned filter thickness t was changed as shown in FIG. 3 to measure the energy characteristics of the ionization chamber with a filter. , T = 1
In addition to the characteristic lines D and E in each case, the characteristic line B shown in FIG. 2 is also shown for convenience of the following description.
Then, in FIG. 2, the γ-rays transmitted through the ionization chamber container 9 ionize the air 11 and the γ-rays transmitted through the container 9 irradiate the nickel in the coating film 17 to knock out the nickel. The generated electrons further ionize the air 11, so that the coating film 17
Is provided, an energy characteristic line having a shape protruding upward as compared with the energy characteristic line 13 of the ionization chamber 1 of FIG. 7 in which this coating film 17 is not provided, and the maximum value of this energy characteristic line is obtained. Indicates that the larger the area B is, the larger the area B is. Also, FIG. 3 shows that low energy γ-rays of the γ-rays are absorbed by the aluminum filter 16 when the ions enter the ionization chamber container 9. In the ionization chamber with a filter, E
It is shown that the relative sensitivity D decreases and the energy characteristic line hangs in the low energy region of. In the above-mentioned FIG. 4, the characteristic line E shown in FIG.
In the energy characteristic explanatory view of the above-described ionization chamber with a filter, which is shown together with the cm characteristic line 14, the characteristic line E closely matches the characteristic line 14 in the vicinity of E = [keV] or less from the fourth.
It is clear that the characteristic line E coincides with the characteristic line 14 within an error range of 10% even when E = 80 [keV] or more. Therefore, in the ionization chamber 15 of FIG. 1, when the inner volume V of the ionization chamber container 9 is 650 [cm ³ ], the area B where the coating film 17 is provided is 15
The area is within the range of 25 [cm ³ ] and the thickness t of the aluminum filter 16 is 1 [mm]. Therefore, in the ionization chamber 15 of V = 650 [cm ³ ], the energy characteristic becomes the characteristic line E shown in FIG. 3 and FIG.
When a predetermined voltage is applied between the terminals 7 and 10, a radiation detection signal 15a that directly expresses H1 cm of the radiation that has passed through the container 9 and has entered the container 9 is output from the collector electrode 4. As a result, H1 cm of the radiation 12 can be easily detected by the signal 15a. Now, in the ionization chamber 15 in which the inner volume V of the ionization chamber container 9 is 650 [cm ³ ], the surface area B of the collector electrode 4 occupied by the coating film 17 and the nickel-containing synthetic resin conductive paint forming this coating film 17 Content G of nickel, the material of the filter 16 and its thickness t
And were set as above. However, the energy characteristic line shown in FIG. 2 projects upward as compared with the characteristic line 13 in FIG. 8 because it is due to the electrons emitted from the nickel of the coating film 17 as described above. In the ionization chamber without a filter having the configuration in which the filter 16 is removed from the ionization chamber 15 having the above configuration, it is clear that the protruding form of the energy characteristic line depends on the ratio B / V between the area B and the volume V and the content rate G. Also, the characteristic lines D and E shown in FIG. 3 hang down in the low energy region of E as compared with the characteristic line B in the filter.
Ionization chamber 15 because it is based on the absorption of γ rays by 16
Then, it is clear that the form of the energy characteristic line in the low energy region depends on the material and thickness of the filter 16. Therefore, in the present invention, the ratio B / V, the nickel content G, and the filter 16 corresponding to the internal volume V of the container 9 are set so that the radiation detection signal 15a in the ionization chamber 15 becomes a signal that directly represents H1 cm. It suffices to set the material and the thickness t. Therefore, in the present invention, the filter 16 has
Obviously, it may be formed of a material having a thickness shown in FIG. 5 other than aluminum having a thickness of [mm]. In addition, in the ionization chamber 15, since the filter 16 is provided over the entire outer surface of the container body 2 except the opening end side, the ionization chamber 15
The function of detecting H1 cm of the radiation 12 is omnidirectional except for the open end side of the container body 2. However, in the present invention, the filter 16 has one outer surface except for the open end side of the container body 2. The H1cm detection function of the ionization chamber 15 may be directional by providing the ionization chamber 15. Further, in all the embodiments of the present invention described above, the filter 16 is provided on the outer surface of the container body 2, but in the present invention, the filter 16 is embedded in the wall pair of the container body 2. May be. Further, in each of the above-described embodiments of the present invention, the coating film 17 is formed on the area B of the collector electrode 4. However, in the present invention, the coating film 17 is replaced by nickel plating. Layers may be provided. FIG. 6 is a longitudinal sectional view of an essential part of an ionization chamber 18 for H1cm detection as an embodiment of the present invention different from the embodiment of the present invention shown in FIG. 1. The difference from FIG. The through-hole 2b having a large area is provided in the bottom portion 2a of 2 and the β-ray incident window 21 including the polyester film 19 and the synthetic resin frame 20 supporting the film 19 penetrates through the film 19. It is detachably fixed to the container body 2 by means not shown so as to close the hole 2b, and the aluminum plate filter 22 having a thickness of 1 mm on one surface side is not shown. Plate-like body portion 23 made of synthetic resin and having the same thickness and the same material as the container body 2 fixed by
The lid 24 composed of and is detachably attached to the frame body 20 by covering the film 19 from the outer surface side of the film 19 with the filter 22, and in this case, the inner surface of the film 19 is a container. A carbon-based conductive film 3 of the same material as that on the inner surface of the main body 2 is provided. Then, Fig. 6 shows the lid.
23 shows a state in which 23 is removed from the frame body 20. The ionization chamber 18 is configured as described above, and further, the film 19 is formed to have a thickness capable of transmitting β rays. Therefore, it is apparent that the β-ray detecting ionization chamber can be obtained immediately by removing the lid 24 from the frame body 20 in the ionization chamber 18. Then, again, in the ionization box 18, the lid 24 is a frame body.
In such a state that the energy characteristics for γ-rays that are sequentially transmitted through the lid main body 23, the filter 22, and the film 19 and are incident on the ionization chamber container 9 in the state of being attached to 20, match the above-mentioned B / V and G is set. Therefore, according to the ionization box 19, since a directional H1cm detection ionization box can be immediately obtained by attaching the lid 24 to the frame body 20, it is easy to use when detecting radiation in which β rays and γ rays are mixed. The convenience of being good is obtained. Although the filter 22 is made of aluminum in the ionization chamber 18,
In this case, it is obvious that the filter 22 may be made of the material and the thickness shown in FIG.

【The invention's effect】

As is apparent from the above description, the γ-rays as the radiation that have passed through the ionization chamber container ionize the air in the container, and the γ-rays that have passed through the container are incident on the nickel in the first conductive region of the collector electrode. By doing so, the electrons knocked out from the nickel and the air in the ionization chamber container are ionized, so that the value of the radiation detection signal is generally larger than that in the conventional ionization chamber in which the first conductive region is not provided in the collecting electrode. In addition, since the low energy γ-rays that pass through this filter and enter the ionization chamber container are absorbed by the filter, the value of the radiation detection signal is small in the low energy region of the radiation entering the ionization chamber container. Therefore, in the end, the present invention has an effect that an ionization chamber capable of easily detecting H1 cm of radiation can be obtained because the energy characteristics of the ionization chamber become characteristics similar to the H1 cm characteristic. That. Then, when configured as described above, the thickness for allowing the β-rays of the membrane to be easily transmitted allows the ionization chamber for β-ray detection to be immediately performed when the lid is removed from the support mechanism of the membrane. It is clear that it can be obtained, and it is clear that the ionization chamber for H1cm detection of γ-rays can be immediately obtained by attaching the lid to the support mechanism of the membrane body, and therefore, in the present invention, β-rays and γ-rays Easy-to-use H1 for detecting radiation including
The ionization chamber for cm detection is effective. Further, a nickel-containing synthetic resin coating material or nickel plating is applied to the surface of the electrode body to form a film-shaped first conductive region and at the same time form a remaining film-shaped second conductive region. Therefore, a collector electrode having desired characteristics can be easily manufactured. In addition, if the electrode body is made of resin, the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an embodiment of the present invention, FIGS. 2 and 3 are diagrams for explaining different experimental results, and FIG. 4 is an explanation of energy characteristics of the embodiment of the present invention shown in FIG. 5 and 5 are explanatory views of the configuration of the main part shown in FIG. 1, FIG. 6 is an explanatory view of the configuration of an embodiment of the present invention different from the embodiment of FIG. 1, and FIG. 7 is a conventional pneumatic ionization system. FIG. 8 is a longitudinal sectional view of a main part of the box, and FIG. 8 is an explanatory view of energy characteristics of the ionization box shown in FIG. 3 ... Carbon-based conductive film, 4 ... Collection electrode, 9 ... Ionization chamber container, 11 ... Air, 12 ... Radiation, 15, 18 ... Ionization chamber for detecting deep dose equivalent, 15a ... Radiation detection Signal, 16,22 ...
... filter, 17 ... coating film (first conductive region), 19 ... polyester film (membrane), 20 ... frame (membrane support mechanism), 24 ... lid, 25 ... carbon conductive film ( Second conductive region).

Claims (2)

(57) [Claims] 1. A carbon-based conductive film is provided on at least a part of an inner surface, and at least a part of an outer surface or at least a part between the outer surface and the inner surface and surrounding the inner surface absorbs low energy radiation. A synthetic resin ionization chamber container provided with a metal filter and filled with air, and a film made of nickel-containing synthetic resin or pure nickel disposed in the ionization chamber container and at least a part of the electrode body surface. And a collector electrode on which a film-shaped second conductive region made of carbon-containing synthetic resin is formed on the remaining portion of the surface excluding the first conductive region, and the filter is provided. A radiation detection signal that directly represents the 1 cm deep dose equivalent of the radiation that has passed through the ionization chamber container and has entered the ionization chamber container at a predetermined position is output from the collector electrode. As described above, the ratio of the inner volume of the ionization chamber container to the surface area of the collector electrode occupied by the first conductive region, the nickel content of the nickel-containing synthetic resin, and the material and thickness of the filter are set. An ionization chamber for 1 cm deep dose equivalent detection characterized by. 2. The ionization chamber according to claim 1, wherein a part of the ionization chamber container is arranged so as to face the inside of the ionization chamber container, and the carbonaceous material is provided on one surface facing the inside. A synthetic resin film body on which a conductive film is formed, and a metal film which is detachably attached to a support mechanism of the film body so as to cover the film body on the other surface side of the film body 1c characterized in that it is formed by an outer surface or a lid made of synthetic resin provided between the inner surface and the outer surface.
An ionization chamber for detecting deep dose equivalents.