JP2014041072A - Ionization chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ionization chamber capable of measuring radiation dose quickly and with high sensitivity without being influenced by an outside electric field even if its opening is not electrostatically shielded.SOLUTION: An ionization chamber 10 includes: a first electrode 13 which is placed in interior space 10s specified by a wall 11 and an opening 12 and to which predetermined voltage is applied; and a second electrode 14 for collecting and outputting electric charge corresponding to radiation dose. The second electrode 14 is placed in the interior space 10s which is located between the opening 12 and the wall area which is squarely faced from the opening 12. Moreover, a shield electrode 16 is interposed between the opening 12 and the second electrode 14 and electrostatically shields the second electrode 14 from the opening 12.

Description

  The present invention relates to an ionization chamber for measuring the amount of radiation.

  The ionization chamber encloses a gas and has a plurality of electrodes (for example, a high voltage electrode and a collecting electrode), collects ions and electrons generated by ionizing the gas by incident radiation, and collects the radiation by the electrode. The amount is measured (Patent Document 1).

  Such an ionization chamber is closed with a gas-filled film (for example, a film formed of synthetic resin) whose opening is extremely thin. This is because the gas-filled film attenuates alpha rays and beta rays when the film thickness is thick, and attenuates alpha rays when the film thickness is relatively thin (if the film thickness is still thick). (2), secondary electrons are emitted when gamma rays pass through the film, and the amount of gamma rays can be measured based on the number of secondary electrons.

  Also, if the ionization chamber is affected by an external electric field, it will affect the collection of ions and electrons. Therefore, at least the collector electrode needs to be electrostatically shielded from an external electric field, and a conductive thin film (for example, a thickness of several microns) is deposited on the gas-filled film, for example. Such a gas-filled membrane is relatively expensive, and if it breaks, it is necessary to replace the gas-filled membrane and re-fill the gas. In addition, the operation rate of the radiation measuring instrument decreases due to repair work.

  By the way, when determining whether or not the amount of radiation is below a certain regulation value, it is not necessary to measure with high accuracy. This is because an error that may occur in the measurement is subtracted from the regulation value to obtain a threshold value, and when the amount of radiation measured is lower than this threshold value, it can be determined that the regulation value or less. In the case of measuring with such accuracy, it is not necessary to enclose the gas, and the gas enclosure can be omitted to facilitate the handling of the ionization chamber.

  However, when the opening is opened to the outside, the collector electrode cannot be electrostatically shielded from the external electric field, and the external electric field becomes a disturbance factor in the measurement, which may cause an error in radiation measurement. As an ionization chamber in which such an error does not occur, an ionization chamber has been developed in which the collector electrode is retracted behind the high-voltage electrode so that the collector electrode cannot be viewed directly from the opening (Patent Document 2).

Japanese Patent Laid-Open No. 10-332835 Japanese Patent No. 4671153

  By the way, in order to measure the amount of radiation with a strict regulation value, it is necessary to measure the amount of radiation with high sensitivity. For that purpose, the area of the ionization chamber opening (opening area) is increased and the incident radiation is increased. Need to be more. Of course, it is also necessary to collect positive ions, negative ions, and electrons ionized by radiation incident from the opening as much as possible (hereinafter, positive ions and negative ions may be simply referred to as ions).

  That is, after widening the opening, it is necessary to collect the ions and electrons by arranging the collecting electrode in a space that can be viewed directly from the opening, and increasing the electric field strength in this space as much as possible.

  In addition, when measuring the amount of radiation of an object to be measured (for example, rice grains, vegetables, seafood, meat), it is possible to measure easily and quickly if the object to be measured can be placed widely and uniformly on a tray or the like. It becomes. In order to cope with such measurement, the ionization chamber is desired to have a wide opening.

  However, as described above, the collector electrode that can be directly viewed from the opening is easily affected by the external electric field, and the wide opening further increases the influence of the external electric field. Certainly, in the technique of Patent Document 2, the collector electrode is disposed at a position where it cannot be directly viewed from the opening, and is not affected by the external electric field. However, such an arrangement of the collector electrode does not increase the electric field strength in the internal space that can be viewed directly from the opening of the ionization chamber (the collector is not disposed in the internal space that can be viewed directly from the opening of the ionization chamber). .

  Therefore, the present invention is not affected by an external electric field even if the opening is not blocked by an electrostatic shielding member, and has a wide opening so that the amount of radiation in various objects to be measured can be quickly and high. The task was to realize an ionization chamber that enables sensitive measurements.

  In order to solve the above-mentioned problems, an ionization chamber according to the present invention is a first ionization chamber according to claim 1, wherein the ionization chamber is disposed in an internal space defined by a wall portion and an opening portion and is applied with a predetermined voltage. Electrode (high voltage electrode) and a second electrode (collector electrode) disposed in the internal space for collecting and outputting charges according to the amount of radiation.

  In the ionization chamber, the second electrode is disposed in the internal space between the opening and the wall region that can be directly viewed from the opening, and further, between the opening and the second electrode. The shielding electrode is disposed, and the shielding electrode electrostatically shields between the opening and the second electrode. Since the second electrode (collector electrode) detects an extremely weak charge, an error occurs in radiation measurement when affected by an external electric field. However, even if the electric lines of force due to the external electric field can pass through the opening, they cannot reach the second electrode shielded by the shielding electrode, so that the external electric field does not affect the radiation measurement. . That is, in the ionization chamber, there is no need to electrostatically shield the opening.

  According to the positional relationship of each electrode in the ionization chamber, if the shielding electrode is removed, the second electrode is disposed in a space that can be directly viewed from the opening. Therefore, a high electric field with the second electrode as one electrode is generated in the internal space that can be viewed directly from the opening. With this high electric field, the ionization chamber can collect ions and electrons ionized by radiation as much as possible (highly sensitive radiation measurement can be performed).

  Note that the potential of the shielding electrode is stabilized in order to enhance the effect of electrostatic shielding (for example, the same potential as that of the high-voltage power source for driving the first electrode or the same polarity as that of the high-voltage power source). . By doing so, an electric field strength is generated between the shield electrode and the second electrode, so that it is possible to measure the radiation dose with higher sensitivity.

  As described in claim 2, a plurality of second electrodes may be provided, and an auxiliary electrode may be further provided between the plurality of second electrodes. Of course, the auxiliary electrode can be seen directly from the opening. The auxiliary electrode has the same potential or the same polarity as that of the first electrode.

  By doing so, an electric field can be further generated between the auxiliary electrode and the second electrode, and the ionization chamber can perform radiation dose measurement with higher sensitivity. Note that an electric field generated between the auxiliary electrode and the second electrode can be increased by making the auxiliary electrode parallel to the second electrode.

  According to a third aspect of the present invention, the opening may be opened to the external space of the ionization chamber, or may be covered with an opening shielding film. The opening shielding film may be for the purpose of simply closing the inner space (for example, for dust prevention), and within such a range (for example, within a range where a desired dustproof effect can be obtained) You may have. However, the aperture shielding film must not significantly affect the radiation to be measured. Since the second electrode is electrostatically shielded from the external electric field by the shielding electrode, the presence or absence of the electrostatic shielding effect in the opening shielding film is not a problem.

  As described in claim 4, the second electrode is preferably disposed substantially in parallel with the surface defined by the opening. When the second electrode is arranged in this way, the distribution of electric field lines radiated from the second electrode (or incident on the second electrode) is made uniform in a plan view from the opening. (It can contribute to high sensitivity of radiation dose measurement.)

  As described in claim 5, the first electrode may form at least a part of the wall portion. This simplifies the structure of the ionization chamber. In addition, if the many regions of the wall or all the regions of the wall are the first electrodes, the structure of the ionization chamber is further simplified, and in many regions of the internal space viewed from the opening side, Since electric lines of force generated between the first electrode and the second electrode are more densely and evenly distributed, the ionization chamber can perform highly sensitive radiation dose measurement.

  For example, the shielding electrode that electrostatically shields between the opening and the second electrode has a substantially U-shaped or semicircular cross-sectional shape perpendicular to the longitudinal direction thereof. In addition, the second electrode is disposed inside the substantially U-shaped or semi-circular groove.

  As described in claim 7, the opening shielding film may be an alpha ray blocking thin film that blocks alpha rays but does not cause significant attenuation of the beta rays to be measured. Alternatively, the opening shielding film may be a gamma ray detection film that blocks alpha rays and beta rays and emits secondary electrons according to the amount of gamma rays. By capturing these secondary electrons, the amount of gamma rays can be measured.

  As described above, the ionization chamber according to the present invention has the opening area of the opening portion widened, and the collector electrode electrostatically shielded from the opening portion side by the shielding electrode is disposed in the internal space that can be directly viewed from the opening portion. Because ions and electrons can be collected efficiently, it is not affected by an external electric field, and it is highly sensitive, quick, and accurate with respect to the radiation regulation value (determining whether the amount of radiation is below the regulation value) ), And radiation measurement.

  In addition, since the ionization chamber according to the present invention can widen the opening, it is possible to place various objects to be measured on a tray or the like, and to make a highly sensitive, quick and accurate determination of the radiation regulation value, and radiation measurement. Is possible.

It is a perspective view for demonstrating the schematic structure in one Embodiment of the ionization chamber concerning this invention. It is a figure for demonstrating the cross-sectional schematic structure of the ionization chamber shown in FIG. In the ionization chamber shown in FIG. 1, it is a figure for demonstrating the influence of the electrostatic induction which an external electric field gives to a collector electrode. It is a figure for demonstrating the influence of the electrostatic induction which an external electric field gives to a collector electrode at the time of mounting the ionization chamber shown in FIG. 1 in a radiation dose measuring apparatus. It is a perspective view for demonstrating schematic structure of the shielding electrode with which the ionization chamber shown in FIG. 1 was equipped. It is a figure for demonstrating distribution of the electric line of force in the internal space of the ionization chamber shown in FIG. It is a figure for demonstrating mounting to the radiation dose measuring apparatus of the ionization chamber shown in FIG. It is a figure for demonstrating the cross-sectional schematic structure in the modification of the ionization chamber shown in FIG.

  Hereinafter, an ionization chamber according to the present invention will be described with reference to the drawings.

<Overall configuration of ionization chamber>
FIG. 1 is a perspective view for explaining a schematic configuration of an ionization chamber in an embodiment of the ionization chamber according to the present invention, and FIG. 2 is a diagram for explaining a schematic cross-sectional configuration of the ionization chamber.

  As shown in FIG. 1, the ionization chamber 10 has a flat rectangular parallelepiped shape (height: 50 mm, width: 300 mm, depth: 420 mm), and the wall portion 11 includes four side walls 11a, 11b, 11c, 11d and a top plate 11e. (The side walls 11a and 11b are side walls in the width direction, and the side walls 11c and 11d are side walls in the depth direction). The side walls 11a, 11b, 11c, 11d and the top plate 11e are mechanically and electrically connected. In FIG. 1, for easy understanding of the schematic configuration of the ionization chamber 10, the top plate 11 e is shown in the lower part of the drawing, and the opening 12 facing the top plate 11 e is shown in the upper part (the same applies to FIG. 2). is there).

  The opening 12 has the opening ends 11w, 11x, 11y and 11z on the side of the opening 12 of the side walls 11a, 11b, 11c and 11d, and the rectangular shape formed by these opening ends 11w, 11x, 11y and 11z. This is an area (surface area). The area of the opening 12 is 1260 square centimeters (the thickness of each side wall is ignored for simplification), and the space defined by the opening 12 and the wall 11 is the internal space 10s of the ionization chamber 10. .

  The ionization chamber 10 measures the amount of incident radiation by detecting ions and electrons ionized by radiation incident on the internal space 10 s from the opening 12.

<Configuration of high voltage electrode>
The wall part 11 is formed with aluminum, The thickness is 1-2 mm, for example. In the ionization chamber 10, the wall portion 11 also serves as the high voltage electrode 13 (first electrode). The high voltage electrode 13 is applied with a negative voltage (for example, a voltage of −25 V) from a high voltage power supply unit (not shown) in order to collect positive ions. The potential of the high voltage electrode 13 is regulated by the negative voltage and is not affected by the external electric field of the ionization chamber 10. If the wall portion 11 is made of stainless steel, the durability is improved while the weight is increased.

<Configuration of collector electrode>
As shown in FIGS. 1 and 2, in the internal space 10s, three collector electrodes 14 are arranged in an intermediate region between the top plate 11e and the opening 12 in parallel with the side walls 11c and 11d. . Here, the top plate 11e and the opening 12 have the same surface shape and are parallel to each other, so that the space between the top plate 11e and the opening 12 can be viewed directly from the opening 12. This is an internal space 12.

  The three collector electrodes 14 are disposed at an interval of about 100 mm, and one adjacent to the side wall 11c and one adjacent to the side wall 11 are separated from the side wall by about 50 mm. The collector electrode 14 is, for example, a stainless cylindrical body having a diameter of 3 to 5 mm. The collector electrode 14 is longer than the depth of the ionization chamber 10 and penetrates the side walls 11a and 11b, and both ends thereof are outside the side walls 11a and 11b. positioned. In the side walls 11a and 11b, an insulating member 15 is disposed at a portion through which the collector electrode 14 penetrates to electrically insulate between the collector electrode 14 and the wall portion 11 (high voltage electrode 13). The three collector electrodes 14 are electrically connected to each other by a connecting member 14a outside the wall 11 and are biased to zero potential (ground potential) by an external circuit (not shown). Biased to zero potential in relation to the electrically connected amplifier circuit, but not grounded.)

  FIG. 3 shows the positional relationship between the collector electrode 14 and the opening 12 arranged as described above (FIG. 3 shows the opening 12 below in the figure). When the internal space 10 s is viewed through the opening 12 from the lower region S of the ionization chamber 10 and from the vicinity immediately below the ionization chamber 10, all the collector electrodes 14 are assumed to have no shielding electrode 16 to be described later. Can be visually observed.

  When the viewpoint for viewing the collector electrode 14 is moved from directly below the ionization chamber 10 in the width direction of the ionization chamber 10 (arrow W1 or W2 in FIG. 3), the position at which the collector electrode 14 cannot be viewed is the opening 12 It is a position that is quite far from directly below. The optical paths OP1 and OP2 connecting the viewpoint and the collector electrode 14 at this time are shown in FIG. 3 (in FIG. 3, only the optical path for the left collector electrode 14 is shown. The optical path OP1 is at the opening end 11y of the side wall 11c. , OP2 is in contact with the open end 11z of the side wall 11d).

  Thus, the left collector electrode 14 in FIG. 3 can be seen from a wide area on the opening 12 side (which is a wider area considering the three collector electrodes 14), so that the opening 12 is open. When at least electrostatically open, the collector electrode 14 is induced by an external electric field and an error occurs in the detection of electrons.

  By the way, the ionization chamber 10 is mounted on a radiation dose measuring device (not shown). In this case, generally, the shielding member M of the radiation amount measuring apparatus is positioned outside the vicinity of the side walls 11a to 11d and below the opening 12 (FIG. 4).

  In such a case, it is only necessary to eliminate the influence of the external electric field from the space surrounded by the shielding member M below the opening 12. At this time, the region where the object OB can be directly viewed from the collector electrode 14 is defined by the optical paths OP1 ′ and OP2 ′ as shown in FIG. 4, and is narrower than the region defined by the optical paths OP1 and OP2 shown in FIG. Become.

<Configuration of shielding electrode>
The inventor provided the shielding electrode 16 in the ionization chamber 10 (see FIG. 2 etc.). As shown in FIG. 5, the shielding electrode 16 is a long member having a U-shaped cross section between the first long side 16a and the second long side 16b, and is made of stainless steel. The shield electrode 16 is disposed between the collector electrode 14 and the opening 12 as shown in FIG. 2, the outer surface of the U-shaped bottom region 16c is positioned toward the opening 12, and the collector electrode 14 is located on the U-shaped groove space 16 s side of the shielding electrode 16 and shields between the opening 12 and the collector electrode 14.

  Here, the collector electrode 14 does not need to be positioned entirely within the groove space 16 s (the collector electrode 14 intersects a plane including the first long side 16 a and the second long side 16 b of the shielding electrode 16. May be.) The shield electrode 16 shields the collector electrode 14 from an external electric field by blocking the optical path from the opening 12 to the collector electrode 14, for example, the optical paths OP1 and OP2 (or optical paths OP1 ′ and OP2 ′) shown in FIG. 3 (or FIG. 4). As long as it can be electrostatically shielded.

  The shielding electrode 16 is biased to the same potential or the same polarity as the high-voltage electrode 13 (meaning that the potentials of the high-voltage electrode 13 and the shielding electrode 16 are the same or the same polarity with respect to the collector electrode 14). .) Thus, the shielding electrode 16 whose potential is defined is not affected by the external electric field for the same reason as the high-voltage electrode 13. The shield electrode 16 only needs to shield electrostatic induction to the collector electrode 14 due to an external electric field, and the cross-sectional shape is not limited to the U-shape. For example, it may be semicircular in cross section.

<Auxiliary electrode>
In the internal space 10s of the ionization chamber 10, two auxiliary electrodes 17 are arranged in parallel with the three collector electrodes 14 (see FIG. 2 and the like). These auxiliary electrodes 17 are, for example, stainless cylindrical bodies having the same cross-sectional shape as the collector electrode 14, and the positional relationship between the top plate 11 e and the opening 12 is the same as that of the collector electrode 14. These auxiliary electrodes 17 are both positioned in the middle of the two collector electrodes 14 and are mechanically and electrically connected to the wall 11 (high voltage electrode 13).

<Electric field in internal space>
When a negative voltage (for example, −25 V) is applied to the high-voltage electrode 13 (wall portion 11) and the collector electrode 14 is biased to zero potential, the electric lines of force D from the collector electrode 1 toward the high-voltage electrode 13 are shown in FIG. (A part of the electric lines of force D is shown in FIG. 6). Since the auxiliary electrode 17 has the same potential as the high-voltage electrode 13, it is between the side wall 11 c in the depth direction and the collector electrode 14 adjacent thereto, between the side wall 11 d in the depth direction and the collector electrode 14 adjacent thereto, and two The density of the lines of electric force between the auxiliary electrode 17 and the three collector electrodes 14 is substantially uniform.

  Therefore, in the ionization chamber 10, when the distribution of the electric force lines D in the internal space 10 s is viewed in plan through the opening 12, almost uniform electric force lines D are distributed over the entire area of the internal space 10 s. Become. The electric field lines D having such a distribution efficiently accelerate ions and electrons ionized by radiation incident on the internal space 10 s from the opening 12 of the ionization chamber 10 toward the high-voltage electrode 13 and the collector electrode 14. Therefore, the high voltage electrode 13 efficiently collects positive ions, and the collector electrode 14 efficiently collects negative ions and electrons (the ionization chamber 10 can perform highly sensitive radiation dose measurement).

<About mounting on ionization chamber>
The ionization chamber 10 is mounted on a radiation dose measuring device. FIG. 7 is a view for explaining an example of mounting the ionization chamber 10 on the housing 20 mounted on the radiation dose measuring device. For the same reason as in FIGS. 1 and 2, the top plate 11 e of the ionization chamber 10 is attached. The opening 12 is shown in the upper part of the figure.

  The casing 20 is a frame formed of aluminum, and the ionization chamber 10 is accommodated in the frame internal space 20s'. The housing 20 has two width direction blocking plates 21 and two depth direction blocking plates 22. For example, after the width direction blocking plate 21 is removed from the housing 20, the ionization chamber 10 is inserted into the frame internal space 20 s ′, fixed to the housing 20, and then removed. This is performed by attaching the width direction blocking plate 21 to the housing 20. The wall portion 11 (which is also the high voltage electrode 13) of the ionization chamber 10 attached to the housing 20 is electrically insulated from the housing 20.

  The casing 20 can prevent the influence of alpha rays and beta rays in the vicinity of the end portion of the collecting electrode 14 disposed outside the wall portion 11 as well as further electrostatically shielding the ionization chamber 10. .

<About measurement of radiation>
When radiation (beta rays) is incident on the opening 12 of the ionization chamber 10 from the outside, the beta rays ionize the molecular elements constituting the air in the internal space 10s, and ions and electrons are generated. Positive ions are collected by a high voltage electrode 13 to which a negative voltage is applied, and negative ions and electrons are collected by a collecting electrode 14 (biased at zero potential) that is positive with respect to the high voltage electrode 13. A minute current flows between the collector electrode 14. A beta ray can be measured by measuring this minute current.

  The amount of ions and electrons generated by ionization varies under the influence of atmospheric pressure and temperature. Although this fluctuation becomes an error factor in radiation measurement, since it has reproducibility, it can be corrected by measuring in advance the fluctuation characteristics with parameters such as atmospheric pressure and temperature.

  Judgment that radiation is below a certain regulation value is less than the value obtained by subtracting the error that can be caused by the above fluctuations (for example, the error taking into account fluctuations in atmospheric pressure, temperature, etc. that can occur in normal measurement) from the regulation value. Since there are few measured values by the box 10, it can be made below a regulation value. Further, if the measurement value obtained by the ionization chamber 10 is corrected based on the fluctuation characteristics due to the atmospheric pressure, temperature, etc., which are actually measured in advance, the accurate amount of radiation can be calculated.

  When the influence of alpha rays is eliminated and the amount of beta rays is accurately determined or measured, the openings 12 are covered with a thin film (for example, a film thickness of 50 μm) such as a synthetic resin to block the alpha rays. Of course, the internal space 10s only needs to be filled with air substantially the same quality as the atmosphere (it is not necessary to enclose gas other than air). Such a thin film is inexpensive and can be replaced if it is torn, and there is no need to replace the gas. Therefore, the replacement operation is simple and low-cost and does not significantly affect the operating rate of the radiation measuring apparatus.

  Such a thin film may be used merely for dust prevention. In this case, the thin film may be breathable as long as desired dustproofing can be achieved. In both the alpha ray shielding and dustproofing cases, since the collecting electrode 14 is electrostatically shielded by the shielding electrode 16, the presence or absence of the electrostatic shielding effect in the thin film is not a problem.

  When determining or measuring the amount of gamma rays, the opening 12 is covered with a gamma ray detection film (gamma ray detection plate) formed of a member that generates two electrons by gamma rays (for example, an aluminum plate having a thickness of 2 mm). The gamma ray detection film blocks alpha rays and beta rays, and emits secondary electrons according to the amount of gamma rays that pass through. Therefore, the amount of gamma rays is detected with high sensitivity by detecting the secondary electrons with the ionization chamber 10. Can be measured. Of course, the presence or absence of the electrostatic shielding effect in the gamma ray detection film is not a problem.

<Auxiliary electrode configuration, etc.>
By the way, since the ionization chamber 10 can be used with the opening 12 open to the outside, the ionization chamber 10 is fine on the inner surface of the wall 11, the surface of the collector electrode 14, the surface of the shielding electrode 16, the surface of the auxiliary electrode 17, and the like. Dust adheres. Such dust can be removed by washing with water (the dust may be burned off with a small burner).

  For such cleaning, the shielding electrode 16 may be pivotally attached to the side walls 11a and 11b with the first long side 16a or the second long side 16b as a rotation axis. Then, the inner surface on the groove space 16s side of the shielding electrode 16 facing the top plate 11e can be redirected to the opening 12 side, and the inner surface on the groove space 16s side is washed from the opening 12 side. The convenience in maintenance of the ionization chamber 10 can be improved.

  Further, the collecting electrode 14 can be seen from the opening 12 by rotating the shielding electrode 16 covering the collecting electrode 14. Therefore, the collector electrode 14 can be washed from the opening 12 side, and convenience in maintenance of the ionization chamber 10 can be enhanced.

  As shown in FIG. 5, a plurality of drain holes 16 h may be provided in the longitudinal direction and the width direction in the U-shaped bottom region 16 c of the shielding electrode 16 or in the vicinity thereof. This facilitates draining when the shielding electrode 16 and the like are washed with water.

<Modification>
FIG. 8 is a diagram for explaining a schematic cross-sectional configuration of an ionization chamber 10 ′ that is a modification of the ionization chamber 10. In addition, about the component which has the function similar to the ionization chamber 10, the same code | symbol is attached | subjected and those description is abbreviate | omitted.

  The ionization chamber 10 ′ has a configuration in which the collecting electrode 14 and the shielding electrode 16 are disposed at the position where the auxiliary electrode 17 is disposed in the ionization chamber 10. In the internal space 10 s of the ionization chamber 10 ′, the electric lines of force D from the collector electrodes 14 are incident on the entire surface of the top plate 11 e, so that the distribution of the electric lines of force D in the internal space 10 s through the opening 12 is viewed in plan view. When this is done, the lines of electric force D are distributed almost uniformly over the entire area of the internal space 10s, as with the ionization chamber 10. Therefore, the ionization chamber 10 ′ can measure the amount of radiation with high sensitivity in the same manner as the ionization chamber 10.

  In addition, the ionization chamber concerning this invention is not limited to embodiment mentioned above, It can change suitably and implement, without changing the meaning. For example, the overall shape of the ionization chamber is not limited to a rectangular parallelepiped shape, and may be, for example, a cylindrical shape. Furthermore, the overall shape of the ionization chamber does not have to be flat as long as the distribution of the electric lines of force in the internal space from the opening is taken into consideration when viewed in plan. The collector electrode and the auxiliary electrode have a cylindrical shape in order to generate electric lines of force with as uniform a density as possible, but are not limited to a cylindrical shape. Similarly, the auxiliary electrode is not limited to a U-shaped or semicircular cross section.

  Since the ionization chamber according to the present invention can be manufactured and used industrially and is subject to commercial transactions, the present invention is an invention that has economic value and can be used industrially.

10, 10 'ionization chamber 10s internal space 11 wall 11a, 11b (width direction) side wall 11c, 11d (depth direction) side wall 11e top plate 12 opening 13 first electrode (high voltage electrode)
14 Second electrode (collector electrode)
16 Shielding electrode 17 Auxiliary electrode

Claims (7)

A first electrode disposed in an internal space defined by the wall and the opening and applied with a predetermined voltage, and disposed in the internal space for collecting and outputting charges corresponding to the amount of radiation In an ionization chamber provided with a second electrode of
The second electrode disposed in the internal space between the opening and the region of the wall that can be viewed directly from the opening;
The shielding electrode interposed between the opening and the second electrode,
The ionization chamber, wherein the shielding electrode electrostatically shields between the opening and the second electrode. The ionization chamber of claim 1,
A plurality of the second electrodes;
An auxiliary electrode disposed between the plurality of second electrodes in the internal space between the opening and the region of the wall that can be directly viewed from the opening;
An ionization chamber characterized in that the potential of the auxiliary electrode is the same or the same polarity as that of the first electrode. In the ionization chamber according to claim 1 or 2,
The opening is open to the external space of the ionization chamber;
Alternatively, the ionization chamber is characterized in that an opening shielding film for keeping air substantially the same quality as the outer space in the inner space is further disposed in the opening.   The ion chamber according to any one of claims 1 to 3, wherein the second electrode is disposed substantially parallel to the opening.   The ionization chamber according to any one of claims 1 to 3, wherein the first electrode forms at least a part or all of the wall portion. The shield electrode has a substantially U-shaped or substantially semicircular cross-sectional shape perpendicular to the longitudinal direction thereof,
4. The device according to claim 1, wherein at least a part of the second electrode is disposed inside the substantially U-shaped or substantially semicircular groove of the shielding electrode. 5. Ionization chamber.   The aperture shielding film is an alpha ray blocking thin film that attenuates alpha rays while not causing significant attenuation of beta rays, or a gamma ray detection film that attenuates alpha rays and beta rays and emits secondary electrons in response to gamma rays. The ionization chamber according to claim 3, wherein the ionization chamber is provided.

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