JP2008256631A - One-centimeter dose equivalent meter-usage scintillation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a one-centimeter dose equivalent meter-usage scintillation detector which adopts a low-cost configuration, while enhancing its mechanical strength and is improved in detection sensitivity, by making the energy dependence of its response low to low-energy photons in a range of 8 keV to 150 keV. <P>SOLUTION: In the one-centimeter dose equivalent meter-usage scintillation detector, the thickness of an incidence window 12 made of a plastic resin is in the range of 1 mm to 4 mm, and the transmittance properties of the incidence window 12 for energies equal to and less than 20 keV is approximated to a one-centimeter dose equivalent conversion factor curve of the energies equal to and smaller than 20 keV, thereby making the energy response flat at the incidence of the low-energy photons, in a range of 8 keV to 150 keV. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a scintillation detector for a 1 cm dose equivalent meter used in a 1 cm dose equivalent meter for detecting a 1 cm dose equivalent of radiation, particularly a low energy photon (for example, γ-ray, X-ray) of 10 keV to 150 keV.

  Various types of radiation utilizing devices using low energy X-rays or γ rays (hereinafter referred to as low energy photons) are used. In a management area where such a radiation utilization apparatus is installed, a 1 cm dose equivalent representing the amount of radiation is measured using a 1 cm dose equivalent meter. Such measurement is performed periodically (for example, measurement is performed every day for a predetermined period from a predetermined time) or irregularly.

  An example of a radiation utilization apparatus is a medical X-ray imaging apparatus. In this X-ray imaging apparatus, the X-ray generation time depends on the imaging time. Furthermore, the shooting time interval varies depending on the shooting target, and is generated from several milliseconds to several hundred milliseconds for each shooting. For these reasons, the generation of radiation (X-rays) is irregular and intermittent, and it is necessary to measure in the integration mode of a 1 cm dose equivalent meter in order to accurately measure the dose. In such a 1 cm dose equivalent meter, in general, only one of the integrated value and the dose rate is displayed as the measured value.

  In general, as a 1 cm dose equivalent meter when measuring a low energy photon of 50 keV or less, an ionization chamber type 1 cm dose equivalent meter which is advantageous in that the energy dependency of detection sensitivity of 50 keV or less is particularly small, Alternatively, a 1 cm dose equivalent meter using a NaI (Tl) scintillation detector, which is advantageous in that the energy dependency is not small but the detection sensitivity is low in the low range, is used. Here, the energy dependence is small means that the response of the detector to the energy of the incident photon is almost constant regardless of the energy.

As another conventional technique related to a radiation measuring apparatus, for example, there is Patent Document 1 (Japanese Patent Laid-Open No. 2004-108796; name of invention “radiation measuring apparatus”). In this radiation measuring apparatus, the detection pulse signal is sent to the counter at the subsequent stage by changing the discrimination threshold of the wave height discriminator with respect to the signal detected by NaI (Tl) scintillation by the DBM method according to a predetermined pattern. An apparatus is disclosed that adjusts the probability of input according to the wave height, and multiplies a coefficient for each energy as represented by a 1 cm dose equivalent conversion coefficient curve diagram for correction.
Such a conventional radiation measuring apparatus such as a 1 cm dose equivalent meter that uses low-energy photons as a measurement target is described above.

JP 2004-108796 A (paragraph number 0020, FIG. 1)

  The conventional 1 cm dose equivalent meter does not consider the detection of low energy photons of 25 keV or less, and when detecting low energy photons of 8 keV to 150 keV, particularly the detection accuracy of low energy photons of 25 keV or less. There was a problem that was not high.

  First, in the ionization chamber type 1cm dose equivalent meter, in order to reduce energy dependency, the material used for the ionization chamber and the gas to be ionized are restricted, and the material is plastic, and the gas is nitrogen (air) at atmospheric pressure. Often used in. Also, the ion chamber 1 cm dose equivalent meter is a portable measuring device, and the size of the ion chamber detector is limited. For these reasons, it has been difficult to increase sensitivity. In addition, although the energy dependence is small and generally good, the response to low energy photons in this case is clear from the explanatory diagram of the photon energy-response characteristics of the ionization chamber type 1 cm dose equivalent meter of FIG. In particular, energy dependency of 25 keV or less is not taken into consideration, and there is a problem that energy dependency on low energy photons of 8 keV to 25 keV is not good (high energy dependency).

In addition, a 1 cm dose equivalent meter using another conventional NaI (Tl) scintillation detector has high detection sensitivity in a low frequency range, but is highly energy dependent. As shown in the photon energy-1 cm dose equivalent conversion coefficient curve diagram of FIG. 9, the 1 cm dose equivalent meter needs to be multiplied by a conversion coefficient that reduces the value in the low energy region (for example, it needs to be multiplied by 0.1 at 10 keV). ), Which indicates that the detection sensitivity is too high. As is clear from FIG. 9, the conversion coefficient is small below 20 keV (0.020 MeV). In other words, there is a demand for reducing the detection sensitivity in the low energy region. Regarding the detection sensitivity, Patent Document 1 has the same problem.
As described above, the radiation measuring apparatus of the prior art such as a 1 cm dose equivalent meter that detects low energy photons of 8 keV to 150 keV is not good in detection sensitivity in the low range, and there is a possibility that a problem may occur in detection accuracy in the low range. It was.

  Therefore, the present inventors have invented a scintillation detector for a 1 cm dose equivalent meter suitable for detecting low energy photons, and have filed a patent application. Such a scintillation detector for a 1 cm dose equivalent meter will be described with reference to the drawings. FIG. 10 is a cross-sectional configuration diagram of a conventional scintillation detector for a 1 cm dose equivalent meter, FIG. 11 is a photon energy-transmittance characteristic diagram according to thickness and material of a conventional incident window (aluminum plate), FIG. Is a calculated photon energy-response characteristic.

  A scintillation detector 100 for a 1 cm dose equivalent meter includes a case 101, an incident window 102, a gap 103, a reflective layer 104, a scintillator 105, an optical window 106, a photomultiplier 107, and a bleeder circuit 108. In the prior art, an entrance window 102 made of an aluminum plate is disposed in front of the scintillator 105. As shown in FIG. 11, the transmittance of the incident window 102 decreases as it decreases from 300 keV, and the detection sensitivity in the low energy region is reduced. Further, by combining the incident window 102 and the scintillator 105, the energy dependency is reduced over the entire area.

  In the photon energy-response characteristics by calculation of FIG. 12, the material of the entrance window 102 is aluminum, and the response of the scintillator 105 to the photon energy for four types of thickness (calculation results of computer simulation or the like) is shown. The energy dependence is improved at 15 keV or less, and particularly when the thickness of the incident window 102 is 0.2 mm to 0.3 mm, the energy dependence in the energy region in the range of 8 to 100 keV is reduced and good characteristics are obtained. can get.

However, the incident window 102 made of aluminum needs to be formed to be relatively thin, such as 0.1 to 0.4 mm. For example, when an inadvertent force is applied to the incident window 102 shown in FIG. 10, there is a problem that the incident window 102 is broken or detached from the case 101, so that subsequent measurement cannot be performed.
Furthermore, if an incident window made of beryllium is used as a material having equivalent characteristics, the thickness can be increased and the strength problem can be solved. However, there is also a problem that the adoption is difficult because the cost increases. .

  Therefore, the present invention has been made to solve the above-mentioned problems, and its purpose is to adopt a low-energy photon in the region of 8 keV to 150 keV while adopting a configuration that is inexpensive and has high mechanical strength. It is an object to provide a scintillation detector for a 1 cm dose equivalent meter in which the sensitivity is small and the detection sensitivity is improved so as to have a small energy dependence.

Such a scintillation detector for a 1 cm dose equivalent meter according to claim 1 of the present invention,
An incident window having a characteristic that a plastic resin is used as a material, and a part of incident photons are absorbed and the rest are allowed to pass, and the transmittance decreases with decreasing energy with respect to a photon having a predetermined energy or less,
A scintillator that emits scintillation light in response to photons that have passed through the entrance window;
A photomultiplier tube that outputs a pulse signal proportional to the intensity of the scintillation light emitted from the scintillator;
A case for accommodating an entrance window, a scintillator and a photomultiplier;
A scintillation detector for a 1 cm dose equivalent meter comprising:
By making the thickness of the entrance window from 1 mm to 4 mm and approximating the transmittance characteristics of the entrance window with respect to energy at 20 keV or less to a 1 cm dose equivalent conversion coefficient curve of 20 keV or less, low energy from 8 keV to 150 keV It is characterized by flattening the energy response when a photon is incident.

A scintillation detector for a 1 cm dose equivalent meter according to claim 2 of the present invention,
The scintillation detector for a 1 cm dose equivalent meter according to claim 1,
The incident window is an integral structure included in a part of the case, and the case itself has a function of the incident window.

A scintillation detector for a 1 cm dose equivalent meter according to claim 3 of the present invention,
An outer incident window having a characteristic that a plastic resin is used as a material, and a part of the incident photons are absorbed and the rest are allowed to pass, and the transmittance decreases with decreasing energy with respect to a photon having a predetermined energy or less,
An inner incident window having a characteristic that the transmittance is reduced as the energy is reduced for a photon having a predetermined energy or less, while absorbing a part of the incident photon and allowing the rest to pass through the material made of aluminum.
A scintillator that emits scintillation light in response to photons that have passed through the outer and inner incident windows;
A photomultiplier tube that outputs a pulse signal proportional to the intensity of the scintillation light emitted from the scintillator;
A case containing an outer incident window, an inner incident window, a scintillator and a photomultiplier;
A scintillation detector for a 1 cm dose equivalent meter comprising:
The thickness of the outer incident window and the thickness of the inner incident window are adjusted so that the thickness of the inner incident window is within the range of characteristics in the thickness range of 0.1 mm to 0.4 mm. By approximating the transmittance characteristics of the outside and inside entrance windows with respect to the energy to a 1 cm dose equivalent conversion coefficient curve of 20 keV or less, the energy response is flattened when low energy photons from 8 keV to 150 keV are incident. It is characterized by planning.

A scintillation detector for a 1 cm dose equivalent meter according to claim 4 of the present invention,
In the scintillation detector for 1 cm dose equivalent meters according to any one of claims 1 to 3,
A gap is interposed between the incident window, the case, and the scintillator.

  According to the present invention as described above, while adopting a configuration that is inexpensive and has high mechanical strength, a response with low energy dependence is provided for low energy photons in the region of 8 keV to 150 keV. Thus, a scintillation detector for a 1 cm dose equivalent meter with improved detection sensitivity can be provided.

  Hereinafter, a scintillation detector for a 1 cm dose equivalent meter of the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional structure diagram of the scintillation detector of this embodiment.

  The 1 cm dose equivalent meter scintillation detector 1 includes a case 11, an incident window 12, a scintillator 13, a reflective layer 14, an optical window 15, a photomultiplier tube 16, a bleeder circuit 17, and a gap 18, as shown in FIG. . In the prior art shown in FIG. 10, the incident window 102 made of aluminum is arranged in front of the scintillator 105. However, in the present invention, the incident window 12 made of plastic resin is arranged instead of the incident window made of aluminum.

Each configuration will be described below.
The case 11 is a metal cylinder having a detection hole in the front and a hole (not shown) for drawing out the signal line and the power line in the rear, and has a function of shielding light and magnetism.
The entrance window 12 is a disc made of an opaque plastic resin. Specifically, polyacetal copolymer resin (Duracon) is adopted as the plastic resin. The thickness is 1 to 4 mm. The operation / function will be described later.

Specifically, the scintillator 13 is a NaI (Tl) scintillator made of a crystal of sodium iodide (NaI) containing a small amount of thallium (Tl). The scintillator is formed in a cylindrical shape. The operation / function of the scintillator 13 will be described later.
The reflective layer 14 is a layer provided on the detection direction side of the scintillator 13 and allows photons to pass therethrough, but prevents the scintillation light from leaking from the inside of the scintillator 13 to the outside.

  The optical window 15 is disposed between the scintillator 13 and the photomultiplier tube 16. The scintillator 13 is joined to the case 11 so that the scintillator 13 can be prevented from deliquescence when exposed to the outside air through a transparent window for allowing the scintillation light generated by the scintillator 13 to enter the photomultiplier tube 16. The optical window 15 is a smooth surface with the light incident window of the photomultiplier tube 16 and the scintillator 13 on the opposite surface, and is securely adhered via a bonding material such as transparent silicon grease, so that the scintillation light is photomultiplied from the scintillator 13. The incident light is surely incident on the tube 16.

  The photomultiplier tube 16 makes the scintillation light emitted from the scintillator 13 incident on the photocathode, converts the scintillation light into photoelectrons on the photocathode, and exchanges and multiplies the photoelectrons into current, and a current proportional to the intensity. It is the converter which outputs the pulse signal by. Specifically, the photoelectrons output from the photocathode are accelerated by dynodes and multiplied by secondary electron emission multiplication to about 100,000 to 1 million times, and finally a pulse signal by current proportional to the photoelectron intensity. Is output.

The bleeder circuit 17 applies an appropriate voltage to each electrode of the photomultiplier tube 16.
The gap 18 is a space interposed between the case 11 and the incident window 12 and the scintillator 13 (specifically, the reflective layer 14 on the surface of the scintillator 13). Due to the presence of this space, even if there is an impact on the incident window 12 or the case 11, the impact does not reach the scintillator 13, and the scintillator 13 is protected. Although detection is possible even if the configuration in which the incident window 12 is in contact with the surface of the scintillator 13 is adopted, it is desirable to provide a gap 18 from the viewpoint of protecting the scintillator 13.

  Next, the operation / function of the 1 cm dose equivalent meter scintillation detector 1 will be described below with reference to the drawings. FIG. 2 is a characteristic diagram of photon energy-detection efficiency of the scintillator. FIG. 3 is a photon energy-transmittance characteristic chart according to the thickness and material of the entrance window made of plastic resin.

First, the scintillator 13 of the scintillation detector 1 for a 1 cm dose equivalent meter will be described.
A phenomenon in which a photon emits light by flashing when passing through a substance is called scintillation, and a substance that emits light is called a scintillator. When the photon enters the scintillator 13, the scintillator 13 emits scintillation light.

  The detection efficiency of the scintillator 13 alone will be described. The example of the detection efficiency with respect to the photon energy which injects into the scintillator (no entrance window) 13 of FIG. 2 is shown. In FIG. 2, the detection efficiency is constant at 1.00 for photon energy up to 50 keV, but for photon energy of 50 keV or more, the detection efficiency decreases as the photon energy value increases. Thus, the scintillator 13 has a large energy dependency at 50 keV or more.

  In such a 1 cm dose equivalent meter scintillation detector 1, if the output from the 1 cm dose equivalent meter scintillation detector 1 without the entrance window 12 is used, a 1 cm dose equivalent conversion coefficient is used for this output. Used to convert. According to the photon energy-1cm dose equivalent conversion coefficient curve diagram based on the recommendation of the International Commission on Radiological Protection (ICRP) 1990 in FIG. 9, the 1cm dose equivalent conversion coefficient increases in the region of 50 keV or more of photon energy. We are trying to reduce energy dependency. However, in the region of 20 keV or less of the photon energy, the 1 cm dose equivalent conversion coefficient is small. In other words, the output from the scintillation detector 1 for the 1 cm dose equivalent meter is high in the low range, The low-frequency sensitivity needs to be lowered in advance. Therefore, an entrance window 12 that absorbs low-frequency photons is disposed on the front side of the scintillator 13.

  The incident window 12 has a function of making a photon incident and absorbing a part of the passing photon. The material of the entrance window 12 is a disc made of plastic resin as described above. Specifically, polyacetal copolymer resin (Duracon) is adopted as the plastic resin. The thickness is 1 to 4 mm. FIG. 3 shows a photon energy-transmittance characteristic diagram (simulation calculation result by EGS4) when the thickness of the entrance window 12 made of plastic resin is changed.

  The transmittance changes with respect to photon energy depending on the material and thickness of the entrance window 12 (thickness is the thickness from the photon entrance surface to the exit surface). FIG. 3 shows the material of the entrance window as polyacetal. Copolymer resin (Duracon) is shown with thicknesses of 1 mm, 2 mm, 4 mm, and 8 mm. As is clear from these characteristics, the transmittance with respect to the photon energy decreases as the photon energy decreases. This result shows that the incident window 12 and the conventional aluminum incident window 102 have the same tendency. Compared to the energy dependence on the thickness of the aluminum entrance window 102, it can be seen that the energy dependence can be made substantially the same when the thickness of the polyacetal resin is 10 times that of aluminum. Since the incident window 102 made of aluminum preferably has the same characteristics as 0.1 to 0.4 mm, the thickness of the incident window 12 made of plastic resin is preferably 1 to 4 mm.

  The 1 cm dose equivalent of a photon incident on the 1 cm dose equivalent meter scintillation detector 1 equipped with the entrance window 12 is calculated by the following equation.

The 1 cm dose equivalent conversion coefficient determined by the photon energy value of the incident photon, the detection efficiency of the detector, and the transmittance of the entrance window are obtained, and the 1 cm dose equivalent is calculated using the entrance window area of the detector.
In the low energy region where the photon energy is 50 keV or less, as shown in FIG. 2, the detection efficiency of the scintillator 13 is almost 100% and constant (= 1.0). If the degree of reduction of the 1 cm dose equivalent conversion coefficient and the degree of reduction of the transmittance due to absorption by the incident window 12 are matched, the dependence of the measured value (1 cm dose equivalent) on the photon energy can be reduced.

  In other words, if the incident window 12 of an appropriate material is inserted between the photon source (not shown) and the scintillator 13, the transmittance characteristic of the incident window 12 with respect to energy at 50 keV or less is 50 keV or less. It can be approximated to a 1 cm dose equivalent conversion coefficient curve, flattening the energy response when low energy photons of up to 50 keV are incident, and reducing the energy dependence of the 1 cm dose equivalent in the low energy region.

  Subsequently, the energy response of the scintillation detector 10 by calculation is examined. For example, in the prior art, as shown in FIG. 12, the energy dependency of the aluminum incident window is improved particularly at 15 keV or less, particularly when 0.2 mm to 0.3 mm. The characteristics substantially the same as the characteristics when the aluminum incident window shown in FIG. 12 is 0.2 mm to 0.3 mm are characteristics shown in FIG. 3, but the thickness of the incident window 12 is between 1 mm and 4 mm. It is assumed that the incident window 12 matches when the thickness is 2 mm to 3 mm. When the incident window 12 made of plastic resin is 1 mm to 4 mm, the energy dependency is improved at 15 keV or less, and the energy dependency in the energy range of 8 to 150 keV is improved. From the above, for example, when measuring 8 keV or more, the material and thickness of the entrance window are preferably 1 mm to 4 mm.

  As described above, in the scintillation detector according to the present invention, if the incident window 12 made of a plastic resin having a thickness of 1 mm to 4 mm is adopted, the energy dependence in the energy region in the range of 8 to 150 keV can be expected to be reduced. Even in comparison, the detection accuracy is improved by reducing the energy dependency especially for low-range photon energy, and can be applied to detection of low-energy photons.

  According to the present embodiment described above, instead of the conventional aluminum entrance window, an opaque plastic resin entrance window with low photon absorption and high mechanical strength is employed. As a result, the incident window shields external light, can be increased in thickness due to less absorption of photons, and the increased mechanical strength prevents damage to the incident window, making it easy to handle. An equivalent meter scintillation detector can be provided.

  Next, another embodiment will be described with reference to the drawings. FIG. 4 is a cross-sectional structure diagram of another form of scintillation detector. As shown in FIG. 4, the scintillation detector 1 ′ for a 1 cm dose equivalent meter includes a scintillator 13, a reflective layer 14, an optical window 15, a photomultiplier tube 16, a bleeder circuit 17, a gap 18, a case 19, a screw portion 19a, An O-ring 19b, an adhesive portion 19c, a case 20, and an incident window 20a are provided. In the embodiment shown in FIG. 1, the case 11 is made of metal and the incident window 12 is made of plastic resin. However, in this embodiment, the case 19 is made of metal and the case 20 including the incident window 20a is made of plastic resin. The difference is that the two are joined by the screw of the screw portion 19a. Therefore, the scintillator 13, the reflection layer 14, the optical window 15, the photomultiplier tube 16, and the bleeder circuit 17 are omitted in the description because they have the same configuration, and only differences are described with emphasis.

The case 19 is an opaque metal cylinder having a hole (not shown) for pulling out a signal line and a power line on the rear side.
The case 20 has a shape in which a plastic resin tube and a ceiling incident window 20a are integrated, and is the above-described polyacetal copolymer resin (Duracon). The incident window 20a is formed to have a thickness of 1 to 4 mm.
When the case 19 and the case 20 are fastened and fixed by the screw portion 19a, the inside of the case 19 and the case 20 is sealed from the outside by the O-ring 19b. Note that the optical window 15 is bonded and sealed to the case 20 by an adhesive portion 19c.
Here, the thickness of 1 to 4 mm of the incident window 20a is set to a thickness corresponding to the incident window of 0.1 to 0.4 mm of aluminum with respect to photons.

  As described above, the case 20 itself of the scintillator 13 is made of plastic resin, so that the photon absorption by the incident window 20a is the same as that of the front surface even when the incident direction of the photon is the side surface. This point will be described with reference to the drawings. FIG. 5 is a characteristic diagram for explaining the direction dependency of a scintillation detector for a 1 cm dose equivalent meter on a photon energy of 10 keV between a case according to the prior art and a case made of plastic resin (polyacetal copolymer resin). In the scintillation detector 100 for a 1 cm dose equivalent meter by the aluminum case 101 of the prior art of FIG. 10, the sensitivity decreases as it deviates from the reference direction, whereas the scintillation for 1 cm dose equivalent meter by the plastic resin case of this embodiment of FIG. In the case of the detector 1 ′, it can be seen that the measurement can be made with a difference of about ± 30% from 0 to 90 degrees. Therefore, it is possible to perform highly accurate measurement without being strictly aware of the direction of arrival of photons.

  As described in the prior art and the previous embodiment, the incident direction of the measurement of the low energy radiation was limited to the window side, but according to the present embodiment, the case 20 (including the incident window 20a) of the scintillator 13 itself is The opaque plastic resin as a whole has a function as an entrance window, so that the energy of sensitivity is secured while ensuring an operating environment for shielding external light to the scintillator, which is a function of the conventional technique and the case described in FIG. 1cm dose equivalent meter scintillation with improved accuracy to measure the 1cm dose equivalent with high accuracy and further simplification of structure, strengthening of mechanical strength and easy handling A detector can be provided.

  Next, another embodiment will be described with reference to the drawings. FIG. 6 is a cross-sectional structure diagram of another form of scintillation detector. As shown in FIG. 6, the scintillation detector 1 ″ for a 1 cm dose equivalent meter includes a case 11, a scintillator 13, a reflective layer 14, an optical window 15, a photomultiplier tube 16, a bleeder circuit 17, a gap 18, an inner incident window ( An aluminum plate 21 and an outer incident window (plastic resin plate) 22. In the prior art shown in Fig. 10, the incident window 102 made of an aluminum plate is disposed in front of the scintillator 105, but in the present invention, an aluminum plate is used. The difference is that an outer incident window 22 made of a plastic resin plate is disposed in addition to the inner incident window 20. Therefore, the scintillator 13, the reflection layer 14, the optical window 15, the photomultiplier tube 16, and the bleeder circuit 17 have the same configuration. The description will be omitted, and only the differences will be emphasized.

The case 11 is a metal cylinder having a detection hole in the front and a hole (not shown) for drawing out the signal line and the power line in the rear, and has a function of shielding light and magnetism.
The inner entrance window 21 is a disk made of aluminum. The thickness is 0.1 to 0.4 mm.
The outer entrance window 22 is a disc made of an opaque plastic resin. Specifically, polyacetal copolymer resin (Duracon) is adopted as the plastic resin. The thickness is 1 to 4 mm.
The thicknesses of the inner incident window 21 and the outer incident window 22 are selected so that absorption with respect to photons is equivalent to 0.1 to 0.4 mm for aluminum.

  FIG. 7 is a photon energy-transmittance characteristic diagram for each combination of the inner entrance window and the outer entrance window. Outer and outer entrance windows of the double-sided entrance window 22 are made of polyacetal copolymer resin and have a thickness of 1 mm, and the inside entrance window 21 is made of aluminum and has a thickness of 0.1 mm. (Simulation calculation result by EGS4) is shown. For comparison, the energy dependence of the scintillation detector 100 for a 1 cm dose equivalent meter of the aluminum entrance window 102 according to the prior art shown in FIG. 10 is shown as being 0.1 mm thick and 0.2 mm thick. .

As shown in FIG. 7, by adding an incident window made of plastic and having a thickness of 1 mm to an incident window having a thickness of 0.1 mm, energy dependence corresponding to an incident window having a thickness of 0.2 mm can be obtained. . In simple terms, the energy dependency of aluminum with a thickness of 0.1 mm coincides with the energy dependency of plastic resin with a thickness of 1 mm. If the energy dependency of 0.3 mm in aluminum is matched, an incident window with a thickness of 2 mm is added to the incident window with a thickness of 0.1 mm, or a plastic is added to the incident window with a thickness of 0.2 mm. By adding an incident window having a thickness of 1 mm, it is possible to obtain energy dependency corresponding to an incident window having a thickness of 0.3 mm. In this way, the energy dependency of the combination of the outer incident window 22 and the inner incident window 21 can be made substantially the same as the energy dependency of the conventional aluminum incident window 102.
In general, when the thickness of the aluminum incident window of the inner incident window 21 is amm and the thickness of the plastic resin of the outer incident window 22 is bmm, 0.1 ≦ a + 0.1b ≦ 0.4 (however, 0 <A, 0 <b) is satisfied.

  In this way, the entrance window is doubled on the inside and outside, the outside entrance window made of a plastic resin plate that absorbs little even with low-energy photons and has high mechanical strength, and the inside entrance window made of an aluminum plate is placed on the inside. The absorption with respect to the total photon of the inner aluminum and the outer plastic resin is set to a thickness corresponding to an absorption equivalent to 0.1 to 0.4 mm with aluminum. In addition to the conventional scintillation detector 100 for a 1 cm dose equivalent meter, it can be said that an outer incident window serving as a protective case made of a strong plastic resin is added to the outside to make it difficult to break. In this way, it is possible to provide a scintillation detector for a 1 cm dose equivalent meter that is easy to handle while increasing the mechanical strength with a simple additional configuration and ensuring the desired energy dependence.

  Thus, the scintillation type low energy photon 1 cm dose equivalent meter of the present invention adopts a configuration that is inexpensive and high in strength, and further has an energy dependency with respect to low energy photons in the energy region of 8 keV to 150 keV. It is possible to provide a scintillation detector for a 1 cm dose equivalent meter with improved usability by improving detection sensitivity so as to have a small response.

1 is a cross-sectional configuration diagram of a scintillation detector of the best mode for carrying out the present invention. It is a characteristic figure of the photon energy-detection efficiency of a scintillator. It is a photon energy-transmittance characteristic view according to thickness and material of an incident window made of plastic resin. It is a cross-section figure of the scintillation detector of another form. It is a characteristic view explaining the direction dependence with respect to the photon energy of 10 keV of the scintillation detector for 1 cm dose equivalent meters of the case by a prior art, and the case made from a plastic resin (polyacetal copolymer resin). It is a cross-section figure of the scintillation detector of another form. It is a photon energy-transmittance | permeability characteristic view according to the combination of an inner entrance window and an outer entrance window. It is explanatory drawing of the photon energy-response characteristic of an ionization chamber type 1 cm dose equivalent meter. It is a photon energy-1cm dose equivalent conversion factor curve figure. It is a cross-sectional block diagram of the scintillation detector for 1 cm dose equivalent meters of a prior art. It is a photon energy-transmittance | permeability characteristic view according to thickness and material of the entrance window (aluminum plate) of a prior art. It is a photon energy-response characteristic by calculation.

Explanation of symbols

1, 1 ', 1 ": scintillation type low energy photon 1 cm dose equivalent meter 11: case 12: entrance window (plastic resin)
13: scintillator 14: reflective layer 15: optical window 16: photomultiplier tube 17: bleeder circuit 18: gap 19: case (metal case)
19a: Screw part 19b: O-ring 19c: Adhesive part 20: Case (plastic resin)
20a: entrance window (plastic resin)
21: Inside entrance window (aluminum plate)
22: Outside entrance window (plastic resin plate)

Claims (4)

An incident window having a characteristic that a plastic resin is used as a material, and a part of incident photons are absorbed and the rest are allowed to pass, and the transmittance decreases with decreasing energy with respect to a photon having a predetermined energy or less,
A scintillator that emits scintillation light in response to photons that have passed through the entrance window;
A photomultiplier tube that outputs a pulse signal proportional to the intensity of the scintillation light emitted from the scintillator;
A case for accommodating an entrance window, a scintillator and a photomultiplier;
A scintillation detector for a 1 cm dose equivalent meter comprising:
By making the thickness of the entrance window from 1 mm to 4 mm and approximating the transmittance characteristics of the entrance window with respect to energy at 20 keV or less to a 1 cm dose equivalent conversion coefficient curve of 20 keV or less, low energy from 8 keV to 150 keV A scintillation detector for a 1 cm dose equivalent meter characterized by flattening an energy response when a photon is incident. The scintillation detector for a 1 cm dose equivalent meter according to claim 1,
The scintillation detector for a 1 cm dose equivalent meter, wherein the incident window is an integral structure included in a part of the case, and the case itself has a function of the incident window. An outer incident window having a characteristic that a plastic resin is used as a material, and a part of the incident photons are absorbed and the rest are allowed to pass, and the transmittance decreases with decreasing energy with respect to a photon having a predetermined energy or less,
An inner incident window having a characteristic that the transmittance is reduced as the energy is reduced for a photon having a predetermined energy or less, while absorbing a part of the incident photon and allowing the rest to pass through the material made of aluminum.
A scintillator that emits scintillation light in response to photons that have passed through the outer and inner incident windows;
A photomultiplier tube that outputs a pulse signal proportional to the intensity of the scintillation light emitted from the scintillator;
A case containing an outer incident window, an inner incident window, a scintillator and a photomultiplier;
A scintillation detector for a 1 cm dose equivalent meter comprising:
The thickness of the outer incident window and the thickness of the inner incident window are adjusted so that the thickness of the inner incident window is within the range of characteristics in the thickness range of 0.1 mm to 0.4 mm. By approximating the transmittance characteristics of the outside and inside entrance windows with respect to the energy to a 1 cm dose equivalent conversion coefficient curve of 20 keV or less, the energy response is flattened when low energy photons from 8 keV to 150 keV are incident. A scintillation detector for a 1 cm dose equivalent meter, characterized by: In the scintillation detector for 1 cm dose equivalent meters according to any one of claims 1 to 3,
A scintillation detector for a 1 cm dose equivalent meter, wherein a gap is interposed between the incident window and the case, and the scintillator.

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