JP2011128053A - Radiation detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem in transportation that in taking-off and landing of an aircraft, in parking a vehicle in a slanting condition for a long period of time and the like, if silicone oil is leaked to infiltrate between a light guide and a cushion, static electricity is accumulated to cause an electric discharge and the discharge light is transmitted to a photomultiplier to generate a noise and the indication suddenly changes. <P>SOLUTION: A radiation detector includes: a scintillator for converting radiation to light; a light guide optically coupled to the scintillator; a photomultiplier for converting the light from the light guide to electrons; an optical coupling oil for optically coupling the photomultiplier to the light guide; an oil fence for preventing the optical coupling oil flowing out by surrounding the photomultiplier; a socket for outputting current pulse by extracting from the photomultiplier; a preamplifier for converting the current pulse from the socket to voltage pulse; a magnetic shield for magnetically shield the photomultiplier; a detector case for housing these members; and a cushion for fixing the light guide to the detector case, wherein an extension fence for increasing the height of the oil fence is provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radioactive gas monitor used for emission management or radiation management of nuclear reactor facilities, spent fuel reprocessing facilities, radioactive isotope usage facilities, particle beam usage facilities, etc., and radiation of gaseous radioactive substances contained in sample gas The present invention relates to a radiation detector for detecting the performance.

A conventional radiation detector used to detect the radioactivity of a gaseous radioactive substance contained in a sample gas is used to detect the radioactivity of a radioactive noble gas with high sensitivity. It is desirable to measure β-rays with a high emission rate and to have high sensitivity to β-rays and low sensitivity to γ-rays from the environment. For this reason, it is required that the sensor can be processed thinly in a large area. The
As a sensor that realizes this requirement, a plastic scintillator that is easy to process, inexpensive, easily available, and physically stable is generally used.
Photomultiplier tubes are more expensive than plastic scintillators, so they are selected to have a smaller aperture than plastic scintillators, and absorb the difference in apertures to efficiently transmit the light emitted by the plastic scintillator to the photomultiplier tubes. A light guide is interposed between them.
The light guide is obtained by machining acrylic, applying a reflecting material containing titanium oxide fine powder on the side surface to form a light reflecting layer, and optically joining the radiation incident surface side to the plastic scintillator with an adhesive. On the other hand, since the photomultiplier tube is made of glass and has a coefficient of thermal expansion that is significantly different from that of the light guide, it is optically bonded to the light guide with high-viscosity silicon oil. (See Patent Document 1)

The light guide is fixed in the detector case with a cushion, and the radiation incident surface side including the plastic scintillator has a pressure boundary. Therefore, the pulsation of the sample gas caused by the pump operation causes the boundary between the light guide and the cushion. Static electricity is generated by friction and accumulates. In addition, when a large pressure fluctuation occurs in the sample gas due to the start / stop of the pump, a large amount of static electricity is generated in a short time.
The accumulated static electricity is discharged when the air insulation limit is exceeded.
Since the light reflecting layer on the side surface of the light guide is easily peeled off if it is too thick, it is controlled to have an appropriate thickness. For this reason, with the light reflection layer thickness, a part of the electrostatic discharge light is transmitted and transmitted to the photomultiplier tube, which may cause a failure in which the indication changes suddenly as noise.

For this reason, black nitrile rubber containing a large amount of carbon is used for the cushion so that static electricity does not accumulate up to a voltage leading to discharge at the interface between the light guide and the cushion.
In general, in a rubber body having a volume resistivity of 10 ¹⁰ Ω · cm or less, static electricity generated by friction is quickly neutralized, so that charges are not accumulated until discharge accompanied by light. Since nitrile rubber has a volume resistivity as low as 10 ¹⁰ Ω · cm can be easily obtained, static electricity is sequentially neutralized before discharge, thereby preventing discharge.
As the cushion, a nitrile rubber cast into a mold so as to be pressed and fixed between the detector case and the light guide, or a potted nitrile rubber poured into a potting material and solidified is used. . Since the nitrile rubber is black, even if electrostatic discharge occurs between the nitrile rubber and the potting material, the nitrile rubber is shielded from light and does not become an obstacle.

In addition, a radiation detector has been proposed in which a light guide and a photomultiplier tube are bonded in close contact with a transparent gel-like bonding material that hardly accumulates static electricity instead of silicon oil. The transparent curable bonding agent generally used when the area is small is intended to solve the weak point that easily causes cracking when used over a wide area by using a transparent gel binder. . (See Patent Document 2)

JP-B-1-32474 JP 2009-20046 A

Conventional radiation detectors are configured as described above. Under normal handling, silicon oil does not leak even if the radiation detector is tilted for a short period of time. When the vehicle stopped on a slope for a long time, and it was in a tilted state, silicon oil could leak. If the leaked silicone oil enters between the light guide and the cushion and adheres between the side of the light guide and the cushion material that fixes it, the silicone oil has a high volume resistivity of 10 ¹⁴ Ω · cm. Due to the silicon oil, static electricity could accumulate due to friction caused by sample gas pulsation during operation, which could cause discharge.
And a very small part of the generated strong discharge light penetrates into the light guide through the light reflection layer on the side of the light guide and is transmitted to the photomultiplier tube, which becomes noise and the indication changes suddenly, causing the detector to malfunction. There was a problem.
In addition, in the case of using a transparent gel binder instead of silicone oil, since the adhesive force is weak, there is a problem that a gap is generated on the joint surface due to temperature change, and light transmission is changed.

  A radiation detector according to the present invention includes a scintillator that absorbs energy of incident radiation and converts it into light, a light guide that is optically coupled to the scintillator with an adhesive and transmits the light, and is transmitted from the light guide. A photomultiplier tube for converting the light into electrons, a photocoupler oil for optically coupling the photomultiplier tube to the light guide, and the photocoupler formed integrally with the light guide and surrounding the photomultiplier tube. An oil fence that prevents oil from flowing out, a socket that applies a voltage to the photomultiplier tube and extracts and outputs a current pulse of a signal, and a pre-converter that converts the current pulse output from the socket into a voltage pulse. An amplifier, a magnetic shield that shields the photomultiplier tube from being affected by an external magnetic field, and the magnetic shield and the scintillator A detector case that houses members such as the light guide, the photomultiplier tube, the socket, and the preamplifier, and a cushion that fixes the light guide to the detector case. An extension fence that raises the height of the oil fence is provided.

In the radiation detector according to the present invention, an oil fence is formed integrally with the light guide, and an extension fence is provided on the oil fence to raise the height of the fence. For example, the radiation detector is tilted for a long time during transportation. However, since the silicone oil does not leak over the oil fence, it is possible to prevent electrostatic discharge caused by the leaked silicone oil entering between the light guide side surface and the cushion, thereby providing a highly reliable radiation detector.
In addition, instead of silicon oil, the light guide and photomultiplier tube are optically coupled with a gel-like binder that does not accumulate static electricity, a screw ring is provided inside the detector case, and the socket is pressed by the screw ring, Since the transparent gel binder is brought into close contact with the light guide and the photomultiplier tube, there is no gap in the joint surface and light transmission does not change, and a highly reliable radiation detector can be provided, It is possible to eliminate the defoaming work of the silicon oil before and after mounting the photomultiplier tube, which is necessary when using silicon oil, and it is possible to greatly reduce the assembly cost.

It is sectional drawing which shows the structure of the radiation detector concerning Embodiment 1 of this invention. It is sectional drawing which simplified and showed the structure of the radiation detector concerning Embodiment 2 of this invention. It is sectional drawing which simplified and showed the structure of the radiation detector concerning Embodiment 3 of this invention. It is sectional drawing which simplified and showed the structure of the radiation detector concerning Embodiment 4 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In addition, the same code | symbol shows the same or an equivalent part between each figure.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing the configuration of the radiation detector according to the first embodiment.
In FIG. 1, a plastic scintillator 1 absorbs incident radiation energy and converts it into light. The light guide 2 having a substantially truncated cone includes a light transmission block 201 that transmits light, a light reflection layer 202 that is provided in close contact (overlap) with the side surface of the light transmission block 201, and light transmission to a neck portion. It is composed of an oil fence 203 processed integrally with a block.
The surface having the large area of the light transmission block 201 is optically bonded to the plastic scintillator 1 with the optical adhesive 3, and the light of the plastic scintillator 1 advances straight to the light transmission block 201 or is reflected by the light reflection layer 202. introduce. The light reflecting layer 202 is obtained by kneading fine titanium oxide powder in a transparent adhesive, and when dried, forms a white layer, and light is reflected by the fine titanium oxide powder.
The photomultiplier tube 4 is optically joined to the light guide 2 with silicon oil (photocoupled oil) 5, converts the light transmitted from the light guide 2 to electrons and multiplies, and the socket 6 is a photomultiplier tube. The high voltage power supply is divided and applied to 4 and a current pulse of the signal is extracted, and the preamplifier 7 converts the current pulse into a voltage pulse and outputs it.

In the light guide 2, the neck portion on the photomultiplier tube 4 side is integrally cut as an oil fence 203 so as to surround the photomultiplier tube 4 and prevent the silicon oil 5 from flowing out.
A screw portion 203a is provided outside the oil fence 203, and the screw portion 8a of the extension fence 8 having a perforated cap shape is screwed into the screw portion 203a.
The magnetic shield 9 shields the photomultiplier tube 4 so as not to be affected by an external magnetic field.
The detector case 10 houses the plastic scintillator 1, light guide 2, optical adhesive 3, photomultiplier tube 4, silicon oil 5, socket 6, preamplifier 7, extension fence 8, and magnetic shield 9 incorporated therein. Thus, the intrusion of light from the outside is blocked and the photomultiplier tube 4, the socket 6 and the preamplifier 7 are shielded so as not to be affected by external electromagnetic noise.
The magnetic shield 9 is attached to a screw ring 13 provided inside the detector case 10. The preamplifier 7 may not be housed in the detector case 10 and may be disposed with an electromagnetic shield provided outside the detector case 10.
When the radiation detector is housed in a separate electromagnetic shield and used, the magnetic shield 9 may be omitted.

The light guide 2 is sealed with an O-ring 11 and attached to the detector case 10.
The light guide 2 is fixed with a cushion 12 between the light guide 2 and the detector case 10, and functions as a pressure boundary (pressure boundary) with respect to the measurement target gas.
The pressure of the gas to be measured is transmitted to the light guide 2 through the plastic scintillator 1, and is transmitted from the light guide 2 to the cushion 12 and finally received by the detector case 10.
As the material of the light guide 2, acrylic is generally used, and since the workability is excellent, the oil fence 203 can be easily processed integrally, and the extension fence 8 can also be easily manufactured by processing acrylic.

After silicon oil 5 is injected into the oil fence 203 and bubbles mixed in the silicon oil 5 are defoamed, the light guide 2 and the photomultiplier tube 4 are optically coupled with the silicon oil 5, and a small amount of the entrained wire is involved in the coupling. The bubble is defoamed, and the oil fence is raised by screwing the screw portion 8a of the extension fence 8 into the screw portion 203a outside the oil fence 203. In addition, since the height of the extension fence 8 needs to be adjusted as will be described later, the height of the extension fence 8 can be adjusted by the screw mechanism 203a and the screw portion 8a.
The height of the oil fence 203 is determined so as not to obstruct the operation of bringing the photomultiplier tube 4 into contact with the defoamed layer of silicon oil 5 at an angle and gradually joining it so as not to entrain air. Further, the height (length) of the extension fence 8 is determined (set) so that the silicon oil 5 does not flow out at the takeoff angle and landing angle of the aircraft transportation when the aircraft takes off and landing.

Pressure fluctuations generated in the gas to be measured by starting and stopping the pump (not shown) and vibrations at the place where the radiation detector is installed are transmitted to the light guide 2 to cause friction with the cushion 12. However, the material of the cushion 12 is nitrile rubber, and since the volume resistivity is as low as 10 ¹⁰ Ω · cm or less, static electricity is not accumulated, so there is no trouble of electrostatic discharge. Furthermore, since the extension fence 8 prevents the silicon oil 5 from flowing out, the contact surface between the light reflecting layer 202 of the light guide 2 and the cushion 7 is maintained in a healthy state.
Further, since the silicon oil 5 is highly viscous, even if the light guide 2 slightly vibrates due to pressure fluctuation and pulsation of the sample gas caused by the pump, the silicon oil is peeled off from the light guide 2 and the photomultiplier tube 4. Does not occur.

  As described above, the oil fence 203 is formed integrally with the light guide 2 and the extension fence 8 having a screw structure is provided on the oil fence 203 to increase the height of the oil fence, so that the radiation detector is inclined for a long time during transportation. Even in such a state, since the silicon oil 5 does not leak out of the fence, electrostatic discharge due to the wet silicon oil 5 can be prevented, and a highly reliable radiation detector can be provided.

Embodiment 2. FIG.
In the first embodiment, the upper portion of the extension fence 8 has an open structure. However, in the second embodiment, as shown in FIG. 2, the curved portion where the diameter of the photomultiplier tube 4 changes (inclined outer peripheral surface) and This gap is sealed with silicon oil 5 by sealing with a packing 14 made of nitrile rubber, for example.
Thus, the silicone oil 5 was sealed with the packing 14 interposed between the hole edge of the perforated cap-like extension fence 8 through which the photomultiplier tube 4 was inserted and the outer peripheral surface of the photomultiplier tube. Therefore, it is possible to prevent the electrostatic discharge that occurs when silicon oil evaporates over time and adheres to the peripheral members of the photomultiplier tube when it is open, providing a highly reliable radiation detector for a long period of time. it can.

Embodiment 3 FIG.
In the first embodiment, the light guide 2 and the photomultiplier tube 4 are optically coupled with the silicon oil 5, but the radiation detector in the third embodiment absorbs the energy of the incident radiation as shown in FIG. A scintillator 1 that converts light into light, a light guide 2 that is optically coupled to the scintillator with an adhesive and transmits the light by traveling straight or reflected, and photomultiplier that converts light transmitted from the light guide into electrons The tube 4, the transparent gel-like binder 15 having the property of not easily accumulating static electricity that optically couples the photomultiplier tube and the light guide 2, the fence portion 204 that prevents the transparent gel-like binder from flowing out, the photomultiplier A high voltage power source is divided and applied to the tube 4 and a current pulse of a signal is extracted and output, and a current pulse output from the socket is converted into a voltage pulse. The preamplifier 7, the magnetic shield 9 that shields the photomultiplier tube 4 from being affected by an external magnetic field, the magnetic shield, the scintillator 1, the light guide 2, the photomultiplier tube 4, the socket 6, and the front A detector case 10 for housing a member such as a preamplifier 7 and a cushion 12 for fixing the light guide 2 to the detector case are provided, and a screw ring 13 is provided inside the detector case 10. The transparent gel binder 15 is brought into close contact with the light guide 2 and the photomultiplier tube 4 by being pressed through a spring 16.

  In this way, the light guide 2 and the photomultiplier tube 4 are optically coupled with the transparent gel binder 15, and the socket 6 is pressed by the screw mechanism 13 a of the detector case 10 and the screw-in ring 13, and the loosening over time is spring-loaded. When the transparent gel binder 15 is absorbed in 16 and the light guide 2 and the photomultiplier tube 4 are brought into close contact with each other, a highly reliable radiation detector can be provided over a long period of time and silicon oil is used. This eliminates the defoaming work required for the radiation detector, so that the assembly cost of the radiation detector can be greatly reduced.

Embodiment 4 FIG.
In the third embodiment, the transparent gel-like binder 15 is pressed through the socket 6, but in the fourth embodiment, as shown in FIG. 18, pressing the curved portion (inclined outer peripheral surface) where the diameter of the photomultiplier tube 4 changes through the magnetic shield 9 and packing (a pressing rubber made of a material provided on the inner side of the magnetic shield and hardly accumulates static electricity); The transparent gel binder 15 is brought into close contact with the light guide 2 and the photomultiplier tube 4 by pressing the photomultiplier tube 4. The description of the same components as those in FIG. 3 is omitted.
In the case of the fourth embodiment, since the mechanical strength of the curved portion (inclined outer peripheral surface) of the photomultiplier tube 4 is large and the contact area of the support can be secured widely, radiation with high reliability over a long period of time. It is possible to provide a detector and to increase the seismic strength.

DESCRIPTION OF SYMBOLS 1 Plastic scintillator 2 Light guide 201 Light transmission block 202 Light reflection layer 203 Oil fence 204 Fence part 3 Optical adhesive 4 Photomultiplier tube 5 Silicon oil 6 Socket 7 Preamplifier 8 Extension fence 9 Magnetic shield 10 Detector case 11 O Ring 12 Cushion 13 Screwed ring 14 Packing 15 Transparent gel binder 16 Spring 17 Packing (pressing rubber) 18 Spring.

Claims (6)

A scintillator that absorbs the energy of the incident radiation and converts it into light, a light guide that is optically coupled to the scintillator with an adhesive and transmits the light, and a photoelectron multiplier that converts the light transmitted from the light guide into electrons A photomultiplier tube, an optical coupling oil that optically couples the photomultiplier tube to the light guide, and an oil fence that is integrally formed with the light guide and surrounds the photomultiplier tube to prevent the photocoupled oil from flowing out. A socket for applying a voltage to the photomultiplier tube and extracting and outputting a current pulse of the signal; a preamplifier for converting the current pulse output from the socket into a voltage pulse; and the photomultiplier tube, A magnetic shield that shields it from being affected by an external magnetic field, the magnetic shield, the scintillator, the light guide, and the photoelectrons With multiplier tube, the socket, and the apparatus case for housing the member such as the pre-amplifier, a cushion for fixing the light guide to the detector casing,
A radiation detector, wherein an extension fence for raising the height of the oil fence is provided on the oil fence.   The radiation detector according to claim 1, wherein the extension fence is attached to the oil fence by a screw mechanism capable of adjusting a raised height.   3. The radiation detector according to claim 1, wherein the extension fence is set to a height at which the optical coupling oil does not flow out according to a take-off angle and a landing angle of aircraft transportation. 4.   A packing made of a material that is unlikely to accumulate static electricity is interposed in a gap between the upper opening edge of the extension fence through which the photomultiplier tube is inserted and the outer peripheral surface of the photomultiplier tube. The radiation detector according to any one of claims 1 to 3, wherein the coupling oil is sealed. A scintillator that absorbs the energy of the incident radiation and converts it into light, a light guide that is optically coupled to the scintillator with an adhesive and transmits the light, and a photoelectron multiplier that converts the light transmitted from the light guide into electrons A tube-like tube, a gel-like binder that is hard to accumulate static electricity that optically couples the photomultiplier tube and the light guide, and a voltage is applied to the photomultiplier tube and a current pulse of a signal is extracted. An output socket, a preamplifier for converting a current pulse output from the socket into a voltage pulse, a magnetic shield for shielding the photomultiplier tube from being affected by an external magnetic field, and the magnetic shield, A detector case for housing members such as the scintillator, the light guide, the photomultiplier tube, the socket, and the preamplifier; Comprising a cushion for fixing the light guide in the vessel casing,
A radiation detection characterized in that a screw ring is provided inside the detector case, and the gel binder is brought into close contact with the light guide and the photomultiplier tube by pressing the socket with the screw ring. vessel.   The gel binder is pressed against the light guide and the light guide by pressing the photomultiplier tube through a packing made of a material that is hard to accumulate static electricity provided inside the magnetic shield while pressing the magnetic shield with the screw ring. The radiation detector according to claim 5, wherein the radiation detector is in close contact with a photomultiplier tube.

Images