JP2009036752A - Radiation sensor - Google Patents

Abstract

An object of the present invention is to provide a radiation sensor in which the loss of scintillator light in an optical fiber is reduced and the measurement range of the radiation sensor is dramatically expanded.
A representative configuration of a radiation sensor according to the present invention includes a scintillator 102 that emits light upon incidence of radiation, an optical fiber 104 mainly composed of quartz that guides light emitted by the scintillator 102, and an optical fiber 104. The scintillator 102 emits light of 1300 nm band or 1550 nm band.
[Selection] Figure 1

Description

  The present invention relates to a radiation sensor using a scintillator that emits light upon incidence of radiation.

  One radiation sensor is a scintillator. A scintillator is a radiation detector that uses the phenomenon (scintillation) that emits light (fluorescence) when radiation is incident on a specific substance and the electrons of the substance are excited by the energy and the electron level drops. is there. The light emitted from the scintillator is guided by an optical fiber, weak light is amplified by a photomultiplier tube, converted into an electrical signal by a light detection unit, and used for counting and analyzing radiation.

  Such a radiation sensor is used for a nuclear power plant in a large size and for medical use in a small size. Examples of radiation detected by the scintillator include X-rays, γ-rays, and neutrons depending on the material. FIG. 9 is a diagram for explaining the types and wavelengths of electromagnetic waves. An electromagnetic wave having a wavelength of about 10 nm to 1 pm is generally called an X-ray, and an electromagnetic wave having a wavelength of 10 pm or less is called a γ-ray. Neutron beams are neutron particle beams.

Conventionally, various configurations have been proposed for radiation sensors that guide light output from a scintillator by an optical fiber. Patent Document 1 discloses a radiation detection system using an optical fiber cable itself that emits light when irradiated with radiation.
JP 2000-065938 A

  However, in Patent Document 1, an inorganic scintillator such as NaI (sodium iodide) or CsI (cesium iodide) is used as the scintillator. These are general scintillator materials, and their emission wavelengths are in the visible light range (400 nm: blue light, see FIG. 9). The light of this wavelength has a very large loss in the optical fiber. FIG. 10 is a diagram showing the wavelength of light and the loss wavelength characteristics of a silica-based visible optical fiber. It can be seen that the transmission loss of light having a wavelength of 400 nm is about 50 dB / km.

  On the other hand, since the light emitted from the scintillator is weak, the length of the optical fiber capable of detecting the transmitted light is only a few meters to a maximum of about 30 m.

  By the way, there is a request to expand the measurement range of the radiation sensor and detect radiation at a remote place. For example, in a large facility such as a nuclear power plant, 30m is so short that even the next building cannot be reached. For this reason, radiation sensors will be installed at the measurement site. However, if the values of radiation sensors installed at the site are centrally managed at remote locations, the radiation sensor devices will be distributed at various locations, so maintenance management is required. There is a problem that becomes troublesome. In addition, when electrical equipment is installed at the measurement site, there is a problem that power supply cannot be promised in the event of an accident, and measurement may not be possible when liver and kidney measurement is required.

  Accordingly, an object of the present invention is to provide a radiation sensor in which the loss of scintillator light in an optical fiber is reduced and the measurement range of the radiation sensor is dramatically expanded.

  As a result of extensive studies by the inventors in order to solve the above-mentioned problems, attention was paid to the fact that the loss of light in the optical fiber for optical communication is extremely small. FIG. 11 is a diagram showing the loss wavelength characteristics of the silica-based communication optical fiber. The loss of the optical fiber at the wavelength for optical communication (near infrared: wavelength 2500 nm to 780 nm, see FIG. 9) is generally 1310 nm. It can be seen that the transmission loss is extremely low, about 0.35 dB / km in the band and about 0.25 dB / km in the 1550 nm band.

  In other words, a wavelength with a small loss in an optical fiber is known from the background of research and development and technological development, and light of that wavelength is used for optical communication. Therefore, it is considered that the measurement range of the scintillator can be dramatically expanded by using light of these wavelengths. In addition, various devices and techniques (direct optical amplification, etc.) used in optical communications that have made remarkable progress in recent years can be applied as they are.

  Therefore, if a scintillator that emits light at the wavelength for optical communication (near infrared region) is used, the emission wavelength matches the wavelength used for optical communication, so the existing measurement range is greatly expanded, and communication optical fibers and the latest The present inventors have found that the optical communication technology can be used and have completed the present invention.

  That is, a typical configuration of the radiation sensor according to the present invention includes a scintillator that emits light upon incidence of radiation, an optical fiber mainly composed of quartz that guides light emitted by the scintillator, and a light detection unit that is connected to the optical fiber. The scintillator emits light of 1300 nm band or 1550 nm band.

  According to the above configuration, the light emitted from the scintillator can be transmitted to a remote place with extremely low loss using the silica-based communication optical fiber, and the measurement range of the radiation sensor can be greatly expanded.

  In addition, another configuration of the radiation sensor according to the present invention includes a scintillator that emits light upon incidence of radiation, an optical fiber mainly composed of quartz that guides light emitted by the scintillator, and a light detection unit that is connected to the optical fiber. The scintillator emits light from the 1000 nm band to the 1800 nm band.

  The transmission loss of the light emitted by the scintillator is 1 dB / km or less in the above wavelength band (see FIG. 11). Therefore, according to the said structure, it becomes possible to reduce the loss at the time of transmission of the light light emitted by the scintillator, and to dramatically expand the measurement range of the radiation sensor.

  The length of the optical fiber used for radiation measurement can be about 30 m or more. This is a length that is possible for the first time by the configuration of the present invention, and by using such a length, it is possible to perform measurement at a remote place without requiring electric facilities on site.

  The scintillator can be formed of a transparent material added with a rare earth element, particularly a rare earth element for an optical amplifier in the field of optical communication. When a rare earth element is used, light in the 1300 nm band or 1550 nm band, or light in the 1000 nm band to 1800 nm band can be emitted by incidence of radiation.

  The rare earth element may be one or more elements selected from erbium, praseodymium, neodymium, thulium, ytterbium, dysprosium, holmium, and samarium. The above element is a specific example of a rare earth element, and by adding such an element, light having a wavelength from 1000 nm band to 1800 nm band can be obtained. In particular, erbium can obtain light having a wavelength of 1550 nm, and praseodymium and neodymium can obtain light having a wavelength of 1300 nm.

  ADVANTAGE OF THE INVENTION According to this invention, the loss of the scintillator light in an optical fiber can be reduced, and the radiation sensor which expanded the measurement range of the radiation sensor dramatically can be provided. Therefore, radiation can be measured from a remote location, and a plurality of locations in a wide area can be managed intensively.

[Embodiment]
Embodiments of a radiation sensor according to the present invention will be described below with reference to the drawings. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a diagram illustrating the overall configuration of the radiation sensor. In the radiation sensor 100 shown in FIG. 1, a scintillator 102 that emits light upon incidence of radiation is connected to one end of an optical fiber 104 mainly composed of quartz. The other end of the optical fiber 104 is connected to a light detection unit 106 such as a photomultiplier tube, and is output as an electrical signal and detected by the sensor 108.

  The radiation sensor 100 mainly targets γ rays, X rays, and neutron rays, but α rays, β rays, and the like are also objects of measurement. These electromagnetic waves have high energy and can be detected by causing the scintillator to emit light.

  The scintillator 102 is obtained by adding (doping) a predetermined element to an optical fiber. In this embodiment, erbium or ytterbium as an example of a rare earth element is added. Erbium is used as an optical amplifier having a wavelength in the 1550 nm band and ytterbium in a wavelength of 1030 nm.

  The optical fiber 104 is a silica-based communication optical fiber. In addition to the silica-based optical fiber, there are a glass-based optical fiber, a plastic optical fiber, and the like, but a silica-based optical fiber is preferable for long-distance transmission.

  For example, a photomultiplier (photomultiplier) can be used as the light detection unit 106. A photomultiplier tube is a device that converts light into an electrical signal using the photoelectric effect and further amplifies (electron multiplication) current. As the light detection unit, an avalanche photodiode (APD), an optical spectrum analyzer, an optical power meter, or the like can be used.

  The sensor 108 is a data processing device that includes an A / D conversion unit that monitors a current output from the light detection unit 106 and that determines and records an output value. For simplicity, a sensor that determines a voltage or current with a threshold, an oscilloscope, or a digital multimeter can be used.

  Here, the light emission principle of the scintillator 102 will be described. FIG. 2 is a diagram for explaining the principle of the scintillator and the optical amplifier.

  FIG. 2A is a diagram for explaining the principle of the scintillator 102. When radiation is incident, the electrons of the additive material are excited from the ground level to the excited level, and the electrons are accumulated at a point where the level has dropped to a stable level called the upper level. Then, when returning from the upper level to the naturally stable ground level, light of a predetermined wavelength is spontaneously emitted. The wavelength of the emitted light is determined by the energy gap from the upper level to the ground level, and is determined for each element.

  FIG. 2B is a diagram for explaining the principle of the optical amplifier, and the numerical value uses erbium as an example. In the optical amplifier shown in FIG. 2B, the electron of the additive element is excited from the ground level to the excited level by entering 980 nm excitation light (laser light), and is accumulated when it falls to the upper level. Is done. When signal light of 1550 nm is incident thereon, the electrons accumulated in the upper level are induced to return to the ground level, and light is emitted and amplified by the stimulated emission energy at that time. At this time, the wavelength of the amplified light is determined by the energy gap between the upper level and the ground level, and amplification is performed only when light of the same wavelength is incident (induction to the ground level does not work). ).

  The inventors paid attention to the fact that the scintillator 102 and the optical amplifier are similar in principle when the pump light is replaced with radiation, although their operations are different. When a scintillator was constructed using rare earth elements used for optical amplification, light emission in the wavelength band used for optical communication was obtained.

  In addition to erbium (1550 nm band) and ytterbium (1030 nm band), the scintillator composition includes praseodymium (1300 nm band), neodymium (1060 nm band, 1300 nm band), thulium (1470 nm band), dysprosium (1300 nm band), holmium. (1100 nm band, 1380 nm band) and samarium (1000 nm band, 1100 nm band, 1380 nm band). These two or more elements may be selected and added.

  By adding the above elements to the scintillator 102, light having a wavelength from 1000 nm band to 1800 nm band can be obtained. Since the transmission loss of light in such a wavelength band is as low as 1 dB / km or less, the light emitted from the scintillator 102 can be transmitted over a long distance. Therefore, the length of the optical fiber 104 can be extended.

  Among them, erbium can obtain light having a wavelength of 1550 nm, and praseodymium and neodymium can obtain light having a wavelength of 1300 nm. These wavelength bands are often used for optical communication, and exhibit extremely low transmission loss in silica-based optical fibers for long-distance transmission. Therefore, the light emitted from the scintillator can be transmitted far, and the light of the scintillator can be transmitted by the optical fiber 104 having a length ranging from 30 m to several km.

  As a result, the measurement range of the radiation sensor can be dramatically expanded, so that radiation can be measured from a remote location, and a plurality of locations in a wide area can be managed in a concentrated manner. In addition, since only scintillators are installed at the site (measurement location) and no electrical equipment is required, measurements can be made without relying on the power supply even in the event of an accident, and the maintenance work is greatly simplified. be able to.

  In addition, since the wavelength is frequently used, various optical communication devices and technologies (direct optical amplification, etc.) that have made remarkable progress in recent years can be applied.

[Other Embodiments]
FIG. 3 is a diagram for explaining another embodiment. As shown in FIG. 3A, the additive element is excited in advance and stimulated emission is caused by radiation. That is, excitation is performed to the excitation level by excitation light (laser light), and irradiation is performed in a state where electrons are accumulated at the upper level, whereby stimulated emission is generated by the stimulation. Thereby, scintillator light can be generated efficiently and the amount of light can be increased. Specifically, as shown in FIG. 3B, excitation light is incident on the optical fiber 104 for guiding the scintillator light from the oscillator 110, and the reflected light that has returned is provided with a filter 112 for cutting the excitation light. Only light can be extracted.

  FIG. 4 is a diagram for explaining still another embodiment. The ground level of an atom actually has a certain width. Therefore, as shown in FIG. 4, by exciting the electrons to the upper level of the ground level with the excitation light, it is possible to facilitate excitation to the excitation level when radiation is incident. As a result, even a slight amount of radiation is easily excited, and the sensitivity can be improved.

  Next, the effect of the radiation sensor 100 according to the present embodiment will be described using measurement results. As described above, in this embodiment, the rare earth element erbium or ytterbium is added to the optical fiber used as the scintillator 102. Hereinafter, an optical fiber added with erbium is referred to as “EDF (Erbium Doped Fiber)”, an optical fiber added with ytterbium is referred to as “YDF (Ytterbium Doped Fiber)”, and EDF and YDF are collectively referred to as “rare earth doped fiber”.

  FIG. 5 is a diagram for explaining the outline of the measurement equipment. The measuring equipment consists of an irradiation room and an operation room. The irradiation chamber includes a module 200 in which a rare earth doped fiber used as the scintillator 102 is accommodated in an aluminum case and is modularized, and an irradiation device 202 that irradiates the module with radiation. The module 200 is installed on the irradiation stand.

  The operation chamber is provided with a photomultiplier tube 204 for measuring the number of photons emitted from the rare earth-doped fiber in the module 200 and an optical terminator 206 for reducing the return light at the open end of the rare earth-doped fiber. Yes. As the photomultiplier tube 204, one that responds to a near infrared wavelength (950 nm to 1700 nm) was used. One end of the rare earth doped fiber is connected to the photomultiplier tube 204 and the other end to the optical terminator 206 via connectors.

  In the above measurement facility, the module 200 was irradiated with radiation (cobalt 60, γ rays) from the irradiation device 202 while changing the dose rate. And the photon number of the light which the rare earth doped fiber in the module 200 emitted by irradiation was measured with the photomultiplier tube 204. In the above measurement, the sampling interval was 1 second, and the measurement time was 360 seconds. In addition, irradiation is performed for 30 seconds to 330 seconds after the start of measurement, and irradiation is stopped for 0 seconds to 30 seconds and for 330 seconds to 360 seconds after the start of measurement.

  FIG. 6 is a diagram showing a change in the number of photons when the EDF is irradiated with radiation. As shown in FIG. 6, when the EDF is irradiated with radiation having a dose rate of 700,000 R / h (Roentgen / hour), the number of photons increases with irradiation. From this, it is considered that light having a wavelength in the 1550 nm band emitted from erbium added to the EDF was measured.

  FIG. 7 is a diagram illustrating a change in the number of photons when the YDF is irradiated with radiation. As shown in FIG. 7, when YDF is irradiated with radiation at a dose rate of 700,000 R / h as described above, the number of photons increases with irradiation. From this, it is considered that light having a wavelength of 1000 nm band emitted from ytterbium added to YDF was measured.

  In addition, even when the dose rates of radiation irradiated to YDF are 200000 R / h and 100000 R / h, the increase rate is lower than that of 700000 R / h, but the number of photons increases at the time of irradiation. From this, it was confirmed that the light emission of YDF can be detected by the photomultiplier tube 204 even at a dose rate as low as about 100,000 R / h.

  From the above results, it can be understood that the scintillator 102 using the rare earth doped fiber can be used for the radiation sensor 100. Next, a long fiber was connected to YDF, and the number of photons during radiation irradiation was measured.

  FIG. 8 is a diagram showing a change in the number of photons when radiation is applied to a YDF connected with a long fiber. As such long fibers, optical fibers having a length of 1 km and 10 km were used. In addition, the dose rate of the radiation irradiated to YDF which connected the long fiber is 70,000 R / h.

  As shown in FIG. 8, the change in the number of photons with irradiation when a 1 km fiber is connected is clear even when a long fiber is not connected (when 0 km). From this, the measurement range of the radiation sensor using the conventional optical fiber is several meters to a maximum of 30 m, whereas the radiation sensor 100 using the rare earth doped fiber as the scintillator 102 can expand the measurement range to 1 km. It could be confirmed. This is because the element added to the rare earth-doped fiber is a rare earth element that emits light in a wavelength band with a transmission loss of 1 dB / km or less, thereby reducing the transmission loss of light in a 1 km fiber to 1 dB or less. This is thought to be due to this.

  In addition, when a 10 km fiber is connected, the change in the number of photons due to radiation irradiation is remarkably small, and a clear change cannot be confirmed. This is presumably due to transmission loss of the optical fiber. That is, in the 1000 nm band wavelength light emitted from ytterbium added to YDF, the transmission loss of the optical fiber is about 1 dB / km, so the loss of about 10 dB is large for the 10 km fiber, and the measurement is large because the loss is large. I think it was difficult.

  However, as the rare earth element added to the rare earth doped fiber, by using an element that emits light in a wavelength band whose transmission loss is lower than 1 dB / km, such as 1300 nm band or 1550 nm band, transmission loss in the optical fiber is further increased. Since it can be reduced, it is considered that the length of the optical fiber can be further extended.

  From the above results, it was proved that the rare earth doped fiber is used for the scintillator 102 and the scintillator 102 is used for the radiation sensor 100, so that the measurement range of the radiation sensor 100 can be dramatically expanded. In this embodiment, since the length of the long fiber connected to the rare earth doped fiber is 1 km and 10 km, the measurable range is confirmed only to 1 km, but if it is about several km (less than 10 km) Similarly, it is considered measurable.

  As mentioned above, although the suitable Example of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the embodiment which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the present embodiment, the scintillator is configured by adding an element to the optical fiber material. However, the element may be added to a transparent material having a block shape or a plate shape, and the scintillator is configured as a chip shape. You may do it.

  The present invention can be used as a radiation sensor using a scintillator that emits light upon incidence of radiation.

It is a figure explaining the whole structure of a radiation sensor. It is a figure explaining the principle of a scintillator and an optical amplifier. It is a figure explaining other embodiment. It is a figure explaining other embodiment. It is a figure explaining the outline of measurement equipment. It is a figure which shows the change of the photon number at the time of irradiating radiation to EDF. It is a figure which shows the change of the number of photons when a YDF is irradiated with a radiation. It is a figure which shows the change of the photon number at the time of irradiating a radiation to YDF which connected the long fiber. It is a figure explaining the kind and wavelength of electromagnetic waves. It is a figure which shows the wavelength of light, and the loss wavelength characteristic of a silica type visible optical fiber. It is a figure which shows the loss wavelength characteristic of the optical fiber for quartz-type communication.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Radiation sensor 102 ... Scintillator 104 ... Optical fiber 106 ... Optical detection part 108 ... Sensor 200 ... Module 202 ... Irradiation device 204 ... Photomultiplier tube 206 ... Optical terminator

Claims (5)

A scintillator that emits light upon incidence of radiation;
An optical fiber mainly composed of quartz that guides light emitted from the scintillator;
A light detection unit connected to the optical fiber,
The scintillator emits light of 1300 nm band or 1550 nm band. A scintillator that emits light upon incidence of radiation;
An optical fiber mainly composed of quartz that guides light emitted from the scintillator;
A light detection unit connected to the optical fiber,
The scintillator emits light from a 1000 nm band to a 1800 nm band.   The radiation sensor according to claim 1, wherein a length of the optical fiber is approximately 30 m or more.   The radiation sensor according to claim 1, wherein the scintillator is configured by adding a rare earth element to a transparent material.   5. The radiation sensor according to claim 4, wherein the rare earth element is one or more elements selected from erbium, praseodymium, neodymium, thulium, ytterbium, dysprosium, holmium, and samarium.

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