JP2001141830A - Temperature-compensated optical transmission type radiation measurement device and its measurement system - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a practical apparatus capable of performing temperature compensation of a scintillator emission intensity in an optical transmission type radiation measurement apparatus. An optical transmission type radiation measurement device achieves effective temperature compensation of scintillation emission intensity by using a transmission medium fiber of light as a light transmission for OTDR temperature measurement. According to the present invention, it is possible to realize a practical device and a measurement system for accurately performing temperature compensation of scintillation emission intensity in a long-distance optical transmission type radiation measurement device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring radiation, and more particularly, to a radiation monitoring apparatus for transmitting and measuring scintillation light of a scintillator through an optical fiber and a measuring system therefor.

[0002]

2. Description of the Related Art FIG. 7 shows a prior art of an optical transmission type radiation measuring apparatus. In this conventional example, a plastic wavelength conversion fiber 62 is inserted into the center of a NaI (Tl) scintillator 61, and scintillation light (wavelength 410 n
m) is absorbed by the wavelength conversion fiber 62 and an optical signal is extracted to the outside at a conversion wavelength of 520 nm. The light extracted to the outside is converted into several tens of light using a plastic transmission fiber 63.
Transmitted to a location 0 m away, the photomultiplier 64 and the amplifier 6
5. The conventional general method is to measure by the measurement circuit 66. Reference: Radiation; Voi. 21, No. 3, P59 (199)
Five)}.

It is known that the light emission intensity of a scintillator changes depending on the temperature of the scintillator. JP-A-6-258446 is disclosed as an invention for compensating for this temperature dependency. This method analyzes and compensates for the photoelectric conversion waveform (such as the rise time of a pulse) of light transmitted through a transmission fiber.

[0004] In general radiation measurement sites, humidity and magnetic fields (lightning)
Environmental conditions such as are often poor. These optical transmission radiation measurement methods do not require an electronic circuit to be installed at the measurement site, and can improve environmental resistance and maintainability.

[0005]

SUMMARY OF THE INVENTION Light is transmitted over a long distance (Equation 1).
(00 m or more), one-photon measurement (single-photon counting) occurs due to transmission loss.
For this reason, the photoelectric conversion signal after long-distance transmission has a disadvantage that the number of measured photons is reduced and waveform information having emission temperature dependency of the scintillator cannot be maintained.

Assuming a radiation measurement point (site) of a general nuclear power plant and estimating a distance from a monitored building (such as a central operation room) to a measurement site, there are many places exceeding several hundred meters.

[0007] A large number of peripheral environment monitors (monitoring posts) provided in nuclear power plants require transmission over km or more. Therefore, in the temperature compensation configuration of the conventional device, the transmission range is limited to within several hundred meters, so that there is a problem that its application is also limited to a limited range.

An object of the present invention is to provide a practical device capable of reliably performing temperature compensation even when the optical transmission distance of the optical transmission type radiation measuring device is a long distance of km or more.

[0009]

In order to solve the above-mentioned problems, a temperature measurement method using light and a temperature compensation method for scintillation light emission intensity, which can be reliably used on a thermometer side even over long distances, use conventional optical transmission methods. It can be achieved by effectively combining with a radiation measuring device of the type.

[0010] An optical pulse reflection method (OTDR: Optical time Domai) is used as an accurate temperature measurement means using an optical fiber and light.
n Reflectrometory). References: Takahashi, et al .: Thermal and Nuclear Power Lines; Vol. 46, No. 8, P851 (1995). This optical transmission type radiation measurement device uses an optical fiber as a light transmission medium, and by using the same fiber, effective and accurate temperature measurement and temperature compensation of scintillation emission intensity can be easily achieved. . By this means, temperature compensation of the luminous intensity of a long-distance optical transmission type radiation measuring device which cannot be achieved conventionally can be realized, and the problem of the conventional device can be solved.

The OTDR irradiates a laser beam from one end of the transmission fiber, and receives and analyzes the reflected light reflected from each section of the transmission fiber (the ratio of Stokes light to anti-Stokes light) to provide each section (the transmission fiber is provided). Position) is accurately measured. The present invention uses OTDR in the optical transmission fiber path of the conventional optical transmission type radiation measurement device.
The input and output fibers for the laser light and the reflected light are branched and provided.
For the measurement of temperature and the measurement of optical transmission of radiation, a measurement circuit is separately provided, and by performing each measurement process, temperature compensation of emission intensity can be performed. Since the OTDR can arbitrarily set the intensity of the incident laser light, long-distance transmission measurement of km or more is easy. However, since the transmission fiber to the detector is also used, the light generated by the radiation and the O
Under conditions in which TDR laser light and reflected light coexist, measurement of both becomes difficult. Therefore, in order to perform both measurements, it is possible to provide an optical filter for the light involved in both measurements in each light receiving unit, or to perform time-division measurement of both. By the operation of the present invention, it is possible to realize a long-distance optical transmission type radiation measurement device capable of compensating for a temperature of km or more, which was impossible with the conventional device, and to construct a measurement system therefor.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments. FIG. 1 shows a configuration of an optical transmission type radiation measuring apparatus of the present invention. Scintillator @ NaI (T
1) The wavelength conversion fiber 2 is inserted into a plastic scintillator or the like # 1, and a transmission optical fiber 3 is connected to one end of the wavelength conversion fiber 2. A branch unit 4 for branching the optical path (3 ′, 3 ″) is provided at the terminal of the transmission optical fiber 3 to provide a configuration that enables optical transmission to both the OTDR circuit 9 for temperature measurement and the radiation measurement circuit. . The light incident surface of the photomultiplier tube 6 of this radiation measurement circuit system has a wavelength of 52
An optical filter 5 that transmits light near 0 nm is provided. An amplifier 7 and a counting circuit 8 are provided at the subsequent stage of the photomultiplier tube 6 to measure the radiation detection light transmitted optically. In the other OTDR circuit 9 for temperature measurement, the temperature of the installation portion of the scintillator 1 is measured, and the light emission intensity correction data of the scintillator 1 is created by the data processing device 10, and the control line 11
The radiation counting value of the counting circuit 8 is compensated for via.

FIG. 2 shows a scintillation light transmission mechanism. Radiation 20 is incident on the scintillator 1 and emits scintillation light 21 (wavelength 410 nm).

The scintillation light is incident on the wavelength conversion fiber 2 built in the scintillator 1, and is converted into the wavelength conversion light 22.
(Wavelength 510 nm). Although the wavelength-converted light 22 emits isotropically, a component 23 that is totally reflected in the wavelength-converting fiber 2 is transmitted along the length direction 24 of the fiber. The transmission fiber 2 is connected to one end of the wavelength conversion fiber 2.
By connecting 5, the detection light can be transmitted to an arbitrary place.

FIG. 3 shows the relationship between the light emission intensity of the scintillator and the temperature. From 20 ° C to 60 ° C a temperature dependence of 5-6% appears. By grasping this relationship in advance, accurate temperature measurement of the scintillator enables easy temperature compensation of the emission intensity.

FIG. 4 shows a conceptual configuration of the OTDR circuit. This circuit is a detailed description of a subsequent circuit of the branch unit 4 in FIG. In the OTDR circuit 9, the laser diode 31 is operated by the pulse drive circuit 30, and the laser light of 800 to 1000 nm is sent to the scintillator 1 installation section via the optical fiber 3 'and the branch unit (4 in FIG. 1). The light reflected by the scintillator installation section returns via the same fiber 3 'path, and is sent to an OTDR temperature measurement circuit including a filter 32, a photodiode 33, an amplifier 34, and a temperature conversion processing device 35. The reflected light is mainly composed of Raman scattering, but includes weak anti-Stokes light and Stokes light before and after the center wavelength. The ratio between the anti-Stokes light and the Stokes light has the temperature information of the reflection part. Therefore,
Two systems of optical filters 32 and 32 'and photodiodes 33 and 33' are provided to discriminately measure the anti-Stokes light and the Stokes light amount. The reflection position of the reflected light can be easily identified from the difference (ΔT) between the time when the laser light is transmitted by the laser diode 31 and the time when the reflected light returns. That is,
Speed of light in fiber (C) and optical path length to reflection position (L)
From ΔT = 2L / C. In the OTDR measurement method of the present invention, since the optical path length to the scintillator to be installed is constant, the temperature of the scintillator section can be easily measured by measuring only the anti-Stokes light and the Stokes light with a fixed time difference (ΔT). The temperature is measured by the temperature conversion processing device 35, and the temperature of the radiation counting circuit 8 is compensated through the data processing device 10 and the control line 11 based on the measurement result.

The reflected light when the laser is incident also enters the radiation measuring system. This reflected light becomes a noise component in radiation measurement. Therefore, the optical filter 5 is provided on the light incident surface of the photomultiplier tube 6 of the radiation measurement system to exclude noise light. Further, in order to surely exclude this noise component, it is desirable to perform the process of temperature measurement and the process of radiation measurement in a time sharing manner. This time division processing can be performed by the data processing device 10 of FIG. This time division processing is shown in FIG. The time division processing is shown by the time chart 40 of the OTDR processing (Tt) of the temperature measurement and the time chart 41 of the radiation measurement (Tm). When performing temperature measurement, turn off radiation measurement processing
And After the temperature measurement, the radiation measurement processing is turned on. This process can be easily performed by an optical switch or electrical switching. The time distribution between Tt and Tm is such that if the temperature change is large, the number of times Tt is increased, and if the change in the measured radiation intensity is large, Tm is increased.

The configuration of the present invention described above is a configuration in which the transmission optical fiber is used for both the radiation measurement system and the OTDR thermometer. However, it is also possible to use a configuration in which two transmission optical fibers are provided independently for both systems. Thus, the effects of the present invention can be achieved.

The above is the configuration of the present invention, and it is possible to easily realize a long-distance transmission optical transmission type radiation measuring device capable of temperature compensation of km or more, and to provide a more practical device.

FIG. 6 shows a configuration example of an optical transmission type multi-point measuring system employing the present invention. Detectors (scintillators and wavelength conversion fibers) 50 provided at the respective measurement points D1-Dn are dispersedly arranged at required measurement points (omitted in FIG. 6), and optical signals detected by the respective radiation detectors 50 are transmitted. The light is transmitted to a measuring device 52 composed of a photomultiplier tube and a counting circuit provided independently by an optical fiber 51. An optical path branching unit 53 is provided in each transmission system at a stage preceding the measuring device 52, and is connected to the OTDR temperature measuring system 54. The measurement information of the measurement circuit 52 is collected by the data collection device 55 at an arbitrary cycle, and each radiation measurement value performs temperature compensation based on the temperature measurement result of the OTDR temperature measurement system 54. Based on the radiation dose value at each radiation measurement point, the data analyzer 56 analyzes and records the distribution of the side environment radiation.

The result is displayed on the display device 5 if necessary.
7 is displayed.

The present invention can be easily applied to monitoring posts of nuclear power plants, components of general radiation handling facilities, and radiation distribution measurement in buildings.

Regarding the transmission light receiving unit described above, a system using a photodetector or other light receiving device instead of the photomultiplier tube can easily achieve the same system construction.

As described above, according to the present invention, a more practical and temperature-compensating long-distance optical transmission type radiation measuring apparatus capable of greatly improving environmental resistance and maintainability and a measuring system thereof can be easily realized. You can do it.

[0025]

According to the present invention, the transmission distance km which can greatly improve the environmental resistance and maintainability which could not be realized until now.
An optical transmission type radiation measuring apparatus capable of temperature compensation as described above and its practical measurement system can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical transmission type radiation measuring apparatus of the present invention.

FIG. 2 is a diagram illustrating a transmission mechanism of scintillation light.

FIG. 3 is a diagram showing a relationship between a light emission intensity of a scintillator and a temperature.

FIG. 4 is a diagram illustrating a conceptual configuration of an OTDR circuit.

FIG. 5 is a diagram showing a configuration of a multipoint measurement system of the present invention.

FIG. 6 is a diagram showing a configuration example of an optical transmission type multi-point measurement system employing the present invention.

FIG. 7 is a diagram showing a configuration of a conventional device.

[Explanation of symbols]

1. Scintillator, 2. Wavelength conversion fiber, 3, 3 '
3 '': transmission optical fiber, 4: branch unit, 5: optical filter, 6: photomultiplier tube, 7: amplifier, 8 ...
Counting circuit, 9 OTDR circuit, 10 data processing device,
11 control line, 20 radiation, 21 scintillation light, 22 wavelength conversion light, 23 total reflection component, 24
... Fiber length direction, 25 ... Transmission fiber, 30 ...
Pulse drive circuit, 31 laser diode, 32.3
2 ': Optical filter, 33, 33': Photodiode, 34: Amplifier, 35: Temperature conversion processor, 40: O
TDR processing time chart, 41: radiation measurement processing time chart, 50: radiation detection unit, 51: transmission optical fiber, 52: measuring device, 53: optical path branching unit,
54: OTDR temperature measurement system, 55: data collection device, 5
6 Data analysis device, 57 Display device.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G01T 7/00 G01T 7/00 C G02B 6/00 G02B 6/00 B 6/02 6/02 A G02F 1/35 502 G02F 1/35 502 F term (reference) 2G088 AA03 EE10 FF04 FF17 GG14 GG15 GG16 JJ01 KK11 KK24 LL15 LL21 MM02 2H038 AA02 2H050 AD04 AD06 2K002 AA04 AB12 BA02 HA23

Claims (3)

[Claims] An optical transmission type radiation measurement device comprising: a scintillator having a wavelength conversion fiber inserted therein; a transmission optical fiber for transmitting fluorescence converted by the wavelength conversion fiber; and a measurement circuit for receiving and measuring the transmitted light. In the apparatus, a branching unit for branching the optical path is provided in a part of the transmission optical fiber, and a temperature measuring device for a scintillator portion including a laser beam incident device and a laser reflected light receiving device is provided in the branching optical path system, and the temperature is measured. An optical transmission type radiation measuring device including a radiation counting device for compensating the temperature dependence of the emission intensity of a scintillator based on information. 2. The optical transmission type radiation measurement apparatus according to claim 1, wherein an optical filter adapted to an emission wavelength region of a wavelength conversion fiber is provided in a radiation measurement system provided at a subsequent stage of said branching unit. apparatus. 3. An optical transmission type radiation measuring apparatus according to claim 1 or 2, wherein a plurality of such apparatuses are dispersed and arranged, and a centralized monitoring is performed at a predetermined location via an optical fiber, a data analyzing apparatus, and a result thereof. An optical transmission type multi-point radiation measurement system provided with a display device for displaying an image.