JPS60133384A - Radiation measuring apparatus - Google Patents

Abstract

PURPOSE:To enable a stable measurement of radiation entirely free from effect of electric and magnetic noises by utilizing the relationship between transmission loss and absorption does in an optical fiber with the irradiation of radiation to detect radiation. CONSTITUTION:Light from a light source 21 is distributed in directions of an optical fiber 24 for detection of radiation and a measurement processing section 27 via a fiber 22a and a light distributor 23. The light distributed to the processing section 27 is converted into an electrical signal with a power meter 28 while into an electrical signal proportional to the intensity of light at the input end of the fiber 24 with a correction circuit 31. On the other hand, light introduced to the processing section 27 via the fiber 24 is converted into an electrical signal with a power meter 29 while into an electrical signal proportional to the intensity of light at the output end of the fiber 24 with a correction circuit 32. Then, output differences between the circuits 31 and 32 are subtracted 33 to make an electrical signal proportional to transmission loss of the fiber 24. This value is proportional to the absorption does of the fiber 24, further to the gamma-ray irradiation dose and is introduced to a correction circuit 34 to make a signal corresponding to the actual irradiation dose.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an apparatus for measuring so-called radiation such as gamma rays, neutron rays, etc.

[Prior art]

Conventionally, radiation measuring devices include those shown in FIGS. 1 and 2.

In FIG. 1, (1) is a detector such as a GM counter or scintillation detector that detects radiation; (21 is a high-voltage power supply that generates a DC high voltage to be supplied to this detector (1);
(3) is a high-voltage supply cable that supplies the high-voltage DC voltage generated by this high-voltage power supply (2) to the detector (1), and (4) is a minute electrical pulse signal generated by the detector (1). The preamplifier [5] is a signal processing unit that processes the electrical pulse signal transmitted from the preamplifier (4) via the electrical signal transmission cable (6), and its main component is a pulse height discriminator (7). ).

It has a waveform shaper (8), a pulse/voltage converter (9), and an integrator Ql. ao is the radiation dose rate output terminal,
aa is a radiation dose output terminal.

In Figure 2, (1) is a detector such as an ionization chamber that detects radiation, (5I is a signal processor that processes minute current signals transmitted from this detector + 11 via electrical signal transmission group (6) section, as its main component.

Current/voltage converter 03. and four integrators.

In addition, the code 121 +31αυa4 in this Figure 2
is the same as that in FIG. 1, so the explanation will be omitted.

Next, the operation of the conventional device shown in FIGS. 1 and 2 will be explained.

First, the apparatus shown in FIG. 1 will be explained.

When DC high voltage is supplied to the detector (1) from the high voltage power supply (2) via the high voltage supply cable (3).

When radiation is incident on the detector f11, a minute electric pulse signal having a pulse rate proportional to the radiation dose rate of the radiation incident on the detector (1) is outputted from the detector fil and sent to the preamplifier (4). The minute electric pulse signal is amplified by a preamplifier (4) and subjected to impedance conversion, and then sent to a signal processing unit (5) via an electric signal transmission cable (6).Signal processing unit The electric pulse signal sent to (5) is discriminated by a wave height discriminator (7) into a noise level or a signal due to radiation below arbitrary energy, and then a waveform shaper (8) is used to generate a pulse having a constant wave height and pulse width. converted to .

It is converted into a voltage proportional to the input pulse rate in a pulse/voltage converter (9). Pulse/voltage converter (9)
The output is taken out as a dose rate output from the dose rate output terminal αυ. In this way, a voltage signal proportional to the dose rate of radiation incident on the detector (11) is taken out from the dose rate output terminal αD as a dose rate output.

Furthermore, since the radiation dose is an integral value of the dose rate with respect to time, it is obtained by integrating the output of the pulse/voltage converter (9) by the integrator a1, and is taken out from the dose output terminal 02. Note that, in response to the desire to widen the measurement range, it is common to add a range switching function or a logarithmic conversion function to the pulse/voltage converter (9).

Next, the operation of the conventional device shown in FIG. 2 will be explained.

When DC high voltage is supplied to the detector (1) from the high voltage power supply (2) via the high voltage supply cable (3).

When radiation enters the detector fil, a minute current proportional to the radiation dose rate of the radiation entering the detector (1) is output from the detector (1), and a signal is transmitted via the electric signal transmission group (6). It is sent to the processing section (5). Signal processing section (5
) is converted into a voltage proportional to the input current by a current/voltage converter. Current/voltage converter 0
The output No. 3 is taken out from the dose rate output terminal aυ as a dose rate output. In this way, a retirement signal proportional to the dose rate of radiation incident on the detector (1) is taken out from the dose rate output terminal aD as a dose rate output. Further, the radiation dose is obtained by integrating the output of the current/voltage converter 03 by an integrator 0Q, and is taken out from the dose output terminal α2. In addition.

In this figure 2, as well as in figure 1,
Due to the desire to expand the measurement range, it is common to add a range switching function or a logarithmic conversion function to current/voltage converters.

Since the conventional radiation measuring device is configured as described above, a minute current signal from the detector (1) or an electric pulse signal from the preamplifier (4) is sent to the signal processing unit using the electric signal transmission cable (6). (5), it is vulnerable to electrical and magnetic noise near the installation location of the detector (1) and the signal transmission route, and it is necessary to take sufficient noise countermeasures. In order to handle electric current, an electric signal transmission cable (6) and an electric signal transmission cable connection connector (not shown) are provided.

The so-called detection and transmission path of the detector (l) 9 and the like has drawbacks such as the need to maintain high insulation.

[Summary of the invention]

The object of this invention is to eliminate the above-mentioned drawbacks of the conventional method, that is, to enable stable radiation measurements without being affected by electrical and magnetic noise in the vicinity of the detector installation site and in the signal transmission route. It was developed for the purpose of using optical fibers as radiation detectors by utilizing the relationship between transmission loss and absorbed dose due to radiation irradiation of optical fibers, and also to use optical fibers for transmission between the detector and the signal processing section. The present invention provides a radiation measurement device using the following methods.

[Embodiments of the invention]

An embodiment of this invention will be explained with reference to FIG.

In Figure 3, 011 is a laser diode (LII
iD).

Light sources such as photodiodes, (22a) (22b)
(22c) (22d) is a transmission optical fiber that transmits light; (c) is an optical distributor that distributes the light transmitted from the light source QD by the transmission optical fiber (22a);
@ is an optical fiber for radiation detection.For example, a silica core doped with germanium (GE) or phosphorus (P),
A silica-clad optical fiber or the like is used. (25
a) is an optical fiber coupler for attaching and detaching the radiation detection optical fiber to and from the transmission optical fiber (22c), and (2sb) is the optical fiber coupler for attaching and detaching the radiation detection optical fiber to and from the transmission optical fiber (22c);
a) Optical fiber coupler for attaching and detaching the radiation detection optical fiber (goods), @ is the optical fiber coupler for transmission (2
2a) (22b) (22c) (22d) A radiation shield that is installed at a location where the radiation is too large to be ignored.

Made of iron, lead, concrete, etc. The part surrounded by the dashed line is the measurement processing section, and the main components (c) ~
It consists of (to). (C) is a first optical power meter that converts the intensity of light transmitted via the optical splitter @ and the transmission optical fiber (22b) into an electrical signal;
The problem is the transmission optical fiber (22d) mentioned above.

a second optical power meter (30a) that converts the intensity of light transmitted via the optical fiber coupler (25b) and the radiation detection optical fiber Q41 into an electrical signal;
(50b) (30a) (50d) (50e) (
30f) (+0g) (30h) is a wire that transmits electrical signals, ? 3υ and 0 are the first and second correction circuits,
The first correction circuit 0υ receives the first optical power meter (to) as input, and the second correction circuit (to) receives the electrical signal output of the second optical power meter (c) as input, and each has a gain. , has a bias adjustment function. (To) is the first subtraction circuit, 041 is the third correction circuit with gain and bias adjustment functions, and @ is the second subtraction circuit that outputs the difference between the input signal level and a set level signal that can be set arbitrarily. , c@ is a differential circuit. Note that all and α are the dose rate output terminal and the dose output terminal as in FIGS. 1 and 2. Next, the principle and operation of an embodiment of the present invention shown in FIG. .

What is the transmission loss of a GI optical fiber that occurs when gamma rays are irradiated to an optical core ino (- (hereinafter referred to as a GI optical fiber) that has a silica core doped with germanium (GK) and phosphorus (P) and a silica cladding?

Regardless of the irradiation dose rate, the absorbed dose of the GI optical fiber (-) is uniquely determined by the dose, and the absorption dose and transmission loss maintain a linear relationship over a wide range, and once the transmission loss occurs, gamma ray irradiation is stopped. It is known that the irradiation dose of gamma rays and the absorbed dose of the axm optical fiber have a close relationship to IJ, as is clear from the definitions of irradiation dose and absorbed dose.

Therefore, the amount of transmission loss caused by gamma ray irradiation of the GI type optical fiber is proportional to the gamma ray irradiation dose, and the differential value of the transmission loss amount with respect to time is proportional to the gamma ray irradiation dose rate. The principle of the radiation measuring device of the present invention is to detect the radiation dose using such characteristics.

Next, to explain the specific operation shown in FIG. 3, the light generated from the light source Qυ passes through the transmission optical fiber (22a),
The light is distributed by the light distributor (c) in the direction of the radiation detection optical core and in the direction of the measurement processing unit.

The light distributed in the direction of the radiation detection optical fiber (c) passes through the transmission optical fiber (22c), passes through the optical fiber coupler (25a), passes through the radiation detection optical fiber@, and then passes through the optical fiber coupler (251).
)) is guided to the measurement processing section (2) via the transmission optical fiber (22a).

The light directly sent from the optical distributor (c) to the measurement processing unit (c) is converted into an electrical signal proportional to the light intensity by the first optical power meter (c), and then the gain, The first correction circuit clυ having an ias adjustment function corrects the distribution ratio of the distributor, the transmission loss of the transmission optical fiber (22c) and the optical fiber kaglar (25a), and the optical intensity at the input end of the radiation detection fiber e4. is converted into an electrical signal proportional to .

On the other hand, optical fiber coupler (251)), transmission optical fiber (
22a) and guided to the measurement processing section @ is converted into an electrical signal proportional to the light intensity by a second optical power meter, and then a second optical power meter having gain and bias adjustment functions.
The optical fiber coupler (25
'b) and the transmission optical fiber (22(1)) are corrected, and the signal is converted into an electrical signal proportional to the light intensity at the output end of the radiation detection optical fiber.

Then, in the first subtraction circuit (to), the first correction circuit at
The difference between the output of 1 and the output of the second correction circuit 0 is calculated. The output of the first subtraction circuit obtained in this way is proportional to the difference in intensity of light between the input end and the output end of the radiation detection optical fiber (product), that is, the transmission loss of the radiation detection optical fiber (product). It becomes an electrical signal.

According to the above measurement principle, this electric signal value is proportional to the absorbed dose of the radiation detection optical fiber 34, and further proportional to the gamma ray irradiation dose.

By leading the output of the first subtraction circuit (c) to a third correction circuit (product) having gain and bias adjustment functions.

Conversion of absorbed dose of radiation detection optical fiber @ to gamma ray irradiation dose rate, Radiation detection optical fiber (foundation)
Corrects the inherent transmission loss when not irradiated with gamma rays, corrects differences in transmission loss coefficient due to fiber length for gamma ray absorption, and calibrates the output signal to correspond correctly to the actual irradiation dose. The third correction circuit G41 obtained in this way
By leading the output signal to the second subtraction circuit (c) that outputs the difference between the input signal level and a set level signal that can be set arbitrarily, the gamma ray irradiation dose output after an arbitrary time can be calculated from the radiation dose output terminal 02. Take it out. Furthermore, since the irradiation dose rate is the time differential value of the dose, by leading the output of the third correction circuit to the differentiation circuit.

The irradiation dose rate output is taken out from the radiation dose rate output terminal U.

By the way, as the radiation detection optical fiber C141 continues to be irradiated with gamma rays, the transmission loss increases, making it gradually difficult to measure the light intensity.In order to avoid this situation in this embodiment, the optical fiber coupler ( 25a)
Optical fiber for radiation detection at (25b)? 2
◇ can be exchanged. When replacing the radiation detection optical fiber (goods), replace the third one as explained above.
Adjust the correction circuit (b).

In addition, in the above embodiment, the optical fiber for radiation detection -t2
4 shows the case where GI type optical fiber is used, but
The transmission loss of light is proportional to the absorbed radiation dose.

Furthermore, the optical fiber is not limited to a Gl type optical fiber, as long as the optical fiber does not change the transmission loss once generated even after the radiation irradiation is stopped. Also.

In the above embodiment, the case of a gamma ray dose and dose rate measuring device has been exemplified.9 For example, even if the present invention is applied to the measurement of neutron rays, the same measurement as in the above embodiment can be performed, and It is not limited.

〔Effect of the invention〕

As described above, this invention uses optical fibers for both the radiation detector and the transmission path between the radiation detector and the signal processing section, and more specifically, the invention uses optical fibers for both the radiation detector and the transmission path between the radiation detector and the signal processing section. A transmission optical fiber on the input side that is supplied to the input side and transmits the supplied light to the other end, and a transmission optical fiber that supplies the light from the other end of this transmission optical fiber to one end and transmits the supplied light to the other end. A radiation detection optical fiber whose transmission loss changes depending on the radiation transmitted and irradiated towards the target, and light from the other end of this radiation detection optical fiber is supplied to one end and the supplied light is transmitted toward the other end. with optical fiber for transmission on the output side.

The configuration includes a measurement processing unit that inputs the light from the other end of the transmission optical fiber on the output side and derives the radiation dose irradiated to the radiation detection optical fiber from this input light, which has not been realized previously. A radiation measuring device using optical fiber can be realized.

In addition, it is possible to perform stable radiation measurements regardless of electrical and magnetic noise in the radiation detector installation location and signal transmission path, and it is necessary to maintain high insulation of the signal transmission path, which was essential with conventional equipment. Therefore, it is possible to obtain a radiation measuring device that has remarkable effects compared to conventional devices, such as eliminating the risk of radiation.

[Brief explanation of the drawing]

1 and 2 are block diagrams showing a conventional radiation measuring device, and FIG. 3 is a block diagram showing an embodiment of the radiation measuring device according to the present invention. In the figure, aυ is the radiation dose rate output terminal, UJ is the radiation dose output terminal, Qυ is the light source, (22a) (22c)
is an optical fiber for transmission on the input side, (22cl) is an optical fiber for transmission on the output side, 341 is an optical fiber for radiation detection, (25a) and (25b) are optical fiber couplers, @ is a measurement processing unit. 0I1g is a differential circuit. Note that the same reference numerals in Figure 9 indicate the same or equivalent parts.

Claims (3)

[Claims] (1) A light source, an optical fiber for transmission on the input side where output light from this light source is supplied to one end and the supplied light is transmitted to the other end, and light from the other end of this optical fiber for transmission is supplied to one end. A radiation detection optical fiber that transmits the supplied light toward the other end and has a transmission loss that changes depending on the irradiated radiation. An optical fiber for transmission on the output side that transmits the transmitted light to the other end. And the light from the other end of the transmission optical fiber on the output side is inputted, and from this input light, the above-mentioned radiation detection optical fiber is inputted.
・A radiation measurement device equipped with a measurement processing unit that derives the irradiation radiation dose. (2) The radiation measuring device according to claim 1, wherein the measurement processing section includes a differentiation circuit, and the radiation dose rate is derived by the differentiation circuit. (3) The radiation detection optical fiber is detachably connected to both the input-side transmission optical fiber and the output-side transmission optical fiber, as set forth in claim 1 or 2. Radiation measurement device.