JPH0854469A - Sensitivity distribution type radiation sensor - Google Patents

Abstract

PURPOSE:To obtain a sensitivity distribution type radiation sensor in which the dynamic range to be measured is not narrowed even when there is the position where the radiation dose of a measuring range is largely varied. CONSTITUTION:The same radiation detecting sensitivity distribution for distributing the radiation detecting sensitivity of a strand 1 of a glass added with rare earth element ions in its longitudinal direction is given to the glass itself. A coating 3 for attenuating the radiation is provided in the outer periphery of a radiation detecting strand 2 to form a radiation detecting sensitivity distribution. The two or more strands 2 having different radiation detecting sensitivities are connected in the axial direction to form a detecting sensitivity distribution. The quantity of hole capturing structure in the glass of the strand 1 is controlled to form a detecting sensitivity distribution. Metal ions are added to the glass to control the quantity of the capturing structure to form the detecting sensitivity distribution. The quantity of the hole capturing structure is controlled by altering the drawing conditions of the strand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensitivity distribution type radiation sensor used for detecting leakage of radiation in a place where radiation is generated, such as a nuclear power plant and a nuclear research institute.

[0002]

2. Description of the Related Art A radiation sensor using an optical fiber has been conventionally known. For example, absorption occurs when a glass fiber doped with rare earth ions is irradiated with radiation such as γ-rays. The distribution of absorption in the longitudinal direction of the glass fiber can be converted into the distribution of radiation, which is several Km.
It is also possible to measure over. Therefore, as for the radiation dose distribution in the longitudinal direction of the optical fiber when the optical fiber is irradiated with radiation, the absorption in the longitudinal direction of the optical fiber is determined by the pulse echo method (OTD).
R method: also called Optical Time Domain Reflectometry method). This measurement method sends the light from the OTDR to the optical fiber, measures the reflected light from the optical fiber with the OTDR, and detects the position of the radiation, the radiation amount (dose), etc. from the reflection amount, the reflection time, etc. Is.

[0003]

However, when the absorption is measured by the above-mentioned OTDR method, when the measurement length becomes long, a large difference occurs in the amount of light returning to the light receiver at the near end and the far end of the incident light source, and as a result, The resolution and dynamic range will be limited. In particular, if there is a large radiation dose in the middle, the area beyond that location will be extremely S / N.
However, there is a problem in that the measurable dynamic range is narrowed (the longitudinal distribution is deteriorated).

As another problem, when controlling the radiation detection sensitivity of glass to which rare earth ions are added,
There is a point that the correspondence between the glass composition and the radiation detection sensitivity is unclear, and the radiation detection sensitivity control method by the glass itself has not been established. That is, it is known that the radiation detection characteristics are exhibited by adding rare earth ions to glass, but a clear correspondence relationship between the concentration of rare earth ions to be added and the radiation detection sensitivity has not been confirmed. It was As a result, there remains a problem that the radiation detection sensitivity control method depending on the factors constituting the glass is unclear.

An object of the present invention is to provide a sensitivity distribution type radiation sensor in which the measurable dynamic range is not narrowed even if the radiation dose in the measurement range changes greatly.

[0006]

According to a first aspect of the present invention, there is provided a sensitivity distribution type radiation sensor in which a filament wire 1 such as a glass wire or an optical fiber doped with rare earth ions is used as a radiation detection medium. In the above, the radiation detection sensitivity of the filament 1 is distributed in the longitudinal direction.

The sensitivity distribution type radiation sensor according to claim 2 of the present invention is the sensitivity distribution type radiation sensor according to claim 1, wherein the radiation detection sensitivity distribution of the filament 1 is on the outer circumference of the radiation detecting filament 2. It is formed by providing a coating 3 that attenuates radiation.

The sensitivity distribution type radiation sensor according to claim 3 of the present invention is the sensitivity distribution type radiation sensor according to claim 1, wherein the distribution of the radiation detection sensitivity of the filamentous body 1 is different from the radiation detection sensitivity. It is formed by connecting the body 2 in the axial direction.

In the sensitivity distribution type radiation sensor according to claim 4 of the present invention, in the sensitivity distribution type radiation sensor according to claim 1, the distribution of the radiation detection sensitivity of the filament 1 exists in the glass itself of the filament 1. It is characterized by doing.

In the sensitivity distribution type radiation sensor according to claim 5 of the present invention, in the sensitivity distribution type radiation sensor according to claim 1 or 4, the distribution of radiation detection sensitivity of the filament 1 is
It is characterized in that it is formed by controlling the amount of the hole trapping structure present in the glass of the linear body 1.

According to a sixth aspect of the present invention, there is provided the sensitivity distribution type radiation sensor according to the fifth aspect, wherein one or more metal ions are combined in the glass forming the filamentous body 1. It is characterized in that the amount of the hole trapping structure present in the glass is controlled by adding it.

According to a seventh aspect of the present invention, in the sensitivity distribution type radiation sensor of the fifth aspect, the sensitivity distribution type radiation sensor according to the fifth aspect is characterized in that the wire condition in the filamentous body 1 is changed by changing the drawing condition in the manufacturing process of the filamentous body 1. -The method is characterized in that the amount of the le capture component is controlled.

[0013]

In the sensitivity distribution type radiation sensor according to claims 1 to 7 of the present invention, since the radiation detection sensitivity of the glass filamentous body 1 to which rare earth ions are added is distributed in the longitudinal direction, By arranging the portion of the strip 1 with low radiation detection sensitivity in a location where radiation easily leaks (high radiation dose), and the portion with high radiation detection sensitivity in a location where radiation is hard to leak (low radiation dose), Radiation can be detected almost uniformly over the entire length of the striatum in the longitudinal direction, and the level of reflected light to the OTDR is made substantially uniform, so that the measurable dynamic range is not narrowed.

In the sensitivity distribution type radiation sensor according to claim 2 of the present invention, the radiation detection sensitivity is distributed by providing a coating 3 for attenuating the radiation on the outer periphery of the radiation detection filament 2 as shown in FIG. Therefore, it is possible to easily bring the detection sensitivity into a predetermined distribution by using the radiation detection filament 2 having the uniform radiation detection sensitivity in the longitudinal direction.

In the sensitivity distribution type radiation sensor according to claim 3 of the present invention, as shown in FIG. 2, since two or more radiation detection filaments 2 having different radiation detection sensitivities are connected in the longitudinal direction, the radiation detection sensitivity Different existing radiation detection striatum 2
By preparing two or more of them, the detection sensitivity can be easily set to a predetermined distribution by using them.

In the sensitivity distribution type radiation sensor according to the fourth aspect of the present invention, since the distribution of the radiation detection sensitivity exists in the glass itself forming the filamentous body 1, the structure of the filamentous body 1 is specially devised. Even if it is not necessary, the detection sensitivity can have a predetermined distribution.

In the sensitivity distribution type radiation sensor according to the fifth aspect of the present invention, the distribution of the radiation detection sensitivity is provided by controlling the amount of the hole trapping structure present in the glass. When manufacturing glass as a raw material for
The detection sensitivity can be made to have a predetermined distribution by selecting the amount of the le capture component so as to have a predetermined sensitivity distribution.

In the sensitivity distribution type radiation sensor according to claim 6 of the present invention, one or a plurality of metal ions are added in combination to the glass to control the amount of the hole trapping constituents in the glass. Therefore, the detection sensitivity can be made to have a predetermined distribution by selecting the type or combination of the metal ions added when the glass as the raw material of the filament 1 is manufactured.

In the sensitivity distribution type radiation sensor according to claim 7 of the present invention, the amount of the hole trapping structure in the filament 1 is controlled by changing the drawing conditions in the process of manufacturing the filament 1. Therefore, it is not necessary to make the striatum 1 itself to have a special structure or composition, and the detection sensitivity can be easily made to have a predetermined distribution simply by changing the drawing conditions.

[0020]

EXAMPLES The basic structure of the sensitivity distribution type radiation sensor of the present invention is that the filament detection element 1 made of glass to which rare earth ions are added has a non-uniform radiation detection sensitivity in the longitudinal direction. To distribute the radiation sensitivity in the longitudinal direction of the radiation sensor in which the striatum itself has a radiation detection function, the following 3
Different configurations are possible. The first is a structure in which a shielding tube having an effect of attenuating radiation is provided on the outer circumference of the radiation detection filament, and the second is to prepare two or more radiation detection filaments having different radiation detection sensitivities, and these are arranged in the longitudinal direction. The third is a configuration in which the radiation detection sensitivity of the striatum itself has a sensitivity distribution.

[0021]

[First Embodiment] A first structure of the three kinds of structures will be described in detail with reference to FIG. Reference numeral 2 in FIG. 1 denotes a radiation detecting filament, which is a wire made of silica glass doped with rare earth ions, an optical fiber (core, clad structure) made of the silica glass, etc. Radiation detection sensitivity is uniform. In FIG. 1, a part of the outer circumference of the radiation detecting filament 2 in the longitudinal direction,
By providing the shield tube 3 having the effect of attenuating the radiation, the irradiation ray detection sensitivity of the portion where the shield tube 3 is provided is made lower than that of the other portion, whereby the radiation detection linear body 2 has a predetermined length in the longitudinal direction. The linear body 1 having the sensitivity distribution of 1 is constituted. In this case, as the shield tube 3 for attenuating the radiation, for example, a metal sheath or a lead cover is used. Further, as the shield tube 3, two or more shield tubes having different radiation attenuation amounts are used, and they are provided continuously in the longitudinal direction as shown in FIG. 1, or provided at arbitrary intervals. The optical fiber shown in FIG. 1 may have non-uniform radiation detection sensitivity in the longitudinal direction. This non-uniformity in radiation detection sensitivity may be created by controlling the amount of hole trapping structures described in Example 3 and the subsequent figures.

[0022]

[Embodiment 2] Of the three types of configurations, the second configuration will be described in detail with reference to FIG. In FIG. 2, two or more radiation detecting filaments 2 having different radiation detecting sensitivities in the longitudinal direction are prepared, and these are connected in the longitudinal direction. These two or more radiation detecting filaments 2 are connected in a straight line in the axial direction by inserting the ends in the longitudinal direction into a sleeve. In this case, various arrangements of the radiation detection striations 2 are possible. For example, there are a method of sequentially arranging the radiation detection filaments 2 having low detection sensitivity, a method of arranging the radiation detection filaments 2 having low detection sensitivity between the radiation detection filaments 2 having high detection sensitivity, and the like. By arbitrarily selecting this array, the radiation detection sensitivity can be distributed at arbitrary positions in the longitudinal direction of the filamentous body 1 for each arbitrary length.

[0023]

[Third Embodiment] A third structure of the three kinds of structures will be described in detail with reference to FIG. As shown in FIG. 3, the radiation detection sensitivity of the striatum 1 itself is not uniform in the longitudinal direction,
It has a sensitivity distribution.

As a result of earnest studies by the present inventors, it was found that in the case of a rare earth-doped optical fiber, a sensitivity distribution type sensor capable of adjusting the radiation detection sensitivity in the longitudinal direction can be adjusted according to the purpose. In this case, it seems that the radiation detection sensitivity can be easily adjusted by controlling the concentration of the rare earth element added to generate absorption, but it was difficult to control in practice by this method. That is,
It was found that the amount of absorption produced by irradiation does not necessarily depend on the concentration of rare earth ions added to the glass. Instead, a hole-capturing structure (hole: hole-capturing structure) formed during the process in which the silica-based glass is processed into a filament, for example, Oxygen Vacanc
It was found to depend on the amount of y, Peroxylinkage, or strain bond generated. Therefore, when the conditions for generating the hole trapping structure were investigated, it was found that the generation amount of the hole trapping structure could be controlled by adding an additive substance to the silica glass.

In order to confirm the effect of the above 1, 5 to 10 mol% of metal ions (additive substances) such as Ge, Sb, Ti and Al are added to pure quartz glass and the glass is irradiated with radiation to generate the effect. When the amount of absorption was examined, it was confirmed that the amount of absorption due to radiation irradiation changed significantly as shown in FIG. 4 and the absorption loss decreased.

FIG. 4 shows the relationship between the added metal ions and the gamma ray irradiation loss, and the irradiation loss when the metal ion is added on the horizontal axis is shown on the vertical axis. In the case of each metal ion Was measured twice. The black square in Fig. 4 is the maximum value of irradiation loss, and the white square is the minimum value of irradiation loss.
That is, it shows variations in irradiation loss.

In the case of FIG. 4, a 1200p sample optical fiber was prepared by using the vapor phase method or the sol-gel method.
Using a short fiber of pmEr-doped glass,
The measurement was performed using light with a wavelength of 633 nm. The gamma ray irradiation was performed under the irradiation rate condition of 5 × 10 ³ R / hour using a ⁶⁰ Co radiation source.

Besides the above substances, Gd and S
n, Ta, Nb, Zr, P, B, etc. are considered. The occurrence of absorption also tended to decrease when these metal ions were added. Some of these metal ions change the refractive index of glass and some do not.
In the third embodiment, there is a degree of freedom that the radiation detection sensitivity can be adjusted while controlling the refractive index, or only the detection sensitivity can be adjusted while keeping the refractive index constant.

[0029]

[Embodiment 4] This embodiment is similar to Embodiment 3 in that the generation amount of the hole trapping structure is controlled so that the radiation detection sensitivity of the filamentous body 1 itself has a sensitivity distribution in the longitudinal direction. is there. Specifically, in the manufacturing process of the filament 1, when the glass base material is thread-proofed (fiber), that is, when the filament is drawn, the drawing tension or the drawing speed is changed. Is.

As a result of intensive studies conducted by the present inventors, the amount of absorption loss due to radiation irradiation changes when the heating temperature (drawing temperature) or the drawing speed, which is a factor controlling the drawing tension, changes. I understood. An example of the change is shown in Table 1 on the next page. Table 1 shows a case where the tension is changed as a drawing condition using an optical fiber in which Er ions are added to silica glass as a sample, and is a result when the tension is increased or decreased by about 20% from the standard condition. .

In this case, in addition to Er, Nd, Y, Y
Lanthanum rare earth ions such as b, Ho and Sm are all applicable for generating absorption by irradiation with radiation. However, the absorption wavelength and the magnitude of the absorption generated differ depending on the type of rare earth ion added. Further, Table 1 shows the loss change due to gamma ray irradiation when the drawing conditions were changed, and the tension was changed as the drawing conditions. The tension was increased or decreased by about 20% from the standard condition.

Further, not only the radiation detection sensitivity but also the saturation level of detection, that is, the dose at which the rate of increase in absorption with respect to the increase in radiation dose decreases, depending on the concentration of the constituents that trap holes. be able to. In addition, the increased absorption by irradiation also affected the effect of restoring absorption when irradiation was gone. These effects are effective not only for detecting the continuous irradiation dose and irradiation speed but also for measuring the integrated dose in the case of intermittent irradiation.

[0033]

[Table 1]

[0034]

The sensitivity distribution type radiation sensor of the present invention has the following various effects. ． The detection sensitivity of the sensitivity distribution type radiation sensor can be obtained by arranging the part having low sensitivity in the sensitivity distribution type radiation sensor of claim 1 to the part having high radiation dose and the part having high sensitivity to low radiation dose. Can be made uniform in the longitudinal direction, and a wide dynamic range at the time of measurement can be maintained.
Therefore, the sensitivity distribution type radiation sensor of the present invention is particularly suitable for measurement using an OTDR device.

.. According to the sensitivity distribution type radiation sensor of claim 2, since the distribution of the radiation detection sensitivity is present in the glass itself constituting the filamentous body 1, the configuration of the filamentous body 1 becomes simple, and when the cable is formed or laid. Workability and workability do not deteriorate.

.. According to the sensitivity distribution type radiation sensor of claim 3, since the radiation detecting filament 2 is covered with the covering body 3, an existing radiation detecting fiber having a constant detection sensitivity in the longitudinal direction is used as the radiation detecting filament 2. It can be used, and only by changing the position to cover the covering body 3, the number of covering bodies 3 to cover, etc., at a desired position in the longitudinal direction of the filamentous body 1, at an arbitrary length, and at a higher sensitivity than other portions. A sensitivity distribution with a low portion can be obtained.

.. Since the sensitivity distribution type radiation sensor of claim 4 connects two or more radiation detection filaments 2 having different radiation detection sensitivities in the longitudinal direction, two or more existing radiation detection fibers having different radiation detection sensitivities are prepared. Then
The linear body 1 having a sensitivity distribution can be obtained only by connecting them, and practical application becomes easy.

.. Since the sensitivity distribution type radiation sensor according to claim 5 controls the amount of the hole trapping structure present in the glass of the filamentous body 1, the structure is apparently different from that of the conventional radiation detecting fiber. It is simple.

.. In the sensitivity distribution type radiation sensor according to claim 6, one or a plurality of metal ions are added to the glass of the striatum 1 in combination to control the amount of the hole-trapping constituent in the glass. Therefore, the desired detection sensitivity distribution can be obtained only by selecting the type or combination of the metal ions added when the glass as the raw material of the filament 1 is manufactured.

.. Since the sensitivity distribution type radiation sensor according to claim 7 controls the amount of the hole trapping structure in the filamentous body 1 by changing the drawing conditions in the manufacturing process of the filamentous body 1,
A desired detection sensitivity distribution can be obtained only by changing the drawing conditions. ． If the sixth and seventh aspects are combined, the measurement sensitivity can be adjusted while maintaining an arbitrary refractive index distribution, and the degree of freedom in sensitivity adjustment is increased.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a first embodiment of a sensitivity distribution type radiation sensor of the present invention.

FIG. 2 is an explanatory diagram showing a second embodiment of the sensitivity distribution type radiation sensor of the present invention.

FIG. 3 is an explanatory view showing a third embodiment of the sensitivity distribution type radiation sensor of the present invention.

FIG. 4 is an explanatory diagram showing loss change due to gamma ray irradiation when various metal ions are added to Er-doped silica glass fiber.

[Explanation of symbols]

 1 is a filament 2 is a radiation detecting filament 3 is a cover

Claims (7)

[Claims] 1. A radiation sensor using a filament (1) such as a glass wire or optical fiber doped with rare earth ions as a radiation detection medium, wherein the radiation detection sensitivity of the filament (1) is the longitudinal direction. A radiation sensor of sensitivity distribution type characterized in that 2. The sensitivity distribution type radiation sensor according to claim 1, wherein the radiation detection sensitivity distribution of the filament (1) has a coating (3) for attenuating radiation on the outer periphery of the radiation detection filament (2). A sensitivity distribution type radiation sensor characterized by being formed by providing. 3. The sensitivity distribution type radiation sensor according to claim 1, wherein the radiation detection sensitivity distribution of the filament (1) connects two or more radiation detection filaments (2) having different radiation detection sensitivities in the axial direction. A sensitivity distribution type radiation sensor characterized by being formed by: 4. The sensitivity distribution type radiation sensor according to claim 1, wherein the radiation detection sensitivity distribution of the filament (1) exists in the glass itself. 5. The sensitivity distribution type radiation sensor according to claim 1 or 4, wherein the radiation detection sensitivity distribution of the filament (1) is present in the glass of the filament (1). A sensitivity distribution type radiation sensor, which is formed by controlling the amount of a capture component. 6. The sensitivity distribution type radiation sensor according to claim 5, wherein one or a plurality of metal ions are combined and added to the glass constituting the striatum (1) to be present in the glass. A sensitivity distribution type radiation sensor, characterized in that the amount of the hole capturing component is controlled. 7. The sensitivity distribution type radiation sensor according to claim 5, wherein the amount of the hole trapping structure in the filament (1) is changed by changing the drawing conditions in the process of manufacturing the filament (1). A sensitivity distribution type radiation sensor characterized by being controlled.