JPS59228183A - Radiation sensor - Google Patents

Abstract

PURPOSE:To improve the detection accuracy by employing an optical fiber almost constant in the variation of light transmission loss regardless of changes in the exposure dose for a detector section and a radiation resistant optical fiber for a lead section. CONSTITUTION:An optical fiber 1 composing a sensor body is mounted on a support 2 in a radiation field A, each one end of optical fibers 5 and 6 composing a lead section is connected to both ends thereof using connectors 3 and 4 while the other ends of the optical fibers 5 and 6 are respectively connected to a light source 7 and a dosimeter 8 arranged in a nonradiation field B through a shielding wall C. The optical fiber 1 therein used shall be the one almost constant in the variation of light transmission loss regardless of exposure dose per hour while the optical fibers 5 and 6 the one having a radiation resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a novel radiation detector having a detection part using an optical fiber whose optical transmission loss changes according to the exposure dose, and a lead part using an optical fiber having radiation resistance. It's about sensors.

Conventionally, various types of radiation sensors have been proposed, and a multi-component glass piece or the like has been used to detect the exposure dose (or irradiation dose). This utilizes optical changes in multi-component glass pieces that change depending on the radiation dose.
A piece of multi-component glass is left in a radiation field, taken out at predetermined intervals to examine its optical changes, and the exposure dose is calculated based on the degree of change. but,
With such methods, the exposure dose can only be determined discretely, and cannot be measured continuously.Also, when detecting radiation, it must be taken out of the radiation field each time and detected using a separately prepared detector. The definition work is troublesome,
There were drawbacks, such as the inability to detect radiation doses in real time.

As a countermeasure to this problem, the inventors discovered that optical fibers with cores doped with specific components such as Ti and/or P have a substantially constant change in optical transmission loss even if the exposure dose per hour changes. We have already filed an application for a radiation sensor that can easily and in real time measure the exposure dose by detecting changes in the optical transmission loss of this extremely optical fiber. Gansho 58-3
No. 1362).

The present invention is a further development of the invention related to the above-mentioned existing application, and when the detection section disposed in a radiation field and the radiation dosimeter disposed in a non-radiation field are separated, a long lead is provided between them. However, if the optical fiber used for this lead section changes its optical transmission loss due to exposure to leakage radiation from the radiation source, even if the radiation sensitivity of the detection section is improved,
This was made to deal with the problem of not being able to obtain sufficient detection accuracy, and its gist is that a radiation detection section consisting of an optical fiber having a core made of quartz glass doped with Ti and/or P; One end of each is connected to both ends of the optical fiber, one of the other ends is connected to a light source, and the other end is connected to a dosimeter.
It is equipped with a lead part using an optical fiber with a core of ppm or less, and by transmitting light in the 1.3 μm band, radiation can be detected through changes in light intensity due to exposure, and radiation detection accuracy has been greatly improved. It is characterized by the fact that it can be obtained.

In addition, in the present invention, the wavelength band used in the 1.3 μm band is 1.31 μm.
It means a band of tm to 1.4 μm.

Hereinafter, the present invention will be specifically explained based on drawings showing embodiments thereof. FIG. 1 is a schematic front view showing the usage state of the radiation sensor according to the present invention (hereinafter referred to as the present invention υ), and FIG.
The figure is also a schematic side view, where A is the radiation field and B is the radiation field.
indicates a non-radiation field, and C indicates a radiation shielding wall. In 1i+11 of the shielding wall C, that is, in the radiation field A, an optical fiber 1 constituting the main body of the sensor is attached to a support 2, and a lead portion is connected to both ends using connectors 3 and 4. (14 optical fibers 5 and 6 are connected at one end, and the other ends of the optical fibers 5 and 6 are connected to a light source 7 and a dosimeter 8 arranged in a non-radiation field B through a shielding wall C. 0 The support 2 has a support 2 in the center of the surface of the rectangular mounting base 21.
2 is erected, and a set screw 23 is used at the upper end of the support column 22 to rotatably fix one end of a swinging rod 25 to which a disk 24 is fixed at the middle part. By loosening the set screw 23, the swinging rod 25 and the disc 24 can be tilted forward and backward over a range of approximately 180 degrees, and by tightening the set screw 23, the swing rod 25 and the disc 24 can be tilted within the above range. It can be fixed in any position.

The disk 24 is made of a material with high radiation transmittance, such as alumite, to a required diameter (approximately 150 mm), has a groove 24a with an arcuate cross section on its outer circumferential surface, and has a set screw (not shown) in the center. It is removably fixed to the swinging rod 25, and the mounting base 21 is attached to the floor or side wall of the radiation field A.
It is designed to be installed by screwing it. Note that there are no particular limitations on the materials of the swinging rod 25, the support column 22, the mounting base 21, etc.;
It is desirable to form the disk 24 using the same material as the disk 24 so that it does not act as a barrier to radiation depending on the arrangement thereof. 26 is a holder for the optical fiber 5.6 for lead products arranged on the top surface of the mount 21. The optical fiber 1 has a core made of quartz glass doped with Ti and/or P in predetermined proportions. For example, when Ti is doped alone, it is 0.5 to 10 mol%, preferably around 5 mol%, and when P is doped alone, it is 0.5 to 30 mol%, preferably around 25 mol%. ,
Furthermore, when Ti and P are doped together, the overall value is 0.
．． It is desirable to set it as 5-30 molar ratios. The reason for setting the Ti doping amount to 0.5 to 10 molar ratio is that if it is less than 0.5 molar ratio, sufficient sensitivity, that is, the amount of optical transmission loss for the exposure dose, cannot be obtained, and if it is more than 10 molar ratio, there is no improvement in sensitivity. Although this is expected, it will (e) be difficult to manufacture the optical fiber base material. The same applies to the doping amount in (2); if it is less than 0.5 molar, the sensitivity will be poor, and if it is more than 30 molar, it will be difficult to manufacture the optical fiber base material.

Furthermore, as the length of the optical fiber is increased, the overall amount of optical transmission loss relative to the exposure dose increases, so it is possible to improve the measurement sensitivity of the dosimeter 8.

Note that there are no particular limitations on the material or dopant for the cladding layer of the optical fiber 1, and conventionally used materials such as polymer cladding, silica glass cladding, etc. can be used as appropriate. is a graph showing the relationship between the irradiation dose and the resulting optical transmission loss of an optical fiber having a core made of quartz glass doped with Ti and/or P. In both cases, the horizontal axis represents the irradiation dose R, and the vertical axis represents the irradiation dose R. is the optical transmission loss fjk (d
B/km). FIG. 3 shows the experimental results for an optical fiber having a core in which quartz glass is doped with 5 moles of Ti, and FIG. 4 shows the experimental results for an optical fiber having a core in which quartz glass is doped with 25 moles of P. The experiment was conducted from one end of the optical fiber at 14.4
Light with a wavelength of 0.88 μm was made incident at μW, the amount of light received was detected at the other end of the optical fiber, and the exposure dose and optical transmission loss amount (dB/km) when γ-rays were irradiated were determined. In Figure 3, the ○ mark plots the result when a 10'm optical fiber with a core doped with 5 moles of Ti is irradiated with γ-rays at a ratio of 5 x 103 (R7), and the Δ mark plots the result. is a similar optical fiber of 10 m with I x 10' (
The results are shown when γ-rays were irradiated at a rate of R7.

On the other hand, what is plotted with a circle in the graph of Figure 4 is that P is 2
50m of optical fiber with 5molar doped core
The results when γ-rays were irradiated at a ratio of The results obtained when irradiating the lines are shown in FIG.

As is clear from the graphs above, although there are slight deviations in the results, the amount of optical transmission loss changes at an almost constant rate, almost unaffected by the set II'≠H per time. I understand what you're doing. Here, both figures 3 and 4 are 0.88.
Although the characteristics at a wavelength of .mu.m are shown, substantially the same tendency is shown when other wavelengths (for example, a wavelength of 1.3 .mu.m) are used.

On the other hand, the optical fiber 5.61 constituting the lead portion is composed of an optical fiber having a core made of impurity quartz glass in which the content of OH groups in the quartz glass is 1 ppm or less. The reason for setting the OH group content to 1 ppm or less is based on the knowledge that in a radiation-exposed environment, the 1.3μIn band is used, and that using fiber with a low OH content is more effective in reducing optical transmission loss. It is.

Note that there are no particular limitations on the material or dopant for the crund layer of the optical fiber, and conventionally known polymer cruds, quartz clads, etc. may be used as appropriate.

Figure 5 is a graph showing the relationship between the content of OH groups in the core and the amount of optical transmission loss after exposure to radiation, with the horizontal axis representing the OH group content in the optical fiber and the vertical axis representing the optical transmission loss. 1tr
(dB/km) is shown. The solid line in the graph represents the case using 1.3 μm band light, and the broken line represents the case using 0.8 μm band light.
The case where light in the 5 μm band is used is shown. Note that the irradiation dose was 105R. As is clear from this graph, 0.
When using light in the 85 μm band, there is an optimal value for the OH group content, but the amount of optical transmission loss is relatively large;
If an optical fiber with a reduced OH group content is used for light in the 3 μm band, the optical transmission loss will be low; at around 10 ppm, the loss will be 1
．． There is not much difference from using light in the 3 μm band, but ipp
It can be seen that below the OH group content of 50 μm, the optical transmission loss is significantly reduced compared to the case of using light in the 0.85 μm band, and the difference is remarkable. When transmitting light of 1.30/Am to an optical fiber having a high-purity quartz core with ppb and 0.8 μm' to an optical fiber having a high-purity quartz glass core with an OH group content of 300 ppm.
This is a graph showing the relationship between the optical transmission loss after radiation exposure and the case of optical transmission of ijF, with the horizontal axis representing the irradiation dose (at R7), and the vertical axis representing the optical transmission loss (dB/k).
m) is shown. The solid line in the graph is OH group 50
In the case of ppb, the broken line is O■ (group content is 30
The results are shown in the case of 0 ppm. As is clear from this graph, when the OH group content is decreased and the wavelength of the light used is increased, the amount of optical transmission loss is lower than when the OH group content is increased and the wavelength of the light used is decreased. It can be seen that it has been significantly reduced.

Therefore, in the product of the present invention configured as described above, it is installed at a suitable location within the radiation field A using the mounting base 21, and the set screw 23 is loosened and the swinging rod 25 is rotated around the set screw 23. The set screw 23 is tightened with the center line of the disk 24, in other words, the axis of the coiled portion of the optical fiber 1 facing, for example, the radiation source. The light emitting unit 7 generates light in the 1.3 μm band, and the light is input to the optical fiber 5 connected to the light emitting unit 7.
#J via optical fibers 1 and 6! The exposure dose is calculated and displayed from the changes in the amount of light captured by the radiation meter 8.

In addition, although the above description was made in the case of γ rays as the radiation, the invention is not limited to this and can of course be applied to neutron rays and other radiations.

As described above, the product of the present invention uses an optical fiber in which the amount of change in optical transmission loss is approximately constant even if the exposure dose per hour changes, and an optical fiber with radiation resistance in the lead part. Because it uses a
The present invention exhibits excellent effects, such as being able to accurately capture the information, making it possible to easily correct the influence of the lead portion, and making it possible to significantly improve detection accuracy.

[Brief Description of the Drawings] Figure 1 is a schematic front view showing the product of the present invention in use;
The figure is also a schematic side view, Figure 3 is a graph showing the relationship between the amount of irradiation i1', A10 and the amount of optical transmission loss in the optical fiber used in the detection part of the product of the present invention, and Figure 4 is a graph of the product of the present invention. Figure 5 is a graph showing the relationship between the radiation dose and optical transmission loss in the optical fiber used for the lead part, and Figure 6 is a graph showing the relationship between the OH group content and optical transmission loss after radiation exposure. is a graph showing the relationship between irradiation rays and optical transmission loss. 1... Optical fiber 2... Supporting tool 3, 4... Connection tool 5.6... Optical fiber 21... Mounting stand 22
...Strut 23...Set screw 24...Circle Dk 2
4 a... Concave (1 way 25... Swinging rod 26... Holder Patent applicant Dainichi Nippon Cable Co., Ltd. Patent attorney Noboru Kono Figure 1 Figure 2

Claims (1)

[Claims] 1. A radiation detection unit equipped with an optical fiber having a core made of quartz glass doped with Ti and/or P; one end of each is connected to both ends of the optical fiber, and one of the other ends is connected to a light source; The other is connected to each dosimeter, and the OH of quartz glass
1. A radiation sensor comprising: a lead portion using an optical fiber having a core having a group content of i ppm or less, and transmitting light in the 1.3 μm band.