JPS61212804A - Radiation-resistant image fiber - Google Patents

Abstract

PURPOSE:To improve the radiation-resistant characteristic of the titled image fiber by disposing an image transmission part constituted of many cores composed of pure quartz glass and clad composed of F-doped quartz glass enclosing each core and a jacket consisting of quartz glass having the softening point higher than the softening point of the quartz glass as the outermost quartz glass layer. CONSTITUTION:The image fiber is formed of the core 1 consisting of the pure quartz, the clad 2 consisting of the F-doped quartz glass enclosing the cores 1 and the jacket 3 consisting of the quartz glass having the high softening point. The quartz glass which is added with nitrogen and has a high softening point of about 50 deg.C is used as the quartz glass having the high softening point. The image fiber having the high radiation resistance is obtd. The high-softening point quartz glass such as, for example the glass added with Al2O3 in place of nitrogen is also usable.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a radiation-resistant image fiber formed from an image fiber structure having multiple cores in a single glass fiber.

BACKGROUND ART Generally, the demand for image fibers for use in industrial endoscopes has been rapidly increasing in recent years. By the way, among the characteristics of industrial image fibers, transmission characteristics such as image quality 8 resolution, mechanical characteristics such as outer diameter size and allowable bending diameter are important, but they are used for purposes such as cooling water piping inspection in nuclear power plants. Special industrial image fibers are required to have minimal deterioration in transmission characteristics even in a radioactive environment, and these requirements are becoming increasingly strict.

In other words, among the radiation resistance characteristics of image fibers, the increase in transmission loss due to radiation exposure is the most important, and this is largely determined by the constituent glass materials of the image fiber and the manufacturing process, so silica-based glass is superior as a glass material. As shown in Fig. 3, the core 1 that transmits light is made of pure silica glass, and the cladding 2 is made of F-doge quartz glass, and the jacket 3 of pure quartz glass surrounds it. It is known that the image fiber made of 'tCfJ is the most excellent.

Also, in the manufacturing process, the drawing conditions are dominant,
The higher the temperature, the better.

This is because when drawn at low temperatures, the glass undergoes processing distortion.
This is because defects occur, and when exposed to radiation, the fibers become mainly colored, resulting in an increase in transmission loss. Conversely, the higher the temperature, the fewer defects will occur and the radiation resistance will improve.

Therefore, conventionally, the above-mentioned test! In order to minimize defects that occur during drawing, the drawing temperature was raised as much as possible and the drawing speed was lowered as much as possible. If the drawing speed is increased and the drawing speed is completely reduced, the viscosity of the glass will be extremely reduced, and the neck-down part of the base material will become extremely soft, causing the drawn image fiber to vibrate violently and cause the wire diameter to become very large. The image fiber becomes unstable and it becomes impossible to draw the image fiber stably. In even more extreme cases, a phenomenon occurs in which the base material flows down due to its own weight, making it impossible to draw the wire.

<Problems to be Solved by the Invention> The present invention was proposed in view of the above circumstances, and relates to an image fiber having a large number of cores in a single glass fiber with excellent radiation resistance characteristics. be.

<Means for Solving the Problems> In particular, the present invention provides an image transmission section comprising a large number of cores made of pure silica glass in an image fiber, and a cladding made of F. Donig quartz glass surrounding each core;
It is characterized in that a layer of quartz-based glass, which has a higher softening point than quartz glass, is placed between the quartz glass layers of the outermost shell.

Effects> The present invention makes it possible to draw wire at a higher temperature and slower speed than before, and can suppress the occurrence of defects in the core and clad glass that are involved in the single image transmission characteristics during drawing. The resulting image fiber has excellent radiation resistance properties.

<Example> Hereinafter, an example of the present invention will be described in detail based on FIGS. 1 and 2.゛Figure 1 shows the cross-sectional structure of the image fiber according to the present invention, where 1 is a pure quartz core, 2 is a cladding made of F-doped quartz glass surrounding the core, and 3 is a jacket made of high softening point silica glass. It is.

Here, as a quartz glass having a higher softening point than pure quartz glass, silica glass doped with borosene (Nk) is currently known, and a small amount of nitrogen may be added. As shown in the examples, the softening temperature is about 50°C higher than that of pure quartz, and radiation resistance can be significantly improved at this level.In addition, glass with a high softening point can be added with nitrogen. The material is not limited to the above, and for example, At20sk-added glass may be used.

FIG. 2 shows the cross-sectional structure of the image fiber according to the present invention.
This shows the cross-sectional structure of a fiber with a pure silica glass layer on the outermost layer.If the entire pure silica glass layer 4, which has a relatively low softening point and excellent chemical stability, is placed on the outermost surface of the image fiber, it can be drawn. Since the amount of minute scratches is less likely to occur, it is possible to create a high-strength and highly reliable image fiber.

The specific structure of the embodiment according to the present invention will be explained below. ' Core diameter 10 μm 1 Core distance M 15 μm 1 Core glass, pure quartz glass, clad glass, F-doped quartz glass,
An image fiber (outer diameter 2ttan) having an N-doped quartz jacket with a jacket thickness of 0.17+μm was used with Δn=1.0% and a pixel count of 12,000 μm.

The above drawing temperature was 2100°C, and the drawing speed was 0.1 t.
tan/1xix+. These drawing conditions are conditions that allow stable drawing in the conventional structure.

The resulting image fiber consists of a core and cladding made of the same material with a pure quartz jacket, and has better radiation resistance than an image fiber of the same size drawn at a temperature of 2050°C and a drawing speed of 0.5 x/mrn. was excellent.

Furthermore, when the obtained image fiber was irradiated with gamma rays, a bright image could be fully transmitted even at a cumulative dose of 105 R or more.

Further, by using N-doped quartz for the jacket, which has a high degree of nitrogen doping, even better characteristics can be obtained.

Furthermore, as shown in Fig. 2, the image fiber obtained by applying a pure quartz layer with a thickness of about 50 μm to the outermost layer and drawing it under the same conditions has a minimum bending radius of 100 μm, and a A very strong product was obtained.

<Effects of the Invention> As described above in detail together with the examples, the radiation-resistant image fiber according to the present invention has a core made of a large number of pure silica glasses in the image fiber, and a core made of F-doped silica glass surrounding each core. It has a structure in which a jacket made of silica-based glass, which has a higher softening point than quartz glass, is placed between the screen transmission part, which is made up of a cladding made of Moreover, it becomes possible to suppress the occurrence of defects in the core and cladding glass that are involved in image transmission characteristics during fencing, and the resulting image fiber has excellent radiation resistance characteristics.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the structure of a radiation-resistant image fiber according to the present invention, FIG. 2 is a cross-sectional view further showing the structure of a radiation-resistant image fiber according to the present invention, and FIG. 3 is a cross-sectional view showing the structure of a conventional radiation-resistant image fiber. FIG. In the drawings, 1 is a core made of pure silica glass, 2 is a cladding made of F-doped silica glass, 3 is a jacket made of high softening point quartz glass, and 4 is a pure silica glass layer.

Claims (3)

[Claims] (1) An image fiber that has multiple cores in one glass fiber consists of a core made of pure silica glass, a cladding made of F-doped quartz glass surrounding each core, and a cladding made of F-doped silica glass surrounding each core. A radiation-resistant image fiber characterized by being surrounded by a jacket made of quartz glass with a high softening point. (2) The radiation-resistant image fiber according to claim 1, wherein the outermost layer of the jacket of the image fiber is coated with pure silica glass. (3) The radiation-resistant image fiber according to claim 1, characterized in that the cladding is made of quartz glass having a higher softening point than the quartz glass and is made of silica glass doped with silicon nitride.