JPS6214604A - Radiation-resisting fiber scope - Google Patents

Abstract

PURPOSE:To suppress an increase in loss due to radiation and to improve the radiation resistance of an optical fiber by charging only hydrogen or mixed gas of hydrogen and inert gas in a fiber scope which is shielded completely against internal pressure. CONSTITUTION:The ocular part 2 of the fiber scope 1 shielded completely against the internal pressure by on O ring, ground packing, etc., is provided with a shield contactor or nozzle 3 and only H2 or mixed gas of H2 is charged through the nozzle 2. The shield connector shield 3 is fitted preferably on the side of the ocular part 2 so as to prevent an objective part 4 from becoming thick.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The fiberscope of the present invention is suitable for use in a radiation environment by suppressing an increase in loss due to radiation.

(Prior Art) Conventionally, in order to suppress the increase in loss caused by radiation in a fiberscope, it has been necessary to improve the essential composition of the optical fiber itself or to perform treatments to suppress the increase in loss.

In order to improve the essential composition of the optical fiber itself, pure quartz is used in the core of the optical fiber, and approximately several hundred ppm of OH is added.
These methods include doping with Cl and reducing the amount of Cl.

Treatments to suppress the increase in loss include a method using the optical bleaching effect, which suppresses the increase in loss by passing high-energy light such as a laser into the optical fiber, and a method to suppress the increase in loss due to radiation by applying thermal energy to the optical fiber from the outside. Methods using thermal annealing effects have been used.

(Problems with the Prior Art) Since the amount of increase in loss due to radiation irradiation depends on the material used, there is a limit to suppressing the increase in loss simply by improving the essential composition of the optical fiber.

Furthermore, even if the same material or base material is used, the radiation irradiation characteristics will vary depending on the manufacturing conditions (e.g. synthesis conditions, drawing conditions, etc.) and structure (e.g. core diameter, image fiber bundled with many optical fibers, etc.) .

(Means for Solving the Problems) The purpose of the present invention is not only to essentially improve the optical fiber to suppress the increase in loss caused by radiation, but also to further reduce the optical fiber μ by performing processing to suppress the increase in loss. The purpose is to improve radiation resistance.

In the present invention, hydrogen (H2) alone or a mixture of hydrogen and an inert gas is sealed or can be sealed in a fiber scope 1 that is completely shielded from internal pressure.

(Embodiment 1) As an example of the present invention, a shield connector or a nozzle 3 is provided in the eyepiece 2 of a fiberscope 1 that is completely shielded from internal pressure with an O-ring, ground backing, etc. From there, fiberscope
This allows H2 alone or a mixture of H2 and an inert gas to be sealed inside. The shield connector or nozzle 3 may be installed anywhere on the fiberscope 1, but it is preferable to install it near the eyepiece 2 in order to avoid making the objective 4 thicker.

(Embodiment 2) As an example of the present invention, as shown in FIG. 2, at least the eyepiece part 2 has a pressure-resistant structure, and the fiber scope from the objective part 4 to the transmission part 5 is equipped with a shield connector or a nozzle 3. It is covered with a shield vibro, and a radiation-resistant treatment gas consisting of H2 alone or a mixture of H2 and an inert gas is sealed in the vibro, and the gas is diffused from the objective section 4 or transmission section 5, which does not have a pressure-resistant structure. The optical fiber inside the fiberscope 1 is subjected to radiation-resistant treatment.

(Embodiment 3) As an example of the present invention, as shown in FIG. 3, a fiberscope l completely shielded against internal pressure is provided with at least two shield connectors or nozzles 3 for radiation-resistant treatment gas, The radiation-resistant processing gas is constantly circulated and can be easily replaced.

(Experiment example) (Experiment method) The sample fiber used in this research was B
t2 and B-3 fibers, which were manufactured by the applicant. The core material of these fibers is pure silica glass containing high 01 (2) by direct method, and the cladding material is F-doped quartz glass.The core diameter is loOILm and the cladding diameter is 125JLm.

The B-2 and B-3 fibers were made from the same preform using different drawing conditions, with the B-3 fiber drawn at a lower temperature and higher tension. In both cases, a 2 eV light absorption band is significantly generated by γ-ray irradiation, and basically they exhibit almost the same characteristics.

The optical properties were measured using hydrogen-treated B-3 fibers (room temperature, 2 atm, 53 hours and exposure to air for 11 days) and untreated B-2 fibers, and the light during γ-ray irradiation at room temperature. The increase characteristics of transmission loss were investigated and compared. In addition, untreated B-2 fibers were irradiated with 5 kG7 gamma rays at room temperature, and then changes in the increase in loss during hydrogen treatment were examined.

For hydrogen treatment, as shown in FIG. 4, the γ-ray irradiated portion 12 of the sample is placed in a beaker 11 in which the wood 10 has been replaced with hydrogen, the lead portion 13 is pulled out of the beaker 11, and the lead portion 13 is set in the optical system 14. It was measured. Hydrogen treatment is a treatment at room temperature at about 1 atmosphere. The dose rate of γ-ray irradiation is 200 G
It is y/h.

(Experimental Results) The wavelength dependence of the loss increase caused by irradiating hydrogen-treated B-3 fiber and untreated B-2 fiber with gamma rays is shown in Figures 5 and 6 using weight as a parameter. shown respectively. The loss increase in untreated fiber is mainly due to 2eVi and the short wavelength tail. In the hydrogen-treated sample, the increases in both of the upper two absorption bands are extremely small. It was found that the formation of color centers due to γ-ray irradiation can be effectively suppressed by pre-hydrogen treatment of Fiaba.

It can be seen that this method is particularly effective in suppressing the increase in loss in the visible light used in image guide fibers.

Figure 7 shows how the untreated B-2 fiber is irradiated with γ-rays for 5 KGY to generate a large tail from the 2 eV band and short wavelengths, and then subjected to hydrogen treatment to reduce loss. Ta. Almost no decrease in loss was observed for 30 minutes after the start of the hydrogen treatment, and a slight decrease began to be seen after 1 hour. After that, a steady decline was observed. After 24 hours, the 2 eV band decreased to 10% of the initial value.

The reason why the loss is reduced by hydrogen treatment as shown in FIGS. 5 to 7 is thought to be due to the following mechanism. By performing hydrogen treatment, hydrogen diffuses into the core glass and reacts with the dangling bonds that are the cause of color centers caused by radiation exposure, terminating the dangling bonds and causing color centers. It is thought that it is disappearing.

In the results shown in Figure 7, the phenomenon of loss was small in the first hour after the start of hydrogen treatment, but this is because hydrogen diffuses through the fiber's nylon coat, silicone buffer layer, and glass cladding layer to the core. This is thought to be because it takes about an hour to complete.

(Effect of the invention) The fiber scope of the present invention has the following effects.

(1) Increase in loss in optical fibers (image fibers, image bundles, ride guide bundles, etc.), particularly in the visible range, can be effectively suppressed.

(2) Using hydrogen treatment for the maintenance of radiation fibers is easier to put into practical use than loss recovery techniques using thermal annealing. Moreover, maintenance f by thermal annealing may cause thermal deterioration of parts other than the fiber and glass, but in the present invention, there is no such concern.

[Brief explanation of the drawing]

Figures 1 to 3 are explanatory diagrams showing various examples of the fiber scope of the present invention, Figure 4 is an explanatory diagram of experiments to confirm the effects of the present invention, and Figures 5 to 7 are explanatory diagrams of experimental results. It is a diagram. 1 is a fiber scope 2 is an eyepiece part 3 is a shield connector, or a nozzle 4 is an objective part 5 and a transmission part 6 is a shield pipe.

Claims (1)

[Claims] A radiation-resistant fiberscope characterized in that hydrogen alone or a mixture of hydrogen and an inert gas is sealed in a fiberscope that is completely shielded against internal pressure.