Hiroyuki Hayami

Radiation resistivity of pure-silica-core image guides

Abstract There are increasing demands for pure-silica-core image guides used in many radiation fields, in which more quantitative estimation of the radiation resistivity is required. We proposed two different methods suited for studying the resistivity of the image guides; one is based on average visual radiation-induced loss in which spectral luminous efficiency is taken into account and the other on shift of a point on the chromaticity diagram. Then, the resistivity of four kinds of core materials was evaluated under repeated irradiation conditions. The results show that the order of good resistivity among test samples is F, F+OH, OH and Cl+OH contained materials. This contradicts the results previously reported as OH-contained material has the best resistivity. Recovery of the radiation-induced loss was observed in each sample, most noticeably in Cl-contained material, when the samples were left in atmospheric ambient at room temperature for a certain period. The recovered transmittance was, however, l...

Radiation Responses Of Pure-Silica Core Image Guides

Radiation resistivity of pure-silica core image guides were investigated in terms of incremental spectral loss and quality of pictures transmitted through the image guides. Radiation-induced spectral losses were measured so as to clarify the dependences of radiation resistivity on such parameters as core materials (OH and Cl contents), picture element dimensions (core packing density and cladding thickness), number of picture elements and drawing conditions. As the results, an image guide with OH-and Cl-free pure-silica core, 30 - 45% in core packing density, and 1.8 - 2.2 μm in cladding thickness showed the lowest loss. The parameters to design the image guide were almost the same as those to obtain a image guide with good picture quality. Radiation resistivity of the image guide was not dependent on drawing conditions and number of picture elements, indicating that the image guide has large tolerances .in production conditions and that reliable quality is constantly obtained in production. Radiation resistivity under high total doses was evaluated using the image guide with the lowest radiation-induced loss. Maximum usable lengths of the image guide for practical use under specific high total doses and maximum allowable total doses for the image guide in specific lengths were obtained by the extrapolating method. Picture quality in terms of radiation-induced degradation in color fidelty in the pictures transmitted through image guides was quantitatively evaluated on the a chromaticity diagram based on the CIE standard colorimetric system and on the color specification charts according to three attributes of colors. The image guide with the least spectral incremental loss gives the least radiation-induced degradation in color fidelty in the pictures as well.

New Techniques to Apple Optical Fiber Image Guide to Nucileas

To apply optical fiber image guide to harsh radiation environments, we have developed new image guide systems for color correction and new type image guide with a semiconductor laser for infrared imaging. We irradiated the image guides utilizing a 60Co gamma source. Measured images with the visible type image guide became dark and yellowish because of radiation induced loss. By using a color correction system, the original color of the images can be obtained. In the case of infrared type image guide, because of low radiation induced loss in the infrared region, the degree of darkening was less than half of that for the visible type of image guide. When irradiating a fixed length of 2.5 m, the dose limit for using image guide was estimated to be 3.0×105 C/kg (7.9×109 R) with the visible type image guide and be 4.5×105 C/kg (1.2×1010 R) with the infrared type image guide. These radiation resistivities were more than 103 times ofthat for usual CCD cameras. With these techniques, image guide can be applied to harsh radiation environment.

New techniques to apply an optical fiber image guide to harsh radiation environments in nuclear facilities

To apply optical fiber image guide (IG) to harsh radiation environments, we have developed two new techniques. One technique is a visible type IG with a color correcting system and the other technique is an IR type IG. We irradiated the IGs utilizing a 60Co gamma source. Measured Images with the visible type IG became dark and yellowish because of radiation induced loss. By using a color correction system, the original color of the images can be obtained. In the case of IR type IG, because of low radiation induced loss in the IR region, the degree of darkening was less than half of that for the visible type of IG. For a fixed irradiated length of 2.5m, the dose limit for using IG was estimated to be 4.6 X 108 with the visible type IG and 1.2 X 109 with the IR type IG. These radiation resistivities were more than 103 times of that for usual CCD cameras. With these techniques, IG can be applied to harsh radiation environment.