Radiation characteristics of fine fibers for image bundle

In order to transmit image information in the application of optical fibers to nuclear industries, the image bundle fibers used so far for medical application, in which many fine fibers are bundled and both ends are evenly arranged and fixed, and the image fibers made by drawing a parent material, in which many optical fibers are bundled, and grinding the end faces, are employed. It has been reported that the radiation characteristics of these fibers are different owing to the material, construction, manufacturing condition and radiation dose rate. In this paper, the radiation characteristics of the fine fibers of 30 μmdiameter used as image bundles which are studied for the application requiring flexibility are reported. 125 μm fibers were used for comparison. Their cores were made of the quartz containing several hundred ppm of OH radical without any dorpant, and F- and B- doped quartz was used as the clads for the purpose of reducing refractive indices. The results of examination on the increase of transmission loss in the visible range by the irradiation at 1.5 x 104 R/h with 60Co γ-ray were as follows: (1) the absorption near 0.63 μm wavelength which seems to be caused by structural imperfection and the ultraviolet absorption due to E and E' centers increased with the increase of irradiation, (2) the increase of loss was larger in 125 μm fibers than in 30 μm fibers, (3) the increase of loss near 0.63 μm in 30 μm fine fibers was about 300 dB/km with 1 x 105 R, Accordingly, those fibers may be practically used depending on the length required. (Wakatsuki, Y)