Application of red and near infrared emission from rare earth ions for radiation measurements based on optical fibers

When optical fiber radiation measurements are applied for high dose rate area, there has been a problem of radiation induced loss in the optical fibers. In this study, red and near infrared (IR) fluorescence from rare earth ions has been used to reduce the problem. From continuous measurements using Gd₂O₂S:Pr³⁺, the superiority of using long wavelength emission has been shown from the view point of radiation hardness. Linear relation between dose rate and peak counts was confirmed and it shows the possibility of using the long wavelength emission for radiation measurements. For calibration of the radiation induced loss, the optical time domain reflectometry (OTDR) technique has been applied. It has been shown that this method can broaden the dose rate limit of the optical fiber based measurements. Also, glass samples doped with rare-earth ions have been made and irradiated by gamma rays. Emission at longer wavelength than 700 nm has been observed for Eu³⁺ ions doped into silica, fluorophosphate and ZBLAN glass samples. Considering that it is easy to make silica glass and to connect it to usual silica glass optical fiber, silica glass doped with Eu³⁺ is thought to be the most promising material for new scintillating fibers with high radiation resistivity