Position-Sensitive Radiation Detector with Flexible Light Guide and Liquid Organic Scintillator to Monitor Distributions of Radioactive Isotopes

Abstract

Position-sensitive detectors consisting of optical fibers such as scintillating fibers, normal optical plastic fibers, and liquid light guides have been developed as radiation sensors to monitor long-range distributions of radioactive isotopes. Because of losses of optical transmission due to radiation damage in high-level radiation environments, however, both scintillating fibers and normal optical plastic fibers are less applicable to areas of high dose rate. In order to develop a flexible fiber-type radiation sensor with good radiation hardness, we propose to use a liquid light guide, the core of which is replaced by a liquid organic scintillator. A liquid light guide consists of flexible cladding material, and can be easily bent. A liquid organic scintillator can generate a much larger number of photons than the original liquid material, leading to a better detection efficiency than a simple liquid light guide; furthermore, it is not significantly damaged by incident radiation. In preliminary experiments using a fast neutron beam, we confirmed that our prototype system can be operated as a position-sensitive radiation detector. Fundamental characteristics such as spatial resolution, detection efficiency and attenuation length of light propagation were examined with two detectors of 2 m and 10 m length. Optical transmission losses due to radiation damage were examined using 60Co gamma rays; no significant transmission loss was observed up to a dose of 1.5 × 104 Gy.