Desarrollo de un sistema de detección de radiaciones ionizantes basado en materiales centelleadores y fibra óptica para entornos de protección ambiental y de salud

Abstract

The main goal of the following thesis is the design of a low cost and easy to use gamma radiation detector which could be used in multiple environments such as early warning in the field of radiation protection. Of the different types of ionizing radiation sensors that exist, the research has focused on improving the design of a scintillation-based sensor of ceramic materials coupled to a plastic optical fiber that serves as a guide to the light produced in the detector taking it to the measuring instrument. The work has been focused in the investigation of the efficiency of two ceramic materials (Gd2O2S: Tb and Gd2O2S: Eu) in powder form. Both materials emit light in the visible when irradiated with X-rays or gamma. According to performance criteria based on the compromise between cost and quantum efficiency, Terpho doped Gadolinium Oxisulfide (Gd2O2S: Tb) was finally chosen as fluorophore, proving that this material is the most efficient for detecting emission from a source Of 137Cs as well as for high energy X-ray sources used in radiotherapy. Also, it´s been possible to improve the coupling of light emitted by the fluorophore to a conventional polymer optical fiber (PMMA), making localized narrowings in the area of the fiber in contact with the ceramic material. A quite important improvement in the signal-to-noise ratio measured with a conventional spectrometer has been observed without the use of photomultiplier elements, which simplifies the final measurement system reducing its costs. Both, narrowing and immobilization process of the material at the end of the fiber have been the object of the investigation of this thesis as part of the process in order to optimize the final design of the detector. The fibers tightened through chemical etching with an homogeneous profile and the immobilization of the dry powder in a Teflon capsule have gotten to a new configuration with better results in the signal-to-noise ratio measured when irradiating the X-ray and gamma-ray detectors. Finally, a discrete detector with gamma rays of medium energy coming from a source calibrated of 137Cs has been characterized. It has also been found that the sensors are effective with lowenergy X-ray sources as well as an X-ray source for application in radiotherapy. The proposed system is cheaper, easier to operate and has an improvement on terms of signal-to-noise ratio compared to detectors of the same type currently on the market.