Sinead O’Keeffe

Optical Fibers and Optical Fiber Sensors Used in Radiation Monitoring

By their very nature, optical fibers and, by extension, intrinsic and extrinsic optical fiberbased sensors are promising devices to be used in very different and complex environments considering their characteristics such as: capabilities to work under strong electromagnetic fields; possibility to carry multiplexed signals (time, wavelength multiplexing); small size and low mass; ability to handle multi-parameter measurements in distributed configuration; possibility to monitor sites far away from the controller; their availability to be incorporated into the monitored structure; wide bandwidth for communication applications. In the case of the optical fibers, the possibility to be incorporated into various types of sensors and actuators, free of additional hazards (i.e. fire, explosion), made them promising candidates to operate in special or adverse conditions as those required by space or terrestrial applications (spacecraft on board instrumentation, nuclear facilities, future fusion installations, medical treatment and diagnostics premises, medical equipment sterilization). Major advantages to be considered in using optical fibers/optical fiber sensors for radiation detection and monitoring refer to: real-time interrogation capabilities, possibility to design spatially resolved solutions (the capability to build array detectors), in-vivo investigations (i.e. inside the body measurements). As information on the behavior and operation of optical fibers/optical fiber sensors under irradiation conditions are scattered over a great variety of journal papers and conference contributions dealing with many different fields (nuclear science and engineering; measurement science; material science; radioprotection; nuclear medicine and radiology; sensor design; radiation dosimetry; fusion installations concepts; particle accelerators; astrophysics and space science; defense and security; lasers, optics, optical fibers and optoelectronics; physics and applied physics; scientific instrumentation; radiation effects) we decided to design this book chapter as a comprehensive review on the subject. The chapter opens with some general considerations on the radiation–matter interaction, and continues with a review of irradiation effects on different types of optical fibers (silica optical fibers, plastic optical fibers, special optical fibers), effects which can be considered when radiation sensors are developed. The next issue addressed refers to environments where optical fibers/optical fiber sensors are employed for radiation monitoring/

Novel optical fiber sensors and their applications in radiotherapy

The aim of this study was to investigate the over-response of an inorganic optical fibre sensor (OFS) when measuring percentage depth dose curves (PDDs) with respect to an ion chamber by means of physical measurements and Monte Carlo (MC) simulations. The sensor was constructed by filling a cavity (700 μm diameter and 7 mm deep), which was made in a PMMA (polymethyl methacrylate) plastic optical fibre, with an inorganic scintillating material: terbium doped gadolinium oxysulphide (Gd2O2S:Tb). The MC software packages BEAMnrc and DOSXYZnrc were used to develop a MC model of an Elekta Versa HD linear accelerator (linac), which was then used to simulate the Gd2O2S:Tb scintillator. The results of the PDD measurements showed a depth dependence of the OFS, however the percentage differences between the ion chamber and the OFS measurements showed that as the radiation field size decreases, the difference between the two measurements decreases from 16.5% to 5.1% for 10x10 cm2 and 2x2 cm2, respectively. The MC simulation of the sensor showed a good agreement compared to physical measurements at shallow depth in the phantom; however, discrepancies were observed at depth, which was less pronounced for 4x4 cm2 than for 10x10 cm2. The results of this study indicate that including Cerenkov radiation measurements is essential to accurately quantify the overresponse and the higher discrepancy between the measured and simulated PDD profiles of the OFS.