Abstract
The paper presents a set of tests carried out in order to evaluate the design characteristics and the operating performance of a set of six X-ray extrinsic optical fiber sensors. The extrinsic sensor we developed is intended to be used as a low energy X-ray detector for monitoring radiation levels in radiotherapy, industrial applications and for personnel dosimetry. The reproducibility of the manufacturing process and the characteristics of the sensors were assessed. The sensors dynamic range, linearity, sensitivity, and reproducibility are evaluated through radioluminescence measurements, X-ray fluorescence and X-ray imaging investigations. Their response to the operating conditions of the excitation source was estimated. The effect of the sensors design and implementation, on the collecting efficiency of the radioluminescence signal was measured. The study indicated that the sensors are efficient only in the first 5 mm of the tip, and that a reflective coating can improve their response. Additional tests were done to investigate the concentricity of the sensors tip against the core of the optical fiber guiding the optical signal. The influence of the active material concentration on the sensor response to X-ray was studied. The tests were carried out by measuring the radioluminescence signal with an optical fiber spectrometer and with a Multi-Pixel Photon Counter.
Highlights
Fiber optic sensors designed for radiation dosimetry, detection or monitoring fall into two categories: intrinsic sensors and extrinsic sensors [1]
Two types of sensor exposures to X-ray were used during these studies: one along the longitudinal axis of the cylinder defining the sensor tip, in 0.5 mm steps, and the other, frontal on the tip cap, masking the optical fiber core end, coaxial with the optical fiber core
The frontal scan was employed for both X-ray fluorescence and radioluminescence tests, while the longitudinal scan was performed for radioluminescence assessment only
Summary
Fiber optic sensors designed for radiation dosimetry, detection or monitoring fall into two categories: intrinsic sensors and extrinsic sensors [1]. In the case of intrinsic sensors the optical fiber constitutes both the sensing medium and the propagation one Effects such as the radiation induced luminescence (RIL), the radiation induced absorption (RIA) [2], the generation of Cerenkov radiation in silica or plastic optical fibers exposed to charged particles [3,4], the change of the silica density [5,6] or the modification of the refractive index of silica under irradiation [7] were used to detect ionizing radiations. In extrinsic optical fiber sensors, the optical fiber is used only to transfer the optical signal from the radiation sensitive head towards the optical detector These sensors are based on: thermoluminescence [8], optically stimulated luminescence [9,10] and scintillation (employing organic or inorganic materials) [11,12,13]. An evaluation of the sensors responsivity to the effects of two optically reflecting materials was studied
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