Abstract
In this study, we provide both theoretical analysis and experimental research aimed at evaluating the optimum sensor configuration for a previously proposed distributed fiber-optic calorimetric dosimeter. We study the effect of the material of the calorimetric point sensors, their shapes and sizes, the direction and energy of incident gamma radiation, as well as the OTDR response, on the accuracy of the dosimeter readings. Six different materials are considered: lead, tungsten, aluminium, copper, carbon and steel, as well as two geometric shapes of point sensors: spherical and cylindrical. Two different gamma radiation sources – with high energy (∼1000 keV) and low energy photons (∼100 keV) – are used for analysis.Several parameters – the steady-state efficiency coefficient, the response time constant, and the auxiliary efficiency function – are introduced to help investigate the efficiency of the dosimeter’ response to incident gamma radiation. Temperature inhomogeneities arising in the volume of point sensors due to radiation absorption are simulated in Geant4 and Ansys. For experiments on fiber heating, a Brillouin optical time domain analyzer is used.A theoretical and experimental evidence is provided that, in extended sensors, certain temperature inhomogeneities can lead to uncertainties in the Brillouin analyzer readings up to 20 %, which is an argument for the use of more compact sensors. A new sensor configuration is presented that consists in winding several turns of fiber on a sensor to ensure a contact length equal to or greater than the spatial resolution. It is shown that, in sensors less than 5 cm in size, due to a relatively large time constant of the dosimeter heating kinetics (of the order of 10–60 min depending on the point sensor parameters), temperature uncertainties become negligible in steady state and do not exceed 1 % at temperatures up to ∼ 220 °C. Lead is shown to be the most efficient material, and an estimate for the optimum sensor size is proposed.
Published Version
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