Advanced thermoluminescence dosimetric characterization of fabricated Ge-Doped optical fibres (FGDOFs) for electron beams dosimetry

Abstract

For fabricated Ge-doped optical fibres (FGDOFs) investigation is made of a range of optical fibre thermoluminescence (TL) characteristics: sensitivity, dose linearity, dose rate dependence and fading together with exploration also made of percentage depth dose (PDD) curves for electron beams dosimetry. The fibres used were of various shapes, cross-section dimensions and germanium (Ge) concentrations. The responses of FGDOFs were compared against commercial fibres as well as that of an ionization chamber (PTW 31010 Semiflex 31010) and Gafchromic™ EBT3 films. All fibres were irradiated at the Royal Surrey County Hospital (UK) using 6-, 9- and 12 MeV electron energies, with 100 cm focus-to-sample distance (FSD) and 10 × 10 cm2 field size, measurements being made up to the depth of dose maximum, Zmax. At a fixed 9 MeV electron energy, dose rates from 100 up to 600 cGy/min were used with field sizes ranging from 6 × 6 cm2 to 25 × 25 cm2. For PDD curves, the fibres were placed at depths from 0 cm to 6 cm, comparison being made against the ionization chamber and films. The water-to-air stopping power ratios and the fluence correction factors, Pfl were required in determining PDD curves when using the ionization chamber. TL yields against dose were highly linear (R2 > 0.99). A low dependence on dose rate was found for all fibres. The 2.3 mol% flat fibre (FF) produced the superior performance, with the highest sensitivity, minimum TL fading for up to 3 months as well as relative difference of less than 2% for the build-up and fall-off region for PDD curves.