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

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 Gafchromie (TM) 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 x 10 cm(2) field size, measurements being made up to the depth of dose maximum, Z(max) At a fixed 9 MeV electron energy, dose rates from 100 up to 600 eGy/min were used with field sizes ranging from 6 x 6 cm 2 to 25 x 25 cm(2). 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, P-fl were required in determining PDD curves when using the ionization chamber. TL yields against dose were highly linear (R-2 > 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.