Thermoluminescence response of doped silicon dioxide optical fibres subjected to electron irradiation

Abstract

This study was focused on the suitability of commercial optical fibres as a new thermoluminescence dosimeter (TLD). The materials doped to silicon dioxide(SiO2) were germanium type A (Ge (A)) of first, second and third batch, germaniumtype B (Ge (B)), erbium (Er), aluminium and thulium (Al + Tm), photonic crystalfibre (PCF) of first and second batch, and multi photonic crystal fibres (MPCF). TheMPCF came with different range of core diameter of 220 μm (MPCF 220 μm) and2 mm (MPCF 2 mm). The study also used pure glasses such as photosensitive flatfibre (PFF), flat fibre (FF) and dummy flat fibre (DFF). A comparison of thethermoluminescence (TL) response of electron irradiation concerning sensitivity,linearity, energy dependence, fading signal, reproducibility, minimum detectable dose(MDD) and effective atomic number, Zeff parameters as well as cross-comparisonwith that of TL dosimeter i.e TLD-100 (LiF:Mg,Ti) rods were investigated. Scanningelectron microscopy (SEM) was used to determine the dopant concentration in eachdoped optical fibres. The irradiation was performed using 6 MeV electrons for dosesranging from 1 – 4 Gy at Pantai Hospital and University of Malaya Medical Centreseparately according to the batch. All the optical fibres produced linear dose-TLresponses for dose range of 1 – 4 Gy. TLD-100 produced greater TL sensitivityfollowed by PFF, FF, Ge (A), MPCF 2 mm, DFF, Al + Tm, Er, MPCF 220 μm,Ge (B) and PCF with their relative sensitivity of 0.2, 0.15, 0.08, 0.04, 0.02, 0.01,0.005, 0.004, 0.003 and 0.002 respectively compared to TLD-100. Ge (A) showed7% signal loss followed by PFF, Er, FF and PCF with 15%, 26%, 28% and 33%signal loss respectively after 14 days of irradiation. Reproducibility of Ge (A),Ge (B), Er, PCF, MPCF 2 mm and MPCF 220 μm were poor due to high degree offading. The lowest MDD obtained from TLD-100, followed by FF, Ge (A) 1st batch,Ge (A) 3rd batch and PFF with their MDD of 0.13, 0.9, 4.0, 5.2 and 5.4 mGyrespectively. The Zeff for Ge (B), Ge (A) and Er doped to SiO2 optical fibres were11.88, 12.95 and 20.69 respectively. Several attractive features offered by these fibrespoint to its use in radiation therapy.