Ge and B doped collapsed photonic crystal optical fibre, a potential TLD material for low dose measurements

Offering a number of advantageous features, tailor-made silica-based fibres are attracting attention as thermoluminesence (TL) dosimeters. We have performed a detailed study of the TL properties of Ge-doped and Ge-B-doped collapsed photonic crystal fibres (PCFc), most particularly with regard to their potential use for the environmental and X-ray diagnostic dose monitoring. Extrinsic doping and defects generated by strain at the fused inner walls of the collapsed fibres result in the PCFc-Ge-B and PCFc-Ge fibres producing markedly greater TL response than that of the phosphor-based dosimeter TLD-100, by some 9 and 7×, respectively. The linearity of TL yield has been investigated for X-ray doses from 0.5 mGy to 10 mGy. For a dose of 1 Gy, the energy response of the PCFs and TLD-100 has been studied using X-rays generated at accelerating potentials from 20 kVp through to 200 kVp and for the 1.25 MeV mean gamma-ray energy from 60Co. The effective atomic number,Zeffof PCFc-Ge and PCFc-Ge-B was estimated to be 12.5 and 14.4, respectively. Some 35 days post-irradiation, fading of the stored TL signal from PCFc-Ge-B and PCFc-Ge were found to be ∼15% and 20% respectively, with mean loss in TL emission of 0.4-0.5% per day. The present doped-silica collapsed PCFs provide greatly improved TLD performance compared to that of previous fibre designs and phosphor-based TLD-100.