Thermoluminescence dosimetric properties of germanium doped, germanium-boron doped optical fibres and calcium borate doped dysprosium nanomaterial

Abstract

Thermoluminescent dosimetric properties of germanium doped and germanium-boron doped optical fibres, and dysprosium doped calcium borate nanomaterial were determined. The optical fibres were produced via modified chemical vapour deposition while dysprosium doped calcium borate nanomaterial was prepared via solution combustion synthesis. The objective was to develop new thermoluminescent material for radiation dose measurements of high energy electron beam. The interest in high dose measurements is due to numerous applications of electron beam in radiation technologies such as health care product sterilization, polymer modification and food processing. Characterization of samples was made by X-ray diffraction (XRD), energy dispersive X-ray (EDX) and transmission electron microscope (TEM) analyses. The particle size of dysprosium doped calcium borate (CaB4O7:Dy) nanomaterial influenced the thermoluminescent signal. From TEM analysis, the average crystal size of CaB4O7:Dy was found to be 12.5 nm. A well-defined peak appeared with maximum thermoluminescent response around 180 ºC to 200 ºC. Both germanium doped and germanium-boron doped optical fibres showed good linearity for dose range of 1 kGy – 150 kGy with correlation coefficient R2 of 0.931 and 0.957, respectively. CaB4O7:Dy nanomaterial also showed good linearity response with R2 = 0.825 and its response saturated beyond 100 kGy. Effective atomic number Zeff were 13.5 for CaB4O7:Dy, 14.4 for germanium doped optical fibre and 15.3 for germanium-boron doped optical fibres, respectively. Germanium doped optical fibres showed the best results for reproducibility and fading with the values of 7.4% and 4% after 60 days of storage. Germanium-boron doped optical fibres showed the highest sensitivity (82.34 nC.mg-1.Gy-1) compared to germanium doped optical fibre (70.68 nC.mg-1.Gy-1) and CaB4O7:Dy nanomaterial (23.02 nC.mg-1.Gy-1). The trap parameters namely kinetic order k, activation energy E and frequency factor s were also determined. The values were, E = 0.722 eV, s = 2.33 × 108 s-1; E = 0.547 eV, s = 7.63 × 106 s-1; and E = 0.515 eV, s = 3.11 × 106 s-1 for germanium-boron doped, germanium doped optical fibres and CaB4O7:Dy nanomaterial, respectively. From the values of geometric factors (Balarin’s formula), germanium-boron doped optical fibre and CaB4O7:Dy obeyed the second kinetics order while germanium doped optical fibre obeyed first kinetics order. This work indicates potential use of germanium doped and germanium-boron doped optical fibres as dosimeters in high energy electron beam irradiation applications.