Recent Advances in Silica Glass Optical Fiber for Dosimetry Applications (original) (raw)
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Nowadays, silica based optical fibres show enough potential to be used as TL dosimeters in different applications. Reuse of optical fibre as a practical dosimeter demands to complete removal of accumulated doses via previous irradiations. This work investigates the existence and/or effect of remnant doses in fibre dosimeter from the previous irradiations, and proposes a method to control this artifact. A single mode Ge-doped optical fibre is used as TL radiation sensor, while a well calibrated Gammacell with 60 Co source is used for irradiations. The effect of irradiation history on the TL response of optical fibres is surveyed extensively for doses ranged from 1 to 1000 Gy. The results show that the absorbed dose history in a fibre affects its response in the next irradiation cycles. It is shown that a dose history of around 100 Gy can increase the response of optical fibre by a factor of 1.72. The effect of annealing at higher temperatures on stabilizing the fibre response is also examined and results revealed that another alteration in the structure of trapping states occurs in glass medium which can change the sensitivity of fibres. Preservation of the sensitivity during successive irradiation cycles can be achieved by a proper annealing procedure accompanied by a pre-dose treatment.
Real-time radiation dosimetry using P-doped silica optical fiber
Measurement, 2019
Radiation dosimetry applications related to radiotherapy have clear importance in determining the accurate and safe delivery of patient prescribed doses. Versatile yet robust, high spatial resolutions, wide dynamic range real-time forms of dosimetry are called for. Doped silica optical fibers of submm spatial resolution exhibit useful radioluminescence (RL) properties when exposed to ionizing radiation. In this study, primary investigations have been carried out on phosphorus-doped silica optical-fiber. High-energy clinical X-ray beams (6 MV and 10 MV) were used to irradiate the optical fiber, RL response being recorded for six dose-rates (between 100 MU/min and 600 MU/min) delivered by a Varian 2100 C/D linear accelerator. The P-doped optical-fiber showed linear RL response, with minimal observable memory and afterglow and plateau effects. The results indicate the P-doped optical-fiber dosimeter to have strong potential for use in radiotherapy applications.
With high-dose applications lacking the benefit of an economic yet versatile dosimeter that provides for a wide dynamic dose range, ongoing research is seeking to introduce suitable thermoluminescent (TL) material for such needs. Acknowledging the high potential of silica fibres, as developed by members of this group over the past few years, in present work evaluation has been made of 13 types of fibre, differing in dopant, dopant concentration and diameter including P-, Al-, Er-, Ge- and Al-Tm-doped fibres, ultra-high numerical aperture and borosilicate fibre, and two non-doped fibres, quartz and suprasil F300. Evaluation is made in terms of TL response to photon and electron irradiations with the objective of determining a TL material that can offer sensitive yet extended dose capability, saturating only above the few tens of kGy range. The various silica fibres that have been investigated were found to show saturation levels from 5 kGy for Ge-doped fibre (4 mol %) to 80 kGy for 2 mol % Al-doped silica fibre. Borosilicate fibres demonstrated the greatest potential for high dose dosimetry, maintaining a highly-linear response, any tendency towards saturation only being indicated to beyond receipt of doses of 100 kGy. For this fibre type detailed TL characterizations were conducted, including glow curve analysis, reproducibility and fading tests. The results suggest borosilicate fibre to be suitable for high dose TL dosimetry, providing sufficient sensitivity and appropriate dosimetric characteristics.
Dosimetric characteristics of fabricated silica fibre for postal radiotherapy dose audits
Present investigation aims to establish the dosimetric characteristics of a novel fabricated flat fibre TLD system for postal radiotherapy dose audits. Various thermoluminescence (TL) properties have been investigated for five sizes of 6 mol% Ge-doped optical fibres. Key dosimetric characteristics including reproducibility, linearity, fading and energy dependence have been established. Irradiations were carried out using a linear accelerator (linac) and a Cobalt-60 machine. For doses from 0.5 Gy up to 10 Gy, Ge-doped flat fibres exhibit linearity between TL yield and dose, reproducible to better than 8% standard deviation (SD) following repeat measurements (n = 3). For photons generated at potentials from 1.25 MeV to 10 MV an energy-dependent response is noted, with a coefficient of variation (CV) of less than 40% over the range of energies investigated. For 6.0 mm length flat fibres 100 µm thick x 350 µm wide, the TL fading loss following 30 days of storage at room temperature was ...
XPS and PIXE analysis of Doped Silica Fibre for Radiation Dosimetry
Journal of Lightwave Technology, 2015
The material characteristics of doped SiO 2 fibre are studied, the electron traps in the product medium creating a situation attractive for their application in thermoluminescence (TL) radiation dosimetry. To-date, rather limited research has been conducted towards gaining an essential understanding of the magnitude of TL signal and material characteristics of doped fibres. Characterization is being sought to ensure that the mechanism of TL yield in optical fibres is well understood, allowing a favourable well controlled production situation to be established. The intended end point is to specify dosimeters, not only for clinical dosimetry but also for their application in S.F. Abdul Sani is with the Centre for Nuclear and Radiation Physics,
Recent Advances in Scintillating Optical Fibre Dosimeters
Toward a Science Campus in Milan, 2018
Scintillating optical fibres have shown interesting results for ionizing radiation monitoring. Since they may enable a remote, punctual and real-time dose assessment, their application in medical dosimetry is very promising. This work aims to summarize some recent progresses in the development and characterization of rareearth doped silica optical fibres. The radioluminescent and dosimetric properties of Ce, Eu and Yb-doped fibres are presented and the advantages and challenges in the use of these sensors for radiation therapy dosimetry are discussed. For such application, an effective approach to deal with the stem effect, i.e. the spurious luminescent signal originated in the light guide as a consequence of its exposition to ionizing radiations (i.e. Cerenkov light and intrinsic fluorescence) must be considered. The stem effect mainly occurs in the UV-VIS region. We demonstrated that the use of a dopant emitting in the near infrared, like Yb, is suitable for an optical discrimination of the dosimetric signal. Indeed, through a characterization of the dosimetric properties of
Dosimetric characteristics of fabricated Ge-doped silica optical fibre for small-field dosimetry
Results in Physics, 2018
We study 3 mm long germanium-doped (Ge-doped) silica fibres for small-field dosimetry, seeking to overcome spatial resolution and charged-particle disequilibrium issues, also any associated dose deviation from that of computerised treatment plan dose delivery. Investigation has been made of the thermoluminescent (TL) dependency of locally fabricated 6 mol% Ge-doped preforms subsequently made into cylindrical (CF) and flat fibres (FF), also commercial Ge-doped fibres (COMM), the dopant and mechanical strain created in fibres production providing the trapping levels generating the TL yield. A Perspex phantom was designed for study of angular dependency, fibres being positioned at angles ranging from 0° to 90° while a scanning electron microscopy with energy dispersive x-ray (SEM/EDX) analysis study allowed evaluation of relative Ge content of the three TL types. Flat Fibre dose repeatability was found to be similar to that for the commercial fibre (in the range 2%-6%), improving appreciably upon that for the cylindrical fibre (< 14%), also exhibiting highly linear response up to 80 Gy (R 2 99%) and near angular independence (< 3%). The notable signal fading of the FF (25%) would need to be carefully accounted for in applications. This work provides support for the viability of 6 mol% Ge-doped preforms subsequently fabricated into Flat Fibres for use in small-field dosimetry, offering a suitably dose-sensitive fibre arrangement.
Radiation-resistant and radiation-sensitive silica optical fibers
Advances in Fiber Optics, 2000
The mechanisms of radiation-induced absorption in silica optical fibers in the visible spectral region and in the telecom spectral windows as well as the technological means to lower the induced absorption are analyzed. Hydrogen loading of large-core silica optical fibers is shown to drastically reduce the induced absorption at megagray doses. It is shown that lowdose transient absorption can degrade the performance of pure-silica-core fibers at l .55 tm. N-doped silica fibers are argued to be the best candidates for low-dose applications (e.g. in space). At megagray doses, the long-wavelength induced absorption is found to be the main induced absorption mechanism. Its origin is not known with certainty, whereas its value may be different in pure-silica-core fibers obtained under different preform fabrication conditions. Different types of radiation-sensitive fibers are investigated with the aim to develop fiber-optic dosimeters. An optimum wavelength region for the operation of P-doped silica fiber dosimeters has been determined. Novel types of dosimeters and neutron detectors are proposed based on the effect of irreversible radiation-induced increase of OH-group absorption.