Influence of dose history on thermoluminescence response of Ge-doped silica optical fibre dosimeters Influence of dose history on thermoluminescence response of Ge-doped silica optical fibre dosimeters (original) (raw)
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Performance of Ge-Doped Optical Fiber as a Thermoluminescent Dosimeter
IEEE Transactions on Nuclear Science, 2000
We have investigated the thermoluminescent response of three Germanium-doped silica-based optical fibers obtained by varying the drawing parameters from a unique preform. We compared under X-ray irradiation, their dosimetric properties to those of two widely used commercial dosimeters based on different technologies. Then, we investigated the potential of these optical fibers to monitor gamma rays at different doses and dose-rates, and to different fluences of particles (0.8 and 14 MeV neutrons and 63 MeV protons). Our results show that the thermoluminescence response of the Ge-doped optical fibers depends linearly on the direct ionizing dose (gamma-, X-rays) or on the indirect ionizing dose (protons, neutrons). As a consequence, this class of fibers is an excellent candidate for passive dosimetry in various fields from medical applications to high-energy physics.
Applied Radiation and Isotopes, 2012
We investigate the ability of high spatial resolution ($ 120 mm) Ge-doped SiO 2 TL dosimeters to measure photoelectron dose enhancement resulting from the use of a moderate to high-Z target (an iodinated contrast media) irradiated by 90 kVp X-rays. We imagine its application in a novel radiation synovectomy technique, modelled by a phantom containing a reservoir of I 2 molecules at the interface of which the doped silica dosimeters are located. Measurements outside of the iodine photoelectron range are provided for using a stepped-design that allows insertion of the fibres within the phantom. Monte Carlo simulation (MCNPX) is used for verification. At the phantom medium I 2 -interface additional photoelectron generation is observed, $ 60% above that in the absence of the I 2 , simulations providing agreement to within 3%. Percentage depth doses measured away from the iodine contrast medium reservoir are bounded by published PDDs at 80 kVp and 100 kVp.
Segments of a commercial Ge-doped optical fiber as a thermoluminescent dosimeter in radiotherapy
Radiation Measurements, 2009
Optical fibers have been proposed as dosimeters in both diagnostic and radiotherapy applications. A commercial germanium (Ge)-doped silica fiber with a 50 mm core diameter which showed good thermoluminescence (TL) properties was selected for this study. The radiation sources used were a high dose rate brachytherapy iridium-192, MV photon and MeV electron beams from a linear accelerator. The coating of the fiber was chemically removed and then annealed at 400 C for 1 h prior to irradiation. After irradiation, the fiber was read on a Harshaw Model 3500 TLD reader. The optical fiber had one welldefined glow peak at 327 AE 2 C at all the radiotherapy energies. The dose response was linear within the clinical relevant dose for all these energies. Reproducibility was mainly within 4-6% (one standard deviation) for high energy photons and electrons. The fiber was found to be energy independent within the MV photon energy range. At room temperature the fading up until 1 month was around 6% which was within the 6% uncertainty of the sensitivity calibration of the fiber. Re-using the fiber four times did not significantly alter the sensitivity factor. The optical fiber was found to be dose rate as well as angular independent. Central axis depth dose curves of both 10 MV photons and 12 MeV electrons using the fiber showed relatively good agreement to standard depth dose curves in water within 4%. The Ge-doped fiber is a promising TL dosimeter but improvements have to be made to reduce the reproducibility within 3% for high energy photons and electrons.
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.
2019
Present investigations concern germanium (Ge) doped (2.3 and 6.0 mol%) silica preforms fabricated into cylindricaland flat-shaped fibre radiation dosimeters. When subjected to 150-MeV proton beam irradiation, the fibres are observed to produce sensitive dose response. The fibres are fabricated via a modified chemical vapour dopant deposition technique and subsequent pulling process. Prior to irradiation, a thermal annealing process was carried out to erase any pre-irradiation signals potentially existing in the samples. For radiation dose in the range from 1 up to 10 Gy, these optical fibres exhibit an excellent linear relationship, offering coefficients of determination (R2) better than 0.99, suggesting reliable calibration and utilisation. The general structure of thermoluminescence (TL) glow curve is presented as a broad peak, differing from that of the phosphor-based TLD-100 dosimeter. The maximum in the TL glow curve peak manifests at a temperature within the readout range 231t...
Radioluminescence of Ge-doped silica optical fibre and Al2O3:C dosimeters
Sensors and Actuators A: Physical, 2018
Using an electron accelerator producing a 6 MV X-ray photon beam several experimentally observed excitation phenomena that are associated with radioluminescence (RL) have been investigated, the signal originating from a Ge-doped silica optical fibre and commercial nanoDot Al 2 O 3 :C dosimeters. Using PMMA optical communication fibres the RL signals have been guided from the beam-delivery room out to the readout instrumentation that has been located beyond the concrete maze providing effective radiation shield. Ge-doped silica fibre memory effects and afterglow (phosphorescence) were compared with that of the commercial Al 2 O 3 :C dosimeter. Immediately following RL, observation was made of the decay curves of the afterglow signal of Al 2 O 3 :C. Conversely, there was little practically observable afterglow for the Ge-doped fibre used for the majority of present investigations (the dopant concentration of this being 3.6 wt %). Among three different concentration of Ge-doped fibres that were subsequently investigated in a follow-up study, the intensity of afterglow was found to be greatest for the more highly doped concentration (7.0 wt % Ge), with progressive reduction of the effect for the Ge 4.7 wt % and Ge 3.6 wt % fibres. These observations can be compared against the much more marked RL memory effect observed using the Al 2 O 3 :C chips. Current results point to the Ge-doped silica optical fibre being a highly promising candidate for real-time RL dosimetry and sensing.
IEEE Transactions on Nuclear Science, 2014
One of the main criteria for choosing a thermoluminescent dosimeter (TLD) is its sensitivity to the radiations under investigation. Increasing the heating rate during readout often appears necessary to reduce the time between the measurements and the dose evaluation, especially in routine dosimetry. However, doing this degrades the radiation sensitivity of common dosimeters, as illustrated in this work for the TLD500 dosimeter. It is shown that the germanium-doped optical fiber (GDF) is not only more sensitive to radiation than these COTS dosimeters but, unlike them, its sensitivity is enhanced when the heating rate increases. The physical origin of this rare effect of sensitivity enhancement is probably due to the temperature dependence of the recombination rate by which the detrapped electrons upon stimulation are transferred to the luminescent centers. The effect of light exposure on the dose information stored in both GDF and a commercial TLD is also reported.
Recent Advances in Silica Glass Optical Fiber for Dosimetry Applications
IEEE Photonics Journal, 2020
In this paper, we review the highly promising silica glass, fabricated as doped and undoped optical fiber for intended use in radiation dosimetry. The dosimetry techniques reviewed here, underpinned by intrinsic and extrinsic defects in silica glass, focus on Thermoluminescence (TL), Optically Stimulated Luminescence (OSL) and Radioluminescence (RL), with occasional references to the much more established Radiation Induced Attenuation (RIA). The other focus in this review is on the various materials that have been reported earlier as dopants and modifiers used in silica glass optical fiber radiation dosimeters. This article also elaborates on recently reported optical fiber structures, namely, cylindrical fibers, photonic crystal fibers and flat fibers, as well as dimensions and shapes used for optimization of dosimeter performance. The various types of optical fiber radiation dosimeters are subsequently reviewed for various applications ranging from medical dosimetry such as in external beam radiotherapy, brachytherapy and diagnostic imaging, as well as in industrial processing and space dosimetry covering a dynamic dose range from μGy to kGy. Investigated dosimetric characteristics include reproducibility, fading, dose response, reciprocity between luminescence yield to dose-rate and energy dependence. The review is completed by a brief discussion on limitations and future developments in optical fiber radiation dosimetry.
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,