Sub kGy photon irradiation alterations in graphite

Present work concerns polymer pencil-lead graphite (PPLG) and the potential use of these in elucidating irradiation-driven structural alterations. The study provides detailed analysis of radiation-induced structural interaction changes and the associated luminescence that originates from the energy absorption. Thermally stimulated emission from the different occupied defect energy levels reflects the received radiation dose, different for the different diameter PPLGs. The PPLG samples have been exposed to photon irradiation, specifically x-ray doses ranging from 1 to 10 Gy, extended to 30–200 Gy through use of a60Co gamma-ray source. Trapping parameters such as order of kinetics, activation energy and frequency factor are estimated using Chen's peak-shape method for a fixed-dose of 30 Gy. X-ray diffractometry was used to characterize the crystal structure of the PPLG, the aim being to identify the degree of structural order, atomic spacing and lattice constants of the various irradiated PPLG samples. The mean atomic spacing and degree of structural order for the different diameter PPLG are found to be 0.3332 nm and 26.6° respectively. Photoluminescence spectra from PPLG arising from diode laser excitation at 532 nm consist of two adjacent peaks, 602 nm (absorption) and 1074 nm (emission), with mean energy band gap values within the range 1.113–1.133 eV

Tailored Ge-doped fibres for passive electron radiotherapy dosimetry

Study has been made of the thermoluminescence yield of various novel tailor-made silica fibres, 6 and 8 mol % Ge-doped, with four differing outer dimensions, comprised of flat and cylindrical shapes, subjected to electron irradiation. Main thermoluminescence dosimetric characteristics have been investigated, including the glow curve, dose response, energy dependence, minimum detectable dose, effective atomic number, linearity of index and sensitivity of the fibres. The studies have also established the uncertainties involved as well as the stability of response in terms of fading effect, reproducibility and annealing. In addition, dose-rate dependence was accounted for as this has the potential to be a significant factor in radiotherapy applications. The 6 and 8 mol % fibres have been found to provide highly linear dose response within the range 1 to 4 Gy, the smallest size flat fibre, 6 mol% Ge-doped, showing the greatest response by a factor of 1.1 with respect to the highly popular LiF phosphor-based medium TLD100. All of the fibres also showed excellent reproducibility with a standard deviation of < 2% and < 4% for 6 and 8 mol % Ge-doped fibres respectively. For fading evaluation, the smallest 6 mol% Ge-doped dimension flat fibre, i.e., 85 × 270 μm displayed the lowest signal loss within 120 days post-irradiation, at around 26.9% also showing a response superior to that of all of the other fibres. Moreover, all the fibres and TLD-100 chips showed independence with respect to electron irradiation energy and dose-rate. Compared with the 8 mol% Ge-doped optical fibres, the 6 mol% Ge-doped flat optical fibres have been demonstrated to possess more desirable performance features for passive dosimetry, serving as a suitable alternative to TLD-100 for medical irradiation treatment applications

Burn-up calculation of the neutronic and safety parameters of thorium-uranium mixed oxide fuel cycle in a Westinghouse small modular reactor

Thorium fuel is presently a globally known future nuclear fuel alternative, having good neutronic, physical and chemical properties in addition to its spent nuclear fuel characteristic proliferation resistance. This research focused on the neutronic and safety parameters of thorium‐uranium mixed oxide fuel cycle, utilising three fissile enrichment zones, a departure from the conventional single enrichment. The aim was to determine the range of three fissile zones adequate for thorium‐uranium fuel cycle; investigating the performance efficiency of the fuel neutronic and inherent safety parameters in response to temperature differentials, which determines the viability of the fuel and core composition. Use was made of the MCNPX 2.7 code integrated with the CINDER90 fuel depletion code for steady‐state and burn‐up calculations. The keff, moderator temperature coefficient (MTC) and fuel temperature coefficient (FTC) of reactivity are affected by the range of fissile enrichment and fuel temperature which decreased with their respective increases. The MTC for all the moderator temperatures was within 0 to −40 pcm/K design value for UO2 fuel. Similarly, the FTC was within −3.5 to −1 pcm/K design value for all the fuel temperatures except after 2000 days, where a positive reactivity feedback was introduced. At ~86 MWd/kgHM single discharge burn‐up, the result shows that ~90% of the initial fissile load was utilised for energy production at the normal reactor operating temperature (600 K) with a slight reduction at higher fuel temperature. The total fissile inventory ratio (FIR), 233U/kg‐232Th and 239Pu/kg‐238U inventory ratios were significantly large and increased with burn‐up. It is remarkable that the FIR and the 233U/kg‐232Th inventory ratio did not reach conversion equilibrium until exit burn‐up. The large percentage fuel utilisation supports the advantage of fissile enrichment zoning in a thermal nuclear reactor core, making the chosen novel three fissile enrichment zones for thorium‐uranium fuel cycle reliable

Investigation of silica-based TL media for diagnostic x-ray dosimetry

We focus on the development of Ge-doped silica thermoluminescent dosimeters with sensitivity superior to that of the LiF (Mg,Ti) phosphors popularly used in x-ray diagnostic imaging dosimetry, typically in the form of the product TLD-100. Of interest are Ge-doped silica telecommunication fibres (SMF) and tailor-made doped photonic crystal fibres (PCFc), the latter Ge-doped or also co-doped with boron. The PCFs are formed of capillaries that at high temperatures and under vacuum are made to collapse inwards (PCFc), the internal walls fusing and generating strain-related defects. To-date, the fabricated PCFc-Ge-B, PCFc-Ge and (SMF) have been observed to provide TL yields which weight-for-weight are some 15, 10 and 2 × that of TLD-100. In present study we test the linearity of TL yield for x-ray doses from 0.1- to 10 mGy, use being made of an x-ray tube operated at 80 kVp, a value typically selected in chest radiography. For a dose of 10 mGy, a study of energy dependence has been conducted using x-ray tube potentials of 80 kVp 100 kVp, and 120 kVp, with inherent filtration 0.9 mm Al measured at 75 kVp, and total filtration of 2.8 mm Al at 80 kVp

Latest developments in silica-based thermoluminescence spectrometry and dosimetry

Using irradiated doped-silica preforms from which fibres for thermoluminescence dosimetry applications can be fabricated we have carried out a range of luminescence studies, the TL yield of the fibre systems offering many advantages over conventional passive dosimetry types. In this paper we investigate such media, showing emission spectra for irradiated preforms and the TL response of glass beads following irradiation to an Am-241-Be neutron source located in a tank of water, the glass fibres and beads offering the advantage of being able to be placed directly into liquid. The outcomes from these and other lines of research are intended to inform development of doped silica radiation dosimeters of versatile utility, extending from environmental evaluations through to clinical and industrial applications. (C) 2015 Elsevier Ltd. All rights reserve

Dosimetric evaluation of gold nanoparticle aided intraoperative radiotherapy with the Intrabeam system using Monte Carlo simulations

Radiosensitization using high atomic number nanoparticles (NPs) has been shown to be an effective method to enhance radiotherapy efficiency. The pathways by which NPs cause sensitization, are generally categorized as physical, chemical and biological effects. Specifically in the case of keV photon radiotherapy where the contribution of physical effects in radiosensitization mechanism is considerable, Monte Carlo (MC) simulations have been an efficient tool to predict the radioenhancement level and to calculate dose enhancement factor (DEF). To-date, several analytical, simulational and experimental studies have reported the radiosensitization effect of gold nanoparticles (GNPs) in various brachytherapy situations. In this work we report for the first time, the DEFs achievable in intraoperative radiotherapy through use of the Intrabeam system and its spherical applicators with addition of GNPs. The MCNPX Monte Carlo code was used for radiation transport and dose calculations. The results of macroscopic and microscopic analysis show that for the Intrabeam system and a homogeneous distribution of 50 nm diameter GNPs, respective DEFs of up to some 1.5, 2, 2.5 and 3 in the tumour bed can be achieved with 5, 10, 15 and 20 mg/g concentrations. Due to rapid change in electron spectra, DEFs greater than 1 mm separation from the applicator surface decrease with distance, offering an additional advantage

Micro-PIXE analysis of doped SiO2 fibres intended as TL dosimeters for radiation measurements

Sample elemental concentrations can be determined using the microbeam proton-induced X-ray emission (PIXE) technique, providing non-destructive simultaneous low-background multi-element analysis. Present interest concerns analysis of Ge-doped SiO2 fibres intended as high spatial-resolution thermoluminescence (TL) dosimeters for radiation measurements in place of their more typical applications in telecommunications. During fibres fabrication, defined amounts of the Ge dopant are added, the dopant more usually having a determining role in the transmission properties of the fibre. Characteristic X-rays produced in PIXE analysis provide information on the relative distribution of elements within a sample, as in for instance Ge and Si concentrations, the Ge acting as point defect centres that promote TL. With the dopant tending to diffuse in and away from the fibre core, it is essential to define the sample matrix composition in order to accurately evaluate the X-ray yield. This is determined in part using simultaneous Rutherford Back Scattering analysis. In present work, PIXE/Rutherford Back Scattering measurements have been employed to ascertain dopant concentrations of fibres that have been fabricated at the University of Malaya with a view to improving TL yield. Present results concern cylindrical fibres, nominally with 4, 6 and 8 weight peak Ge concentrations and flat fibres of nominal 6 weight Ge concentration. For the cylindrical fibres, Ge dopant concentration has been found to be in the range of 2.41-4.56, 6.44-8.29 and 10.27-12.25 weight, respectively, while for the flat fibres, the Ge concentration range is broader, at 0.07-6.55 weight. Copyright (c) 2014 John Wiley & Sons, Ltd

Feasibility study of a minibeam collimator design for a 60Co gamma irradiator

Recently much attention has been paid to microbeam and minibeam irradiations, present interest focusing on their use in study of the behaviour of single cells, groups of cells, also their application in spatially fractionated radiotherapy. Synchrotrons are the most common source for microbeam radiotherapy (MRT), albeit limited in access and typically offering photon energies very much lower than familiar in the practice of conventional radiotherapy. In this study of feasibility, the design has been investigated of a collimator coupled to a conventional 60Co gamma-irradiator sample chamber to produce a minibeam. MCNPX code Monte Carlo simulations were used to model a Gammacell 220 60Co irradiator with lead and tungsten collimators. The dose profile was evaluated in the absence and presence of the collimator, seeking to optimize collimator design. The results pertain to specific shapes of lead and tungsten collimators producing narrow (millimeter dimension) beams, sufficient in thickness but yet still fitting within the sample chamber, with a peak-to-valley dose ratio (PVDR) greater than 15. The beam size can be tailored with modification in the size of the perforated part, the collimator optimized to minimize the dose-rate at points away from the collimator centre. However the dose-rate at the centre is reduced to between 2 to 20% of that in the absence of collimator. The findings of this study encourage the development of minibeam collimator for gamma irradiators, useful for preclinical minibeam radiotherapy research in centres with little or no access to other appropriate sources

Measurement of photoelectron generation in a gold coated glass slide

In thin low-Z media irradiated by photon energies of several tens of keV, the presence of a high-Z additive can result in manifest locally modified secondary electron dose. Present study analyses the photoelectron dose enhancement resulting from nanometre thickness gold (atomic number Z = 78) coated on commercial borosilicate (B2O3) glass microscope cover-slips. Two thicknesses of B2O3 cover-slip have been utilized, 0.13 ± 0.02 mm and 1.00 ± 0.01 mm, with single-sided Au coatings of 20, 40, 60, 80 and 100 nm. An additional uncoated glass slide has been kept as a comparator. The samples have been exposed to X-rays generated at kVp potentials, delivering a fixed dose of 2 Gy. Dose enhancement resulting from the 1.00 mm glass has been observed to be ~1.32 × that of the 0.13 mm thickness glass. The elemental composition of the samples has been obtained via Electron Dispersive X-ray (EDX), elemental content differences between the two thicknesses of glass leading to a difference in effective atomic number of less than 0.3%. The influence on photon yield of the gold coating and variations in elemental content has been modelled using Monte Carlo simulation, allowing comparison with the measured values of enhanced TL yield

Advanced glow curve analysis of fabricated fibres for various sources of ionizing radiation

Determination is made of glow curves attributes of Ge-doped silica fibres fabricated from Ge-doped preforms. In particular interest is in Ge-doped cylindrical (Ge-CF) and Ge-doped flat (Ge-FF). The fabrications are irradiated using various ionizing radiation sources types, protons (150 MeV, 210 MeV), 6 and 10 MV photons, 6 MeV electrons, and 60Co gammas (mean energy 1.25 MeV), all at a constant dose of 5 Gy. The fibres have been fabricated using the MCVD technique, notably with a Ge-CF having a larger core compared to the commercial cylindrical fibres (CF). Using WinGCF software the glow curves have been deconvolved, revealing five contributory glow peaks, evaluation being made of three kinetic parameters: maximum temperature (Tmax), activation energy (Ea) and peak integral (PI). Ge-CF Ea and PI values are found to be greater than those for Ge-FF. Moreover, for Ge-CF, the activation energy for electromagnetic irradiation (gamma photons) achieves a maximum reading at peak number 3 while its PI is found to be the least. The PI for photon irradiation is shown to be greater than that for electron and proton irradiation. For Ge-FF, Ea again achieves its greatest value at peak 3, the PI being maximum at peak 2 and least at peak 3. Particle irradiations are more greatly associated with deeper trapping levels. Additionally, the overall conclusion is that Ge-CF offers superior TL yield to that of Ge-FF. One-way analysis of variance (ANOVA) for the individual peaks shows there to be significant differences in terms of PI and Ea, p < 0.05 for all types of radiation, but weakly significant in terms of Tmax for both types of fibres (p < 0.05), mostly for proton and photon irradiation