TL Output Research Articles

Graphite as a Skin and Epithelium Dosimeter at mammographic energies

Use is made of 50 μm high purity graphite foils, investigating the potential of these in evaluation of dose in dermal and epithelial layers, measuring the thermoluminescence yield obtained as a result of irradiation at mammographic energies. In particular the effort supports the ICRU recommendation that skin dose be assessed at a skin depth 0.07 mm, equating to the uniquely mitotically active dermal layer responsible for the replenishment of skin cells. Support for the results of empirical investigation have been sought from Monte Carlo simulations using the TOPAS code. In study of x-rays generated in the 25- to 30 kVp range, the energetic electrons produced in interaction with the graphite have an approximate range of ∼7 μm, so that with a stacked graphite layer arrangement dose assessment is provided at 7 μm, 57 μm, 107 μm etc. TL yield results for the first three layers of graphite, covering nominal depths from the surface through to 150 μm, obtained on a 50 μm spatial resolution scale, show deposited dose values to be approximately flat to within ±5% throughout this depth. The indication is that for irradiations made using x-ray energies of a few tens of keV use of the present graphite layer arrangement can provide estimation of dermal and epithelial dose.

Non-monotonic dose dependence of thermoluminescence in spatially correlated systems

TL dose dependences were simulated following the semi-localized transitions (SLT) model and the model with cluster defects which contain TL-active electron traps, luminescence centers and deep hole traps. Monte-Carlo method was used to calculate cluster occupancy at the irradiation and relaxation stages. At the heating stage, TL yield was calculated with Monte-Carlo method and with the proposed analytical approach. This approach expressed TL yield via cluster occupancy after relaxation stage. The results showed that non-monotonic dose dependence emerges in both models when the excited level of TL-active trap is deep enough. The reported effect was demonstrated to be directly related to intracluster non-radiative recombination of electron at the excited level of the trap and hole in the luminescence center. The intracluster competition between hole centers makes dose response less non-monotonic. When the heating rate decreases, TL yield at high doses drops and TL dose dependence becomes more non-monotonic.

Modeling of thermoluminescence in SrY2O4:Eu3+and their concentration quenching effect

In this work, we present mathematical models which describe the thermoluminescence process of SrY2O4 and their concentration quenching by europium (Eu3+) ions; experimental data used here have been previously published by V. Dubey et al. They studied the TL glow curve of Eu3+ doped SrY2O4 under UV exposure. In the first step of this study, the set of trapping parameters were evaluated using the general glow curve deconvolution program (GCD). These parameters are used to run the main program of the proposed models. The two electron traps-one-recombination center (2T1R) has been used to explain the TL output behavior in SrY2O4:Eu3+. Thermoluminescence intensity dependence on the excitation dose have been simulated for dose ranging from 1 × 105 cm−3 to 1 × 106 cm−3. An excellent linearity has been observed. The concentration quenching effect of TL in SrY2O4 by increasing of Eu3+ ions concentration will be studied by the same model (3T1R) proposed and published by R. Chen et al. Numerical results obtained here show a good agreement with the previously published paper for the SrY2O4 single crystal doped Eu3+ ions.

Structure, and opto-dielectric investigations of Cu2+ -doped calcium bismuth silicate glass ceramics

CuO inclusive silicate glasses are well known for various semiconductor applications. However, there is a lot of demand and necessity of high efficient opto-dielectric materials. In view of this, the glasses of chemical composition (30 – x) CaO + (10) Bi2O3 + (60) SiO2 + (x) CuO have been synthesized and studied for their structural, optical and dielectric characterization techniques. Glassy behaviour of CuO undoped glass and ceramic behaviour of all other CuO doped glasses conformed by structural characterization. The elastic modulus and micro hardness of glass and glass ceramics reveal their inter connected covalent structure. Trap depth parameters (Tm, Eτ, Eδ, Eω & μs) have been determined and analysed under irradiation, and found that 0.3 mol% CuO -doped glass ceramic under 30 kGy of irradiation dose exhibiting better TL output. Dielectric relaxation studies of the glass ceramics suggested that mixed conduction of both ionic and electronic. Observed dielectric results; dielectric constant (εr), dielectric loss (tanφ), temperature region of relaxation (ΔT), low activation energie's for conduction (Ea) and AC Conductivity (σac) suggesting that the glass ceramics are dielectric. Optical band gap (Eo), transition probability (At) and emission cross section (σ) corresponding to the emissive transition 3D1 → 1S0 assessed by optical techniques. All the results suggests that 0.3 mol% CuO -doped glass ceramic is a useful opto-dielectric resource.

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.

Luminescence properties of natural dead sea salt pellet dosimetry upon thermal stimulation

In the event of a radiological accident or attack, immediate need arises for reliable estimation of dose to the population from an affected environment. This would contribute to proper medical treatment and any need for isolation of affected areas. As such, it is important to improve dosimetry assessment through use of locally available materials, the latter acting as accident/prospective dosimeters. Present investigation has examined the TL properties of natural salt collected in Jordan, from the Dead Sea, and exposed using 60Co gamma radiation. Entrance doses ranging from 2 to 10 Gy have been delivered, providing desirable luminescence features. Natural Dead Sea NaCl are produced in cylindrical pellet form, achieved with 0.1 and 0.3 cm thickness sized from the salt grains obtained by a compression force of 5.0 ± 0.1 tonnes. With these NaCl pellets, linear dose response has been achieved, producing strong TL yield for a 0.1 cm thick layer, exceeding that of 0.3 cm thickness by a factor of 3. The shape of the glow curves was found to be independent of delivered dose, the main TL dosimetric peak remaining within the range 180 °C to 280 °C and 300 °C to 400 °C for the 0.1- and 0.3 cm NaCl pellets respectively. Computerised glow curve deconvolution was carried out, comprising of ten peaks, with associated activation energies and frequency factors. TL response per unit mass of NaCl pellets for both thicknesses were found to be energy dependent, predominating in yield at 60 keV. Over a period of 35 days the 0.3 cm NaCl pellet showed the least effect of fading, with loss of TL signals of 56% compared to an 81% loss for the 0.1 cm pellet. It is also noted that the combination of low activation energy and high frequency factors for the electrons to escape a trap for the 0.1 cm NaCl pellet samples subjected to 2 Gy gamma irradiation resulted in a highly substantial loss of TL signal over the first 7 days in comparison to the 0.3 cm NaCl pellet. Both samples thicknesses were unable to produce reproducible TL responses for the second and greater use. It has also been found that in addition to particle size, moisture and pre-irradiation annealing influence the TL properties. The excellent TL properties achieved by 0.1 cm NaCl pellets indicate their potential use as an accident/prospective dosimeter.

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.

Simulation of thermoluminescence dose response in cluster systems with deep traps

The TL dose response was simulated within the framework of a kinetic model with cluster defects which contain electron TL-active traps and deep traps. It was shown that superlinearity of the TL dose dependence arises due to the temperature-dependent competition between the intracluster capture of electrons by deep traps and their thermal release into the conduction band. The regularities of the influence of the main parameters of the model (heating rate, activation energies of the ground and excited levels of TL-active traps) on the TL yield and nonlinearity of the dose dependence were found.

Influence of carbon doping on the thermoluminescence properties of LaAlO&lt;SUB align="right"&gt;3 crystal grown by solid state reaction method

In this paper, we report a modelling investigation of the thermoluminescence mechanisms for the important dosimetric LaAlO3:C crystals, which were grown by solid state reaction method. The aim of this work is to develop for the first time an algorithm that permits the numerical solution of the relevant sets of differential equations governing the different stages of the experimental procedure. The glow curve measured at 10K/s typically consists of three prominent peaks at 417 K, 494 K and 549 K and a minor glow peak at around 372 K. In this work, we show that this TL output behaviour can rather easily be explained within the framework of the 4T1R model. Good agreement between the experimental data and calculations from the model is obtained for this kind of dosimetric material. Results presented here confirm that the LaAlO3:C system an excellent candidate that can be used as a TL dosimeter in UV fields.

Influence of carbon doping on the thermoluminescence properties of LaAlO&lt;SUB align="right"&gt;3 crystal grown by solid state reaction method

In this paper, we report a modelling investigation of the thermoluminescence mechanisms for the important dosimetric LaAlO3:C crystals, which were grown by solid state reaction method. The aim of this work is to develop for the first time an algorithm that permits the numerical solution of the relevant sets of differential equations governing the different stages of the experimental procedure. The glow curve measured at 10K/s typically consists of three prominent peaks at 417 K, 494 K and 549 K and a minor glow peak at around 372 K. In this work, we show that this TL output behaviour can rather easily be explained within the framework of the 4T1R model. Good agreement between the experimental data and calculations from the model is obtained for this kind of dosimetric material. Results presented here confirm that the LaAlO3:C system an excellent candidate that can be used as a TL dosimeter in UV fields.

Comparison of Thermoluminescence Dosimeter’s Response to Neutron and Gamma in a Mixed Radiation Field

Measuring radiation dose in a mixed radiation field cannot be performed by using only one dosimeter, but a pair of dosimeters TLD600 and TLD700 can be successfully used to estimate that radiation dose. Therefore, in the present study, the response of TLD600 and TLD700 to neutron/gamma mixed radiation field was deeply discussed. Moreover, the sensitivity and stability of TLD600 and TLD700 were studied. A strong correlation between TL output signal intensity of TLD700 to gamma dose was appeared, with a linear coefficient of R2 = 0.99. Likewise, a strong correlation between TL output signal intensity of TLD600 to gamma dose and neutron irradiation was also appeared, with a linear coefficient of R2 = 0.99. Thus, TLD700 can be applied to measure gamma dose with good sensitivity, while TLD600 can be applied to measure both gamma and neutron dose. Hence, a combination of TLD700 and TLD600 can be successfully employed to assess the radiation doses characterizing a mixed radiation field of neutron and gamma rays.

The peculiarities of anion vacancy distribution and the relationship between their concentration and the Tld-500 detector Tl output

A procedure has been developed for estimating the uniformity of anion vacancy distribution in TLD-500 detectors on the basis of anion-deficient corundum single crystals. Vacancy distribution topograms were constructed for TLD-500 detectors with different sensitivities to irradiation. Analysis of the topograms provided correlations between average anion vacancy concentrations and thermoluminescent (TL) yields in the main peak with a maximum at 450 K. To confirm the pattern of regularities, the effects of high-temperature annealing of TLD-500 samples in air at T = 1700 K were studied depending on its duration. Increasing the annealing time from 40 to 105 minutes was found to correlatedly reduce the anion vacancy concentrations and TL-yields in the basic and high-temperature peaks at 450 and 830 K, respectively.

Pulse cathodo- and thermoluminescence of alumina ceramic with manganese

Alumina ceramics with manganese in concentration range 0.001-18 wt. % are synthesized. Luminescent properties of obtained ceramics at temperatures 1500-1700°C of sintering in vacuum are investigated. An increase in the manganese concentration leads to quenching of the pulse cathodoluminescence band at 420 nm and the main dosimetric peak at 460 K. The intensity of luminescence in the 676 nm band at manganese concentrations of more than 1 wt. % and the TL yield for all the observed peaks increase when annealing temperature rises. Sublinear increase in TL intensity with a growing dose is observed in the range of 3-1000 Gy in 460 and 620 K peaks.

Thermoluminescent response of beta-irradiated silica beads

Research into the potential for silica based materials as TLDs continues to increase, harnessing the various advantages that the materials have to offer as a dosimeter, including; affordability, chemical inertness, geometry and size, while producing suitable TL yields. Studies into the possibility of beta source dosimetry open another range of applications for this type of dosimeter, including procedures involving the possibility of in vivo dosimetry (Morino et al., 2002). This work aims to further investigate the properties of a much-studied batch of Mill Hill silica beads of various colours, irradiated with a Sr90/Y90 source yielding a dose rate of 0.02 Gy/s, activity 37 MBq and maximum energy of 2.27 MeV, facilitated by the Risø TL/OSL reader. The TL yield is compared to that in previous work, with the same set of beads irradiated by a 6 MV photon beam provided by a Varian electron linac (Varian Medical Systems, Palo Alto, CA) X-ray source, delivering a dose of 10 Gy. Present study shows a decrease in the mass normalised TL yield from X-ray to beta source by a factor of 10, assumed to be accounted for by the estimated mean penetration depth of the beta particles in the doped silica beads. Investigating the potential for doped silica beads to be used as a beta source dosimeter a linearity study is reported with a dose range of 5–20 Gy. The studies show that all coloured beads except green show a strong conformity to a linear fit of the data over the tested range of doses. Fading studies conducted with clear petite beads (producing the greatest TL yield/mg) for doses of 5 Gy and 20 Gy have shown that the majority of fading occurs within the first hour following irradiation, with a plateau in the fading to approximately 17% and 22% loss of signal for 5 Gy and 20 Gy respectively in the interval of 24–70 h after irradiation. The decay of the TL yield/mg was fitted to a logarithmic trend of reduction for both the 5 Gy and 20 Gy irradiation, with R2 values of 0.9883 and 0.9705 respectively.

Doped silica fibre thermoluminescence measurements of radiation dose in the use of 223Ra

Using tailor-made sub-mm dimension doped-silica fibres, thermoluminescent dosimetric studies have been performed for α-emitting sources of 223RaCl2 (the basis of the Bayer Healthcare product Xofigo®). The use of 223RaCl2 in the palliative treatment of bone metastases resulting from late-stage castration-resistant prostate cancer focuses on its favourable uptake in metabolically active bone metastases. Such treatment benefits from the high linear energy transfer (LET) and associated short path length (<100µm) of the α-particles emitted by 223Ra and its decay progeny. In seeking to provide for in vitro dosimetry of the α-particles originating from the 223Ra decay series, investigation has been made of the TL yield of various forms of Ge-doped SiO2 fibres, including photonic crystal fibre (PCF) collapsed, PCF uncollapsed, flat and single-mode fibres. Irradiations of the fibres were performed at the UK National Physical Laboratory (NPL). Notable features are the considerable sensitivity of the dosimeters and an effective atomic number Zeff approaching that of bone, the glass fibres offering the added advantage of being able to be placed directly into liquid. The outcome of present research is expected to inform development of doped fibre dosimeters of versatile utility, including for applications as detailed herein.

β-Irradiated thermoluminescence response of nanocrystalline YAGG:Pr3+ for radiation dosimetry

Garnet type Y2.99Al5−xGaxO12:0.01Pr3+ (YAGG:Pr3+) nanocrystals with varying Ga concentration (x=0, 1, 2.5, 4) were synthesized by combustion synthesis. X-ray diffraction revealed highly crystalline structure with an increase in the lattice parameter and distortion of the cubic crystal upon Ga incorporation. XPS results demonstrated the presence of desired compositional elements and the substitution of Ga at the Al site. Thermoluminescence glow curves exhibit complex shapes comprising of four main peaks with a shift in the peak maxima and decreasing sensitivity from x=0–4. Ga incorporation altered the distribution of trap levels enhancing the dose-response behavior of the samples. The reproducibility studies displayed that the nanophosphors are reusable with minimal changes in the TL output. The results indicate the potential of YAGG:Pr3+ for dosimetry applications.

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, the latter typically being referred to through use of the product identifier 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 SMF, PCFc-Ge and PCFc-Ge-B have been observed to provide TL yields which weight-for-weight are some 2, 10 and 15x that of TLD-100. In present study we test the linearity of TL yield for x-ray doses from 0.1- to 10mGy, use being made of an x-ray tube operated at 80 kVp, an operating potential typically selected in chest radiography. For a dose of 10mGy, a study of energy dependence has been conducted using x-ray tube potentials of 80 kVp 100 kVp, and 120 kVp, with inherent filtration 0.9mm Al measured at 75 kVp, and total filtration of 2.8mm Al at 80 kVp.

High-temperature thermoluminescence of anion-deficient corundum and its connection with Ti impurity

Absract Anion-deficient corundum (α-Al2O3-δ) was studied for a possible correlation between the TL yield in the high-temperature peak at 830 K and the contents and transformation of intrinsic defects and impurities. Only 40–60% of TLD-500 detectors based on α-Al2O3-δ were found to have a 830 K TL peak. Increasing the concentration of the titanium impurity from 7·10−4 to 21·10−4 wt% was found to reduce the TL yield in the 830 K peak to an undetectable level. Similar variations of Mg, Si, Ca, Cr and Fe impurity concentrations did not allow us to reveal correlations with the TL yield at 830 K. Nevertheless, the measurements of active center concentrations at step-annealing from 300 to 1400 K suggest that the anion deficiency and related cation interstitials participate, as well as chromium ions, in the formation of the 830 K TL peak. Presumably, UV emission with a maximum at 4.1 eV observed in the 830 K TL peak may be caused by transitions from higher excited states in F+, F or other centers, including impurities and multi-component centers with intrinsic defects.

Trapping parameters determination and modeling of the thermoluminescence process in SiO2-P2O5 vitroceramics doped with different Y2O3 concentrations

The xY2O3∙(60−x)P2O5·40SiO2 vitroceramic compounds exhibited excellent TL output following beta irradiation, especially when doped with high Y2O3 concentrations, as showed in a recent work conducted by Biró et al., 2015. In the first section of this paper, the previous recorded TL glow peaks were further analyzed and their corresponding kinetic parameters such as an order of kinetics (b), trap depth (E) and frequency factor (s) were determined using the Chen’s peak shape method. In the second section, the thermoluminescence characteristics of SiO2-P2O5 doped with different Y2O3 concentrations were simulated using the TTOR (Two traps & one recombination center) model. All calculated TL glow curves were in good agreement with the experimental results.

Composite right/left‐handed transmission lines in use for ultra‐wideband matching of front‐end amplifiers with modified cuckoo search optimization

SummaryIn this work, the broadband capability of composite right/left‐handed transmission lines (CRLH TLs) in the balanced condition is exploited for ultra‐wideband matching of a compact single transistor front‐end amplifier. For this purpose, the LC element values and the number of identical asymmetric CRLH TL cells are taken as optimization variables. The minimum noise and maximum power delivery at each operation frequency of the chosen high technology transistor are considered as the feasible design target provided that the stability of the transistor is ensured. This feasible design target is expressed simply by a single objective function in terms of the port impedances of the input and output matching circuits together with the realization conditions of the CRLH TLs. Thus, human efforts for the design optimization process are reduced as much as possible. A novel metaheuristic algorithm ‘modified cuckoo search’ is used as a fast and accurate tool to find out ‘the global optimum’ within the feasible design variable space in the design procedure. In the study case, BPF640 is chosen as a high performance low‐noise microwave transistor. The design optimization results in a low‐noise amplifier using a single CRLH TL cell input and output matching circuits provided that a good agreement is obtained with the targetted performance and verified by Applied Wave Research, Inc. (AWR) simulation software. Thus, it can be concluded that CRLH TLs enable a designer to design high‐performance miniaturized low‐noise amplifiers. Copyright © 2016 John Wiley &amp; Sons, Ltd.