TL Materials Research Articles

Thermoluminescence Properties of Optical Fibers Doped with RE<sup>+3</sup> (RE=Sm, Nd) Ions Subjected to X-Ray Irradiation

This paper describes the thermoluminescence properties of RE+3(RE=Nd, Sm) doped optical fiber SiO2 prepared by CorActive company in Canada. The samples were exposed to 6 MV X-ray irradiation at dose ranging from 0.5 to 4 Gy at hospital Sultan Ismail, Johor Bahru, Malaysia using the LINAC accelerator. After exposure and a certain delay of 12 h to get uniform control of thermal fading, the optical fiber TL yield was readout using a TL reader. The optical fiber demonstrated a linear TL response versus of the absorbed dose. The linearity increases with the increasing dose while in the case of Sm-doped optical fiber; the response is comparatively smaller than Nd-doped optical fiber. Also, the glow curve of RE+3 ions doped optical fiber is compared with the undoped fibers. The results exhibit that the glow curve peaks are shifted to higher temperature due to rare-earth doping. As the results indicate the TL response strongly depends on the doping type of materials. All these TL characteristics are proposing this commercial optical fiber very decisive TL material.

Production and characterization of spodumene dosimetric pellets by prepared by pechini and proteic sol–gel route

Spodumene is an aluminosilicate that has proven suitable for high-dose TL dosimetry of beta or gamma rays. Due to the presence of lithium in its chemical composition (LiAlSi2O6 – β-LAS), it has potential as neutron dosimeter as well. This silicate may be obtained naturally or synthetically. The synthetic LAS has been produced by solid state reaction and conventional sol–gel, whose difficulty arises from the need to employ high temperatures and high cost reagents, respectively. Alternative routes like Pechini and proteic sol–gel methods are promising, because they can reduce production costs and the possibility of environmental pollution. This work aimed at producing spodumene with the proteic sol–gel method using edible unflavored gelatin as a precursor and also with the Pechini method. The products were characterized physically and morphologically, and their applicability as TL dosimeter was investigated, comparing the sensitivity of samples produced by different methods. Two sets of samples were produced using different sources of silicon, tetraethyl orthosilicate (TEOS, Si(C2H5O)4) and silica (SiO2). The materials produced were characterized by X-ray diffraction and by thermal analysis in order to evaluate their structural properties, as well as possible temperature-dependent changes in physical or chemical properties. The syntherized pellets produced with these crystals were irradiated with a 90Sr–90Y source and their TL glow curves were evaluated. The production of β-LAS was successful by both methods, either using silica or TEOS as a silicon source. The crystals were obtained using much lower temperatures than by methods described in literature. We observed that the method of powder production was critical to develop a radiation detector: the best TL material was the powder produced using silica and the Pechini Method.

Nanostructured layers of anion-defective gamma–alumina – New perspective TL and OSL materials for skin dosimetry. Preliminary results

Thin- layer material based on nanostructured Al2O3 of the surface density 5 mg/cm2 was obtained. The material is characterized by high OSL and TL yields comparable with those for TLD-500 which is one of the leaders among the TL and OSL detectors. The dose response, fading and dependence of TL yield on heating rate was studied. It is established that high luminescence yield of the samples under study correlates with the content of anion vacancies and γ-phase of Al2O3. The data for time-resolved luminescent spectroscopy are presented, which evidence for possible correlation between high TL and OSL activity and the F-type centers. It is noted that the material needs to be modified for successful use in dosimetry. In addition further studies to decrease the contribution of unstable (at 300 К) components to OSL and TL yields are required.

TL emission spectra measurements using a spectrometer coupled to the Risoe TL/OSL reader

A high sensitivity spectrometer (Ocean Optics QE65 Pro) was coupled to the Risoe TL/OSL reader to measure TL emission spectra of four different dosimeters. This spectrometer is based on a Hamamatsu FFT-CCD detector with a 2-D arrangement of pixels (1044×64), which detects luminescence in a range of 200–950 nm. An optical fiber was used to guide the signal from the sample to the spectrometer. TL spectra from LiF, CaSO 4 :Dy, BeO and Al 2 O 3 :C detectors were obtained and they are presented in this work. The proposed detection system showed good response; spectra shape, in accordance with the literature, were obtained, validating the system. • A spectrometer based on a CCD detector was coupled to a TL/OSL reader via optical fiber. • TL emission spectra of well-known TL materials were measured. • The measured spectra showed the expected shapes; thus the system proved a good performance. • The set-up is very easy to use and it shows good potential to study new materials.

Optimization of the performance of segmented scintillators for radiotherapy imaging through novel binning techniques

Thick, segmented crystalline scintillators have shown increasing promise as replacement x-ray converters for the phosphor screens currently used in active matrix flat-panel imagers (AMFPIs) in radiotherapy, by virtue of providing over an order of magnitude improvement in the detective quantum efficiency (DQE). However, element-to-element misalignment in current segmented scintillator prototypes creates a challenge for optimal registration with underlying AMFPI arrays, resulting in degradation of spatial resolution. To overcome this challenge, a methodology involving the use of a relatively high resolution AMFPI array in combination with novel binning techniques is presented. The array, which has a pixel pitch of 0.127 mm, was coupled to prototype segmented scintillators based on BGO, LYSO and CsI:Tl materials, each having a nominal element-to-element pitch of 1.016 mm and thickness of ∼1 cm. The AMFPI systems incorporating these prototypes were characterized at a radiotherapy energy of 6 MV in terms of modulation transfer function, noise power spectrum, DQE, and reconstructed images of a resolution phantom acquired using a cone-beam CT geometry. For each prototype, the application of 8 × 8 pixel binning to achieve a sampling pitch of 1.016 mm was optimized through use of an alignment metric which minimized misregistration and thereby improved spatial resolution. In addition, the application of alternative binning techniques that exclude the collection of signal near septal walls resulted in further significant improvement in spatial resolution for the BGO and LYSO prototypes, though not for the CsI:Tl prototype due to the large amount of optical cross-talk resulting from significant light spread between scintillator elements in that device. The efficacy of these techniques for improving spatial resolution appears to be enhanced for scintillator materials that exhibit mechanical hardness, high density and high refractive index, such as BGO. Moreover, materials that exhibit these properties as well as offer significantly higher light output than BGO, such as CdWO4, should provide the additional benefit of preserving DQE performance.

Thermoluminescence dosimetry: State-of-the-art and frontiers of future research

The state-of-the-art in the use of thermoluminescence for the measurement of energy imparted by ionizing radiation is discussed. Emphasis is on the advantages obtainable by the use of computerized glow curve analysis in (i) quality control, (ii) low dose environmental dosimetry, (iii) medical applications (especially precision) and microdosimetric applications, and (iv) mixed field ionization-density–dosimetry. Possible frontiers of future research are highlighted: (i) vector representation in glow curve analysis, (ii) combined OSL/TL measurements, (iii) detection of sub-ionization electrons, (iv) requirements for new TL materials and (v) theoretical subjects involving kinetic modeling invoking localized/delocalized recombination applied to dose response and track structure theory including creation of defects.

Thermoluminescence of Ge- and Al-Doped SiO2 Optical Fibers Subjected to 0.2–4.0 Gy External Photon Radiotherapeutic Dose

In this work, we studied the thermoluminescence response of Ge- and Al-doped optical fibers, its linearity, energy dependence, and sensitivity. The Ge-doped optical fibers demonstrate useful TL properties and represent an excellent candidate for use in TL dosimetry of ionizing radiation. The TL response increases monotonically over a wide photon dose range, from 0.2 Gy to 4.0 Gy. The TL results for these fibers have been compared with similar TL data for phosphor TLD-100. Commercially available Al- and Ge-doped optical fibers have both been found to yield a linear dose-TL signal relationship, although the Al-doped fiber provides only 5 % of the sensitivity of the Ge-doped fibers. The TL characteristics of Ge-doped optical fiber, plus its small size (125 μm diameter), high flexibility, ease of handling, and low cost compared with other TL materials, make this commercial optical fiber a very promising TL material for use in medicine, industry, reactor operation, and a variety of other areas.

Electron absorbed dose measurements in LINACs by thermoluminescent dosimeters

In this work, electron absorbed doses measurements in radiation therapy (RT) were obtained. Radiation measurements were made using thermoluminescent dosimeters of calcium sulfate doped with dysprosium (CaSO4:Dy) and zirconium oxide (ZrO2). TL response calibration was obtained by irradiating TLDs and a Farmer cylindrical ionization chamber PTW 30013 at the same time. Each TL material showed a typical glow curve according to each material. Both calcium sulfate doped with dysprosium and zirconium oxide exhibited better light intensity to high energy electron beam compared with lithium fluoride. TL response as a function of absorbed dose was analyzed. TL response as a function of high energy electron beam was also studied.

Thermoluminescent sensitivity of single clad neodymium doped SiO2 optical fibres measured with 6 MeV photons

This study investigates the thermoluminescent sensitivity of neodymium doped SiO2 optical fibre with various dose ranges from 0.5Gy to 4.0Gy by 6MeV photon irradiations. The TL responses of the neodymium doped silica fibres are compared with available TLD-100 dosimeter in order to determine the suitability as a TL material. We found that the TLD-100 and neodymium doped silica fibre have a significant linear signal to dose relationship. Neodymium doped fibres sensitivity is approximately 11% of TLD-100.

Thermoluminescence in medical dosimetry

Thermoluminescence dosimetry (TLD) is applied worldwide for personal and medical dosimetry. TLD method has resulted in many interesting findings in medicine as TL dosimeters have many relevant advantages such as high sensitivity, small physical size, tissue equivalence, etc. The main characteristics of various TL materials used in radiation measurements and their practical consequences are overviewed: well defined TL glow curve, batch homogeneity, signal stability after irradiation, precision and accuracy, response with dose, and influence of energy. In this paper a brief summary of the advances in the application of thermally stimulated luminescence (TSL) to dosimetry in radiation therapy application is presented.

Comparison of thermoluminescence energy response of optical fiber subject to photon irradiation between Monte Carlo simulation and experiments

This study is focused on energy response of Ge-doped silicon dioxide optical fiber subjected to photon irradiation. The TL responses for photon energies, ranging from 20 keV to 20MeV, were investigated as energy absorbed in the TL materials of Ge-doped silicon dioxide optical fiber. The simulation was performed using Monte Carlo N-particle transport code version 5 (MCNP5). The input parameters included in this study are source information, geometry specification, material information and tallies F6. Comparisons of energy response were done between simulation and previous results of experiments. A flat response can only be seen in the energy range of 200 keV to 10 MeV.

Results from an investigation of the physical origins of nonproportionality in CsI(Tl)

Abstract The relative scintillation response per energy deposited by Compton electrons, or nonproportionality, has traditionally been considered an intrinsic scintillator property. However, such an interpretation is inconsistent with recent results that show nonproportionality to depend on external factors such as shaping time, temperature and supplier. Apparently, at least some of the overall nonproportionality has an extrinsic origin. In this work we describe the results from a suite of measurements designed to test the hypothesis that nonproportionality in CsI(Tl) material has an extrinsic component that correlates with impurity levels. Our choice of material was motivated by the excellent energy resolution observed in one bulk crystal (6.4%)—a marked departure from that measured with conventional CsI(Tl) stock (8–8.5%). Six bulk CsI(Tl) crystals were procured and diced into 44 wafers. Using X-ray fluorescence techniques no conclusive evidence for impurities was found in any of the wafers at the 1–50 ppm level. One crystal exhibited a distinct correlation among energy resolution, decay lifetimes, nonproportionality and a very low level of Tl doping.

Electron irradiation response on Ge and Al-doped SiO 2 optical fibres

This paper describes the thermoluminescence response, sensitivity, stability and reproducibility of SiO 2 optical fibres with various electron energies and doses. The TL materials that comprise Al- and Ge-doped silica fibres were used in this experiment. The TL results are compared with those of the commercially available TLD-100. The doped SiO 2 optical fibres and TLD-100 are placed in a solid phantom and irradiated with 6, 9 and 12 MeV electron beams at doses ranging from 0.2 to 4.0 Gy using the LINAC at Hospital Sultan Ismail, Johor Bahru, Malaysia. It was found that the commercially available Al- and Ge-doped optical fibres have a linear dose–TL signal relationship. The intensity of TL response of Ge-doped fibre is markedly greater than that of the Al-doped fibre.

Influence of dopants on the glow curve structure and energy dependence of LiF:Mg,Cu,Si detectors

LiF thermoluminescent material doped with Mg, Cu and Si recently developed by the Korea Atomic Energy Research Institute (KAERI) has shown very good dosimetric properties. Since the thermoluminescence in LiF was found to be dependent on the proper combination of dopants, the investigation of the concentration and type of dopants is very important in developing and characterisation of new TL materials. The aim of this work was to determine the influence of type and concentration of activators on the glow curve structure, sensitivity, reproducibility and on the photon energy response of LiF:Mg, Cu, Si detectors. The energy response was studied in air and on the ISO water phantom in the range of mean photon energies between 33 keV and 164 keV. The morphology and local chemical composition of LiF:Mg, Cu, Si detectors were examined using high resolution scanning electron microscopy (FE-SEM). The results show that type and concentration of activators influence the glow curve and sensitivity. Different dopant concentrations did not show influence on the photon energy response. The sensitivity of LiF:Mg, Cu, Si detector with dopant concentration of Mg=0.35 mol%, Cu=0.025 mol% and Si=0.9 mol% was very high (up to 65 times higher than that of TLD-100). The photon energy response of LiF:Mg, Cu, Si detectors containing all three dopants in various concentrations is in accordance with the IAEA recommendations for individual monitoring.

Thermal quenching of thermoluminescence in TLD-200, TLD-300 and TLD-400 after β-irradiation

The dosimetric characteristics of many TL materials are influenced by changes in location, size and shape of the glow curves due to changes in the heating rate. In this study, the effect of heating rate on the integrated peak areas of CaF 2:Dy (TLD-200), CaF 2:Tm (TLD-300) and CaF 2:Mn (TLD-400) crystals have been investigated after β-irradiation. It was observed that the peak temperatures of all peaks shifted to the high temperature sides and the integrated peak areas decrease as the heating rate increases due to thermal quenching, whose efficiency increases as temperature increases.

A study on thermal degradation of LiF:Mg,Cu,P and LiF:Mg,Cu,Si

Abstract We investigated the thermal degradation of LiF:Mg,Cu,P (NTL-250) and LiF:Mg,Cu,Si (MCS) for the development of TL sheet. By thermogravimetry and differential scanning calorimetry (TG-DSC), the exothermic reaction was observed between 320 °C and 400 °C in MCS as well as NTL-250. The heat value of MCS was twice as large as that of NTL-250. This ratio corresponded with that of Mg amount in these TL materials measured by ICP-OES (inductively-coupled plasma optical emission spectrometry). X-ray diffraction (XRD) measurements were also carried out, and the peaks of MgF 2 phase were also observed in degraded MCS sample as well as NTL-250. Moreover, X-ray absorption near-edge structures (XANES) of Cu in these LiF TLDs were measured. The valences of Cu did not change before and after degradation. It indicates that the thermal degradation is caused by not Cu but Mg ion state change. The exothermic reaction is possible caused by the stabilization reactions, and then it was expected to correspond with MgF 2 precipitation. From these results, we concluded that the thermal degradations of these LiF TLDs are caused by the precipitation of MgF 2 .

TL tandem systems for the determination of effective energy in X radiation beams

Tandem systems usually comprise two detectors with different radiation energy responses and are utilized to determine the effective energy of unknown radiation beams. The aim of this paper was to evaluate the influence of absorbed dose on tandem curves obtained for different TL materials. In the studied dose interval, the results demonstrate that there is no significant influence of dose on the tandem curves. Therefore, the reliability of these systems for the determination of radiation beam effective energy was confirmed.

Thermoluminescent dosimetry (TLD) for megavoltage electron beam energy determination

Megavoltage electron beams are used in many institutions for the treatment of superficial malignant diseases. Accurate dosimetry of electron beams is a fundamental requirement for patient safety. To ensure this, national and international regulatory bodies conduct electron dosimetry audits utilising thermoluminescent dosimeters such as LiF:Mg, Ti (TLD100). TLD100 has been shown to exhibit energy dependence which can introduce errors in dosimetry. In this study commercially available TL materials have been used for a practical method developed to ascertain electron beam energy. This method could be applied in these dosimetry audits to reduce inaccuracies due to energy dependence of TLD100.

Response of TL materials to diagnostic radiology X radiation beams

The main objective of this study was to carry out a direct performance comparison among some known types of TLDs-three types of CaSO(4):Dy pellets, sintered Al(2)O(3) pellets, LiF:Mg,Ti (Harshaw TLD-100), CaF(2):Dy (Harshaw TLD-200) and CaF(2):Mn (Harshaw TLD-400)-in the energy and dose ranges of diagnostic radiology beams. Several dosimetric characteristics were evaluated, such as reproducibility, sensitivity, calibration curves, lower dose limits and energy dependence.

Effect of dopants on TL characteristics of LiF:Mg,Cu,P detectors

Abstract LiF:Mg,Cu,P detectors produced at the Institute of Nuclear Physics in Krakow have shown very good dosimetric characteristics. Understanding of the effect of the concentration and type of dopants is important in the characterization of TL materials. The aim of work was to investigate the influence of the type and concentration of the dopants on the photon energy response of these detectors by irradiations “in air” and on the ISO water phantom in the range of mean photon energies between 33 and 164 keV. The influence of dopants on the glow curves, sensitivity and reproducibility was also examined. Results showed that measured energy dependence values are lower compared to the theoretical values both “in air” and on phantom. The type and concentration of the dopants influence the shape of the glow curves and sensitivity while for energy dependence is more important the presence of certain activators, namely copper.