TL Peak Research Articles

Particle size effects on the dosimetry characteristics of K3Na(SO4)2:Eu TLD micro- and nanophosphors

K3Na(SO4)2:Eu is a highly sensitive TLD material in its microcrystalline form. It has been found that the material in its nanocrystalline form could also be used for very high dose measurements (of the order of 100 kGy) of high-energy radiations, like γ rays. However, it is not known whether the nanoparticle prepared by different methods of preparation, i.e., prepared using chemical coprecipitation method (by bottom up approach) and by ball milling (top down approach) behave in a similar manner. In the present paper, the TLD material was prepared by the standard solid state diffusion method, crushed and sieved/ball milled for different time periods to get particles of different sizes ranging from micro- to nanosize ranges. TL dosimetry characteristics of the material were studied and compared with our earlier results on the nanoparticles prepared by chemical coprecipitation method. It has been found that the K3Na(SO4)2:Eu powder sample in the particle size range 75–106 µm show the highest sensitivity and could be used up to 10 kGy dose of γ radiation. It has also been found that the nanoparticles prepared by two different approaches behave differently, i.e., the nanoparticles prepared by chemical coprecipitation method though are less sensitive than the microcrystalline but they do not saturate even up to very high doses (∼100 kGy, whereas the nanoparticles prepared by ball milling are equally sensitive to that of prepared by solution coprecipitation method but saturate early (at lower doses). It has been concluded that the surface defects might be playing an important role. The effect of high energy γ radiation on its repeated use as TLD phosphor for high doses (radiation hardening) was also studied and found that another TL peak at high temperature appears and its intensity varies on repeated use but the dosimetry peak remains invariant making the phosphor reusable for several times.

Effect of dopants on the TL response of the new LiF:Mg,Cu,Ag material

The new TL LiF:Mg,Cu,Ag material was prepared and investigated in this study. The TL intensity of LiF:Mg,Cu,Ag is strongly dependent on the concentration of dopants and the preparation procedure. Any small change in these factors can cause alterations in TL response. In this study, the influence of Cu and Ag concentrations on the response of the LiF:Mg,Cu,Ag sample was investigated and showed that the height of the low, main and high temperature peaks changes with Ag concentration. Their intensities increased with increasing Ag concentration to a maximum value and decreased with higher Ag concentration. It was also found that Cu concentration less than 0.05 mol% influences the maximum peak height and TL intensity. The optimum Cu and Ag concentrations were found to be 0.05 and 0.1 mol% at 1005 °C QT, respectively. The role of dopants in LiF:Mg,Cu,Ag material was also investigated. The results showed that presence of three dopants is important for having material with sensitivity higher than LiF:Mg,Ti. The Mg dopant plays a crucial role in the formation of the trapping center and the position of the main dosimetric peak.

Thermoluminescence of the persistent-luminescence phosphor, BaAl2O4; A stuffed tridymite

BaAl2O4 is a stuffed tridymite used as a long-lasting phosphor. The thermoluminescence of BaAl2O4 prepared by solution-combustion is reported. Analysis of the sample using X-ray diffraction shows that it formed as a single phase compound with a hexagonal structure following annealing at 1200 °C. A broad photoluminescence emission band between 300 and 650 nm was detected due to excitation at 248 nm. The phosphor showed a natural TL peak at 102 °C for measurement at 1 oCs−1 and, when beta irradiated to 100 Gy, two broad peaks at 123 and 318 °C also for heating at 1 oCs−1. The analysis of the main glow peak at 123 °C suggests that it is a combination of several collocated peaks, that is, peaks embedded within each other. We resolved four such components labelled peaks 1 to 4. The thermoluminescence decreases with heating rate in a way consistent with thermal quenching whose activation energy was determined as ∼0.65eV using peak 3. Interestingly, this value of the activation energy for thermal quenching for BaAl2O4, a stuffed derivative of silica, is similar to literature values for quartz (a silica), suggesting that the recombination centre in the two cases may be similar.

Thermoluminescence properties of undoped diamond films deposited using HF CVD technique

Abstract Natural diamond has been considered as a perspective material for clinical radiation dosimetry due to its tissuebiocompatibility and chemical inertness. However, the use of natural diamond in radiation dosimetry has been halted by the high market price. The recent progress in the development of CVD techniques for diamond synthesis, offering the capability of growing high quality diamond layers, has renewed the interest in using this material in radiation dosimeters having small geometricalsizes. Polycrystalline CVD diamond films have been proposed as detectors and dosimeters of β and α radiation with prospective applications in high-energy photon dosimetry. In this work, we present a study on the TL properties of undoped diamond film samples grown by the hot filament CVD (HF CVD) method and exposed to β and α radiation. The glow curves for both types of radiation show similar character and can be decomposed into three components. The dominant TL peaks are centered at around 610 K and exhibit activation energy of the order of 0.90 eV.

Some novel features of post-500°C heating blue stimulated OSL emission of fired natural quartz

Abstract In this study, some novel features of the post 500°C blue stimulated optically stimulated luminescence (OSL) of fired geological quartz are reported. Different observations (i) pulse annealing and (ii) impact of bleaching on high temperature TL glow peak suggested 510°C (heating rate of 2°C/s) TL peak trap to be responsible for the observed emission. The dosimetric properties of this emission were seen to make its applicability for dose assessment till kGy range. The signal was seen to be easily bleachable, reaching background value within 100 s with blue light at 125°C. The signal qualified all the tests (i) reproducibility, (ii) negligible recuperation and (iii) accuracy of dose recovery needed for reliable assessment of the radiation dose with modified Single aliquot regenerative (SAR) protocol. Considering the bleachability and high dynamic dose range of this signal, it has the potential to stretch the upper dose limit of dating by one order of magnitude than possible with conventional OSL, corresponding to 325°C TL trap. So, combining all the results, the signal reported here could be very useful for dosimetric applications involving measurement of high radiation dose, like dating.

PHOTOLUMINESCENCE, THERMOLUMINESCENCE AND OPTICALLY STIMULATED LUMINESCENCE STUDIES IN ZINC-BASED FLUOROPERVOSKITES.

The optically stimulated luminescence, thermoluminescence and photoluminescence in various Cu and Ag doped zinc based fluoropervoskites are studied. In all the samples, photoluminescence of Cu+ and Ag+ is observed which could be attributed to 3d94 s1←→3d10 and 4d95 s1←→5d10 transitions, respectively. The observed emission is double humped and the main emission band shifts to the lower wavelength side with increasing ionic size of the alkali ion. All the studied fluoropervoskites show reasonable OSL sensitivity. Highest sensitivity is observed for Cu doped ZnNaF3 and is 25% compared to commercial Al2O3:C. Weak thermoluminescence is observed in all samples. In all Ag doped samples the TL peak is observed at 200°C whereas for Cu doped samples peak is observed at 150°C, and correlated with the OSL. The samples show good linear dose response in the 10 mGy-1.2 Gy range and show good reusability characteristics. This study will lead to the development of zinc-based fluoropervoskite phosphors for the radiation dosimetry using OSL.

Phototransferred thermoluminescence of α-Al2O3:C: Experimental results and empirical models

The thermoluminescence glow curve of α-Al2O3:C consists of a prominent apparently-single peak and a number of weaker intensity secondary peaks. Phototransferred thermoluminescence (PTTL) from secondary glow peaks in α-Al2O3:C is reported. For completeness and to aid discussion, complementary results for the main peak are included. The problem studied is one of phototransferred thermoluminescence for a system of multiple acceptors and multiple donors. A TL glow curve recorded at 5 °C/s following irradiation to 0.5 Gy shows the main peak (labelled II) at 240 °C and two secondary peaks at 86 °C (peak I) and 360 °C (peak III). Peak I is reproduced under phototransfer after any preheating between 100 and 500 °C. Peak II is also reproduced as a PTTL peak after preheating to any temperature up to 800 °C. For the latter, the duration of preheating matters because if the sample is preheated at 800 °C for say, 6 min, PTTL is obtained but not when this is extended to say, 15 min. No PTTL was observed from peak III at all. A study of the time dependence of the PTTL intensity from peak III, following preheating that removes peaks I and II, shows that its electron trap acts as an acceptor when the duration of illumination to stimulate electrons from deep traps is brief but that when the illumination time is extended, the electron trap for peak III loses some of its trapped electrons to the shallower traps thus acting as a donor trap. Kinetic analysis of PTTL peak I shows that its activation energy is ∼0.70 eV and its frequency factor, of the order of 1010 s−1, the same as for the corresponding conventional TL peak. It is shown, for the first time, that this secondary peak (I) can be used to study thermal quenching in α-Al2O3:C. The PTTL peak was found to be affected by thermal quenching with an activation energy for thermal quenching of 1.03±0.08 eV. Thermal quenching is also adduced to be responsible for lack of any PTTL for peak III. Phenomenological mathematical models have been developed to explain the time-dependence of PTTL from peaks I and II corresponding to various preheating temperatures.

Synthesis, thermoluminescence, defect center and dosimetric characteristics of LiF:Mg,Cu,P,Si phosphor

LiF:Mg,Cu,P,Si (MCPS), a new tissue equivalent phosphor, was synthesized by solid state method. Powder x-ray diffraction and scanning electron microscope were employed to determine the structural features. The dosimetric characteristics, electron spin resonance (ESR) and defect centers of this newly prepared phosphor were investigated. The MCPS phosphor is highly sensitive when compared with LiF:Mg,Ti and LiF:Mg,Cu,P (MCP), with the TL sensitivity being 35 times and 1.3 times higher respectively. The dosimetric peak occurs at 220°C with a well defined glow curve structure similar to MCP. MCPS phosphor shows a linear dose response till 10Gy. The minimum detectable dose has been found to be 8μGy. The thermal stability of the phosphor could be enhanced by 20°C from 240°C to 260°C when compared to MCP. Defect centers formed in the phosphor by gamma irradiation have been studied by ESR to identify the centers associated with the TL process in this phosphor. Thermal annealing experiments reveal the presence of several defect centers. Center I which shows an isotropic g factor of 2.0233 has been found to relate with the TL peaks at 160°C, 220°C and 265°C. Centers II and III are characterized by isotropic g values of 2.0096 and 2.0019 respectively and are attributed to F centers.

Evidence of luminescence modification with structure of zirconia phases

Three crystallographic phases of nanocrystalline zirconium oxide (ZrO2) are prepared by solution combustion technique. Tetragonal and cubic phases are stabilized at low temperature by adding yttrium content. Phase stabilization is confirmed by X-ray diffraction and Raman spectroscopy. The XRD results are analyzed using rietveld refinement and average crystallite size is found to be 50−60nm. Characteristic PL emission of Dy3+ ions are observed at 490, 578, 672 and 764nm corresponding to 44F9/2→6H15/, 4F9/2→6H13/2, 4F9/2→6H11/2 and 4F9/2→6H9/2 transitions respectively. The spectral peak shape changes and variation of blue to yellow intensity ratio in different symmetry of ZrO2 has been discussed. CIE chromaticity color coordinates (x, y) are calculated for Dy3+ doped zirconia phosphors and fall near white light region. A high intense TL glow peak at 441K and a less intense peak at 550K are observed in monoclinic ZrO2. The intensity of 441K TL glow peak is drastically reduced and a new TL peak at 703K is found in tetragonal ZrO2. Whereas, cubic ZrO2 exhibit a single TL glow with peak at 703K. Dy3+ doped ZrO2 (monoclinic) exhibit two prominent TL peaks at 457 and 695K whereas tetragonal and cubic samples shows only high temperature peak. It is concluded that TL curve is modified in three zirconia system and TL kinetic parameters are discussed.

A comparative investigation of Ce3+/Dy3+ and Eu2+ doped LiAlO2 phosphors for high dose radiation dosimetry: Explanation of defect recombination mechanism using PL, TL and EPR study

This study describes a comparative analysis of γ-ray irradiated thermoluminescence properties of Ce3+/Dy3+ and Eu2+ doped LiAlO2 phosphor. LiAlO2: Ce3+/Dy3+/Eu2+ phosphors were synthesized by solution combustion method. The as synthesized phosphors were characterized by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) for structural and morphological study. Rietveld Refinement of XRD patterns were executed by using Fullprof suit software program. Thermoluminescence characteristics of these phosphors show a linear dose response for a wide range of gamma radiation, especially Eu2+ doped LiAlO2 phosphor. The presence of large number of lithium vacancies in LiAlO2 phosphor was supposed to be responsible for TL characteristics. Electron paramagnetic resonance (EPR) study of un-doped and Ce3+/Dy3+/Eu2+ doped LiAlO2 phosphor was carried out to confirm the presence of Eu2+ ion and cation, anion vacancies in the host lattice. The responsible defect recombination mechanism for observed TL peak in LiAlO2 was developed on the basis of TL and EPR study of irradiated and un-irradiated samples. TL kinetics was studied through glow curve deconvolution, Chen's peak shape method and initial rise method. A good match of kinetic parameters was observed between Chen's peak shape method and IR method. The present phosphors may find application in the dosimetry of high dose ionizing radiation.

Photo-transferred thermoluminescence of shallow traps in β-irradiated BeO ceramics

Photo-transferred thermoluminescence signals from beryllium oxide (BeO) ceramics were measured in the low temperature range of 10–300K. Samples irradiated at room temperature using a Sr90/Y90 beta source were cooled down to 10K and trapped charges were photo-transferred at this low temperature using the light from a high power blue LED emitting at ~470nm (2.6eV). Thermoluminescence glow curve recorded at 0.2K/s heating rate exhibited three peaks around 90, 160 and 185K. The analyses of the TL peaks of the glow curve were accomplished using curve fitting, differential and peak shape methods. Results obtained from these techniques are in good agreement about the presence of three trapping centers in BeO ceramics with activation energies of 0.24, 0.48 and 0.56eV. Moreover, the analyses indicated that first-order kinetics (slow retrapping) is the dominant mechanism in the luminescence process. Heating rate dependence of the glow curves was also investigated between 0.2 and 0.8K/s rates.

LiAlO2 with nanocrystals of Al2Tb4O9 / Tb(AlO3) synthesized by sol-gel technique for TL and OSL applications

Using a sol-gel route, powder samples of γ-LiAlO2 and doped with Tb were synthesized successfully. X-ray diffraction (XRD) results demonstrated that doped samples were composed of two phases Al2Tb4O9 and Tb(AlO3), which form long nanostructure crystals reveled by SEM images on the surface of γ-LiAlO2 grains. The undoped and doped samples supplied intense and complex TL glow curves, which were studied by Tm-Tstop method. A minimum detection dose (MDD) of 2.2 mGy was obtained with the 210 °C TL peak of γ-LiAlO2:Tb. OSL results of γ-LiAlO2:Tb showed strong thermal and optical charges transfer behavior. The OSL response of γ-LiAlO2:Tb could be sensitized by high dose irradiation and supplied a MDD of 5 mGy.

Effect of dopants’ concentration on high-dose high-temperature thermoluminescence of LiF:Mg,Cu,P detectors: Mg and Cu influence

In search of origin and mechanism of the high-dose high-temperature TL emission with presence of the peak ‘B’ about thirty batches of LiF:Mg,Cu,P detectors with different dopants' concentration were produced and comprehensive studies of their high-dose TL features have been performed. Within each step of the research, these characteristics were compared with the high-dose TL properties of the typical MCP-N detectors' batch highly exposed simultaneously with the detectors from batches of varying dopants concentration. We determined the effect of concentration of specific dopants on the TL peak ‘B’. It was found that both magnesium and copper are necessary to obtain high-dose TL signal, however, the important for high-dose TL features seems to be also concentration of phosphorus. In the framework of this study we present results of magnesium and copper concentration changes to the TL signal after high-doses of electron radiation.

Thermally stimulated transformations of luminescence centers in TLD-500 detectors and their correlation with TL properties

TLD-500 detectors based on anion-deficient corundum with the 830 K TL peak and without it have been studied comprehensively for thermoluminescence in an extended temperature range of 300–1000 K, changes in the concentrations of active centers and their photoluminescence as a function of the annealing temperature up to 1400 K along with corresponding thermostimulated changes in the TL spectra and TL yields in the main peak at 450 K, including in individual bands. Such a comprehensive approach has enabled us to not only relate the observed TL with thermally stimulated transformations of centers and their interactions, but also to understand more profoundly the nature of the thermally stimulated processes in both the main and high-temperature peaks at 450 and 830 K, respectively.

Thermoluminescent response of C-modified Al2O3 thin films deposited by parallel laser ablation plasmas

Aluminium oxide thin films modified with different amounts of carbon were prepared using a parallel laser ablation plasmas configuration. The effect of the amount of carbon incorporated in the films on their compositional, morphological, structural, and thermoluminescent properties was studied. The results showed that films with different C content, from 11 to 33 at. %, were obtained. The structural characterization revealed the growth of an amorphous material. Surface morphology of the obtained thin films showed smooth surfaces. The films were exposed to UV and gamma radiation (Co-60) in order to study their thermoluminescence response. The results tend to indicate that carbon incorporation into the alumina favours the increase of a high temperature TL peak.

Luminescence Characteristics of LaAlO<sub>3</sub>:Eu<sup>3+</sup> Obtained by Modified Pechini’s Method

The aim of the present work was to investigate the luminescent properties of europium-doped lanthanum aluminate (LaAlO3) powder prepared by Modified Pechini (MP) method. Samples were prepared at different Eu3+ concentrations and calcined at 1600°C. Structural and morphology characterizations were obtained by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). Luminescent properties were analyzed by photoluminescence (PL) and thermoluminescent phenomena. The XRD pattern shows pure lanthanum aluminate oxide LaAlO3 with a rhombohedral structure. Photoluminescence studies of the powders was related to 4f → 4f(5D0 → 7Fi) (i = 1, 2, 3, 4) transitions of Eu3+ ion, the most intense emission of Eu3+ in LaAlO3 was registered for the transition 5D0 → 7F1, for 5% of Eu3+. The recorded TL glow curves of excited samples showed a main TL peak, the main peak appeared its maximum as a function of excitation energy. The investigation demonstrates that polycrystalline LaAlO3:Eu3+ powders calcined at 1600°C have interesting luminescent characteristics.

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.

Thermoluminescence Characterisation of Ceramic Mineral China Clay

<div><p><em>Many natural minerals are used as the raw materials required for the manufacturing ceramic ware. Most of the minerals are from Indian mines of Gujarat and Rajasthan states, some of are imported from Russian sub continent.</em><em> </em><em>The present paper reports the thermoluminescence characteristics of mineral China Clay collected from Morbi, Rajkot, Gujarat, India. The TL of mineral at various heat treatments was recorded and also 5Gy beta dose was given to </em><em>each sample</em><em> prior to TL recording. The mineral is annealed for 1 hour and quenched from 600 and 800</em><em><sup>o</sup></em><em>C</em><em>. It displayed a well resolved peak around 132</em><em><sup>o</sup></em><em>C</em><em> annealing and quenching from 600 and for annealing and quenching from 800</em><em><sup>o</sup></em><em>C</em><em> the TL peak temperature is found around 138</em><em><sup>o</sup></em><em>C</em><em> and 161</em><em><sup>o</sup></em><em>C</em><em>. XRD and TGA of China Clay mineral </em><em>were</em><em> reported.</em></p></div>

Optically stimulated luminescence in doped K3Na(SO4)2 phosphors

Optically stimulated luminescence (OSL) in Cu and Eu doped K3Na(SO4)2 is reported for the first time. The Cu-doped sample shows OSL sensitivity which gets enhanced by co-doping with Mg2+ ions. The Cu-doped and quenched sample shows better sensitivity which is almost double than that of the slowly cooled sample, whereas the sensitivity of Mg co-doped sample remains nearly same irrespective of the thermal treatment. The Cu-doped sample shows TL peak around 200 °C and moderate OSL sensitivity. Doping of Mg shifts the TL peak to around 160 °C and is correlated with good OSL sensitivity. Eu-doped sample does not show OSL sensitivity. However, relatively good OSL sensitivity is observed in Aluminium co-doped and slowly cooled sample, which is about 15% of the commercial Al2O3:C(Landuer Inc.). A near fully optically sensitive TL peak around 155 °C is observed. The dose response is linear and practically no OSL fading is observed in first five days of storage in slowly cooled sample. This study on conventional sulphate-based TL phosphors will be useful in developing OSL phosphors for radiation dosimetry.

Dose response on the 110 °C thermoluminescence peak of un-heated, synthetic Merck quartz

Studies on 110°C TL peak have been carried out using natural quartz from different origins and synthetic quartz produced by different suppliers. The interest in quartz is due to its usage in dating and retrospective dosimetry as a main material; both synthetic and natural types of quartz yield the 110°C TL peak in their glow curve. In most studies to understand the physical mechanism behind the TL system, synthetic quartz samples are used and there are many investigations about dose response, in both low and high radiation dose region. In these studies generally synthetic quartz samples produced by Sawyer Research Products are used and the studies showed that both heated and un-heated synthetic quartz samples have intense supra-linear responses. Supra-linearity was enhanced by applying a pre-irradiation while several models have been developed towards an explanation to these supra-linearity effects. In this study commercially available synthetic Merck quartz was used. Different combinations of optical filters were used to obtain dose response curves upto 266Gy and the effect of pre-dose to these dose response curves was studied. Un-pre-dosed Merck quartz samples dose supra-linearity index is below 1 independently on the optical filters; so Merck quartz showed linear or sub-linear dose response.