Thermoluminescence Sensitivity Research Articles

Thermal and structural properties of magnesium tetraborate produced by solid state synthesis and precipitation for use in thermoluminescent dosimetry

Magnesium tetraborate is a phosphor with relevant characteristics for radiation dosimetry purposes. One of the main challenges on this material is still the understanding of its structure and luminescent processes involved in dosimetric performance. In this work, all the steps of the material production through DTA/TG, XRD and SEM techniques were evaluated to understand the main physical and chemical changes during the thermal process (calcination and sinterization) to produce the MgB4O7 samples. Two synthesis processes of MgB4O7 were studied: precipitation (P.S) and solid state (S.S). Finally, the luminescence efficiency of the pellets was investigated in function of different sintering temperatures. The initial stage of DTA/TG curves of the material just after the mixing of starting materials, regardless the synthesis, is marked by endothermic events caused by dehydration, decomposition of hydroxyl groups and hydrated borate phases. At higher temperatures, the curves are marked by exothermic events related to crystalline transitions, but the peak obtained for the S.S is better defined in comparison to P.S. Moreover, the DTA/TG analyses of the pellets prior and after the sinterization, showed that the process is more relevant for the MgB4O7 pellets produced by S.S (950 °C), dramatically reducing its higroscopicity. The SEM images reinforce the importance of the sintering process to create a resistant detector and with a more homogenous and cohesive surface, therefore increasing it luminescence properties. The thermoluminescent (TL) sensitivity of MgB4O7:Dy0,5% pellets produced via S.S, sintered at 950 °C, is 4 times higher compared to the ones sintered at 950 °C, via P.S. The materials produced via P.S did not present relevant changes in their TL sensitivity for sintering temperatures above 400 °C.

Synthesis and thermoluminescence characterization of self-agglomerating CaSO4 exposed to beta radiation

The synthesis and thermoluminescence (TL) characterization of self-agglomerating pellet-shaped CaSO4 phosphors, through a low cost and environmentally friendly method is reported. In order to investigate their TL features, some samples were exposed to beta particle irradiation in the dose range from 0.07 to 10 Gy. Characteristic TL glow curve consists of a single main maximum located at 216 °C, which is considered stable, hence, suitable for dosimetry applications. The dose-response was remarkable linear. Moreover, the lower detection limit was determined to be 6.0 μGy, and the relative TL sensitivity twice the one from the commercial TLD-100 dosimeter.

Preparation, kinetic analysis and thermoluminescent dosimetry features of highly sensitive SrF2:Dy phosphor

Dy doped SrF2 microcrystalline was prepared by co-precipitation technique. Thermoluminescence (TL) glow curve of γ irradiated SrF2:Dy phosphor consists of a main glow peak at 485 K with small shoulders at around 384 K and 590 K. The effects of different dopant concentrations and annealing regimes on TL sensitivity were investigated and the optimum conditions were achieved at 1 mol% of Dy dopant and annealing at 700 °C for 30 min. Initial rise, variable heating rate, isothermal decay and computerized glow curve deconvolution (CGCD) methods were applied to obtain kinetic parameters of the prepared material. TL sensitivity of this phosphor is about 10 times more than that of LiF;Mg;Ti (TLD-100). Based on the obtained results, the synthesized phosphor is appropriate for dosimetry applications.

The effect of water on the thermoluminescence properties in various forms of calcium sulfate samples

The present study investigates whether thermoluminescence (TL) features are prevalent over calcium sulfate samples, regarding their lever of hydration. Three groups of calcium sulfates -dihydrate (gypsum), hemihydrate (bassanite) and anhydrous (anhydrite)- are investigated, of both commercial and mineral origin. The study includes TL features such as TL glow curve shapes, the stability of TL peaks after successive cycles of measurements, and the estimation of the kinetic parameters of stable TL peaks. Moreover, the slurry of calcium sulfate with water is being studied, to investigate its prevalence as an effective zeroing mechanism. The results indicate the presence of stable TL peaks around 280 °C for all of the groups of calcium sulfates, while the TL sensitivity of the samples depends on their water content and stabilizes after three heating cycles up to 500 °C. Anhydrite shows stability even from the initial measurement, while the hemihydrates and dihydrates could be used for dating applications using TL by means of a multiple aliquot protocol.

Effect of co-activation on the thermoluminescence and photoluminescence properties of nano-crystalline K2Ca2(SO4)3:Eu,Cu

The effect of co-doping and change in dopant concentration on thermoluminescence (TL) properties of K2Ca2(SO4)3:Eu,Cu has been studied by varying the concentration of the two dopants europium and copper (0.05, 0.10, 0.20, 0.30 and 0.40 mol% equally divided between Eu and Cu). Chemical co-precipitation technique was used to prepare the co-doped phosphor K2Ca2(SO4)3:Eu,Cu. Using Williamson-Hall plot in the X-ray diffraction pattern of the phosphor, the size of the crystallites was estimated to be around 51.3–73.6 nm. Maximum TL sensitivity was obtained for 0.2 mol% concentration (0.1 mol% Eu and 0.1 mol% Cu). The co-doped phosphor was compared for its TL sensitivity with that of the singly doped phosphors K2Ca2(SO4)3:Eu, and K2Ca2(SO4)3:Cu and the standard TL dosimeter LIF:Mg, Ti (TLD-100). Higher TL peak intensity of co-doped phosphor compared to the singly doped phosphors K2Ca2(SO4)3:Eu and K2Ca2(SO4)3:Cu has been explained on the basis of energy transfer between the dopants. Photoluminescence studies of the co-doped and the singly doped samples confirm a positive energy transfer from Cu2+ to Eu2+. A linear TL response curve over a wide range of doses (10 Gy to 1 kGy) is a key factor that makes the present phosphor quite capable for dosimetric purposes.

THERMOLUMINESCENCE OF NEWLY DEVELOPED HIGHLY SENSITIVE α-Al2O3:C BY THE VERTICAL GRADIENT FREEZING METHOD.

A highly sensitive α-Al2O3:C crystal was directly grown by the vertical gradient freezing (VGF) method using Al2O3 and graphite powder as the raw materials. The main thermoluminescence (TL) characteristics of α-Al2O3:C detectors grown by the VGF method and TLD-500K detectors were compared. The α-Al2O3:C grown by the VGF method shows good dosimetric properties, such as high TL sensitivity (152 times higher than that of the TLD-100 at heating rate of 1°C/s), an extremely low residual signal of 0.03%, a minimum measurable dose of 0.12 μGy and an excellent linear response within the dose range studied from 1 μGy to 10 Gy. The α-Al2O3:C detectors grown by the VGF method have a higher sensitivity and a better linear response compared to the TLD-500K detectors. Both kinds of α-Al2O3:C can be used in an unannealed form and to measure the very low dose in environmental monitoring and personnel dosimetry.

Thermoluminescence and optically stimulated luminescence properties of the Eu2+-doped KMgF3 produced by a hydrothermal microwave method

The purpose of this work is to study the optically stimulated luminescence (OSL) and thermoluminescence (TL) properties of the Eu2+-doped KMgF3 (KMgF3:Eu). KMF powders were synthesized by a microwave – assisted hydrothermal method. The structural phase identification was performed by X-ray diffraction combined with Rietveld refinement. The TL and OSL sensitivity due the annealing (800 °C in air) was also performed. Properties as TL glow curve, step-annealing OSL, stability of the OSL signal, dose response curve and minimum detectable dose were investigated. The results showed that KMgF3:Eu display TL peaks in a range suitable for dosimetry applications. TL measurements also show that the material has shallow traps with a TL peak at around 90 °C, responsible for a short time afterglow emission (phosphorescence). However, a pre-heating before each measurement can reduce the shallow traps signal contribution. The results showed that the OSL signal is due the same trap centers responsible for the TL signal in this material. The OSL signal does not decay completely over 300 s reading due to stimulation of trapped charges from very deep traps. The dose response signal was evaluated in a range from 0.1 Gy up to 100 Gy using beta 90Sr/90Y, showing a linear response over this range. The estimated fading of the OSL signal, using initial intensity signal was 4% in 24 h and 15% over one week. Considering the total OSL area and the first 10 s of OSL decay, no fading was observed for the first 24 h and the signal was 10% faded over one week.

Carbon doping controlled thermoluminescent defect centers in nanoporous alumina for ion beam dosimetry

The flexibility of amorphous anodized alumina (AAO) in developing radiation dosimeter for hadron therapy is reported by controlled carbon ion implantation, followed by thermoluminescence (TL) measurements. The efficacy of amorphous AAO in controlling TL sensitivity is found to be governed by an increase in F+ defect centers as a function of carbon concentration, as revealed from the close resemblance of the trend in photoluminescence intensity. Moreover, its nanoporous structure is demonstrated to be advantageous for defect engineering due to the increase in the surface-to-volume ratio. Detailed X-ray photoelectron spectroscopy analysis suggests the formation of F+ centers by substituting Al3+ ions with C2+ in the vicinity of oxygen vacancies, where depth-dependent study showed the evolution of conducting channels owing to sp2 hybridized C–C bonding, leading to a differential charging effect. This work provides a direction to tune nanoporous AAO in its amorphous form for future ion beam dosimetry.

Thermally and optically stimulated luminescence of natural red and blue corundum (Al2O3)

We report the thermoluminescence (TL) and optically stimulated luminescence (OSL) of natural corundum (Al2O3) of two varieties; one red and the other blue. X-ray fluorescence spectroscopy of the samples show that the concentration of Al2O3 in the red corundum is 43.05% and 46.87% in the blue corundum. TL measurements carried out on un-annealed samples and samples annealed at 700 °C, 900 °C and 1200 °C show that the TL sensitivity increases with annealing. The sensitivity of the red corundum reaches a maximum after annealing at 900 °C whereas that of the blue corundum increases with annealing up to the maximum annealing temperature of 1200 °C used in this study. Both samples have a complex glow curve between 30 °C and 500 °C. The composite nature of the glow curves is deduced to be due to a continuum in the trap distribution in the crystal. The activation energy of the traps vary between 0.70 eV and 1.15 eV. The dose response of the red corundum under TL is linear within 100‒1000 Gy whereas that of the blue corundum is superlinear for the same dose range. The TL of both samples is reproducible but the signal fades with time between irradiation and measurement. Both samples produce OSL under 470 nm blue light stimulation. The dose response of the OSL is superlinear within 100‒1000 Gy. It is found that the samples also produce thermally-assisted OSL (TA-OSL) at elevated temperature. The TA-OSL intensity of the red corundum increases with dose up to 400 Gy and saturates thereafter. On the other hand, the intensity of the blue corundum increases consistently with dose from 100 Gy to 1000 Gy.

The effect of Na2O co-doping on the TL characteristics and kinetic parameters of Cu-doped calcium lithium borate glass irradiated with the cobalt-60 gamma rays, 6 MeV electron and 6 MV X-ray photon

The influence of co-dopant Na2O on the thermoluminescence (TL) properties and kinetic parameters of Cu2O doped Calcium Lithium borate glass (CLB:Cu) are comprehensively examined and studied in this paper. The glasses were prepared by melt quenching method upon adding various Na2O concentrations of 0.1% to 1 mol%, and irradiated with 60CO gamma-ray, 6 MeV electron and 6 MV X-ray photon. The glow curve exhibits a prominent peak (TM) at 188 °C. The TL intensity and sensitivity was enhanced by a factor of 2 and 1.7 respectively due to the incorporation of Na2O, and this was attributed to the creation of extra electron traps mediated by radiative recombination energy transfer. We achieved good linearity of the TL yield with dose low fading, excellent reproducibility and a promising effective atomic number (Zeff = 8.85), all of which are highly suitable for dosimetry. The effects of sunlight on the TL are also tested and investigated. These attractive features demonstrate that our dosimeter is useful in personal, environmental and medical radiation therapy application.

Effect of annealing temperature and dopant concentration on the thermoluminescence sensitivity in LiF:Mg,Cu,Ag material.

LiF:Mg,Cu,Ag is a new dosimetry material that is similar to LiF:Mg,Cu,P in terms of dosimetric properties. The effect of the annealing temperature in the range of 200 to 350°C on the thermoluminescence (TL) sensitivity and the glow curve structure of this material at different concentrations of silver (Ag) was investigated. It has been demonstrated that the optimum values of the annealing temperature and the Ag concentration are 240°C and 0.1mol% for better sensitivity, respectively. The TL intensity decreases at annealing temperatures lower than 240°C or higher than 240°C, reaching a minimum at 300°C and then again increases for various Ag concentrations. It was observed that the glow curve structure altered and the area under the low temperature peak as well as the area under the main dosimetric peak decreased with increasing annealing temperature. The position of the main dosimetric peak moved in the direction of higher temperatures, but at 320 and 350°C annealing temperatures, it shifted to lower temperatures. It was also observed that the TL sensitivity could partially be recovered by a combined annealing procedure.

CHARACTERISTICS OF THERMOLUMINESCENCE LiF:Mg,Cu,Ag NANOPHOSPHOR.

A nanophosphor of LiF:Mg,Cu,Ag was prepared by planetary ball milling for the first time in the laboratory. The size and shape of the nanophosphor were confirmed by XRD and SEM, which showed that it was cubic in shape and ~53 nm in size. The thermoluminescence (TL) characteristics of this nanophosphor were then investigated. It was found that the optimum annealing condition was 250°C for 10 min. The TL sensitivity of the prepared nanopowder was less than that of its micropowder counterpart and the TL glow curve structure exhibited several peaks. The LiF:Mg,Cu,Ag nanophosphor exhibited a linear response over a range of doses from 1 Gy to ~10 kGy. From this study, it appears that LiF:Mg,Cu,Ag nanophosphor is a good candidate for dosimetry because of its linearity over a range of doses, low tendency to fade, good repeatability and simple glow curve structure.

Thermoluminescent response of differently doped lithium magnesium phosphate (LiMgPO4, LMP) crystals to protons, neutrons and alpha particles

Differently doped lithium magnesium phosphate crystals have been investigated with respect to their thermoluminescent properties. The LiMgPO4 crystals with Tb, B, Eu, Er, Tm, Y rare-earths elements were grown by the micro pulling down method. Different radiation qualities, such as protons of different energies, neutrons and alpha particles, have been used for samples irradiation. Thermoluminescent sensitivity to ionizing radiation, dose-response characteristics and relative thermoluminescence efficiency have been evaluated for all radiation qualities and compared for all analyzed crystal samples. It was found that the radio-sensitivity of the studied compound varies within several orders of magnitude depending on the applied doping ion and its concentration. The highest response was measured for the samples doped with thulium ions. In this case, the signal amplitude was about 3 times higher as compared to the standard LiF:Mg,Ti samples in the form of cold-pressed and sintered pellets. The dose-response of the studied LiMgPO4 crystals was found to be linear up to kGy range, regardless of the applied dopant and its concentration. An interesting behavior was observed in case of relative efficiency vs. linear energy transfer dependence. For protons of different energies the analyzed samples show a similar behavior as the reference LiF:Mg,Ti samples, showing a maximum efficiency evaluated for 20 MeV particles. The response of LiF-based samples for alpha particles decreases significantly to the value of around 0.08. The response of the analyzed lithium magnesium phosphate samples also decreases, but the decrease is not so significant in this case. This probably corresponds to the wide linear dose-response range and also indicates that the local signal saturation effects occur in this material in the range of much higher doses as compared to the reference LiF-based samples.

Study of constraints in using household NaCl salt for retrospective dosimetry

Abstract Thermoluminescence (TL) characteristics of 5 different household NaCl salts and one analytical salt were determined to investigate the possible factors that affect the reliability of using household salt for retrospective dosimetry. Salts’ TL sensitivities were found to be particle-size dependent and approached saturation at the largest size, whereas for salts that have the same particle size, the TL sensitivity depended on their origin. TL dependence on the particle size interprets significant variations in TL response reported in the literature for the same salt patch. The first TL readout indicated that all salts have similar glow curves with one distinctive peak. Typical second TL readout at two different doses showed a dramatic decrease in TL sensitivity associated with a significant change in the glow curve structure possessing two prominent peaks. Glow curve deconvolution (GCD) of the first TL readout for all salts yielded 6 individual glow peaks of first-order kinetics, whereas in GCD of second TL readouts, 5 individual glow peaks of second-order kinetics were obtained. Similarities in the glow curve structures of the first and second TL readouts suggest that additives such as KIO3 and MgCO3 have no effect on the TL process. Fading effect was evaluated for the salt of highest TL sensitivity, and it was found that the integral TL intensity decreased gradually and lost 40% of its initial value over 2 weeks, after which it remained constant. Results conclude that a household salt cannot be used for retrospective dosimetry without considering certain constraints such as the salt’s origin and particle size. Furthermore, preparedness for radiological accidents and accurate dose reconstructions require that most of the commonly distributed household salt brands should be calibrated in advance and stored in a repository to be recalled in case of accidents.

Synthesis and dosimetry features of novel sensitive thermoluminescent phosphor of LiF doped with Mg and Dy impurities

Lithium fluoride doped with Mg and Dy was fabricated for the first time using melting method. The optimum concentrations of impurities and thermal treatment were studied to achieve high thermoluminescence (TL) sensitivity. TL sensitivity of the fabricated phosphor is close to that of TLD-100 powder. Tm-Tstop technique was used to identify the number of overlapped TL glow peaks. Initial rise, isothermal decay and computerized glow curve deconvolution (CGCD) methods were applied to obtain kinetic parameters of the prepared TL material. Three component glow peaks were distinguished at temperatures 395, 448 and 510 K. Other TL properties such as fading, linearity of dose response and reusability are also presented and discussed.

Preparation and thermoluminescent dosimetry features of high sensitivity LiF:Mg,Ce phosphor

Thermoluminescence (TL) kinetics and dosimetry features of newly produced LiF doped with Mg and Ce were investigated. Different contents of Mg (0–1 mol%) and Ce (0–2 mol%) were introduced in host material by melting method. The most TL sensitivity of the fabricated phosphor was obtained at 0.7 and 0.05 mol% concentrations of Mg and Ce impurities, respectively. The optimum pre-irradiation annealing regime of the synthesized LiF-based material was found at 350 °C for 10 min. Kinetic parameters of LiF:Mg,Ce dosimeter were obtained using different methods of computerized glow curve deconvolution (CGCD), initial rise (IR) and isothermal decay (ID). A good conformity are observed between the results obtained from different kinetic analysis methods. Other TL features such as fading, dose response and reusability were also examined.

Radiophotoluminescence and thermoluminescence characteristics of undoped and Mg doped LiF phosphor in the high dose region

Radiophotoluminescence (RPL) and thermoluminescence (TL) from undoped and Mg-doped LiF powder samples were investigated for high dose dosimetric applications. F-aggregate centres in LiF are created by radiolysis. The RPL emission at 530 nm and 650 nm from F3+ and F2 centres respectively (on excitation at 450 nm) in undoped commercial LiF powder enhanced with increasing sintering temperature. Its TL glow curve showed peaks at 145, 290 and 365 °C. The RPL-TL correlation studies carried out for the first time showed that the thermal annihilation of F3+ and F2 centes following Fi0 - Va (interstitial-vacancy) recombination cause 290 °C and 365° TL peaks respectively. This showed that F2 centres are thermally more stable than F3+ centres. Its integrated TL response kept increasing nearly linearly up to 14 kGy, in contrast to the response of the TL peaks in dosimetry grade LiF:Mg, Ti (TLD-100). However, the TL from LiF suffers from fading problems. A 100 °C, 15 min pre-read annealing treatment erased most of the 145 °C TL peak without disturbing the other high temperature peaks. A 750° C, 22 h sintering treatment in carbon atmosphere shifted the major TL glow peak of undoped LiF to 200 °C but reduced its TL sensitivity by more than a factor of 10. Mg-doped LiF samples exhibit a TL glow curve peaking at ∼240 °C with satellite peaks typical of Mg doped LiF whose shape did not change significantly with gamma dose. However it showed lower TL and RPL sensitivities as compared to those of undoped LiF. All LiF except LiF alfa (750 °C, 1 h, CB) showed sublinear increase in TL with dose and therefore will cause inaccuracy in dose measurements especially at high doses due to reduced sensitivity. LiF alfa 750 °C, 22 h and 1000 °C, 6 min sintered powder samples are better than others because their RPL sensitivity increases nearly linearly with dose. However, a low fading observed in the latter sample supports its application. The bright yellow RPL emission seen through a 550 nm cut on filter illuminated with a 450 nm blue LED or He-Cd laser light could quickly confirm an irradiated consignment on which LiF samples are affixed. The increase in green to red emission ratio with dose and post-irradiation storage period might be related to slow migration of anion vacancies created by one secondary electron track to F centres created by another track and consequent conversion of F2 → F3+ centres.

Optical and luminescence properties of silicon doped alumino-phosphate‑sodium glass system

Transparent thermoluminescent alumino-phosphate‑sodium glass system of 15Al2O3-35P2O5-25CaO-25Na2CO3 (all in mol%) doped with different concentrations of SiO2 were prepared by conventional melt quenching technique. X-ray diffraction (XRD) studies checked the amorphous nature of the prepared glass. Fourier Transform Infrared (FTIR) of the glass system was investigated to find the effect of SiO2-dopant concentrations on the absorption spectra in comparison with that of bulk sample (without dopants). Direct and indirect energy band gaps (Eopt) were determined and found to be in the range of 2.47–3.65eV for m=½ and 2.24–3.3eV for m=2. Refractive index (n) for each Eopt value vary from 2.42 to 2.55 and from 2.32 to 2.63 for the direct and indirect transition, respectively. Urbach energy values of the newly prepared glasses are found to be from 0.57 to 0.98eV. In addition, effect of UV exposure on thermoluminescence (TL) sensitivity was also examined for APCNSi5 (contains 500ppm SiO2 concentration) and a linear response to dose was obtained, indicating that this type of glass is promising as a TL dosimeter within the UV range.

BaSO4:Eu as an energy independent thermoluminescent radiation dosimeter for gamma rays and C6+ ion beam

BaSO4:Eu nanophosphor is delicately optimized by varying the concentration of the impurity element and compared to the commercially available thermoluminescent dosimeter (TLD) LiF:Mg,Ti (TLD-100) and by extension also to CaSO4:Dy (TLD-900) so as to achieve its maximum thermoluminescence (TL) sensitivity. Further, the energy dependence property of this barite nanophosphor is also explored at length by exposing the phosphor with 1.25MeV of Co-60, 0.662MeV of Cs-137, 85MeV and 65MeV of Carbon ion beams. Various batches of the phosphor at hand (with impurity concentrations being 0.05, 0.10, 0.20, 0.50 and 1.00mol%) are prepared by the chemical co-precipitation method out of which BaSO4:Eu with 0.20mol% Eu exhibits the maximum TL sensitivity. Further, the optimized nanophosphor exhibits a whopping 28.52 times higher TL sensitivity than the commercially available TLD-100 and 1.426 times higher sensitivity than TLD-900, a noteworthy linear response curve for an exceptionally wide range of doses i.e. 10Gy to 2kGy and a simple glow curve structure. Furthermore, when the newly optimized nanophosphor is exposed with two different energies of gamma radiations, namely 1.25MeV of Co-60 (dose range- 10–300Gy) and 0.662MeV of Cs-137 (dose range- 1–300Gy), it is observed that the shape and structure of the glow curves remain remarkably similar for different energies of radiation while the TL response curve shows little to no variation. When exposed to different energies of carbon ion beam BaSO4:Eu displays energy independence at lower doses i.e. from 6.059 to 14.497kGy. Finally, even though energy independence is lost at higher doses, the material shows high sensitivity to higher energy (85MeV) of carbon beam compared to the lower energy (65MeV of C6+) and saturation is apparent only after 121.199kGy. Therefore the present nanophosphor displays potential as an energy independent TLD.

Dosimetric characterization of highly sensitive OSL phosphor: LiCaAlF6:Eu,Y

The paper presents the dosimetric characterization of lithium calcium aluminum fluoride doped with europium and yttrium (LiCaAlF6:Eu,Y), synthesized by simple melt process. The characterization involved thermoluminescence (TL), optically stimulated luminescence (OSL), photoluminescence (PL) spectra, OSL emission spectra, minimum measurable dose, fading, dose response and photon energy dependence measurements. The OSL sensitivity of this phosphor to ionizing radiation was found to be ∼20 times to that of commercially available Al2O3:C, whereas, the TL sensitivity was ∼2.5 times to that of CaSO4:Dy (0.05 mol%). Photoluminescence (PL) and OSL emission spectra suggest that the Eu2+ ions are responsible for OSL emission. The reusability of OSL discs for 50 cycles for a test dose of 20 mGy has been established. Minimum detectable dose for the phosphor in continuous wave OSL (CW-OSL) mode was found to be 0.5 μGy with negligible fading post 9 days of irradiation. Owing to its excellent dosimetric characteristics the phosphor is a highly sensitive dosimetric grade phosphor and is a serious contender for various radiological applications.