Thermoluminescence properties of irradiated chickpea and corn

A study was carried out to establish a detection method for irradiated chickpea and corn by thermoluminescence (TL) method. The leguminous were packed in polyethylene bags and then the packets were irradiated at room temperature at different doses by ⁶⁰Co gamma source at 1, 4, 8 and 10 kGy. Minerals extracted from the leguminous were deposited onto a clean aluminum disc and TL intensities of the minerals were measured by TL. It was observed that the extracted samples from both leguminous exhibit good TL Intensity and the TL intensity of glow curves of them increased proportionally to irradiation doses. The TL glow curve of both irradiated leguminous presents a single broad peak below 400 °C. The TL trapping parameters glow peaks were estimated by the additive dose (AD), T_m(E_a)-T_stop and computerized glow curve deconvolution (CGCD) methods. The fading characteristics of glow curves were also recorded up to 6 months.     

The thermoluminescence properties of natural CaF2 after β-irradiation

In this study, the thermoluminescence (TL) properties of natural CaF₂ were investigated after β-irradiation at room temperature (RT). The additive dose (AD), T_m(E_a)-T_stop, repeated initial rise (RIR), and computerized glow curve deconvolution (CGCD) methods were used to analyze the thermoluminescence (TL) glow peaks in natural CaF₂ after β-irradiation between 0.015 Gy and ≈2 kGy dose level. These methods were used to determine the number of peaks and kinetic parameters (kinetic orders b, activation energy E_a, and attempt-to-escape frequency s) associated with the thermoluminescence (TL) glow peaks of natural CaF₂. The E_a-T_stop and CGCD methods indicate that the glow curve of this material is the superposition of at least six glow peaks, which were dealt with as P1-P6, in the temperature range between room temperature (RT) and 400 °C. Dose variation experiments revealed that TL glow curve of natural CaF₂ has both first and general-order glow peaks. The dose responses and fading process, which are very useful in radiation dosimetry, of individual TL peaks of this material were also examined. In addition, the influence of heating rates on the response of dosimetric glow peaks of natural CaF₂ was studied. It was observed that the total area of glow peak and peak intensities of all glow peaks are continuously decreasing with increasing heating rate.     

LiMgPO4:Tb,B OSL phosphor - CW and LM OSL studies

In the adjoining paper, the authors have proposed LiMgPO₄:Tb,B (LMP) OSL phosphor as a potential alternative to α-Al₂O₃:C for dosimetry applications. This calls for developing an understanding on TL and OSL aspects of this highly sensitive LMP phosphor. CW and LM OSL processes were therefore studied experimentally and kinetic analysis was carried out using theoretical models. Continuous wave (CW) OSL curve for LMP phosphor was found not to follow single decaying exponential implying that the CWOSL curve does not follow first order kinetics. Under pre-readout annealing at 125, 200 and 300 °C for 10 s, the nature of decay profile was unaffected and same holds true for optically bleached CWOSL curves. From linearly modulated (LM) OSL studies, it was found that the shape/geometrical factor μ_g was ∼0.72 ± 0.03 for wide range of doses (up to 12 Gy studied) and peak position “t_m” was also independent of dose. The μ_g was found to be unaffected with pre-readout annealing at 125, 200 and 300 °C for 10 s and optical bleaching, however it was found that peak position “t_m” shifted towards higher side in time with increase of optical bleaching. Dose dependence tests were also carried out for LMOSL curves and it was found that peak position “t_m” was independent of dose, which is typical characteristic of curves following first order kinetics. Hence LM-OSL curve might be mixture of more than one component.Further from CW and LM OSL studies, it was also found that the individual contribution from first, second and third TL peak toward OSL is ∼33%, ∼45% and ∼22%, respectively. Traps beyond 350 °C were found not to contribute towards OSL when stimulated using blue LEDs. In the present paper, the CW and LM OSL processes for LMP phosphor were studied experimentally and their kinetic analysis was carried out.     

Study on TL and OSL characteristics of indigenously developed CaF2:Mn phosphor

CaF₂:Mn phosphor is known for its high thermoluminescent sensitivity and dose linearity up to few kGy. In the present study CaF₂ phosphor with different concentration of Mn dopant was prepared and was characterized through different techniques. The phosphor was prepared through chemical root using CaCO₃, HF acid and MnCl₂ as raw materials following co-precipitation method. TL sensitivity of the prepared phosphor was compared with other well established phosphors used for radiation dosimetry. It was found that the TL sensitivity is higher by a factor of 10 with respect to LiF:Mg, Ti, TLD-100 and half to that of CaSO₄:Dy (0.05 mol%) phosphor. X-ray diffraction, TL emission spectrum and ESR spectrum taken of the prepared phosphor confirms the crystal structure, Mn²⁺ emission and incorporation Mn in the crystal, respectively. No significant fading of the dosimetric peak was observed of the prepared phosphor for a storage period of 45 days. The dose linearity of the phosphor was found to be in the range of 50 Gy-3 kGy within an uncertainty of about 10%. An attempt was made to determine the kinetic parameters of TL glow curve and the parameters related to optically stimulated luminescence. In view of its long range of dose linearity, it can be used for the dosimetry of commercial irradiator generally used for the irradiation of food and grains in our country.     

LiMgPO4:Tb,B - A new sensitive OSL phosphor for dosimetry

Optically Stimulated Luminescence (OSL) technique has emerged as a serious competitor to Thermally Stimulated Luminescence (TSL) technique in various dosimetric applications, especially after the development of crystalline alumina (Al₂O₃:C) doped with carbon. Since then, several attempts are being made to develop other possible materials for OSL based dosimetric applications. Efforts conducted in our laboratory in this direction have led to the development of a new phosphor, Lithium Magnesium Phosphate doped with terbium and boron (LiMgPO₄:Tb,B). This phosphor is prepared by solid-state diffusion method involving conventional air furnaces with operating temperature 1000 °C and easily amenable to large scale production without compromising primary dosimetric advantages. In this work we present some of the dosimetric OSL characteristics of this phosphor. The phosphor exhibits a main TSL peak at 250 °C. The phosphor also emits OSL, when the irradiated phosphor is stimulated with 470 nm light with the OSL sensitivity 1.3 times that of commercially available Al₂O₃:C. Photoluminescence (PL) emission spectrum consists of sharp lines characteristics of Tb³⁺ emission. The OSL discs made out of this phosphor are reusable up to at least 50 cycles, the phosphor exhibits dose linearity up to 1 kGy. Minimum detectable dose is found to be 20 μGy and fading of the OSL signal is found to be about 16% in four days, after which the OSL signal stabilizes.     

A versatile integrated system for thermoluminescence and optically stimulated luminescence measurements

A versatile integrated reader system for TL and OSL measurements of phosphor materials has been described for luminescence research applications. The developed integrated reader system works either in TL or OSL or TL-OSL mode. In the OSL operation, besides the conventional CW-OSL, POSL and LM-OSL modes a novel non-linear OSL (NL-OSL) method has been incorporated in the reader system. The optical stimulation unit consists of four high power LEDs fitted in four channels and optically focused on the sample. Each of the LED is capable of delivering up to 80 mW/cm² light power at the sample position. The LEDs with peak wavelength λ_p ≈ 470 nm and 530 nm and Δλ ≈ 20 nm have been used for optical stimulation of the samples. A PID temperature controller has been used for generating and controlling user defined heating profiles for the TL measurements in the reader system. The reader system covers a wide dynamic dose range of 10 μGy to 10³ Gy for TL/OSL measurements. The OSL grade α-Al₂O₃:C phosphor was used to test the reader system and investigate its impact on low dose assessment for personnel and environmental monitoring. The design concept of the reader system and the results of dose measurements are discussed.     

Study of the luminescent properties of KMgF3:Sm

The photoluminescence (PL), radioluminescence (RL) and thermoluminescence (TL) of KMgF₃ doped at several Sm concentrations have been investigated. The maximum TL and RL yield under beta irradiation has been observed in KMgF₃:Sm 0.02 mol%. The glow curve of this doped perovskite is made up of at least five peaks located at 95, 120, 160, 270, and 330 °C. The third peak appears to be the most convenient for personal or environmental dosimetry, since it shows no fading and good linearity within the investigated dose range (0.020-200 Gy). From the RL and PL spectra it has been found that most of KMgF₃:Sm emission is located at wavelengths higher than 650 nm. This emission, which is characteristic of Sm²⁺, makes this doped compound attractive for fiber-optic dosimetry.     

The thermoluminescent properties of lithium triborate (LiB3O5) activated by aluminium

In this paper, the thermoluminescence (TL) dosimetric characteristics of Al-doped LiB₃O₅ compounds are presented. The powder samples were prepared by the solid-state reaction method and the formation of the compounds were confirmed by an X-ray diffraction study. The TL studies of undoped and Al-doped LiB₃O₅ samples showed similar glow curve structures. They have three TL glow peaks at about 60, 130 and 200 °C after heating at a constant heating rate of 1 °C/s. Their comparative TL studies indicated that 5 wt% Al-doped LiB₃O₅ compound was approximately 240 times more sensitive than undoped compound. The TL emission spectra of Al-doped LiB₃O₅ showed a maximum band at around 520 nm. The main dosimetric characteristics, which are namely the TL dose response, TL sensitivity, fading, minimum detectable dose, reproducibility, precision of dose measurement and annealing procedure, indicated that Al-doped LiB₃O₅ sample, can be used in dosimetric applications. The trap parameters namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the glow peaks in beta irradiated undoped and Al-doped LiB₃O₅ samples were obtained by glow curve deconvolution (GCD) program.     

Possibility of pure thermal sensitization in the pre-dose mechanism of the 110 °C TL peak of quartz

The role of thermal activation in the pre-dose sensitization of the 110 °C TL glow peak of quartz has been hypothesized to transfer holes from reservoir centre, R, to luminescence centre, L. But, the thermal treatment has been reported to sensitize this peak, also, in an independent mode. So, a comparative analysis of the impact of thermal and pre-dose treatment on the TL properties of the 110 °C signal, observed by various workers, has been undertaken in this paper. Also experiments were carried out to observe thermal sensitization component at the temperatures which are used in the pre-dose sensitization measurements. The study seems to support the existence of an inherent pure thermal sensitization component in the pre-dose sensitization mechanism.     

Comparison between the low temperature thermoluminescence spectra in annealed LiF:Mg,Cu, LiF:Mg,Cu,P and LiF:Mg,Cu,Si

Two strong thermal peaks in the wavelength range 220-420 nm have been detected at 128 and 140 K in LiF:Mg,Cu, at 123 and 135 K in LiF:Mg,Cu,P and at 125 and 133 K in LiF:Mg,Cu,Si, respectively. The origin of these main TL peaks is discussed in terms of defect perturbed H-F and V_K-e type recombination, respectively. The relative intensity between the two peaks in each sample and the emission spectra are dependent on the dopants.Annealing at 240-390 °C can modify the low temperature TL features, especially in those samples doped with three impurities. The low temperature data give some clues to select most favourable dopants for future LiF-type dosimeters.     

DyF3: A promising new TL material for gamma dosimetry

This research describes preliminary investigation of some radiation dosimetry characteristics of commercial dysprosium fluoride powder. The as-received aliquot has strong thermoluminescence (TL) emission with one sharp peak at ∼234 °C. The TL characteristics have been examined under excitation of gamma (γ) doses in the range 1 Gy-50 kGy from a ⁶⁰Co gamma source. The dose response was linear up to 100 Gy and a sub-linear response was observed at higher doses. The TL signal is observed to remain stable for aliquots irradiated to γ-doses in the range 1-10 Gy over one month storage period in dark at ambient temperature and humidity conditions. This paper recommends using DyF₃ in doping of TL materials which may be promising for future dosimeter development.     

Enthalpy measurements of La2Te3O9 and La2Te4O11

Enthalpy increment measurements on La₂Te₃O₉(s) and La₂Te₄O₁₁(s) were carried out using a Calvet micro-calorimeter. The enthalpy values were analyzed using the non-linear curve fitting method. The dependence of enthalpy increments with temperature was given as: H°(T) − H°(298.15 K) (J mol⁻¹) = 360.70T + 0.00409T² + 133.568 × 10⁵/T − 149 923 (373 ? T (K) ? 936) for La₂Te₃O₉ and H°(T) − H°(298.15 K) (J mol⁻¹) = 331.927T + 0.0549T² + 29.3623 × 10⁵/T − 114 587 (373 ? T (K) ? 936) for La₂Te₄O₁₁.     

Nanoparticles of Al2O3:Cr as a sensitive thermoluminescent material for high exposures of gamma rays irradiations

Aluminum Oxide (Al₂O₃) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from γ-rays of ¹³⁷Cs. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of γ-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al₂O₃:Cr nanoparticles might be used for the dosimetry of food and seed irradiations.     

Study of electron beam curing process using epoxy resin system

Polymeric matrix composite (PMC) has been used in engineering applications instead of metal in the last few years, due to its corrosion resistance and excellent relation between tensile strength/density and elastic modulus/density. However, PMC materials cured by thermal process require high temperature and are time-consuming. The electron beam (EB) curing technology allows its use at room temperature and reduced curing times, and this is one of the main advantages over thermal technology. The aim of this work is to investigate electron beam curable epoxy formulations to use in filament winding processes to produce composite material with similar or better properties than thermal curable composites. The study has been made with commercial epoxy resins and cationic initiators. The epoxy resin samples were irradiated for few minutes with total dose of 150 kGy. The glass transition temperatures (T_g) were determined by dynamic mechanical analyzer (DMA) and the result was 137 °C. The thermal process was carried out in a furnace following three steps: 4 h at 90 °C, increasing temperature from 90 °C to 130 °C during 4 h and 12 h at 130 °C. The total process time was 20 h. The T_g of this sample was 102 °C.     

Phase relations in the U-Mo-Al ternary system

The phase relations in the U-Mo-Al system of quenched samples annealed at 800 °C for 2 weeks and at 400 °C for 2 months have been established using X-ray powder diffraction, scanning electron microscopy and energy dispersive spectroscopic analysis performed at room temperature. Two ternary Al-rich phases, UMo_2−xAl_20+x and U₆Mo_4+xAl_43−x are found stable at 800 °C and 400 °C. They show significant homogeneity ranges resulting from Mo/Al substitution mechanism on various mixed crystallographic sites, as evidenced by single-crystal structure refinements. Substitution of up to 25 at.% of Al by Mo atoms is also observed for UAl₂ (cubic MgCu₂-type) giving a quite large extension (UAl_2−xMo_x, 0 < x < 0.5) into the ternary system. Larger substitution (0.6 < x < 0.7 at T = 800 °C) stabilizes another ternary Laves phase, UAl_2−xMo_x with the hexagonal MgZn₂-type. There is no detectable solubility of Mo in UAl₄, and it is of the order of 1 at.% in UAl₃. The interaction layers between the γU-Mo alloys and the Al matrix in nuclear fuel plates can be successively estimated as composed of the two- and three-phase fields equilibrium indicated on the assessment of the phase relations drawn for samples heat-treated at 400 °C.     

Thermoluminescent characteristics of topaz from Sabser mine near Sakardu in northern Pakistan

Topaz, a naturally occurring aluminium fluorosilicate mineral, shows thermo-luminescence (TL) after irradiation to gamma rays. The TL characteristics (glow curve, dose response/intensity, sensitivity, energy response, fading, reusability and mechanical stability) of topaz collected from the Sabser mine in the vicinity of Sakardu in northern Pakistan were studied. The purpose of this study was to design and develop a TLD (thermoluminescence dosimeter) based on topaz. The samples of topaz from this mine were cut into square chips of dimensions 3.2 × 3.2 mm with thickness 0.9 mm, which are suitable for the TLD reader. Gamma dose was given to the chips from ⁶⁰Co and/or ¹³⁷Cs gamma irradiators. The TL glow curves of the chips revealed stable peak at about 260 °C. The height of this peak rose linearly with increase of dose levels. The TL response versus dose (calibration curve) showed the linear behaviour between 10⁻² and 10² Gy without saturation. Dose response was independent of gamma energies of ⁶⁰Co and ¹³⁷Cs. The response of standard sized chips of topaz remained constant within ±11% deviation from initial value after 30 cycles of reuse. The rate of fading of topaz chips of this mine were studied up to four months, which was fast for initial few hours and slowed after a few days. The chips remained mechanically stable during handling in all types of experiments. Standard sized topaz chips of Sabser mine can effectively and efficiently be used as a TLD.     

The pre-dose effect in natural white mica (H2KAl3(SiO4)3)

A comprehensive study of the pre-dose effect was carried out for natural white mica. A pre-dose of 1 kGy of γ-radiation followed by thermal activation to 550 °C of fired mica (heated at 800 °C for 10 h) leads to a large increase in the TL sensitivity. The TL response to γ-rays of sensitized aliquots was found to be linear-sublinear while that of unsensitized aliquots was linear-superlinear referring specifically to graphs drawn on a linear-linear scale. The change in the TL sensitivity of mica was explained by using the recombination during heating model. This study is of importance in dating and retrospective dosimetry.     

Microstructure evolution of Ge implanted silicon oxide thin films upon annealing treatments

The structural evolution of silicon oxide films with Ge⁺ implantation was traced with a positron beam equipped with positron annihilation Doppler broadening and lifetime spectrometers. Results indicate that the film structure change as a function of the annealing temperature could be divided into four stages: (I) T < 300 °C; (II) 300 °C ? T ? 500 °C; (III) 600 °C ? T ? 800 °C; (IV) T ? 900 °C. In comparison with stage I, the increased positron annihilation Doppler broadening S values during stage II is ascribed to the annealing out of point defects and coalescence of intrinsic open volumes in silicon oxides. The obtained long positron lifetime and high S values without much fluctuation in stage III suggest a rather stable film structure. Further annealing above 900 °C brings about dramatic change of the film structure with Ge precipitation. Positron annihilation spectroscopy is thereby a sensitive probe for the diagnosis of microstructure variation of silicon oxide thin films with nano-precipitation.     

Permeability of hydrogen and deuterium of Hastelloy XR

Permeation of hydrogen isotope through a high-temperature alloy used as heat exchanger and steam reformer pipes is an important problem in the hydrogen production system connected to be a high-temperature engineering test reactor (HTTR). An experiment of hydrogen (H₂) and deuterium (D₂) permeation was performed to obtain permeability of H₂ and D₂ of Hastelloy XR, which is adopted as heat transfer pipe of an intermediate heat exchanger of the HTTR. Permeability of H₂ and D₂ of Hastelloy XR were obtained as follows. The activation energy E₀ and pre-exponential factor F₀ of the permeability of H₂ were E₀=67.2±1.2 kJ mol⁻¹ and F₀=(1.0±0.2)×10⁻⁸ m³(STP) m⁻¹ s⁻¹ Pa^−0.5, respectively, in the pipe temperature ranging from 843 K (570 °C) to 1093 K (820 °C). E₀ and F₀ of the permeability of D₂ were respectively E₀=76.6±0.5 kJ mol⁻¹ and F₀=(2.5±0.3)×10⁻⁸ m³(STP) m⁻¹ s⁻¹ Pa^−0.5 in the pipe temperature ranging from 943 K (670 °C) to 1093 K (820 °C).