On the peculiarities of peak 4 in LiF TLD-100

A detailed study of the different glow curves that can be obtained from LiF TLD-100 is presented. This study has been made measuring glow curves after different preparation and readout conditions, and using computerized glow curve analysis to resolve individual glow peaks. In particular, the evolution of peak 4 has been carefully followed. This peak is detected with very different intensity, shape and temperature position depending on the characteristics of the cooling stage of the preparation thermal treatment, and also on the readout heating rate. After very fast cooling and also for fast readout, peak 4 is the most intense peak in the TLD-100 glow curve. The unique behaviour of peak 4 is discussed in the light of the current models for thermoluminescent processes.     

Thermoluminescence kinetics analysis of α-Al2O3:C at different dose levels and populations of trapping states and a model for its dose response

Kinetic analysis of a α-Al₂O₃ (TLD-500) thermoluminescent (TL) dosimeter was performed following irradiating the samples with ⁶⁰Co gamma rays. The number of glow peaks contained in the complex glow curve of this phosphor was identified using the T_m ? T_stop method, which demonstrates three component glow peaks. A computerized glow curve deconvolution (CGCD) program was used to determine the trapping parameters of the three constituent glow peaks obtained at different dose levels and different populations of trapping states. To analyze the number of constituent glow peaks, we used a kinetic model to describe both the irradiation and heating stages. The predictions of the model for the TL response agreed well with the experimental data when three dosimetry traps were incorporated.     

Non-linearity of the high temperature peak area ratio of 6LiF:Mg,Ti (TLD-600)

Thermoluminescent dosemeters of ⁶LiF:Mg,Ti (TLD-600) were exposed to high-energy heavy ion beams (He, C, Ne, and Ar) and ¹³⁷Cs γ-rays and the glow curves were analyzed. The height of the main peak (peak 5) at about 200°C slightly increased for He from γ-rays and decreased for heavier ions with increasing Linear Energy Transfer (LET). Whereas the high temperature peak (peak 7) area around 260°C simply increased. Non-linearity was seen between the LET and the high temperature peak (peak 7) area ratio (HTR) which was calculated as the TL integrated over 225–275°C from the peak 5 normalized glow curve. Based on these results, average LET and quality factor were estimated for an assumed LET spectra of space radiation by using the HTR method. Considerable differences were found between these estimations and true values.     

Feasibility study of CaSO4:Eu,CaSO4:Eu,Ag and CaSO4:Eu,Ag(NP) as thermoluminescent dosimeters

This work evaluates the dosimetric properties of crystals of CaSO₄ doped with unusual elements, such as europium (Eu) and silver (Ag), including their nanoparticle forms, after the incorporation of glass or Teflon and compares them with well-known thermoluminescent dosimeters (TLD). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. Optical spectroscopy confirmed the presence of Eu³⁺ in the crystal matrix and a luminescent gain due the presence of silver nanoparticles. The composites showed thermoluminescent emission glow curves, with a single peak centered at approximately 200 °C for pellets with Teflon and at 230 °C for pellets with glass. The dosimeters based on calcium sulfate doped with europium and silver nanoparticles provided the most intense thermoluminescent (TL) emission of the composites studied. In comparison with commercial TLD, such as LiF:Mg,Ti and CaSO₄:Dy, the CaSO₄:Eu,Ag(NP)+glass produced in this work presented similar low detection limits and higher sensitivity. The new methods for the preparation of dosimeters and the incorporation of glass are shown to be viable because all of the samples presented a linear, reproducible and first order kinetic TL emission.     

Dose response of thermoluminescence emission spectra of LiF:Mg,Ti with different Mg, Ti impurity concentrations

The dose response of the TL emission spectra of an LiF:Mg,Ti (TLD-100) sample and three LiF:Mg,Ti samples with different impurity concentrations (0–6 ppm Ti and 80–100 ppm Mg) have been measured. At a dose less than 22 Gy the emission spectrum of the TLD-100 sample comprises one emission band at 420 nm. The sample without Ti shows also one emission band but now at 620 nm. The spectra of the other two samples comprises two emission bands at 420 nm and 620 nm of which the intensity of the 420 nm band increases with increasing Ti concentration. The dose response of the glow peaks is different for peaks at different temperatures and emission bands. From these observations it can be concluded than in LiF:Mg,Ti at least some of the traps and luminescent centers are coupled.     

Thermoluminescence of nanocrystalline LiF:Mg, Cu, P

Nanocrystalline LiF:Mg, Cu, P of rod shape (about 30-40 nm in diameter and 0.3-0.5 μm in length) has been prepared by the chemical co-precipitation method. Thermoluminescence (TL) and dosimetric characteristics of the nanocrystalline phosphor are studied and presented here. The formation of the material was confirmed by the X-ray diffraction (XRD). Its shape and size were also observed by transmission electron microscope (TEM). The TL glow curve of the nanocrystalline powder shows a single peak at 410 K along with four overlapping peaks of lesser intensities at around 570, 609, 638 and 663 K. The observed TL sensitivity of the prepared nanocrystalline powder is less than that of the commercially available “Harshaw TLD-700H hot-pressed chips” at low doses but it still around three times more than that of LiF:Mg, Ti (TLD-100) phosphor. The 410 K peak of the nanomaterial phosphor shows a very linear response with exposures increasing up to very high values (as high as 10 kGy), where all the other thermoluminesent dosimeters (TLD) phosphors show saturation. This linear response over a large span of exposures (0.1 Gy-10 kGy) along with negligible fading and its insensitivity to heating treatments makes the nanocrystalline phosphor useful for its application to estimate high exposures of γ-rays. The ‘tissue equivalence’ property of this material also makes it useful over a wide range of high-energy radiation.     

An improved experimental procedure of separating a composite thermoluminescence glow curve into its components

We present an improved experimental procedure of separating a composite thermoluminescence glow curve into its components. Careful monitoring of the isothermal cleaning process using the initial rise method ensures the complete thermal removal of TL peaks. Digital subtraction of two experimental TL glow curves yields individual experimental TL glow peaks. Several standard methods (initial rise and whole glow curve) are used to obtain the energy values and frequency factors of the traps. The method has been used successfully to analyze the well-known composite TL glow curve of the dosimetric material LiF (TLD-100). The limitations of the method are illustrated by analyzing the highly complex TL glow curve of a UV irradiated synthetic calcite consisting of at least 6 TL peaks. Although the method works best for TL glow curves described by first order kinetics, it should also be applicable to more general kinetics.     

OSL and TL in TLD-100 following alpha and beta irradiation: Application to mixed-field radiation dosimetry

The optically stimulated luminescence (OSL) of LiF:Mg,Ti (TLD-100) following irradiation by beta and alpha particles was investigated by measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. The OSL excitation spectra of all the samples following both beta and alpha irradiation are very similar.Identical emission bands with very similar relative intensities following both beta irradiation and alpha particle irradiation have been recorded in the OSL induced in nominally pure LiF mono and TLD-100 polycrystals. The identical excitation and emission bands in the doped and pure crystals are strong evidence indicating that the observed OSL is due to an intrinsic trapping structure. The OSL has indeed been previously attributed to F₂ centers and F₃⁺ centers.The preferential excitation of OSL compared to TL following high ionisation density (HID) alpha irradiation is naturally explained via the identification of OSL with the “two-hit” F₂ or F₃⁺ center, whereas the major component of composite TL glow peak 5 is believed to arise from a “one-hit” complex defect. This discovery allows near-total discrimination between HID radiation and low ionisation density (LID) radiation and may have significant potential in mixed-field radiation dosimetry.     

Computerized glow curve deconvolution of thermoluminescent emission from polyminerals of Jamaica Mexican flower

The aim of this work is to study the main thermoluminescence (TL) characteristics of the inorganic polyminerals extracted from dehydrated Jamaica flower or roselle (Hibiscus sabdariffa L.) belonging to Malvaceae family of Mexican origin. TL emission properties of the polymineral fraction in powder were studied using the initial rise (IR) method. The complex structure and kinetic parameters of the glow curves have been analysed accurately using the computerized glow curve deconvolution (CGCD) assuming an exponential distribution of trapping levels. The extension of the IR method to the case of a continuous and exponential distribution of traps is reported, such as the derivation of the TL glow curve deconvolution functions for continuous trap distribution. CGCD is performed both in the case of frequency factor, s, temperature independent, and in the case with the s function of temperature.     

Nanodosimetric kinetic model incorporating localized and delocalized recombination: Application to the prediction of the electron dose response of the peak 5a/5 ratio in the glow curve of LiF:Mg,Ti (TLD-100)

A kinetic model combining both localized and delocalized recombination is described which is based on different filling rates as a function of irradiation electron energy of a spatially correlated trapping center/luminescent center (TC/LC) complex. Following irradiation and thermal de-trapping the locally trapped electron-hole configuration is assumed to give rise to peak 5a and the e-only configuration to peak 5 in the glow curve of LiF:Mg,Ti (TLD-100). The model is capable of simulating the linear/supralinear dose response of composite peak 5, the dependence of the supralinearity on photon energy and the ratio of the intensities of peak 5a to peak 5 as a function of dose. However, this is achieved only by invoking the presence of band-tail states which allow thermally induced hopping leading to semi-localized recombination in the recombination mechanism of the e-only configuration.     

A computer program for the deconvolution of the thermoluminescence glow curves by employing the interactive trap model

An efficient computer program has been developed to deconvolute thermoluminescence (TL) glow peaks and optically stimulated (OSL) curves by employing a method of the interactive trap model (ITM). The program is designed to be used easily on the MS Windows-based computer with a graphical user interface. This program could be used to analyze the TL glow curves by using the traditional first-order kinetics (1OK), second-order kinetics (2OK), general order kinetics (GOK), mixed order kinetics (MOK) and the general approximation (GA) method as well as ITM. The program was tested with the generated data and the experimental results of deconvoluted TL glow curves of LiF TLD-100 by assigning five interacting traps and one recombination center. A complete version with full functionalities of this program can be downloaded from the web site http://physica.gnu.ac.kr/TLanal.     

Newly developed highly sensitive LiF:Mg,Cu,Si TL discs with good stability to heat treatment

The preparation method and some dosimetric properties of the new LiF:Mg,Cu,Si discs are presented. The effect of heat treatments on LiF:Mg,Cu,Si was investigated. The shape of the glow curve for LiF:Mg,Cu,Si is similar to that for standard LiF:Mg,Cu,P (GR-200A), and shows minimal differences when annealed in the range from 260 °C to 290 °C for 10 min. The TL sensitivity for LiF:Mg,Cu,Si is much lower than that for GR-200A, but is 35 times larger than that for TLD-100 and is slightly higher than that for HMCP. The height of the high-temperature peaks for LiF:Mg,Cu,Si is not only lower than that for GR-200A, but also lower than that for HMCP. The glow curve shape of LiF:Mg,Cu,Si annealed at 260 °C for different times shows minimal differences and TL response remains stable. These results indicate that the new LiF:Mg,Cu,Si disc has a good stability to thermal treatments and a lower residual TL signal.     

Dose response of F center optical absorption in LiF:Mg,Ti (TLD-100)

Optical absorption (OA) of nominally pure single crystal LiF following beta irradiation was measured in order to estimate, the energy and width of the dominant F-band with minimum interference from dopant-related bands. The OA dose response of LiF:Mg,Ti was measured to 30,000 Gy, a level of dose sufficiently high to observe total saturation of the F band, which, we believe, reduces uncertainty in the estimation of the dose filling constant. The dose filling constants for the OA bands associated with the trapping center (4 eV) and competitive center (5.45 eV) responsible for the major dosimetric TL glow peak 5 were also determined. The results of these studies will be used in the framework of a kinetic model which includes the effects of radiation created defects and which will aid in the investigation of the capability of Track Structure Theory to predict OA heavy charged particle (HCP) relative efficiencies.     

Synthesis and thermoluminescence characterization of Na6Mg(SO4)4:RE (RE = Ce,Tb) phosphors

Thermoluminescence (TL) properties of sulfate-based phosphors activated by different rare earths have received tremendous attention to the field of radiation dosimetry. Those TL materials based on CaSO₄ have been widely applied for medical and environmental dosimetry. Taking this fact into account we have synthesized Na₆Mg(SO₄)₄ doped with Ce and Tb by wet chemical method. The prepared phosphor was characterized by XRD, FTIR, photoluminescence (PL) and thermoluminescence. For TL study, the phosphor is irradiated with γ-rays from ⁶⁰Co source. For studying luminescence properties, the prepared phosphor was annealed at different temperatures and effects of these annealing temperatures on Na₆Mg(SO₄)₄ samples are investigated and quantified. The changes in the glow curve and PL emission spectrum are also investigated as a function of annealing temperature and the annealing temperature was optimized. For calculation of trapping parameters various methods such as peak shape (PS) method, initial rise (IR) method, various heating rate (VHR) method, and computerized glow curve deconvolution (CGCD) are employed.     

Study of a new Lif:Mg,Cu,P formulation with enhanced thermal stability and a lower residual TL signal

This paper presents results obtained for a new LiF:Mg,Cu,P (HMCP) preparation with modified Mg and Cu concentrations. The shape of the HMCP glow curve shows minimal differences for annealing in the range from 523 to 543 K for 10 min. The thermoluminescence (TL) readout value remained stable when annealed in the range from 513 to 543 K for 10 min. The new formula allows heating of the material to higher temperatures than that originally employed for the well-known GR-200A dosemeter, practically without losses in sensitivity. The TL sensitivity is approximately half of that for the GR-200A, and still 29-fold greater than that for the TLD-100 dosemeter, and the residual signal is approximately five-fold lower than for the GR-200A. These results indicate that the new TL material shows enhanced thermal stability and a lower residual TL signal at a small TL sensitivity cost. The heat treatment temperatures are related to concentrations of Mg and Cu in LiF:Mg,Cu,P.     

Thermoluminescence glow curve deconvolution of LiF:Mg,Cu,Si with more realistic kinetic models

Thermoluminescence (TL) glow curves of LiF:Mg,Cu,Si were deconvoluted with the introduction of enhanced physical model which envisages that both electrons and holes, produced by ionization radiation and trapped at the respective traps, can be thermally released into the conduction and the valence band, respectively and the holes may also radiatively recombine with electrons at the electron recombination centers. The model is more generalized than the ordinary trap interaction model which only permits the traffic of electrons through the conduction band. An effective numerical analysis method was developed to calculate the glow curve to be compatible with the measured curves. The validity of the numerical method was verified through artificially generated TL glow curves for a wide range of trap parameters. In order to identify TL kinetics of LiF:Mg,Cu,Si with higher accuracy, its glow curves were deconvoluted for two more generalized models, namely, the Schön–Klasens model and the Chen–Pagonis–Lawless model as well as the ordinary trap interactive model. The parameters in the more generalized multi-trap multi-recombination center (MTMR) model were found to be consistent with the quasi-static approximation(QSA) method.     

Analysis of neutron and gamma ray doses accumulated during commercial Trans-Pacific flights between Australia and USA

During recent commercial Trans-Pacific passenger flights between Sydney and several major cities in the USA, the neutron and gamma dose equivalents in the aircraft cabin were evaluated with superheated Bubble dosimeters, thermoluminescence dosimeter chips (TLD-600 and TLD-700) and a miniature electronic dosimeter. After a total 73-hour flight time the accumulated neutron and gamma dose equivalents were evaluated to be 39.7 μSv and 74.0 μSv respectively. The thermoluminescence (TL) glow curves of the dosimeter chips were assayed at a ramp heating rate of 10°C s⁻¹ up to 400°C. By using the Bubble and electronic dosimeter data it was possible to isolate explicitly the neutron and gamma dose components from the deconvoluted TL-glow curve of the TLD-600 chips. The application of Bubble dosimeter and TLD for an accurate estimation of the radiation exposure to air crews and frequent flying passengers is suggested.     

Energy dependence of TLD-900 dosimeters exposed to low energy X-rays

This work investigates the energy dependence of CaSO₄:Dy (TLD-900) thermoluminescent dosimeters to low energy X-rays. Dosimeters were exposed to X-ray radiation qualities between 30 and 250 kVp for three air kerma values: 100, 250 and 500 mGy. The detector thermoluminescent response as a function of air kerma and the detector's relative kerma sensitivity with respect to ⁶⁰Co as a function of effective energy were obtained. Monte Carlo and analytical calculations were also performed. A maximum relative kerma sensitivity of 12 is found for a 22 keV effective energy corresponding to the 50 kVp X-ray beam. Monte Carlo and analytical calculations accurately describe trends in the energy dependence curve as a function of photon energy though they predict lower values for the relative kerma sensitivity. Maximum difference is observed at the lowest energy measured (16 keV) where experimental data is 2.1 and 2.3 times greater than Monte Carlo and analytical calculations, respectively. The difference between measurements and Monte Carlo-calculated predictions is attributed to the intrinsic energy dependence of TLD-900. Values of intrinsic energy dependence estimated from the measured relative TL kerma sensitivity together with the MC and analytical calculated values of kerma energy dependence were found to be independent of beam quality in the region from 33 to 142 keV effective energies.     

Thermoluminescence and photoluminescence characteristics of K2YF5: Tb3++PTFE irradiated with 90Sr/90Y beta particles

This article presents results of thermoluminescence (TL) and photoluminescence (PL) measurements performed on beta-irradiated K ₂YF ₅:Tb ³⁺+PTFE pellets. K ₂YF ₅ crystals doped with 0.1% of trivalent optically active Tb ³⁺ ions in pellets form were investigated. The TL glow curve of K ₂YF ₅:Tb ³⁺+PTFE has a simple structure with two well-defined peaks centered at 170 and 307 °C. The TL sensitivity of the K ₂YF ₅:Tb ³⁺+PTFE irradiated with beta radiation was found to be higher than that of commercial phosphor TLD-100 (LiF:Mg,Ti), at the same conditions of irradiation and readout. Moreover, PL measurements performed on the terbium doped material show the presence of Terbium as Tb ³⁺ in the material.     

Investigations of thermoluminescence properties of multicrystalline LiF: Mg,Cu, Si phosphor prepared by edge defined film fed growth technique

Thermoluminescence (TL) properties of LiF: Mg, Cu, Si phosphor prepared in multicrystalline form using edge defined film fed growth (EFG) technique has been investigated. The effect of preparation route on TL properties and thermal stability has been studied. To improve the TL dosimetry properties, phosphor is subjected to different annealing temperatures ranging from 250 °C to 450 °C. The shape of the glow curve structure and peak temperature remains similar at different annealing temperatures, however peak intensities vary. The consistency in the glow curve structure with annealing temperature elucidate that TL trapping states are stable in nature. Thermal annealing at 300 °C for 10 min gives maximum TL intensity with main dosimetry peak at 209 °C. The TL intensity of the main dosimetry peak is increased by a factor of five as compared to as-grown crystal. The thermal stability of LiF: Mg, Cu, Si is found to be better than LiF: Mg, Cu, P. Trapping parameters are calculated to have an insight study of defect states. A simple glow curve structure, tissue equivalency, thermal stability, low residual signal, linear response and reusability makes LiF: Mg, Cu, Si a suitable phosphor for radiation therapy, radio diagnostics and personnel dosimetry applications.