TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Relative response of TL and component-resolved OSL to alpha and beta radiations in annealed sedimentary quartz

Knowledge of the relative luminescence response to alpha and beta radiation is very important in TL and OSL dating. In the present study the relative alpha to beta response is studied in a sedimentary quartz sample, previously fired at 900 °C for 1 h, in the dose region between 1 and 128 Gy, for both thermoluminescence (TL) and linearly modulated optically stimulated luminescence (LM – OSL). The LM – OSL measurements were performed at room temperature and at 125 °C. All OSL signals were deconvolved into their individual components. Comparison of OSL curves after alpha and beta irradiation strongly supports that quartz OSL components follow first order kinetics in both cases. In the case of TL, the relative alpha to beta response is found to be very different for each TL glow-peak, but it does not depend strongly on irradiation dose. In the case of LM – OSL measurements, it is found that the relative behaviour of the alpha to beta response is different for three distinct regions, namely the fast OSL component, the region of medium OSL component originating from the TL glow-peak at 110 °C when stimulation takes place at room temperature and finally the region of slow OSL component. Following stimulation at ambient temperature, the relative alpha to beta response of all components was not observed to depend significantly on dose, with the value of ratio being 0.03 and a tendency to decrease with increasing dose. However, in the case of measurements performed at 125 °C, the relative response of the fast components is much enhanced, and for the remaining components it increases with increasing dose. Special care must be taken to examine the relative alpha to beta response of the fast component at 125 °C which contrasts the relative response of the TL peak at ca. 325 °C. The implications for the dating of annealed quartz are also briefly discussed.     

OSL and TL retrospective dosimetry with a fluorapatite glass-ceramic used for dental restorations

Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) properties of a fluorapatite glass-ceramic have been investigated, with a view to developing a dose assessment technique for medical triage following unplanned exposures of individuals to ionizing radiation. The ceramic is an innovative material used in dental prostheses and restorations. It is strongly sensitive to radiation and the intensity of both the OSL and TL signals are proportional to the absorbed radiation dose. We focused on the optimization of the measuring procedure and investigated characteristics such as reproducibility, fading, minimum detectable dose (MDD), dose response and photon energy response of TL and OSL signals. The dental ceramic exhibited very good reproducibility (<5% at 2σ level) when measured and a linear dose response for a wide range of doses (50 mGy–20 Gy). The MDD values for the samples investigated were ∼5 mGy. The material is not tissue equivalent and the OSL and TL signals are strongly dependent on incident photon energy. Both the luminescence signals exhibited significant fading during the first few hours after irradiation. Its rate was dependent on the parameters of measurement. The results indicate that the material can be used for the purposes of accident dosimetry, however, the fading and photon energy response have to be properly corrected for a reliable dose assessment.     

Photon dosimetry methods outside the target volume in radiation therapy: Optically stimulated luminescence (OSL), thermoluminescence (TL) and radiophotoluminescence (RPL) dosimetry

Dosimetry methods outside the target volume are still not well established in radiotherapy. Luminescence detectors due to their small dimensions, very good sensitivity, well known dose and energy response are considered as an interesting approach in verification of doses outside the treated region. The physical processes of thermoluminescence (TL), radiophotoluminescence (RPL) and optically stimulated luminescence (OSL) are very similar and can be described in terms of the energy band model of electron-hole production following irradiation.This work is a review of the main dosimetric characteristics of luminescence detectors which were used in experiments performed by EURADOS Working Group 9 for in-phantom measurements of secondary radiation (scattered and leakage photons). TL LiF:Mg,Ti detectors type MTS-7 (IFJ PAN, Poland), types TLD-100 and TLD-700 (Harshaw), OSL Al₂O₃:C detectors type nanoDot™ (Landauer Inc.) and RPL rod glass elements type GD-352M (Asahi Techno Glass Coorporation) are described. The main characteristics are discussed, together with the readout and calibration procedures which lead to a determination of absorbed dose to water.All dosimeter types used show very good uniformity, batch reproducibility and homogeneity. For improved accuracy, individual sensitivity correction factors should be applied for TL and OSL dosimeters while for RPL dosimeters there is no need for individual sensitivity corrections.The dose response of all dosimeters is linear for a wide range of doses.The energy response of GD-352M type dosimeters (with Sn filter) used for out-of-field measurements is flat for medium and low energy X-rays.The energy dependence for TLDs is low across the range of photon energies used and the energy correction was neglected. A significant over response of Al₂O₃:C OSLDs irradiated in kilovoltage photon beams was taken into account. The energy correction factor f_en was calculated by using the 2006 PENELOPE Monte Carlo code.With suitable calibration, all dosimeter types are appropriate for out-of-field dose measurements as well as for the in-phantom measurements of radiotherapy MV X-rays beams.     

Interlaboratory beta source calibration using TL and OSL on natural quartz

Laboratories using luminescence methods for dose reconstruction have to make interlaboratory source calibrations—initially this will be a single isotope beta or gamma source using one particular reference material. The procedure requires not only the administration of exact doses to the material but also the uniform handling of the dosimetric material and standardization of the procedures. An interlaboratory calibration of an Sr-90 beta source was recently carried out by our five laboratories which are involved in a retrospective project. The reference material was quartz but there were difficulties finding sufficient suitable quartz. Five different batches were obtained from the Merck company and tested for sensitivity, linearity and stability of the 340°C peak, the 1992 batch was found to be the most appropriate. The irradiations were performed at the Secondary Standard Dosimetry Laboratory at GSF using a Co-60 source as well as the in situ measurements with an ionization chamber, calibrated to the primary standards of PTB Braunschweig. Irradiated and unirradiated quartz was distributed to the five laboratories and although different procedures were used for thermoluminescence and optically stimulated luminescence, the source calibrations for the different laboratories agreed within ±3% compared to the previous calibrations of the laboratories.     

Comparison of luminescence lifetimes in quartz following alpha and beta irradiation

The change in optically stimulated luminescence sensitivity of quartz associated with annealing is accompanied by a change in luminescence lifetime, whereas, in contrast, the change in sensitivity associated with irradiation by alpha particles rather than by beta particles is not accompanied by any change in luminescence lifetime. This is compatible with the usual ‘saturation’ explanation for the significantly lower luminescence sensitivity of quartz to alpha irradiation compared to the luminescence sensitivity to beta irradiation.     

OSL, RL and TL characterization of rare-earth ion doped K2YF5: Application in dosimetry

Optically stimulated luminescence (OSL) properties of K₂YF₅ crystals singly doped with different concentrations of Tb³⁺ ions and doubly doped with Tb³⁺ and Ce³⁺ or Tb³⁺ and Dy³⁺ have been investigated for the first time. Radioluminescence spectra and OSL efficiency for stimulation with different wavelengths of light have been analyzed for each compound. Also, dosimetric characteristics of the most efficient composition, namely K₂YF₅:1 at.% Tb³⁺, have been studied. Finally, the OSL signal peculiarities for K₂YF₅:1 at.% Tb³⁺ have been compared to those of a commercial Al₂O₃:C dosimeter.     

Crushing effects on TL and OSL on quartz: relevance to fault dating

The effect of crushing on the TL and OSL signals in quartz was investigated to examine the feasibility of using OSL and TL for dating of faulted rocks. 275°C TL signals were not reduced by crushing by hand (mortar and pestle), in a pellet die press, or using an automatic mortar and pestle, but the sensitivity of the 100°C TL signal to a test dose decreased in crushed samples. Green light-stimulated OSL signal intensities were not decreased after crushing, but showed strongly increased inter-aliquot variability after crushing. We concluded that OSL and TL in quartz might be useful to characterize the crushing history of quartz in fault rocks, but their usefulness in dating fault events was not evident because we did not find evidence of signal zeroing under the conditions used in this study.     

Accumulation features and TL of TLD-500 detectors in a wide temperature range at pulsed and continuous high-dose irradiation

The results of a comparative research of thermoluminescence (TL) of TLD-500 detectors based on anion-defective corundum irradiated with continuous and pulsed X-ray and pulsed electron beams in a range of doses of 0.3 ÷ 10⁷ Gy, dose rates of 0.02–2.6·10¹¹ Gy/s, and in a temperature range of 300–950 K are presented. It is found that, in contrast to continuous irradiation, upon pulsed irradiation with a duration of 10 ns and dose rate of P_P ≥ 5·10⁶ Gy/s, the first linear region of dose dependences for TL peaks at 450, 580 and 830 K is, instead of saturation, followed by a second one with a smaller slope at doses near 2, 200 and 10³ Gy. Moreover, the slope of the second region increases with growing P_P. It was also found that dose dependence for the peak at 830 K in the area of the first linear region at 10–10³ Gy remains invariable at P_P ≤ 10¹⁰ Gy/s. It is shown that the upper limit of doses registered by TLD-500 detectors can be increased to 2·10³ and 6·10⁶ Gy for continuous and pulsed irradiation, respectively. New broadband UV luminescence with a maximum hν = 4.1 eV and half width H = 0.85 eV was registered within the TL peak spectrum at 830 K. Besides, the optical depletion spectrum in which a single band with hν = 5.2 eV and H = 1.6 eV is observed was investigated for a trap causing a peak at 830 K.     

OSL properties of NaCl relative to dating and dosimetry

The luminescence properties of NaCl are discussed. Attention is focussed predominantly upon the optically stimulated luminescence (OSL) signal (UV emission) of NaCl (420–560 nm stimulation). The results from experiments relevant to geological dating applications, such as signal resetting, dose response and thermal stability, are described. The behaviour of the OSL signal observed was found to be favourable for dating, with both the thermal stability and dose response suggesting a range of at least 10 ka. Signal resetting via optical exposure was found to be extremely rapid and no evidence of either thermoluminescence or OSL signals was found following re-crystallization. The potential for dating natural salt deposits, as found in various arid environments, appears to be good.     

LiF:Mg,Ti (MTT) TL detectors optimised for high-LET radiation dosimetry

The properties of LiF:Mg,Ti (distributed as, e.g., TLD-100 or MTS-N), the most frequently used thermoluminescent detector, have been optimised for measurements of sparsely ionising radiation (gamma rays), typically encountered in radiation protection or clinical dosimetry. However, these detectors need also to be applied in conditions of mixed-field dosimetry with a high-LET component, such as those encountered in heavy ion beams or in space.

At the Institute of Nuclear Physics in Kraków a new type of LiF:Mg,Ti detector (named MTT) has been recently developed through modification of its dopant composition. This composition is intended to increase the detection efficiency after a dose of high-LET radiation. The concentration of dopants in the MTT material is: C_Mg=50 ppm, and C_Ti=120 ppm, i.e. about a three times less of magnesium and about 10 times more of titanium content, compared with the standard MTS-N. The MTT TL detectors feature an increased relative efficiency to high-LET radiation, which for 5 MeV alpha-particles is about twice that of standard LiF:Mg,Ti. The response of MTT detectors has been studied in charged particle beams of the HIMAC accelerator in Chiba, Japan and in Dubna, Russia. The main foreseen application of MTT detectors are dose measurements in space. The dose after high-LET exposure can be estimated from the difference of the response of MTS and MTT detectors. In the near future MTT detectors will be applied in the “Matroshka” experiment. Within this experiment a specially constructed human phantom will be exposed in free space (outside the International Space Station) for 1 year. The phantom will incorporate a few thousand measuring points enabling radiation doses to particular organs to be determined.     

Thermoluminescence energy response of TLD-100 subjected to photon irradiation using Monte Carlo N-particle transport code version 5

Useful TL properties of TLD-100 that is an excellent candidate for using in TL dosimetry of ionizing radiation are demonstrated. This study is focused on response of TLD-100 subjected to photon irradiation. The thermoluminescence (TL) response of TLD-100 subject to various photon energy, ranging from 20 keV to 6 MeV, was investigated as energy absorbed in the TL material using Monte Carlo N-Particle transport code version 5 (MCNP5). The input parameters included in this study are experimental geometry specification, source information, material information, and tallies. Tally F6 is used in this simulation. The results from MCNP5 simulation show good agreement with previous experimental data. However, the data obtained from the simulation are greater than the experimental data especially in lower energy ranges.     

Application of the optically stimulated luminescence (OSL) technique in space dosimetry

This paper reviews the state of the optically stimulated luminescence (OSL) technique for space dosimetry applications, focusing on the properties of carbon-doped aluminum oxide (Al₂O₃:C). New data presented include the most complete and recent values for the relative efficiency η_HCP,γ for heavy charged particles as a function of the incident radiation's linear energy transfer (LET), obtained through ground-based experiments at heavy ion accelerators. We also discuss the factors influencing the OSL efficiencies, the LET-dependent properties of Al₂O₃:C, and the experience gained from past space experiments using Al₂O₃:C. The characterization of the OSL efficiency values as a function of LET allows the use of the OSL of Al₂O₃:C in combination with plastic nuclear track detectors for personal dosimetry of astronauts, as proposed by the NCRP Report 142.     

Monte Carlo simulations of TL and OSL in nanodosimetric materials and feldspars

The study of luminescent materials consisting of nanoclusters is an increasingly active research area. It has been shown that the physical properties of such nanodosimetric materials can be very different from those of similar conventional microcrystalline phosphors. In addition, it has been suggested that traditional energy band models may not be applicable for some of these nanodosimetric materials, because of the existence of strong spatial correlations between traps and recombination centers. The properties of such spatially correlated materials have been previously simulated by using Monte Carlo techniques and by considering the allowed transitions of charge carriers between the conduction band, electron traps and recombination centers. This previous research demonstrated successfully the effect of trap clustering on the kinetics of charge carriers in a solid, and showed that trap clustering can significantly change the observed luminescence properties. This paper presents a simplified method of carrying out Monte Carlo simulations for thermoluminescence (TL) and optically stimulated luminescence (OSL) phenomena, based on a recently published model for feldspar. This model is based on tunneling recombination processes involving localized near-neighbor transitions. The simulations show that the presence of small clusters consisting of a few traps can lead to multiple peaks in both the TL and linearly modulated OSL signals. The effects of donor charge density, initial trap filling and cluster size are simulated for such multi-peak luminescence signals, and insight is obtained into the mechanism producing these peaks.     

Features of OSL and TL properties of anion-defective corundum crystals exposed to thermo-optical treatment

The results of systematic investigation of the mechanisms and role of phototransfer in TL and OSL processes in α-Al₂O_3−δ crystals under controlled filling of the main and deep traps depleted at 450 and 720 K, respectively, are presented.Optical depletion spectra of the main and deep traps were measured and compared. It was found that green light stimulation only depletes the main trap, while blue light depletes both the main and deep traps. Optical depletion of the deep trap results in phototransfer of charges that can be realized by 2 mechanisms: either through the main trap to recombination centers or directly to the latter. However, the dominant contribution to the OSL signal is provided by phototransfer through the main trap. It is also found that UV emission at 3.7 eV dominates over F-emission at 3.0 eV in the phototransferred TL spectrum. It is assumed that this UV emission is not related to the F⁺ centers.     

Kinetics of isolated peak 5 in TLD-100 following 165°C post-irradiation annealing

Peak 5 in the glow curve of TLD-100 (at a temperature of approximately 200°C) was studied as a function of post-irradiation annealing at 165°C. Computerized glow peak analysis shows that the order of kinetics of peak 5 increases from 1.2 ± 0.05 (1 SD) following 165°C annealing for five minutes to 1.72 ± 0.07 (1 SD) following annealing at 165°C for thirty minutes. Extrapolation of the results to zero annealing time yields a value of kinetic order consistent with unity. The glow curve analysis also indicates that peak 4 (the satellite peak at approximately 175°C) is undetectable even at the lowest annealing duration of 5 minutes. The high temperature satellite of peak 5 (peak 6 at approximately 225°C) grows with increasing annealing time to 10% of the intensity of peak 5 after annealing for 30 min. Glow curve analysis including peak 6, however, does not significantly change the conclusions regarding the increase in the order of kinetics of peak 5 as a function of annealing time or the consistency of the extrapolated results with kinetic order unity at zero annealing time. Analysis of isothermal decay curves at 165°C shows that the relative intensity of peak 4 to peak 5 decreases with increasing annealing time, from 8% after 5 min annealing to 0.5% after 30 min annealing.     

TL, OSL, and phototransferred TL in beta-irradiated anion-defective Al2O3

The behavior of TL, OSL and PTTL under thermal and/or optical stimulation in beta-irradiated -Al₂O₃ was investigated. The noticeable change of the shape of the main TL peak after thermal or optical stimulation clearly shows that this peak is related to at least two traps. The OSL curves recorded after preheating up to a given increased end temperatures are described by two exponential decays curves. The first one is associated to the decay of the traps responsible for the main TL peak. The second exponential is related with the phototransfer from the deep to the main traps. A simple model of the OSL process, based on simultaneous refilling of shallow traps and their reverse filling due to phototransfer from deep traps, under illumination with light is proposed. The model describes well the obtained experimental data.     

Comparative investigations of TL and OSL in KCI:Eu2+ crystals irradiated with UV and X-rays

Abstract

We present thermoluminescence (TL) glow curves and optical stimulated luminescence (OSL) response from both KCl:Eu²⁺ crystals irradiated with soft X-rays (20 KV, 80 μA) and ultraviolet light (230 nm). Two situations take place. First, we observed that for long time F-light bleaching (560 nm) the typical TL glow curve of X-rays irradiated KCl:Eu²⁺ resembles the TL glow curve of UV-irradiated samples. Second, along with OSL measurements, we have performed a thermal bleaching and we have addressed F and F_z participation in OSL. These results provide us a supportable correlation between F and F_z as responsible centers for OSL and TL processes.     

Synthesis and luminescence in some fluoro-silicates for the possible applications in OSL dosimetry

Various fluoro-silicates, viz. M₂SiF₆ (M=Li, Na, K) were synthesized by reacting the mixture of corresponding salt and silicic acid with Hydrofluoric acid. The thermal analysis of these materials was performed. These materials were doped with ions Ce³⁺, Cu⁺, Ag⁺ and photoluminescence, TL, OSL properties were studied. Intense TL and OSL was observed from these materials. Due to decomposition during heating, these materials may not be suitable as TL Phosphors, but will be good phosphors for radiation dosimetry using OSL.