Influence of the irradiation temperature on TL sensitivity of Al2O3:C (original) (raw)
Geochronometria, 2013
The influence of electron-phonon interaction on the shape of the optically stimulated luminescence decay curve of Al 2 O 3 :C has been studied using thermally assisted optically stimulated luminescence (TA-OSL). The minimum detectable dose (MDD) of a phosphor depends on the standard deviation of the background signal which affects the signal-to-noise ratio. The standard deviation of the background signal reduces at lower stimulation light intensity while the readout time increases. Further, measurement at higher temperature enhances the OSL signal with faster decay due to the temperature dependence of photo-ionization cross-section. To achieve the same decay constant and more signal, the temperature of measurement was raised. As a result of lowering the stimulation intensity at higher temperature (85°C) the overall MDD of α-Al 2 O 3 :C was found to improve by 1.8 times. For extension of dose linearity in higher range, deeper traps were studied by simultaneous application of CW-OSL and thermal stimulation up to 400°C, using a linear heating rate of 4K/s. By using this method, two well defined peaks at 121°C and 232°C were observed. These TA-OSL peaks have been correlated with two deeper defects which can be thermally bleached at 650°C and 900°C respectively. These deeper defects are stable up to 500°C, so they can store absorbed dose information even if the sample is inadvertently exposed to light or heat. The dose vs. TA-OSL response from deep traps of α-Al 2 O 3 :C was found to be linear up to 10 kGy, thus extending its application for high dose dosimetry.
TL, OSL, and phototransferred TL in beta-irradiated anion-defective Al2O3
Radiation Measurements, 2004
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 ÿrst 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 reÿlling of shallow traps and their reverse ÿlling due to phototransfer from deep traps, under illumination with light is proposed. The model describes well the obtained experimental data.
Recovery of α-Al2O3 from Ionizing Radiation Dosimetric Sensors
Materials Research, 2015
Corundum, sapphire or α-Al 2 O 3 is an important technological material in many optical and electronic applications such as solid-state lasers, optical windows and, more recently, as a radiation detector. Landauer (Glenwood, IL, USA) accumulated large number of archived and stored Luxel™ dosemeters composed of Al 2 O 3 :C, which were subjected to a recovery process. Due to the importance of this advanced crystalline material in OSL dosimetry, a recovery process was developed based on the dosemeters calcination and Al 2 O 3 :C has been reused in manufacturing of new dosemeters. This paper does not aim to optimize the recovery process, but provides an opportunity to study the involved process parameters and to recover this valuable crystalline material from used dosemeters. To the best of our knowledge no other recovery process involving this dosimetric material was described in scientific literature. Fourier Transform Infrared Spectrometry (FTIR), Thermogravimetry/Differential Thermoanalysis (TG/DTA), Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Optically Stimulated Luminescence (OSL) and Rietveld Refinement were used to characterize the recovered material and to check for the stability of its structural and dosimetric properties.
Effect of high-dose irradiation on the optically stimulated luminescence of Al2O3:C
Radiation Measurements, 2004
This paper examines the e ect of high-dose irradiation on the optically stimulated luminescence (OSL) of Al2O3:C, principally on the shape of the OSL decay curve and on the OSL sensitivity. The e ect of the degree of deep trap ÿlling on the OSL was also studied by monitoring the sensitivity changes after doses of beta irradiation and after step-annealing of samples previously irradiated with high doses. The OSL response to dose shows a linear-supralinear-saturation behavior, with a decrease in the response for doses higher than those required for saturation. This behavior correlates with the sensitivity changes observed in the samples annealed only to 773 K, which show sensitization for doses up to 20-50 Gy and desensitization for higher doses. Data from the step-annealing study leads to the suggestion that the sensitization is caused by the ÿlling of deep electron traps, which become thermally unstable at 1100-1200 K, whereas the desensitization is caused by the ÿlling of deep hole traps, which become thermally unstable at 800-875 K, along with a concomitant decrease in the concentration of recombination centers (F + -centers). Changes in the shape of the OSL decay curves are also observed at high doses, the decay becoming faster as the dose increases. These changes in the OSL decay curves are discussed in terms of multiple overlapping components, each characterized by di erent photoionization cross-sections. However, using numerical solutions of the rate equations for a simple model consisting of a main trap and a recombination center, it is shown that the kinetics of OSL process may also be partially responsible for the changes in the OSL curves at high doses in Al2O3:C. Finally, the implication of these results for the dosimetry of heavy charged particles is discussed.
A quantitative kinetic model for Al2O3:C: TL response to ionizing radiation
Radiation Measurements, 2007
This paper presents a quantitative kinetic model for the important dosimetric material Al 2 O 3 :C. The model consists of two traps and two centers, and reproduces the experimental thermoluminescence (TL) vs. dose behavior, as well as the experimental variation of the optical absorption coefficient K with beta dose. Initial estimates of the kinetic parameters in the model are obtained either from published experimental data, or by using reasonable physical assumptions. Good agreement between the experimental data and calculations from the model are obtained for three different types of samples of alumina. This is achieved by keeping the trapping and recombination probabilities constant for all three samples, while the concentrations of the carriers are varied. The kinetic model provides also a quantitative description of the experimentally observed nonmonotonic behavior of the TL dose-response curves for all three samples.
On the relationship between dose-, energy- and LET-response of thermoluminescent detectors
Radiation Protection Dosimetry, 2006
Measurements of the response of thermoluminescent (TL) detectors after gamma ray doses high enough to observe signal saturation provide input to microdosimetric models which relate this gamma-ray response with the energy response after low doses of photons (gamma rays and low-energy X rays) and after high-LET irradiation. To measure their gamma ray response up to saturation, LiF:Mg,Ti (MTS-7 and MTT), LiF:Mg,Cu,P (MCP-7), CaSO 4 :Dy (KCD) and Al 2 O 3 :C detectors were irradiated with 60 Co gamma rays over the range 1-5000 Gy. The X-ray photon energy response and TL efficiency (relative to gamma rays) after doses of beta rays and alpha particles, were also measured, for CaSO 4 :Dy and for Al 2 O 3 :C. Microdosimetric and track structure modelling was then applied to the experimental data. In a manner similar to LiF:Mg,Cu,P, the experimentally observed under response of a-Al 2 O 3 :C to X rays <100 keV, compared with cross-section calculations, is explained as a microdosimetric effect caused by the saturation of response of this detector without prior supralinearity (saturation of traps along the tracks). The enhanced X-ray photon energy response of CaSO 4 :Dy is related to the supralinearity observed in this material after high gamma ray doses, similarly to that in LiF:Mg,Ti. The discussed model approaches support the general rule relating dose-, energy-and ionisation density-responses in TL detectors: if their gamma ray response is sublinear prior to saturation, the measured photon energy response is lower, and if it is supralinear, it may be higher than that expected from the calculation of the interaction cross sections alone. Since similar rules have been found to apply to other solid-state detector systems, microdosimetry may offer a valuable contribution to solid-state dosimetry even prior to mechanistic explanations of physical phenomena in different TL detectors.
Optimization of CW-OSL parameters for improved dose detection threshold in Al2O3:C
Radiation Measurements, 2014
h i g h l i g h t s CW-OSL parameters are optimized to obtain best SNR and MDD in Al 2 O 3 :C. MDD is found to depend on signal integration time and stimulation intensity. With time, MDD initially improves, stabilizes then deteriorates. At a given intensity, MDD is optimum for a certain range of integration time.
Al2O3:C as a sensitive OSL dosemeter for rapid assessment of environmental photon dose rates
Radiation Measurements, 1997
The use of A1203:C single crystals as optically stimulated luminescence (OSL) dosemeters for rapid assessment of the environmental photon dose rate is proposed. It is shown that AI~O3:C possesses higher OSL sensitivity than TL sensitivity, in TL measurements thermal quenching is a major problem that crucially depends on the heating rate used and, therefore, the all-optical nature of the OSL procedure is an obvious advantage as it obviates the necessity to heat the material thereby avoiding destruction of the luminescence signal. It is demonstrated that the exceptional high OSL sensitivity and the energy response (equal to that of quartz) make A1203:C ideal for measuring the environmental dose rates in connection with luminescence dating and retrospective dosimetry using natural materials and ceramics.
Recent advances in dosimetry using the optically stimulated luminescence of Al2O3:C
Radiation Protection Dosimetry, 2004
This paper presents an overview of some very recent developments in optically stimulated luminescence (OSL) dosimetry using aluminium oxide (Al 2 O 3 :C), with special emphasis given to the work of the research group at Oklahoma State University. Some of the advances are: (i) the development of a real-time optical ®bre system for in vivo dosimetry applied to radiotherapy; (ii) the development of a ®bre dosimetry system for remote detection of radiological contaminants in soil; (iii) the characterisation of Al 2 O 3 :C in heavy charged particle ®elds and the study of ionisation density dependence of the OSL from Al 2 O 3 :C; and (iv) fast and separate assessment of beta and gamma components of the natural dose rate in natural sediments. These achievements highlight the versatility of the OSL technique associated with the high-sensitivity of Al 2 O 3 :C for the development of new dosimetry applications.
Calibration and Statistical Performance of Al2O3
Health Physics, 2019
A series of experiments were conducted using commercially available Al 2 O 3 :C optically stimulated luminescent dosimeters to provide a technical basis for their precise calibration and statistical performance at irradiated air kerma doses between 0.02 mGy and 5 mGy using 137 Cs. This study examines the dose response linearity, studies the background signal for annealed dosimeters, and compares the statistical performance of dosimeters that were annealed and not annealed prior to their irradiation and readout. The average and standard deviation for the response of groups of dosimeters annealed and nonannealed prior to their irradiation were determined at each delivered dose. The batch of dosimeters that were annealed prior to their irradiation exhibited a coefficient of variation in its mean dose response below 10% when using three or more irradiation trials at each delivered air kerma dose between 0.02 mGy and 5 mGy. The reader calibration factor was calculated using the response of the annealed batch of dosimeters and was determined to be 756 ± 7 photomultiplier tube counts per mGy. Best estimates of the individual sensitivity factors were determined to be between 0.79 and 1.12 for the annealed batch of dosimeters. The minimum number of irradiations required to accurately determine the sensitivity factor of each individual dosimeter is reported with the recommended reader and dosimeter calibration procedures.
Thermally assisted OSL from deep traps in Al2O3:C
Radiation Measurements, 2010
The present work suggests an alternative experimental method in order to not only measure the signal of the deep traps in Al 2 O 3 :C without heating the sample to temperatures greater than 500 C, but also use this signal for high dose level dosimetry purposes as well. This method consists of photo transfer OSL measurements performed at elevated temperatures using the blue LEDs (470 nm, FWHM 20 nm) housed at commercial Risø TL/OSL systems, after the sample was previously heated up to 500 C in order to empty its main TL dosimetric trap. The influence of this procedure on specific features such as glow curve shape and sensitivity of the main TL glow peak was also studied.
Radiation Measurements, 2004
The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al2O3 dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al2O3 single-crystal chips, of the type usually known as TLD-500, and Luxel TM dosimeters (Al2O3:C powder in plastic) from Landauer Inc. The samples were exposed to 4 He (150 MeV=u), 12 C (400 MeV=u), 28 Si (490 MeV=u) and 56 Fe (500 MeV=u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV= m in water and doses from 1 to 100 mGy (to water). A 90 Sr= 90 Y beta source, calibrated against a 60 Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The e ciencies (ÁHCP; ) of the di erent HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel TM ) and the luminescence method used to deÿne the signal-i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation ÿelds. A discussion of the results is given, including the potential use of OSL from Al2O3 in the areas of space radiation dosimetry and radiation oncology.
AIP Conference Proceedings, 2017
The dose measurement using Al 2 O 3 OSL dosimeter (OSLD) was carried out at low and high energy x-ray. The dose at low energy x-ray was measured at 40, 71 and 125 kVp x-ray energies. The dose ar high energy x-ray was measured at 6 and 10 MV x-ray energies measured at the depth of maximum dose (Z max). The results were compared to that in ionization chamber and LiF: Mg,Ti thermoluminescent dosimeters (TLD100). The results showed that the dose of OSLD were less in agreement to ionization chamber compared to that in TLD100. The dose of OSLD however was in good agreement to that in ionization chamber at high energy x-ray. The dose measured using OSLD were found to be more consistence at high energy x-ray shown by the standard deviation of the readings. The measurement of x 2 showed that the readings of OSLD were close to that in ionization chamber with values of 2.21 and 4.63 for 6 and 10 MV respectively. The results indicated that OSLD is more suitable for dose measurement at high energy x-ray.
Journal of Physics: Conference Series
RE 3+ (Rare Earth) activated calcium aluminates (CaAl2O4) form an excellent class of phosphors for various applications. The multi-functionality of this class of phosphor is tailored by optimising the relative concentration of the trap-levels within the large band gap (Eg=7.4eV). In this paper we determine the trap-levels in Dy 3+ activated nanocrystalline calcium aluminate (CaAl2O4: Dy 3+) phosphor by rigorous analysis of the complex TL curves by computerised-glowcurve-deconvolution (CGCD) technique. We assume the kinetics to be the general order kinetic (1≤ b ≤ 2). Six trap levels have been identified with a lifetime ranging from 8 hours to 10 8 years at room temperature. The ones with τ300 = 6.46×10 05 years, 1.02×10 07 years and 9.02×10 08 years in principle can be the candidates for TL dosimetric application.
Geochronometria
In situ dosimetry (active, passive dosimeters) provides high accuracy by determining environmental dose rates directly in the field. Passive dosimeters, such as α-Al2O3:C, are of particular interest for sites with desired minimum disturbance (e.g., archaeological sites). Here, we present a comprehensive approach obtaining the environmental cosmic and γ-dose rate using α-Al2O3:C chips. Our procedure consists of (1) homemade field containers, (2) a homemade bleaching box, (3) a rapid measurement sequence and (4) software based on R to process the measurement results. Our validation steps include reproducibility, irradiation time correction, cross-talk evaluation and source calibration. We further simulate the effect of the container against the infinite matrix dose rate, resulting in attenuation of ca. 6%. Our measurement design uses a lexsyg SMART luminescence reader equipped with green LEDs. The irradiation is carried out under the closed β-source. The minimum dose that can be deter...
Radiation Protection Dosimetry, 1999
Several -Al 2 O 3 samples were studied in order to determine the mechanism of electron-hole processes of the 430 K (D') thermoluminescence (TL) and thermally stimulated exoelectron emission (TSEE) dosimetric peak. Single crystals prepared in highly reducing conditions were treated in different atmospheres (reducing / oxidising) and their optical absorption (after isochronous annealing), fluorescence and TL properties were investigated. From these results an electron trap is suggested for the 430 K peak which is in contradiction with some data taken from the literature: this problem is discussed then. Pure and Th 4+ doped -Al 2 O 3 powders were studied by TL method in function of doping concentration and preparation conditions. The role of aluminum vacancies is proved this way. Considering these new results, literature data and different hypotheses, the possible nature of the trap is discussed.
Characterization of nanoporous Al 2O 3:C for thermoluminescent radiation dosimetry
Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment, 2007
Thermoluminescent (TL) α-Al2O3:C dosimeters, produced in the form of single crystals, show a high sensitivity to ionizing radiation (about 40–60 times higher than LiF:Mg,Ti). However, the crystal growth requires high temperatures (2050°C) and highly reducing atmospheres. This paper presents the TL response of thin nanoporous Al2O3:C membranes obtained by electrochemical anodizing of aluminum in organic acid solutions at room temperature.
Effect of pre-thermal treatment on the OSL response of Al 2O3:Si,Ti
158, 191, 276 and 355ºC for a heating rate of 4 Ks -1. In order to investigate the contribution of individual TL traps to OSL signal, CW-OSL was studied as a function of pre-thermal treatment in the temperature range 27-450ºC. The integrated CW- OSL intensity of the phosphor remains constant up to 100ºC; beyond this temperature the integrated intensity goes on decreasing with increase in temperature. After a pre-thermal treatment at 225ºC the CW-OSL intensity falls by 73% of its initial value. Hence, it can be concluded that the TL traps up to 225ºC are responsible for the major contribution to the CW-OSL signal in this phosphor. The OSL indicates that all the TL traps, up to 400ºC, give measurable contribution to the OSL signal. The OSL signal becomes insignificant when the exposed phosphor is annealed beyond 400ºC. It decreases nearly to zero for the sample annealed at 400ºC as compared to the OSL intensity of the sample without any pre-thermal treatment. Optical bleaching results...