In this work the kinetic parameters of the main peak of the TL glow curve of alumina (α-Al2O3) irradiated at different doses are reported. Samples were irradiated at different X-ray doses using a 6 MeV linear accelerator (LINAC), in air at room temperature.
Radiation Measurements 153 (2022) 106749 Contents lists available at ScienceDirect Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas Kinetic analysis of the main thermoluminescence glow peak in α-Al2O3 Yulissa Espitia a, Rafael Cogollo a, *, Amalia Osorio a, Omar D Guti´errez b a Grupo de Materiales y Física Aplicada, Departamento de Física, Universidad de C´ ordoba, Cra # 76-103, Montería, 230002, Colombia Grupo de Química B´ asica, Aplicada y Ambiente, Facultad de Ciencias Exactas y Aplicadas, Instituto Tecnol´ ogico Metropolitano, Calle 73 No 76A – 354, Medellín, 050034, Colombia b A R T I C L E I N F O A B S T R A C T Keywords: Al2O3 Thermoluminescence Kinetic-parameters Dose-response Reproducibility In this work the kinetic parameters of the main peak of the TL glow curve of alumina (α-Al2O3) irradiated at different doses are reported Samples were irradiated at different X-ray doses using a MeV linear accelerator (LINAC), in air at room temperature The Initial rise, peak shape, whole glow peak and curve fitting methods were used for the kinetic analysis The glow curves of the α-Al2O3 samples exhibited a total of three experimental glow peaks, the main peak located between 160 and 170 ◦ C The behavior of the kinetic parameters (activation energy E, frequency factor s and order parameter b) of the main peak of the TL glow curve, is independent of the radiation dose received by the material Introduction parameters of α-Al2O3 matrices doped with Cerium (Al2O3:Ce) The in crease of Ce affected the shape of the curve, the positions of its peaks and in general the trapping parameters In addition, it generated new traps in the material, which became evident by the appearance of new peaks or TL signals in the glow curve This work contributes by addressing simultaneously: the thermolu minescent behavior (via its kinetic analysis) and the dosimetric behavior of the α-Al2O3 matrix, presenting in the first case a discussion on the kinetic parameters obtained with various methods in order to conclude which is the most suitable to use as a starting point in the understanding of thermoluminescent recombination and re-trapping processes Com plementing the above, the dosimetric study provides fundamental as pects to validate the implementation of α-Al2O3 as a TL dosimeter in a real application The scientific (TL kinetic analysis) and technological (dosimetric analysis) approaches considered here seek to contribute towards the development of new alumina-based TL dosimeters Aluminum oxide (α-Al2O3) has been reported in the literature for use as a thermoluminescent (TL) dosimeter, in clinical, personal and envi ronmental monitoring of ionizing radiation (Duggan et al., 2000; Kortov ´r et al., 2001; Osorio et al., 2012; Papin et al., and Milman, 1996; Molna 1996; Rocha et al., 2003) Alumina has been used as a host matrix in thermoluminescent materials with different doping (Duggan et al., 2000; Kalita and Chithambo, 2017; Rojas et al., 2019) In all cases the material retained its most prominent TL properties, such as its sensi tivity, but also maintained thermal fading as its major problem to be solved (Osorio et al., 2012; Rocha et al., 2003) P´erez Díaz et al (2013) reported the calculation of the kinetic pa rameters of α-Al2O3 samples by the three-point method (Rasheedy et al., 2007) and by the Kitis curve fitting technique using the four-parameter logistic asymmetric function (Pagonis and Kitis, 2002) By both methods, recombination processes were found to take primacy over re-trapping processes in the α-Al2O3 matrix, although mixed behavior was found in the intermediate region of the glow curve Kalita and Chithambo (2017) investigated the influence of dose (0.1–100 Gy) on the kinetic parameters and dosimetric characteristics of the main glow peak of α-Al2O3:C,Mg, using several methods for kinetic analysis of TL glow curves They found that the activation energy and kinetic order are independent of the dose of beta radiation received between 0.1 and 100 Gy Rojas et al (2019) reported the calculation of the trapping Experimental methods The procedure described by Osorio et al (2012) and Rojas et al (2019) was used for sample preparation: alumina boehmite powders (99.995%, W R Grace & Co-Conn), were used to prepare pellets of 30 mg with a diameter of mm and mm of thickness by uniaxial pressing at 27.6 MPa for 30 s Afterwards, the samples were heated at ◦ C/min from room temperature up to 1000 ◦ C and sintered for h In order to validate the reproducibility of the thermoluminescent behavior, two * Corresponding author E-mail address: rafaelcogollo@correo.unicordoba.edu.co (R Cogollo) https://doi.org/10.1016/j.radmeas.2022.106749 Received December 2021; Received in revised form 17 March 2022; Accepted 22 March 2022 Available online 25 March 2022 1350-4487/© 2022 Elsevier Ltd All rights reserved Y Espitia et al Radiation Measurements 153 (2022) 106749 replicates (called ALO3 and ALO5) obtained with the treatment described above were studied in this work The sintered pellets were irradiated in triplicate (dose of 200, 400, 500, 700 and 1000 cGy) in an air atmosphere at room temperature using a linear accelerator (Clinac 600, MeV, irradiation dose rate of 100 cGy/min) at Instituto M´ edico de Alta Tecnología-IMAT in Montería, Colombia The samples were positioned at 100 cm from the source inside a radiation field of 10 × 10 cm2 in the irradiation plane (Rojas et al., 2019) The pellets were placed between two 5-mm-thick acrylic sheets in order to create conditions of electronic equilibrium Samples were heated at Ks− in a Harshaw TLD 4500 Reader (Bicron®) between 50 and 400 ◦ C All the readings were carried out in nitrogen atmosphere To remove residual signal from the material, before each irradiation, samples were annealed at 400 ◦ C for h, followed by cooling in air to room temperature (Rojas et al., 2019) bars correspond to the standard deviation of the average Tm obtained 3.3 Kinetic analysis 3.3.1 Initial rise method Fig shows the plot of ln(I) versus 1/kT for the initial rise part (up to 15% of the maximum intensity) of the main peak recorded for ALO3 and ALO5 irradiated at different doses (β = Ks− 1) From these plots, the activation energies were calculated and reported in Table For ALO3 and ALO5, the activation energy values (E) fall within ± two standard deviations of the average value reported in Table The E values for the ALO5 sample show the same behavior as with ALO3, since for the lowest doses (200 and 400 cGy) the activation energy takes similar values, but for the highest doses it decreases with respect to the first ones As the temperatures at which the maximum intensity (Tm) is found are different, the activation energy values also differ because Tm is associated with the depth of the energy trap For sample ALO3 the Tm is 437.15 K for the lowest doses but decreases to 435.15 K for the highest doses (700 and 1000 cGy) Results and discussion 3.1 Glow curve features Fig shows the glow curve of the sintered α-Al2O3 pellet called ALO3 and ALO5, irradiated at 1000 cGy, read between 50 and 400 ◦ C (β = Ks− 1) In the temperature range used, the curve exhibits three glow peaks around 162 ◦ C, 265 ◦ C and 338 ◦ C respectively for ALO3 For sample ALO5 the glow curve is similar but with a slight shift in the position of the glow peaks Three peaks are observed at 169 ◦ C, 273 ◦ C and 346 ◦ C respectively Although the samples were prepared under identical con ditions, the ALO3 sample is lower intensity than sample ALO5 3.3.2 Peak shape method Starting from the geometrical shape parameters (Fig 4) τ, δ and ω defined in this method (Pagonis et al., 2006) and the expressions developed by Chen (Pagonis et al., 2006) to calculate the activation energies Eτ, Eδ and Eω associated with these geometric parameters Table shows the results obtained with the peak shape method for ALO3 and ALO5 (β = Ks− 1) The values of the geometric shape factor μ corresponding to the main peak are between 0.45 ± 0.04 and 0.50 ± 0.07, indicating a general order kinetics for all the doses studied being consistent with Rojas et al (2019) The values of the activation energy Eτ are between 0.96 and 1.06 eV for sample ALO3 and 0.99 and 1.10 eV for ALO5 It can be seen that the energy values calculated using τ are closer to those estimated with the IR method 3.2 Dependence of peak position on dose for the main glow peak Fig shows to the glow curves for samples ALO3 and ALO5 irradi ated to different doses The signal intensity increases proportionally with dose Inset shows that there is a shift in the position of the TL peak, suggesting that main peak follows a general order kinetic or it is a combination of multiple peaks This last one option is discarded since the curve fitting method (see section 3.3.4) shows a single peak Error 3.3.3 Whole glow peak method This method is based on the measurement of the integral n(T) of the TL intensity over a certain temperature region May and Partridge and Muntoni (Pagonis et al., 2006) deduced for a general order kinetics the Fig Glow curves of sintered alumina pellets irradiated at a dose of 1000 cGy Y Espitia et al Radiation Measurements 153 (2022) 106749 Fig Glow curves of samples recorded at ◦ C/s after irradiation at different doses for: (a) ALO3 and (b) ALO5 The inset shows the change in the position of the main peak with irradiation dose expression: ln(nIb ) = ln(βs ) − E kT maximum order of 1010 s− 1, being agree with those predicted in the kinetic theory In ALO5 the values of b (1.10) corresponding to 200, 400, 700 and 1000 cGy indicate that the main peak follows a first order ki netics as a mechanism of deactivation of the energetic traps, while as in the previous case, for 500 cGy b = 1.3 evidences a general order kinetics The value of the activation energy obtained with this method is consistent with the results obtained by the initial rise method and with the energy values Eτ, obtained by the peak shape method especially for the lower doses To obtain the kinetic order (b) several lines are drawn with various values of b and the best straight line is chosen As an example Fig shows the plots obtained with different values of b for samples ALO3 and ALO5 irradiated with 200 cGy Table shows the results obtained with the whole glow peak method indicating the kinetic order which best fitted the data for all doses (β = Ks− 1) In ALO3 the best linear fit was achieved with b = 0.90 (for 400 and 700 cGy), b = 1.00 (for 200 and 1000 cGy), and b = 1.20 (500 cGy) In all cases R2 have a value of 0.99 The values of b corresponding to doses of 200, 400, 700 and 1000 cGy indicate that the main peak follows first order kinetics while for the 500 cGy dose it follows general order ki netics The activation energy values coincide with those obtained with the initial rise method The values of the frequency factors (s) are of a 3.3.4 Curve fitting method Glow curves were fitted with the expressions developed by Pagonis et al (2006) for general-order kinetics Table and Figs and present the results obtained with the curve fitting method for samples ALO3 and Y Espitia et al Radiation Measurements 153 (2022) 106749 Fig ln(I) vs 1/kT plots for the initial rise portion of the main peak at different doses for: (a) ALO3 and (b) ALO5 Table Activation energy obtained with IR method Dose (cGy) ALO3 Tm (K) Im (a.u) E (eV) 200 437.15 232771 400 437.15 470483 500 437.15 577057 700 435.15 828261 1000 435.15 1.20E+06 0.950 0.008 0.950 0.008 0.983 0.010 0.888 0.016 0.852 0.017 Table Activation energy obtained with PS method ALO5 ALO3 Tm(K) Im (a.u) E (eV) ± 444.15 296857 ± 444.15 598693 ± 443.15 732767 ± 442.15 1.06E+06 ± 442.15 1.59E+06 1.05 ± 0.01 1.05 ± 0.01 1.08 ± 0.01 0.98 ± 0.01 0.93 ± 0.01 Dose (cGy) Tm (K) Im (a.u) μ ±Δμ Eτ (eV) Eδ (eV) Eω (eV) 200 437.15 232771 400 437.15 470483 500 437.15 577057 700 435.15 828261 1000 435.15 1.20E+06 0.50 ± 0.04 0.47 ± 0.04 0.45 ± 0.04 0.47 ± 0.04 0.50 ± 0.07 1.06 ± 0.06 1.06 ± 0.06 0.96 ± 0.05 1.05 ± 0.05 1.05 ± 0.05 0.76 ± 0.04 0.85 ± 0.05 0.85 ± 0.05 0.84 ± 0.05 0.84 ± 0.01 0.91 ± 0.03 0.96 ± 0.03 0.91 ± 0.03 0.95 ± 0.03 0.95 ± 0.03 ALO5 Dose (cGy) Tm (K) Im (a.u) μ ±Δμ Eτ (eV) Eδ (eV) Eω (eV) 200 444.15 296857 400 444.15 598693 500 443.15 732767 700 442.15 1.06E+06 1000 442.15 1.59E+06 0.45 ± 0.03 0.48 ± 0.03 0.47 ± 0.03 0.48 ± 0.03 0.48 ± 0.03 1.06 ± 0.06 1.10 ± 0.05 0.99 ± 0.04 1.04 ± 0.05 1.04 ± 0.05 1.08 ± 0.06 1.13 ± 0.06 1.02 ± 0.05 1.07 ± 0.05 1.07 ± 0.05 1.08 ± 0.03 1.12 ± 0.03 1.08 ± 0.03 1.06 ± 0.02 1.06 ± 0.03 results indicate that ALO5, like ALO3, follows a general order mecha nism where recombination takes precedence over retrapping The fre quency factor is around 1012 s− 1, close to that predicted by kinetic theory The kinetic parameters show a dose-independent behavior as with ALO3 Based on the above methods and their results, it is evident that the value of the activation energy of the main energy trap of the glow curve of the alumina matrices used is around 1.00 eV, regardless of the absorbed dose Regarding parameter b, the values obtained (b~1.32) with the whole glow peak and curve fitting methods seem to be more consistent because in addition to having lower variability, they are in line with those reported in the literature (P´erez Díaz et al., 2013; Rojas et al., 2019) Fig The geometrical shape parameters τ, δ, ω and μ defined for a glow curve ALO5 It can be seen that the FOM (figure of merit) values were less than 5% in all cases, validating the kinetic parameters obtained with the curve fitting method, and also validating the application of initial rise, peak shape and whole glow peak methods, since the main peak is composed of a single TL peak For ALO3 a mean value of E of (1.08 ± 0.01) eV was determined; an order of kinetics b with a mean value of 1.35 ± 0.01 and the frequency factors being of a maximum order of 1011 s− The mean value of b evidences a general order kinetics as a mech anism of deactivation of the energetic traps, where recombination takes precedence over retrapping, as concluded in the previous methods The results obtained are similar with increasing dose, indicating that the kinetic parameters are independent of the dose For ALO5, E and b have a mean value of (1.16 ± 0.03) eV and 1.33 ± 0.01 respectively These 3.4 Dosimetric analysis Fig 8(a) shows the variation of the maximum peak intensity as a function of dose, where a linear behavior is observed from 200 cGy to 1000 cGy for ALO3 and ALO5 The dose response can be fitted quite well, over the dose range used, with a linear equation of the form: Y Espitia et al Radiation Measurements 153 (2022) 106749 Table Kinetic parameters obtained with curve fitting method ALO3 Dose (cGy) Tm (K) Im (a.u) E (eV) s (s− 1) b FOM 200 400 500 700 1000 437.71 437.77 436.43 435.10 435.70 232771 470483 577057 828261 1.20E+06 1.09 1.09 1.08 1.07 1.07 2.42E+11 2.28E+11 2.12E+11 1.78E+11 1.70E+11 1.37 1.36 1.37 1.33 1.33 3.11% 3.23% 3.25% 4.15% 4.03% ALO5 Dose (cGy) Tm (K) Im (a.u) E (eV) s (s− 1) b FOM 200 400 500 700 1000 443.20 443.22 443.85 443.21 442.30 296562 598693 732767 1.06E+06 1.59E+06 1.10 1.10 1.16 1.10 1.10 2.11E+11 2.35E+11 1.14E+12 1.59E+11 2.50E+11 1.32 1.32 1.35 1.35 1.34 2.27% 2.32% 4.14% 3.82% 3.77% S(D) = a + cD (1) Where D is the given dose, a = − 16093.8 and c = 1210.4 for sample ALO3 and a = − 49850.6 and c = 1616.9 for ALO5 3.4.1 Reproducibility An optimum TL material for dosimetry should have an uncertainty in its measurements no greater than 4% after repeating up to ten or twelve continuous reading cycles (Azorín Nieto, 1993) To study reproduc ibility, the ALO3 samples were subjected to ten identical reading cycles using the same conditions: thermal bleaching, irradiation and reading The doses administered were 50 and 100 cGy Fig shows that the results for each group of measurements present approximately the same dispersion In each case, the data are normalized to the mean value of all measurements In the first case it is found that the uncertainty associated with respect to the mean value of the measurements has a value of 2.4%, while in the second case the uncertainty in the measurements with respect to the mean value is 2.3% Fig ln(I/nb) vs 1/kT with different values of kinetic order (b) for: (a) ALO3, (b) ALO5 (200 cGy) The best linear fit were achieved for b = (ALO3, R2 = 0.99) and b = 1.1 (ALO5, R2 = 0.99) 3.4.2 Fading To study the thermal fading of the signal, one single ALO3 sample was irradiated at a dose of 50 cGy, stored at ambient conditions and read during the 30 days following irradiation, at regular time intervals Three days after irradiation, the ALO3 pellet showed a signal fading of 18% Six days after irradiation, the signal fading was 25% After 10 days, the sample showed a signal fading of 28% 21 days later it reached 36% and finally stabilized at 40% twenty-five days after irradiation The high decrease in response may be related to the storage conditions: high relative humidity (70%) and high ambient temperature (32 ± ◦ C) Regarding this fading phenomenon, Kalita and Chithambo (2017) studied α-Al2O3:C and α-Al2O3:C, Mg matrices, finding that carbon and magnesium induced the formation of five (α-Al2O3:C) and seven (α-Al2O3:C,Mg) energy traps with similar activation energies, in which Kalita and Chithambo (2017) propose charge hopping between traps as an explanation for the fading phenomenon at room temperature In the present study (α-Al2O3), given the high storage temperature (32 ± ◦ C) and the calculated activation energy values for the trap associated with the main peak, charge hopping may also be one of the feasible expla nations for the fading Table Kinetic parameters obtained with whole glow peak method ALO3 Dose (cGy) Tm (K) Im (a.u) E (eV) s (s− 1) b R2 200 437.15 232771 0.99 437.15 470483 0.90 0.99 500 437.15 577057 1.20 0.99 700 435.15 828261 0.90 0.99 1000 435.15 1.20E+06 (7.70 ± 0.29) E+09 (8.42 ± 0.43) E+10 (1.12 ± 0.47) E+09 (7.01 ± 2.11) E+09 (1.78 ± 0.36) E+09 1.00 400 0.96 ± 0.01 0.97 ± 0.01 0.99 ± 0.01 0.88 ± 0.01 0.89 ± 0.01 1.00 0.99 ALO5 Dose (cGy) Tm (K) Im (a.u) E (eV) s (s− 1) b R2 200 444.15 296857 0.99 444.15 598693 1.10 0.99 500 443.15 732767 1.30 0.99 700 442.15 1.06E+06 1.10 0.99 1000 442.15 1.59E+06 (4.20 ± 1.42) E+10 (3.88 ± 1.42) E+10 (2.38 ± 1.08) E+09 (2.85 ± 1.08) E+09 (8.65 ± 1.41) E+08 1.10 400 1.06 ± 0.01 1.06 ± 0.01 1.08 ± 0.01 0.97 ± 0.01 0.93 ± 0.01 1.10 0.99 3.4.3 Detection limit The minimum dose given to the ALO3 samples was cGy In all cases the samples exhibited a glow curve similar to that observed for high doses Measurements in this range presented an uncertainty of 4.7% It should be noted that cGy is the minimum dose administered by the radiation equipment Y Espitia et al Radiation Measurements 153 (2022) 106749 Fig Results of curve fitting method for the main peak of ALO3 irradiated at different doses Fig Results of curve fitting method for the main peak of ALO5 irradiated at different doses Conclusions The effect of dose on the kinetic parameters of the main glow peak of an alumina (α-Al2O3) sample has been studied using several methods The results show that the kinetic parameters, E, b and s of the main peak are dose independent The main peak follows general order kinetics with recombination as the main read-out mechanism In general, for all irradiation doses, the value of the activation energy The glow curves of the alumina samples exhibit three peaks around 162 ◦ C, 265 ◦ C and 338 ◦ C for ALO3 and around 169 ◦ C, 273 ◦ C and 346 ◦ C for ALO5 The main peak is located at 162 ◦ C and 169 ◦ C respectively Y Espitia et al Radiation Measurements 153 (2022) 106749 Fig (a) Maximum peak intensity as a function of the dose from 200 to 1000 cGy, (b) Area of the main peak of the glow curve as a function of the dose from 200 to 1000 cGy Fig The peak intensity of the main peak of ALO3 for 10 repeated identical measurements for different irradiation doses is around 1.00 eV The response of the material with dose is linear in the range used (≤10 Gy), showing a signal fading of 32% after 10 days of irradiation Reproducibility analysis shows that the alumina (α-Al2O3) samples reproduce their response under identical experimental conditions with an uncertainty of 2.3% Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper Acknowledgements The authors acknowledge the financial support received from Y Espitia et al Radiation Measurements 153 (2022) 106749 ´rdoba at Montería and Instituto Tecnolo ´gico Metro Universidad de Co politano at Medellín Pagonis, V., Kitis, G., 2002 Fit of second order thermoluminescence glow peaks using the logistic distribution function Radiat Protect Dosim 101, 93–98 Pagonis, V., Kitis, G., Furetta, C., 2006 Numerical and 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Maximum peak intensity as a function of the dose from 200 to 1000 cGy, (b) Area of the main peak of the glow curve as a function of the dose from 200 to 1000 cGy Fig The peak intensity of the main peak. .. parameters of the main glow peak of an alumina (α-Al2O3) sample has been studied using several methods The results show that the kinetic parameters, E, b and s of the main peak are dose independent The. .. parameters obtained with the curve fitting method, and also validating the application of initial rise, peak shape and whole glow peak methods, since the main peak is composed of a single TL peak For