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Thermoluminescence response and glow curve structure of Sc2TiO5 ß-irradiated
Applied Radiation and Isotopes 90 (2014) 58–61
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Thermoluminescence response and glow curve structure of Sc2TiO5 ß-irradiated I.C. Muñoz a,n, F. Brown b, H. Durán-Muñoz b, E. Cruz-Zaragoza c, B. Durán-Torres a, V.E. Alvarez-Montaño b a
Departamento de Ciencias Químico-Biológicas, Universidad de Sonora, A.P.130, Hermosillo, Sonora C.P. 83000, México Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, A.P.130, Hermosillo, Sonora C.P. 83000, México c Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P.70-543, México D.F. 04510, México b
H I G H L I G H T S
Discandium titanate was synthesized, and its TL properties were analyzed. The beta dose–response has a linear behavior on the dose range 50–500 Gy. The kinetic parameters were obtained by the CGCD procedure. Results support the possible use of Sc2TiO5 as a new phosphor for ß-dose dosimetry.
art ic l e i nf o
a b s t r a c t
Article history: Received 8 January 2014 Received in revised form 4 March 2014 Accepted 10 March 2014 Available online 19 March 2014
Discandium titanate (Sc2TiO5) powder was synthesized in order to analyze its thermoluminescence (TL) response. The TL glow curve structure shows two peaks: at 453–433 K and at 590–553 K. The TL beta dose–response has a linear behavior over the dose range 50–500 Gy. The Tstop preheat method shows five glow peaks that were taken into account to calculate the kinetic parameters using the CGCD procedure. TL results support the possible use of Sc2TiO5 as a new phosphor in high ß-dose dosimetry. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Scandium titanate Beta radiation Thermoluminescence Kinetic parameters
1. Introduction Thermoluminescence (TL) dosimetry has been actively developed because of its successful applications, such as the monitoring of ionizing radiations in exposed personnel, in therapy radiation, in the environment, in spacecraft, in food sterilization, etc. (Benton and Benton, 2001; Correcher and Delgado, 1998; Cruz-Zaragoza et al., 2010; Huston et al., 2001; Kortov, 2007; Mathur, 2001). The TL phenomenon is based on the fact that inorganic phosphors emit light when stimulated by heat after being exposed to ionizing radiation (Chen and McKeever, 1997). Nowadays, the development of new materials, which can be used for TL dosimetry, and the analysis of their properties are very important. Actually, in our laboratory, efforts are being made to look for new materials with
n
Corresponding author. Tel./fax: þ 52 66 22592163. E-mail address: [email protected] (I.C. Muñoz).
http://dx.doi.org/10.1016/j.apradiso.2014.03.011 0969-8043/& 2014 Elsevier Ltd. All rights reserved.
thermoluminescence properties that can be used in high dose dosimetry. Discandium titanate is a compound suggested by Ito (1971) to have a pseudobrookite structure. Kolitsh and Tillmanns (2003) characterized the crystal structure of Sc2TiO5 and confirmed the pseudobrookite structure type. Sc2TiO5 contains two octahedrally coordinated metal sites; the strongly distorted octahedral share edges form trioctahedral units, linked into double chains. The sharing of octahedral edges results in a threedimensional framework. It is known that discandium titanate is insoluble in water, and that its density is 3.611 g cm 3 (Weber, 2003), but its other important properties remain unknown. For instance, previous reports about thermoluminescence properties of discandium titanate do not exist. This paper reports the thermoluminescence property of Sc2TiO5 phosphor, and its glow curve structure is analyzed by thermal stability of TL signals, i.e., the Tstop method and fading. The kinetic parameters were obtained by using CGCD deconvolution program assuming first and second order kinetics.
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
59
2. Experimental procedure
3. Results and discussion The XRD patterns of the sample obtained exhibit all the peaks (Fig. 1) corresponding to the data base ICDD reported for Sc2TiO5 (ICCV no. 00-25-1333) which crystallizes into an orthorhombic pseudobrookite structure. Scanning electron microscopy images of Sc2TiO5 show that a homogeneous phase was obtained. A distribution of particles with rounded borders and different sizes between 1 and 2 mm was observed (Fig. 1). Some agglomerates of about 15 mm can also be observed. The EDS elementary analysis indicates that the sample composition was Sc, Ti and O ions. 3.1. Glow curve structure and dose–response Fig. 2 shows the TL glow curves obtained after exposing the samples to beta radiation on the dose interval of 50 to 3000 Gy. The shape of curves in relative lower doses is similar to that of the highest doses; two prominent broad glow peaks at 453–433 K and at 590–553 K were observed. As it can be seen, the TL intensity increases as the irradiation dose increases. The TL intensity maxima in both peaks (453 K and 590 K) shift to lower temperatures when the dose increases. In the inset of Fig. 2, the TL integrated as a function of dose for Sc2TiO5 phosphor is shown. TL dose–response has a linear behavior at a 50–500 Gy dose range followed by a saturation stage at a high dose level. As observed previously in some oxide compounds like KAlSiO4, Bi4Ge3O14, perovskite ABO3-type, and sandstone (Garcia-Guinea et al., 2001;
Intensity (a. u.)
1500
1000
Sc2TiO5 ICDD # 00-25-1333
500
0 10
20
30
40 2θ (°)
50
60
70
Fig. 1. X-ray powder diffraction pattern of Sc2TiO5 synthesized by the solid state reaction. The standard XRD pattern [(▪) ICDD no. 00-25-1333] is also presented in the peaks. The inset shows the scanning electron microscopy image of Sc2TiO5 sample.
2.0x10
1.5x104
50 Gy 100 Gy 200 Gy 500 Gy 1000 Gy 1500 Gy 3000 Gy
TL Integrated (a. u.)
4
TL Intensity (a. u.)
Sc2TiO5 was prepared in a conventional solid state reaction (Ito, 1971) by mixing the highest purity, commercially-available reagents: Sc2O3 (99.9%) and TiO2 (99.9%). Starting materials were weighted in right stoichiometric ratios and thoroughly mixed in ethanol in an agate mortar for about 25 min. The samples were heated in air in a platinum crucible to 1100 1C for two days. After the heating treatment, the samples were cooled fast to room temperature (RT) and were prepared for X-ray powder diffraction measurements. An X-ray powder diffractometer (Rigaku D/Max) equipped with CuKα radiation and a graphite monochromator were used for the phase identification of the samples. The diffraction patterns were obtained at RT, 20 mA and 40 kV by step scanning from 51 to 701 2θ in steps of 0.0201. Equilibrium was considered to be attained when X-ray powder diffraction patterns did not show any change after successive heating treatments. Scanning electron microscope images and semiquantitative elementary analyses were obtained using a JEOL JSM-5410LV apparatus equipped with an Oxford X-ray Energy Dispersive Spectroscopy (EDS) analyzer operating at 20 kV. The grain size in the Sc2TiO5 powder obtained was ranged between 4 and 6 mm and agglomerates at around 15 mm were present too. TL measurements were carried out using an automated Risø TL/OSL system model DA-15 provided with an EMI 9635QA photomultiplier. It is also provided with a 40 mCi 90Sr/90Y beta source with a dose rate of 5 Gy/min. A linear heating rate of 5 K/s from room temperature (298 K) up to 723 K was used. No filters were used in the TL measurements. Nitrogen gas was flowed into the sample-chamber during the readout process to avoid spurious TL signals. Two aliquots of 30 mg each of Sc2TiO5 powder from a large batch were placed in stainless steel cups, and were used for the TL measurements: dose–response, reproducibility and fading, except in the TM–Tstop experiment, where only one powder aliquot (30 mg) was used. The fading studies were carried out at room temperature (ca. 295 K), and samples were kept in dark. TL measurements were carried out under red light.
60 μm
2000
Dose (Gy)
1.0x104 5.0x103 0.0 300
400
500 Temperature (K)
600
Fig. 2. TL glow curves of Sc2TiO5 after exposure to different doses of beta radiation. The inset shows the dose–response from 50 to 3000 Gy.
Muñoz et al., 2012; Raymond and Townsend, 2000; Soliman and Salama, 2009; Thangadurai and Weppner, 2002), it is possible to observe a distribution of traps for the glow curves. The glow curve structure of Sc2TiO5 phosphor exhibits a distribution of traps. The analysis of the glow curve's structure is performed using a preheat method (McKeever, 1980) that consists of linear heating of the samples up to a Tstop temperature followed by fast cooling to room temperature. Subsequently, a final readout to record the whole residual TL glow curve is achieved. The preheating varies in a range of 313–623 K performed at 5 K/s. Fig. 3 shows the two broad glow peaks; as the preheating temperature (Tstop) increases, the maximum moves towards higher temperatures of the glow curve, and both the intensity of the maximum and the peak area decrease. The distribution of traps changes towards higher values of energy when increasing TM of the glow peaks (Table 1) as a consequence of the emptying the shallower energy traps. As a result, there is a deeper trap distribution with higher values of the frequency factor (s). 3.2. Fading analysis and TL signal reproducibility Fig. 4 shows the glow curves of fading measurement carried out at RT after the sample was exposed to 200 Gy. The two glow peaks remain at the same temperature position during fading,
60
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
Sc2TiO5 500 Gy β
1.2x104
TL Intensity (a. u.)
630
315 K 325 355 395 425 455 485 515 555 575 595 625
9.0x103 6.0x103 3.0x103
600 570 540
TM (K)
1.5x104
510 480 450 420
0.0
390
200
300
400
500
600
700
360
Temperature (K)
300
350
400
Tm
Peak Peak Peak Peak Peak
Im
E (eV) s (s 1) (CGCD)
Peak Area width
388.8 2818.2 45.67 1.37E þ05 422.2 5959.1 41.99 2.72Eþ05 449.5 12,069.3 52.10 7.26Eþ 05 551.1 4511.9 66.69 3.48E þ 05 593.5 2344.8 48.48 1.25Eþ 05
1 2 3 4 5
0.67 0.85 1.09 0.92 1.50
b
9.74E þ07 3.77Eþ 09 5.48E þ 11 3.73Eþ07 5.25E þ 11
1 1.1 1.9 1.05 0.99
E (eV) (IRM) 0.87 0.94 1.06 1.15 1.60
500
1.4x104
550
600
Exp Peak 1 Peak 2 Peak 3 Peak 4 Peak 5 Total fit FOM = 1.8%
1.2x104
TL Intensity (a. u.)
Table 1 Kinetic parameters obtained using the CGCD deconvolution method, and the activation energy (E) values by using the Initial Rise Method (IRM), for glow curve at 500 Gy ß-dose.
450
Tstop (K)
Fig. 3. Thermal stability of the TL emission after different preheatings in the range 315–625 K performed at 5 K s 1.
1.0x104 8.0x103 6.0x103 4.0x103 2.0x103 0.0 350
400
2500
500
550
600
Fig. 5. (a) TM–Tstop relationship after 500 Gy ß-irradiation of Sc2TiO5. (b) Deconvolution of the experimental glow curve (continuous gray line), and computed glow peaks (dashed lines).
0 min 200 Gy 60 min
2000
TL Intensity (a. u.)
450
Temperature (K)
360 min 1440 min
irradiation-readout cycles at the same beta dose (200 Gy). The reproducibility was off by less than 1% of the standard deviation.
1500
1000
3.3. Kinetic parameters
500
0 300
350
400
450
500
550
600
650
700
Temperature (K) Fig. 4. Glow curves from fading of Sc2TiO5 exposed at 200 Gy beta dose. The inset shows the fading of TL signals integrated from 0 to 24 h.
except for the shoulder at the low temperature side of the first glow peak, since it disappears quickly because it corresponds to shallow traps. The great influence of the shoulder over the glow peak causes the latter to experiment an immediate decrease of response. The second peak shows a decrease in intensity but in a slower manner, compared to the high temperature peak. In the inset of Fig. 4, it is shown that the fading decays quickly during the first 60 min (13%), and a 27% decay was observed at the end of a 24 h period. On the other hand, reproducibility was measured, which is considered to be another dosimetric property. The TL response of Sc2TiO5 was tested over ten consecutive
A complex glow curve's structure was observed for discandium titanate. The TM–Tstop method (McKeever, 1980) was used in order to determine the number of peaks and their temperature was present in the glow curve. Fig. 5 shows the TM–Tstop relationship from 313 to 583 K. This method shows approximately five glow peaks, which were taken into account to calculate the kinetic parameters by using the glow curve deconvolution program (CGCD) and by an Initial Rise Method (IRM) considering every peak (Table 1). The kinetic and geometrical parameters of the glow peaks were obtained using the CGCD procedure (Pagonis et al., 2006). The CGCD calculation was performed considering Kiti's expressions to first and second orders (Kitis et al., 1998): "
IðTÞ ¼ Im exp 1 þ
# E T T m T 2 E T Tm 2kT 2kT 2m 1 2 exp E kT T m kT T m E Tm
ð1Þ
E T Tm kT T m !2 T2 2kT E T T m 2kT m exp þ1þ 2 1 E kT T m E Tm
IðTÞ ¼ 4I m exp
ð2Þ
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
where T (K) is the different temperature values, E (eV) is activation energy, s (s 1) is the frequency factor, k (eV K 1) is the Boltzmann constant, Tm is the temperature at maximum intensity and Im the maximum intensity of each peak. The frequency factor (s) is calculated using Eq. (3), where β is the linear heating rate βE 1 E exp s¼ 2 ð3Þ kT m kT m 1 þ ðb 1Þ2kT m =E The goodness of the fit was measured from the figure of merit (FOM) given by Balian and Eddy (1977): n
FOM ¼ ∑
i¼1
100jY exp Y f it j A
ð4Þ
where n is the number of data points, Yexp is the experimental and Yfit is the data fitted points, and A is the integral of the fitted glow curve in the region of interest. CGCD analysis was applied to the glow curve of Sc2TiO5 exposed to beta radiation with 500 Gy dose and recorded with a heating rate of 5 K/s. For deconvolution purposes, one peak at 375–386 K, two peaks in the 438–506 K temperature range, and other two more peaks in the interval 558–597 K were considered. The temperature of the maximum (Tm) calculated by CGCD program is shown in Table 1. The FOM obtained is equal to 1.8%, which indicates a good result of the deconvolution process (Horowitz and Yossian, 1995). Fig. 5 shows the results of the deconvolution calculation, and Table 1 reports the kinetic parameters obtained for the five glow peaks. The activation energy values, obtained using CGCD deconvolution, were at about 0.67– 1.50 eV for the traps; similar values were calculated by the Initial Rise Method. The variation of the activation energy values indicates that the two broad experimental glow peaks are not a simple one; they are composed of more than one component or complex trap distribution, and the main effect of that distribution is the broadening of the glow peaks. Furthermore, the glow peaks numbers 3 and 4 peak approximately at 450 K and 551 K, respectively, with second- and first-order kinetics (see Table 1). Therefore, peaks 3 and 4 could be considered for dosimetric purposes because of their thermal stability observed under fading stage. 4. Conclusions The Sc2TiO5 orthorhombic phase was synthesized by a solid state reaction. The compound was obtained in a high purity. The TL dose–response was linear over the dose range of 50–500 Gy followed by saturation stage at high dose levels. A good TL reproducibility was found: at 200 Gy, it was less than 1% of the standard deviation after ten cycles of irradiation-readout. The fading shows a TL response decrease of 27 % at the end of a 24 h period. Discandium titanate shows a complex structure in its glow curves, since the preheat Tstop method revealed the existence of a possible distribution of traps. The kinetic and geometrical parameters were calculated by using a glow curve deconvolution procedure (CGCD) and the Initial Rise Method (IRM). First and second-order kinetics for the glow peaks was obtained. The frequency factor is close to physical meaning, i.e. 108–109 s 1
61
(Furetta and Weng, 1998). The range of energy activation values calculated with CGCD (0.67–1.50 eV) was similar to those obtained with the IRM method.
Acknowledgments The authors gratefully acknowledge the financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT), (México), under Grant number CB-2008-106041. Also, we would like to thank the financial support from Oficina de Colaboración Interinstitucional de la Universidad Nacional Autónoma de México (UNAM), and Dirección de Desarrollo y Fortalecimiento Académico-Universidad de Sonora (UNISON) under annual collaboration project UNAM-UNISON 2012. Authors are grateful to Hugo Borbón Nuñez for technical support and to Francisco Brown-Muñoz for language reviewing. References Balian, H.G., Eddy, N.W., 1977. Figure-of-merit (FOM), an improved criterion over the normalized chi-squared test for assessing goodness-of-fit of gamma-ray spectral peak. Nucl. Instrum. Methods 145, 389. Benton, E.R., Benton, E.V., 2001. Space radiation dosimetry in low-Earth orbit and beyond. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 255. Chen, R., McKeever, S.W.S., 1997. Theory of Thermoluminescence and Related Phenomena. World Scientific, Singapore. Correcher, V., Delgado, A., 1998. On the use of natural quartz as transfer dosemeter in retrospective dosimetry. Radiat. Meas. 29 (3–4), 411. Cruz-Zaragoza, E., Ruiz-Gurrola, B., Wacher, C., Flores-Espinosa, T., Barboza-Flores, M., 2010. Gamma radiation effects in coriander (Coriandrum sativum L) for consumption in Mexico. Rev. Mex. Fís. 57, 80. Furetta, C., Weng, P.S., 1998. Operational Thermoluminescence Dosimetry. World Scientific, Singapore. Garcia-Guinea, J., Correcher, V., Rodriguez-Badiola, E., 2001. Analysis of luminescence spectra of leucite (KAlSiO4). Analyst 126, 911. Horowitz, Y.S., Yossian, D., 1995. Monograph on computerised glow curve deconvolution: application to thermoluminescence dosimetry. Radiat. Prot. Dosim. 60, 1. Huston, A.L., Justus, B.L., Falkenstein, P.L., Miller, R.W., Ning, H., Altemus, R., 2001. Remote optical fiber dosimetry. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 55. Ito, J., 1971. Synthesis of scandium pseudobrookite, Sc2TiO5. Am. Mineral. 56, 1105. Kitis, G., Gomez-Ros, J.M., Tuyn, J.W.N., 1998. Thermoluminescence glow-curve deconvolution functions for first, second and general orders of kinetics. J. Phys. D: Appl. Phys. 31, 2636. Kolitsh, U., Tillmanns, E., 2003. Sc2TiO5, an entropy-stabilized pseudobrookite-type compound. Acta Crystallogr. 59, 136. Kortov, V., 2007. Materials for thermoluminescence dosimetry: current status and future trend. Radiat. Meas. 42, 576. Mathur, V.K., 2001. Ion storage dosimetry. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 190. McKeever, S.W.S., 1980. On the analysis of complex thermoluminescence glowcurves: resolution into individual peaks. Phys. Status Solidi A 62, 331. Muñoz, I.C., Cruz-Zaragoza, E., Favalli, A., Furetta, C., 2012. Thermoluminescence property of LiMgF3 erbium activated phosphor. Appl. Radiat. Isot. 70, 893. Pagonis, V., Furetta, C., Kitis, G., 2006. Numerical and Practical Exercises in Thermoluminescence. Springer, USA. Raymond, S.G., Townsend, P.D., 2000. The influence of rare-earth ions on the lowtemperature thermoluminescence of Bi4Ge3O12. J. Phys.: Condens. Matter 12, 2103. Soliman, C., Salama, E., 2009. Investigation on the suitability of natural sandstone as a gamma dosimeter. Nucl. Instrum. Methods Phys. Res. B 267, 3323. Thangadurai, V., Weppner, W., 2002. Development and investigation of perovskite (ABO3)-type oxides for power generation. Ionics 8, 360. Weber, M.J., 2003. Handbook of Optical Materials. CRC Press, USA.
Contents lists available at ScienceDirect
Applied Radiation and Isotopes journal homepage: www.elsevier.com/locate/apradiso
Thermoluminescence response and glow curve structure of Sc2TiO5 ß-irradiated I.C. Muñoz a,n, F. Brown b, H. Durán-Muñoz b, E. Cruz-Zaragoza c, B. Durán-Torres a, V.E. Alvarez-Montaño b a
Departamento de Ciencias Químico-Biológicas, Universidad de Sonora, A.P.130, Hermosillo, Sonora C.P. 83000, México Departamento de Investigación en Polímeros y Materiales, Universidad de Sonora, A.P.130, Hermosillo, Sonora C.P. 83000, México c Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, A.P.70-543, México D.F. 04510, México b
H I G H L I G H T S
Discandium titanate was synthesized, and its TL properties were analyzed. The beta dose–response has a linear behavior on the dose range 50–500 Gy. The kinetic parameters were obtained by the CGCD procedure. Results support the possible use of Sc2TiO5 as a new phosphor for ß-dose dosimetry.
art ic l e i nf o
a b s t r a c t
Article history: Received 8 January 2014 Received in revised form 4 March 2014 Accepted 10 March 2014 Available online 19 March 2014
Discandium titanate (Sc2TiO5) powder was synthesized in order to analyze its thermoluminescence (TL) response. The TL glow curve structure shows two peaks: at 453–433 K and at 590–553 K. The TL beta dose–response has a linear behavior over the dose range 50–500 Gy. The Tstop preheat method shows five glow peaks that were taken into account to calculate the kinetic parameters using the CGCD procedure. TL results support the possible use of Sc2TiO5 as a new phosphor in high ß-dose dosimetry. & 2014 Elsevier Ltd. All rights reserved.
Keywords: Scandium titanate Beta radiation Thermoluminescence Kinetic parameters
1. Introduction Thermoluminescence (TL) dosimetry has been actively developed because of its successful applications, such as the monitoring of ionizing radiations in exposed personnel, in therapy radiation, in the environment, in spacecraft, in food sterilization, etc. (Benton and Benton, 2001; Correcher and Delgado, 1998; Cruz-Zaragoza et al., 2010; Huston et al., 2001; Kortov, 2007; Mathur, 2001). The TL phenomenon is based on the fact that inorganic phosphors emit light when stimulated by heat after being exposed to ionizing radiation (Chen and McKeever, 1997). Nowadays, the development of new materials, which can be used for TL dosimetry, and the analysis of their properties are very important. Actually, in our laboratory, efforts are being made to look for new materials with
n
Corresponding author. Tel./fax: þ 52 66 22592163. E-mail address: [email protected] (I.C. Muñoz).
http://dx.doi.org/10.1016/j.apradiso.2014.03.011 0969-8043/& 2014 Elsevier Ltd. All rights reserved.
thermoluminescence properties that can be used in high dose dosimetry. Discandium titanate is a compound suggested by Ito (1971) to have a pseudobrookite structure. Kolitsh and Tillmanns (2003) characterized the crystal structure of Sc2TiO5 and confirmed the pseudobrookite structure type. Sc2TiO5 contains two octahedrally coordinated metal sites; the strongly distorted octahedral share edges form trioctahedral units, linked into double chains. The sharing of octahedral edges results in a threedimensional framework. It is known that discandium titanate is insoluble in water, and that its density is 3.611 g cm 3 (Weber, 2003), but its other important properties remain unknown. For instance, previous reports about thermoluminescence properties of discandium titanate do not exist. This paper reports the thermoluminescence property of Sc2TiO5 phosphor, and its glow curve structure is analyzed by thermal stability of TL signals, i.e., the Tstop method and fading. The kinetic parameters were obtained by using CGCD deconvolution program assuming first and second order kinetics.
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
59
2. Experimental procedure
3. Results and discussion The XRD patterns of the sample obtained exhibit all the peaks (Fig. 1) corresponding to the data base ICDD reported for Sc2TiO5 (ICCV no. 00-25-1333) which crystallizes into an orthorhombic pseudobrookite structure. Scanning electron microscopy images of Sc2TiO5 show that a homogeneous phase was obtained. A distribution of particles with rounded borders and different sizes between 1 and 2 mm was observed (Fig. 1). Some agglomerates of about 15 mm can also be observed. The EDS elementary analysis indicates that the sample composition was Sc, Ti and O ions. 3.1. Glow curve structure and dose–response Fig. 2 shows the TL glow curves obtained after exposing the samples to beta radiation on the dose interval of 50 to 3000 Gy. The shape of curves in relative lower doses is similar to that of the highest doses; two prominent broad glow peaks at 453–433 K and at 590–553 K were observed. As it can be seen, the TL intensity increases as the irradiation dose increases. The TL intensity maxima in both peaks (453 K and 590 K) shift to lower temperatures when the dose increases. In the inset of Fig. 2, the TL integrated as a function of dose for Sc2TiO5 phosphor is shown. TL dose–response has a linear behavior at a 50–500 Gy dose range followed by a saturation stage at a high dose level. As observed previously in some oxide compounds like KAlSiO4, Bi4Ge3O14, perovskite ABO3-type, and sandstone (Garcia-Guinea et al., 2001;
Intensity (a. u.)
1500
1000
Sc2TiO5 ICDD # 00-25-1333
500
0 10
20
30
40 2θ (°)
50
60
70
Fig. 1. X-ray powder diffraction pattern of Sc2TiO5 synthesized by the solid state reaction. The standard XRD pattern [(▪) ICDD no. 00-25-1333] is also presented in the peaks. The inset shows the scanning electron microscopy image of Sc2TiO5 sample.
2.0x10
1.5x104
50 Gy 100 Gy 200 Gy 500 Gy 1000 Gy 1500 Gy 3000 Gy
TL Integrated (a. u.)
4
TL Intensity (a. u.)
Sc2TiO5 was prepared in a conventional solid state reaction (Ito, 1971) by mixing the highest purity, commercially-available reagents: Sc2O3 (99.9%) and TiO2 (99.9%). Starting materials were weighted in right stoichiometric ratios and thoroughly mixed in ethanol in an agate mortar for about 25 min. The samples were heated in air in a platinum crucible to 1100 1C for two days. After the heating treatment, the samples were cooled fast to room temperature (RT) and were prepared for X-ray powder diffraction measurements. An X-ray powder diffractometer (Rigaku D/Max) equipped with CuKα radiation and a graphite monochromator were used for the phase identification of the samples. The diffraction patterns were obtained at RT, 20 mA and 40 kV by step scanning from 51 to 701 2θ in steps of 0.0201. Equilibrium was considered to be attained when X-ray powder diffraction patterns did not show any change after successive heating treatments. Scanning electron microscope images and semiquantitative elementary analyses were obtained using a JEOL JSM-5410LV apparatus equipped with an Oxford X-ray Energy Dispersive Spectroscopy (EDS) analyzer operating at 20 kV. The grain size in the Sc2TiO5 powder obtained was ranged between 4 and 6 mm and agglomerates at around 15 mm were present too. TL measurements were carried out using an automated Risø TL/OSL system model DA-15 provided with an EMI 9635QA photomultiplier. It is also provided with a 40 mCi 90Sr/90Y beta source with a dose rate of 5 Gy/min. A linear heating rate of 5 K/s from room temperature (298 K) up to 723 K was used. No filters were used in the TL measurements. Nitrogen gas was flowed into the sample-chamber during the readout process to avoid spurious TL signals. Two aliquots of 30 mg each of Sc2TiO5 powder from a large batch were placed in stainless steel cups, and were used for the TL measurements: dose–response, reproducibility and fading, except in the TM–Tstop experiment, where only one powder aliquot (30 mg) was used. The fading studies were carried out at room temperature (ca. 295 K), and samples were kept in dark. TL measurements were carried out under red light.
60 μm
2000
Dose (Gy)
1.0x104 5.0x103 0.0 300
400
500 Temperature (K)
600
Fig. 2. TL glow curves of Sc2TiO5 after exposure to different doses of beta radiation. The inset shows the dose–response from 50 to 3000 Gy.
Muñoz et al., 2012; Raymond and Townsend, 2000; Soliman and Salama, 2009; Thangadurai and Weppner, 2002), it is possible to observe a distribution of traps for the glow curves. The glow curve structure of Sc2TiO5 phosphor exhibits a distribution of traps. The analysis of the glow curve's structure is performed using a preheat method (McKeever, 1980) that consists of linear heating of the samples up to a Tstop temperature followed by fast cooling to room temperature. Subsequently, a final readout to record the whole residual TL glow curve is achieved. The preheating varies in a range of 313–623 K performed at 5 K/s. Fig. 3 shows the two broad glow peaks; as the preheating temperature (Tstop) increases, the maximum moves towards higher temperatures of the glow curve, and both the intensity of the maximum and the peak area decrease. The distribution of traps changes towards higher values of energy when increasing TM of the glow peaks (Table 1) as a consequence of the emptying the shallower energy traps. As a result, there is a deeper trap distribution with higher values of the frequency factor (s). 3.2. Fading analysis and TL signal reproducibility Fig. 4 shows the glow curves of fading measurement carried out at RT after the sample was exposed to 200 Gy. The two glow peaks remain at the same temperature position during fading,
60
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
Sc2TiO5 500 Gy β
1.2x104
TL Intensity (a. u.)
630
315 K 325 355 395 425 455 485 515 555 575 595 625
9.0x103 6.0x103 3.0x103
600 570 540
TM (K)
1.5x104
510 480 450 420
0.0
390
200
300
400
500
600
700
360
Temperature (K)
300
350
400
Tm
Peak Peak Peak Peak Peak
Im
E (eV) s (s 1) (CGCD)
Peak Area width
388.8 2818.2 45.67 1.37E þ05 422.2 5959.1 41.99 2.72Eþ05 449.5 12,069.3 52.10 7.26Eþ 05 551.1 4511.9 66.69 3.48E þ 05 593.5 2344.8 48.48 1.25Eþ 05
1 2 3 4 5
0.67 0.85 1.09 0.92 1.50
b
9.74E þ07 3.77Eþ 09 5.48E þ 11 3.73Eþ07 5.25E þ 11
1 1.1 1.9 1.05 0.99
E (eV) (IRM) 0.87 0.94 1.06 1.15 1.60
500
1.4x104
550
600
Exp Peak 1 Peak 2 Peak 3 Peak 4 Peak 5 Total fit FOM = 1.8%
1.2x104
TL Intensity (a. u.)
Table 1 Kinetic parameters obtained using the CGCD deconvolution method, and the activation energy (E) values by using the Initial Rise Method (IRM), for glow curve at 500 Gy ß-dose.
450
Tstop (K)
Fig. 3. Thermal stability of the TL emission after different preheatings in the range 315–625 K performed at 5 K s 1.
1.0x104 8.0x103 6.0x103 4.0x103 2.0x103 0.0 350
400
2500
500
550
600
Fig. 5. (a) TM–Tstop relationship after 500 Gy ß-irradiation of Sc2TiO5. (b) Deconvolution of the experimental glow curve (continuous gray line), and computed glow peaks (dashed lines).
0 min 200 Gy 60 min
2000
TL Intensity (a. u.)
450
Temperature (K)
360 min 1440 min
irradiation-readout cycles at the same beta dose (200 Gy). The reproducibility was off by less than 1% of the standard deviation.
1500
1000
3.3. Kinetic parameters
500
0 300
350
400
450
500
550
600
650
700
Temperature (K) Fig. 4. Glow curves from fading of Sc2TiO5 exposed at 200 Gy beta dose. The inset shows the fading of TL signals integrated from 0 to 24 h.
except for the shoulder at the low temperature side of the first glow peak, since it disappears quickly because it corresponds to shallow traps. The great influence of the shoulder over the glow peak causes the latter to experiment an immediate decrease of response. The second peak shows a decrease in intensity but in a slower manner, compared to the high temperature peak. In the inset of Fig. 4, it is shown that the fading decays quickly during the first 60 min (13%), and a 27% decay was observed at the end of a 24 h period. On the other hand, reproducibility was measured, which is considered to be another dosimetric property. The TL response of Sc2TiO5 was tested over ten consecutive
A complex glow curve's structure was observed for discandium titanate. The TM–Tstop method (McKeever, 1980) was used in order to determine the number of peaks and their temperature was present in the glow curve. Fig. 5 shows the TM–Tstop relationship from 313 to 583 K. This method shows approximately five glow peaks, which were taken into account to calculate the kinetic parameters by using the glow curve deconvolution program (CGCD) and by an Initial Rise Method (IRM) considering every peak (Table 1). The kinetic and geometrical parameters of the glow peaks were obtained using the CGCD procedure (Pagonis et al., 2006). The CGCD calculation was performed considering Kiti's expressions to first and second orders (Kitis et al., 1998): "
IðTÞ ¼ Im exp 1 þ
# E T T m T 2 E T Tm 2kT 2kT 2m 1 2 exp E kT T m kT T m E Tm
ð1Þ
E T Tm kT T m !2 T2 2kT E T T m 2kT m exp þ1þ 2 1 E kT T m E Tm
IðTÞ ¼ 4I m exp
ð2Þ
I.C. Muñoz et al. / Applied Radiation and Isotopes 90 (2014) 58–61
where T (K) is the different temperature values, E (eV) is activation energy, s (s 1) is the frequency factor, k (eV K 1) is the Boltzmann constant, Tm is the temperature at maximum intensity and Im the maximum intensity of each peak. The frequency factor (s) is calculated using Eq. (3), where β is the linear heating rate βE 1 E exp s¼ 2 ð3Þ kT m kT m 1 þ ðb 1Þ2kT m =E The goodness of the fit was measured from the figure of merit (FOM) given by Balian and Eddy (1977): n
FOM ¼ ∑
i¼1
100jY exp Y f it j A
ð4Þ
where n is the number of data points, Yexp is the experimental and Yfit is the data fitted points, and A is the integral of the fitted glow curve in the region of interest. CGCD analysis was applied to the glow curve of Sc2TiO5 exposed to beta radiation with 500 Gy dose and recorded with a heating rate of 5 K/s. For deconvolution purposes, one peak at 375–386 K, two peaks in the 438–506 K temperature range, and other two more peaks in the interval 558–597 K were considered. The temperature of the maximum (Tm) calculated by CGCD program is shown in Table 1. The FOM obtained is equal to 1.8%, which indicates a good result of the deconvolution process (Horowitz and Yossian, 1995). Fig. 5 shows the results of the deconvolution calculation, and Table 1 reports the kinetic parameters obtained for the five glow peaks. The activation energy values, obtained using CGCD deconvolution, were at about 0.67– 1.50 eV for the traps; similar values were calculated by the Initial Rise Method. The variation of the activation energy values indicates that the two broad experimental glow peaks are not a simple one; they are composed of more than one component or complex trap distribution, and the main effect of that distribution is the broadening of the glow peaks. Furthermore, the glow peaks numbers 3 and 4 peak approximately at 450 K and 551 K, respectively, with second- and first-order kinetics (see Table 1). Therefore, peaks 3 and 4 could be considered for dosimetric purposes because of their thermal stability observed under fading stage. 4. Conclusions The Sc2TiO5 orthorhombic phase was synthesized by a solid state reaction. The compound was obtained in a high purity. The TL dose–response was linear over the dose range of 50–500 Gy followed by saturation stage at high dose levels. A good TL reproducibility was found: at 200 Gy, it was less than 1% of the standard deviation after ten cycles of irradiation-readout. The fading shows a TL response decrease of 27 % at the end of a 24 h period. Discandium titanate shows a complex structure in its glow curves, since the preheat Tstop method revealed the existence of a possible distribution of traps. The kinetic and geometrical parameters were calculated by using a glow curve deconvolution procedure (CGCD) and the Initial Rise Method (IRM). First and second-order kinetics for the glow peaks was obtained. The frequency factor is close to physical meaning, i.e. 108–109 s 1
61
(Furetta and Weng, 1998). The range of energy activation values calculated with CGCD (0.67–1.50 eV) was similar to those obtained with the IRM method.
Acknowledgments The authors gratefully acknowledge the financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT), (México), under Grant number CB-2008-106041. Also, we would like to thank the financial support from Oficina de Colaboración Interinstitucional de la Universidad Nacional Autónoma de México (UNAM), and Dirección de Desarrollo y Fortalecimiento Académico-Universidad de Sonora (UNISON) under annual collaboration project UNAM-UNISON 2012. Authors are grateful to Hugo Borbón Nuñez for technical support and to Francisco Brown-Muñoz for language reviewing. References Balian, H.G., Eddy, N.W., 1977. Figure-of-merit (FOM), an improved criterion over the normalized chi-squared test for assessing goodness-of-fit of gamma-ray spectral peak. Nucl. Instrum. Methods 145, 389. Benton, E.R., Benton, E.V., 2001. Space radiation dosimetry in low-Earth orbit and beyond. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 255. Chen, R., McKeever, S.W.S., 1997. Theory of Thermoluminescence and Related Phenomena. World Scientific, Singapore. Correcher, V., Delgado, A., 1998. On the use of natural quartz as transfer dosemeter in retrospective dosimetry. Radiat. Meas. 29 (3–4), 411. Cruz-Zaragoza, E., Ruiz-Gurrola, B., Wacher, C., Flores-Espinosa, T., Barboza-Flores, M., 2010. Gamma radiation effects in coriander (Coriandrum sativum L) for consumption in Mexico. Rev. Mex. Fís. 57, 80. Furetta, C., Weng, P.S., 1998. Operational Thermoluminescence Dosimetry. World Scientific, Singapore. Garcia-Guinea, J., Correcher, V., Rodriguez-Badiola, E., 2001. Analysis of luminescence spectra of leucite (KAlSiO4). Analyst 126, 911. Horowitz, Y.S., Yossian, D., 1995. Monograph on computerised glow curve deconvolution: application to thermoluminescence dosimetry. Radiat. Prot. Dosim. 60, 1. Huston, A.L., Justus, B.L., Falkenstein, P.L., Miller, R.W., Ning, H., Altemus, R., 2001. Remote optical fiber dosimetry. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 55. Ito, J., 1971. Synthesis of scandium pseudobrookite, Sc2TiO5. Am. Mineral. 56, 1105. Kitis, G., Gomez-Ros, J.M., Tuyn, J.W.N., 1998. Thermoluminescence glow-curve deconvolution functions for first, second and general orders of kinetics. J. Phys. D: Appl. Phys. 31, 2636. Kolitsh, U., Tillmanns, E., 2003. Sc2TiO5, an entropy-stabilized pseudobrookite-type compound. Acta Crystallogr. 59, 136. Kortov, V., 2007. Materials for thermoluminescence dosimetry: current status and future trend. Radiat. Meas. 42, 576. Mathur, V.K., 2001. Ion storage dosimetry. Nucl. Instrum. Methods Phys. Res. B 184 (1–2), 190. McKeever, S.W.S., 1980. On the analysis of complex thermoluminescence glowcurves: resolution into individual peaks. Phys. Status Solidi A 62, 331. Muñoz, I.C., Cruz-Zaragoza, E., Favalli, A., Furetta, C., 2012. Thermoluminescence property of LiMgF3 erbium activated phosphor. Appl. Radiat. Isot. 70, 893. Pagonis, V., Furetta, C., Kitis, G., 2006. Numerical and Practical Exercises in Thermoluminescence. Springer, USA. Raymond, S.G., Townsend, P.D., 2000. The influence of rare-earth ions on the lowtemperature thermoluminescence of Bi4Ge3O12. J. Phys.: Condens. Matter 12, 2103. Soliman, C., Salama, E., 2009. Investigation on the suitability of natural sandstone as a gamma dosimeter. Nucl. Instrum. Methods Phys. Res. B 267, 3323. Thangadurai, V., Weppner, W., 2002. Development and investigation of perovskite (ABO3)-type oxides for power generation. Ionics 8, 360. Weber, M.J., 2003. Handbook of Optical Materials. CRC Press, USA.