Thermoluminescence dosimetry properties and kinetic parameters of lithium potassium borate glass co-doped with titanium and magnesium oxides

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Thermoluminescence dosimetry properties and kinetic parameters of lithium potassium borate glass co-doped with titanium and magnesium oxides S. Hashim, Y.S.M. Alajerami, A.T. Ramli, S.K. Ghoshal, M.A. Saleh, A.B. Abdul Kadir, M.I. Saripan, K. Alzimami, D.A. Bradley, M.H.A. Mhareb www.elsevier.com/locate/apradiso

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S0969-8043(14)00226-7 http://dx.doi.org/10.1016/j.apradiso.2014.05.023 ARI6700

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Applied Radiation and Isotopes

Received date: 22 March 2014 Revised date: 20 May 2014 Accepted date: 24 May 2014 Cite this article as: S. Hashim, Y.S.M. Alajerami, A.T. Ramli, S.K. Ghoshal, M.A. Saleh, A.B. Abdul Kadir, M.I. Saripan, K. Alzimami, D.A. Bradley, M.H.A. Mhareb, Thermoluminescence dosimetry properties and kinetic parameters of lithium potassium borate glass co-doped with titanium and magnesium oxides, Applied Radiation and Isotopes, http://dx.doi.org/10.1016/j.apradiso.2014.05.023 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Thermoluminescence dosimetry properties and kinetic parameters of lithium potassium borate glass co-doped with titanium and magnesium oxides S. Hashima, Y. S. M. Alajeramia,b*, A.T. Ramlia, S.K. Ghoshala, M. A. Saleha, A. B. Abdul Kadirc, M. I. Saripand, K. Alzimamie, D. A. Bradleyf,g and M H A Mhareba a

Department of Physics, Universiti Teknologi Malaysia, 81310 Skudai, Johor, MALAYSIA. b Department of Medical Radiography, Al-Azhar University, Gaza Strip, PALESTINE. c Secondary Standard Dosimetery Lab, Malaysian Nuclear Agency, 4300 Selangor, Malaysia. d Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor, MALAYSIA. e Department of Radiological Sciences, Applied Medical Sciences College, King Saud University P.O. Box 10219, Riyadh 11433 SAUDI ARABIA. f Centre for Nuclear & Radiation Physics, Department of Physics, University of Surrey, Guildford, GU2 7XH, U.K. g Department of Physics, Faculty of Science, University of Malaya 50603 Kuala Lumpur, MALAYSIA.

*Author for correspondence: [email protected] (Yasser Alajerami)

Abstract Lithium potassium borate (LKB) glasses co-doped with TiO2 and MgO were prepared using the melt quenching technique. The glasses were cut into transparent chips and exposed to gamma rays of 60Co to study their thermoluminescence (TL) properties. The TL glow curve of the Ti-doped material featured a single prominent peak at 230 oC. Additional incorporation of MgO as a co-activator enhanced the TL intensity threefold. LKB:Ti,Mg is a low-Z material (Zeff = 8.89) with slow signal fading. Its radiation sensitivity is 12 times lower that the sensitivity of TLD-100. The dose response is linear at doses up to 103 Gy. The trap parameters, such as the kinetics order, activation energy, and frequency factor, which are related to the glow peak, were determined using TolAnal software. Keywords: Thermoluminescence; lithium potassium borate glass; titanium oxide; glow curve deconvolution.

1. Introduction Lithium borate dosimeters show promising TL properties that passed the disturbance of phosphors and gave opulence applications in both medical and environmental fields (Magdalyna et al., 2004). Manganese was the first activator for lithium borate dosimeter proposed by Schulman et al. (1967). The thermoluminescence of the material was promising, but its radiation sensitivity was low. The low sensitivity was attributed to the incompatibility of the manganese emission (600 nm) with the spectral sensitivity of photomultiplier (PM) tube. An improvement in the sensitivity was achieved by replacing manganese with copper. The Li2B4O7 powder doped with copper showed an emission band that was more compatible with the spectra of PM tubes (‫׽‬400–460 nm) (Takenaga et al., 1980). A study conducted by Wall et al. (1982) proved that the sensitivity of the Cu-doped Li2B4O7 to 90Sr β-rays is nearly eight times higher than the sensitivity of Li2B4O7 doped with Mn. The same study showed that, in 10 days after irradiation, the fading of the signals of Li2B4O7:Cu and Li2B4O7:Cu,Ag was about 85%. The dose response of the Mn-doped glass was essentially linear up to 1 Gy, whereas the dose responses of glasses doped with Cu, or Cu and Ag, were linear up to 10 Gy (Wall et al., 1982). Dosimetric advantages of this phosphor, either undoped or Cu-doped, were reported (Lakshmanan et al., 1982, Takenaga et al., 1983, Srivastava et al., 1989, Martini et al., 1995 and Alajerami et al., 2013). El-Faramawy et al. investigated the promising properties of Li2B4O7:Cu, particularly the high linearity of its response and high sensitivity. They demonstrated the ability of Li2B4O7:Cu to measure low doses down to 20 µGy. The sensitivity of home-made Li2B4O7:Cu to 137Cs radiation was twice as high as that of TLD-100, and the signal fading three months after the irradiation was 11%. The authors attributed the absence of supralinearity to copper in lithium borate (El-Faramawy et al., 2000). Recently, many researchers explored the mechanism of luminescence in borate glasses (Alajerami et al., 2013; Prokic, 2002; Liu et al., 2005; Elkholy, 2010; Puppalwar et al., 2012). In 2001, Furetta et al. used lithium borate with copper as a dopant and indium as a co-dopant. That material exhibited higher sensitivity and was capable to detect doses down to 10 µGy (Furetta et al., 2001). The dose responses of both Li2B4O7:Cu,In and Li2B4O7:Cu were linear in the range 10-4 - 103 Gy (60Co). Moreover, the fading was slower, about 10% in 3 months (Furetta et al., 2001). Prokic (2002) determined characteristics of sintered Li2B4O7 co-doped with several dopants, such as Cu, In; Cu, In, Ag; and Mg, Cu, P; exposed to 60Co gamma radiation in the dose range 10−4 - 3×103 Gy. The glow curve of Li2B4O7 doped with Cu, Ag, and P featured a pronounced peak at 185 – 190 °C, and the radiation sensitivity of the material was five times higher thatn that of LiF:Mg,Ti. The signal of Li2B4O7:Cu,In faded 6% 3 months after irradiation; the fading of the signal of Li2B4O7:Cu,In,Ag was 10% in the same period. The dose detection limit, defined as the dose producing a signal equal to three standard deviations of readings of unirradiated samples, was estimated to be 10 μGy (Prokic, 2002). Alkaline-earth borates, unlike the glasses with other modifiers, were less hygroscopic (Fukuda et al., 1984; Fukuda et al., 1985; Fukuda et al., 1986; McKeever et al., 1995). Venkateswara Rao and his colleagues (2002) studied the thermoluminescence properties of a new borate glass system after an X-ray irradiation (35 kVp, 10 mA) at room temperature for 1 h. The phosphor was modified with lithium oxide and calcium fluoride (Li2O–CaF2–B2O3) and doped with MnO in various concentrations. They found

that the TL intensity was decreasing with increasing MnO concentration. This quenching was attributed to the presence of Mn3+ ions (Venkateswara et al., 2002). The authors assumed that there was a competition between the trapping of the electrons released during the excitation and the readout process. At the maximal concentration, the contiguous activator (traps) inhibited the radiative luminescence, and the opposite effect was observed in the TL intensity. According to an interesting paper by Pekpak et al. (2009), the glow curve consists of several peaks, with the main peak at 185 - 235 oC. The range of the linearity of the dose response extended as far as to 1000 Gy, and the signal lost about 5% of its intensity in one month (the dosimeters were exposed to the 90Sr-90Y beta radiation at a dose rate of 0.5 Gy/min at room temperature for 5 minutes). Elkholy (2010) showed that adding magnesium oxide to the lithium borate glass produced a dosimeter capable to work in the dose range of 0.1 – 20 kGy (60Co). However, there was no significant research to investigate the effect of TiO2 on the TL properties (dose response) of the borate glass. Despite the general agreement between the studies of the role of titanium ions in the glassy host, the mechanism of the TL enhancement is far from being understood. It is assumed that titanium occurs in the glass mixture as Ti3+ and Ti4+. In a material with a higher relative Ti4+ concentration, some of the electrons released by the thermal treatment would be effectively captured by the Ti4+ ions, whose energy levels are close to the Fermi level, by non-radiative recombination. The remaining free electrons would be trapped by other holes on the network. It is well known that hosts with high concentrations of Ti4+ have weaker TL responses (Balaji et al., 2004; Balaji, et al., 2005; Nageswara, et al., 2005). The aim of the present work was to study a new material, namely, a borate glass modified with lithium and potassium carbonate and co-doped with titanium and magnesium oxides (LKB:Ti,Mg). Of the primary interest were potential applications of this glass in the dosimetry of high-energy photons and electrons. 2. Experimental 2.1 Glass preparation Boric acid was used as a glass former; lithium and potassium carbonate were added as glass modifiers. This mixture was initially activated with a small amount of titanium oxide (0.3 - 1.0 mol%). Then, magnesium oxide was added as a co-activator in a concentration between 0.05 and 0.50 mol% to provide the optimal TL response. All the used reagents were of high purity (main component concentration at least 99.99%) and obtained from Sigma-Aldrich (Germany). The composite was well mixed for 40 min and then kept in an alumina crucible in an electrical furnace with the temperature around 1200 oC for 45 to 60 minutes (depending on the dopant concentration). The melt was poured into a steel mold (400 °C) and kept on it for 3 h to reduce the mechanical stress. The glass transition temperature was determined by thermal analysis of a preliminary sample; it was slightly lower than the first annealing temperature. Table 1 lists the compositions of the prepared samples and their thermal parameters.

2.2 Dosimeter preparation and irradiation All the prepared glass samples had a rectangular form (2.5 x 2.5 x 1 mm3) and were transparent. The transparency of the glass varied with the dopant concentration. Transparency of a TLD dosimeter facilitates the collection of recombination light from its inner parts (Bos, 2007). The optical properties of these mixtures have been previously described (Alajerami et al., 2012). Measurements of glow curves of the samples were performed with a Harshaw TLD reader Model 4500 at a secondary standard dosimetry laboratory (SSDL) at the Malaysian Nuclear Agency. The reader had an infrared filter to absorb the thermal noise. Background signals were subtracted from all the TL glow curves. The samples were irradiated with a 60Co source to various doses in a “solid water” phantom (dose rate ~5.232 mGy.min-1) at room temperature. The samples were at dmax, SSD was 100 cm, and the filed size was 10 × 10 cm2. Initially, the glow curves were recorded at a fixed heating rate (20 oC.s-1) in the temperature range 50 - 400 oC. A continuous flow of gaseous nitrogen was used during the readouts to reduce chemiluminescence in the heated samples. Before the TL measurements, the irradiated samples were kept in a dark room at the ambient temperature (25 - 30 oC) to avoid any influence of the background light. The curves were recorded 24 h after the irradiation to allow spurious signals to fade. Comprehensive calibrations and quality assurance measurements were implemented to obtain consistent and precise results. For each experimental data point, at least three replicate samples were irradiated and measured to determine the average response and the standard deviation. The reader was calibrated by measurements of LiF:Mg,Ti (TLD-100) dosimeters irradiated under the same conditions.

3. Results and discussion 3.1 Sample characterization The amorphous phase of the prepared samples was described in an earlier paper (Alajerami et al., 2012). Fig. 1 shows the differential thermal analysis (DTA) thermograms of the co-doped samples. The glass transition temperature (Tg) 520 ± 2 °C is shown with an arrow at an endothermic peak. An exothermic peak at 630 °C has been assigned to the crystallization temperature (Tc) of the sample, and yet another endothermic peak at 920 °C corresponds to the melting temperature (Tm) of the glass. Clearly, with the increasing concentration of MgO, the glass transition temperature increases, while the crystallization temperature decreases. The parameter Tc - Tg, which characterizes the glass stability, was found to decrease with the increasing concentration of the dopant. The single peak corresponding to Tg of the pure glass in all the spectra indicated that the prepared glasses were highly homogenous.

3.2 Dosimetric characterization The first step of the activation of the lithium potassium borate (LKB) matrix was a variation of the titanium oxide concentration between 0.3 and 1.0 mol%. The TL dose response was found to be maximal at 0.5 mol%. Consequently, MgO as a co-dopant was added to a glass with this optimal titanium oxide concentration; the MgO concentration varied from 0.05 to 0.50 mol%. Fig. 2 shows TL glow curves of the glasses with various concentrations of magnesium oxide, which feature a peak at 240 oC. We had preliminarily optimized the procedure of sample processing and measurements. The best annealing regimen for this glass composition was found to be 400 oC for 30 min. These annealing temperature and time were favorable for erasing the majority of the background and stored signals. The optimal heating rate was 20 oC s-1; the optimal preheating and maximal temperatures were 50 and 400 oC, respectively. The glass transition (Tg) and maximum crystallization (Tc) temperatures had no influence on the annealing temperature and the TL glow peak because both the preheating and maximal temperature values were well below 500 oC. The temperature lag was further minimized by using small glass chips and placing a flat metal plate between the planchet and the dosimeters to facilitate the heat transfer. The structures of the TL peaks were practically unchanged, although there was a slight shift of the glow peak (Tm). It is important to note that both of the crystallization onset temperatures of the dosimeter occur above the temperature of the TL glow peak, which was used to construct calibration curves. This concentration-independent behavior suggested that the impurities were strongly related to the intrinsic defects. The relationship between the peak intensity and co-dopant concentration clearly showed the increase in the intensity with an increase of the MgO concentration, with the maximum at 0.25 mol% (three-fold enhancement). The intensity gradually reduces beyond this concentration. This behavior can be attributed to the well-known concentration quenching phenomena. Fig. 3 shows the TL response of LKB:Ti,Mg to various absorbed doses as a function of the MgO concentrations. The shape of the glow peak did not change significantly with the increasing co-dopant concentration. One can see that the TL intensity markedly increased with the increasing MgO concentration up to 0.25 mol% and then fell dramatically. This behavior was in line with the assumption that the trapping in this glass is directly related to the host lattice, i. e., there is an relation between the dopants and the trapping centers. The glow peak of LKB:0.5Ti,0.25Mg (mol%) was deconvoluted and analyzed with TolAnal software to determine the kinetic TL parameters (Chung et al., 2010). This software is based on fast, efficient algorithms. There is no restriction on the stimulation profile, and the program can be used in the case where the temperature and/or stimulation light change linearly or arbitrarily.

Fig. 4 shows results of the deconvolution, which produced five prominent peaks with different peak temperatures (Tm). Table 2 lists the corresponding kinetic parameters obtained by the glow curve deconvolution method (GCDM). The kinetic parameters of the peaks agree with the glow peak temperatures. The activation energy (E) gradually increases with Tm. These results support the hypothesis that introduction of MgO creates deep traps (Prokic, 2002). The activation energy and the frequency factor of the whole glow peak were found to be 0.807 and 1.77 x 109, respectively. The temporal post-irradiation stability of the TL signal (the 240 oC peak) was doseindependent in the studied dose range 0.05 – 10 Gy (Fig. 5). The signal faded approximately 8% in 10 days and 17% in 3 months after irradiation. The response of the proposed dosimeters to doses of the 60Co radiation in the range 10-2 103 Gy was linear, with the linear regression coefficient 0.995 (Fig. 6). Generally, linearity of the TL dose response at doses above 10 Gy is exceptionally rare, as supralinearity of the response is typical of a large variety of TL materials. In this work, the TL sensitivity of the material was expressed as glow curve area per unit mass of the dosimeter and per unit dose (TL.g-1.Gy-1). The obtained results were normalized to the sensitivity of TLD-100. The TL sensitivity of LKB:Ti,Mg is about three times higher than the sensitivity of LKB:Ti, but twelve times lower than the sensitivity of TLD-100. Consequently, the material has a potential in measuring higher doses. Although the sensitivity of LKB:Ti,Mg is significantly lower than that of TLD100, this material has an effective atomic number 8.89, which is close to that of soft tissue (7.4). The probability of escape of charge carriers (electrons and holes) from their trapping centers can theoretically be estimated from the values of activation energy and frequency factor. This probability has a direct effect on the stability of the stored signals. Applying the Arrhenius equation, the probability of releasing an electron can be expressed with the equation:

p = s .e

−

E kT

,

(1)

where p is the probability of escape per unit time, s is the frequency factor of trapped electron, E is the activation energy, k is Boltzmann’s constant, and T is the absolute temperature (the temperature of the storage environment). The half-life for thermal fading is given by: t1 = 2

ln2 0.693 = . E − p kT s.e

(2)

The estimated value of t1/2 for the thermal fading was 1.52 x 108 at room temperature (~27 oC). The fading factor λ (d –1) can be calculated using the expression

λ = - (1 / t) ln (φ / φ0) ,

(3)

where t is the elapsed time, φ is the TL intensity at time t, and φ0 is the TL intensity immediately after the irradiation. The fading was fairly significant in the first 10 days after exposure, but became slower in the subsequent days (Table 3).

4. Conclusion In this work, samples of the LKB glass doped with TiO2 (0.50 mol%) and co-doped with various concentrations of MgO were prepared. The glow curves featured a single TL peak at 230-240 oC. A drastic reduction in the TL response with an increase in the MgO concentration above 0.25 mol% was observed. The main dosimetric advantages of the newly prepared TL dosimeters are the closeness of their effective atomic number to that of soft tissue and a wide range of linear dose response (10-2-103 Gy). The radiation sensitivity of the material is 12 times lower less than that of TLD-100. A deconvolution of the glow curve revealed five superimposed peaks with different maximal glow peak temperatures, activation energies, and frequency factors. Finally, the signal fading, halflife (t1/2), and the fading factor of the proposed dosimeter were determined. The mechanism for TL in the proposed glasses is discussed. This detailed study can be useful for further development of highly efficient ionizing radiation dosimetry. Acknowledgment The authors would like to acknowledge Universiti Teknologi Malaysia for providing financial assistance through Research University Grant Scheme (RUGS), Project number (Q.J130000.2526.07H59) and Postdoctoral Research University Fellowship (PDRU) vote number (Q.J130000.21A2.01E52). This research project was partially supported by the Ministry of Education Malaysia through Fundamental Research Grant Scheme (FRGS), Vote number (R.J130000.7826.4F168). 

References Alajerami, S.M.Y., Hashim, S., Ramli, A.T., Saleh, M.A., Kadni, T., 2013. Thermoluminescence properties of Li2CO3–K2CO3–H3BO3 glass system co-doped with CuO and MgO. Radiat. Prot. Dosim. 155, 1-10. Alajerami, Y., Hashim, S., Saridan, W., Ramli, A., 2012. The effect of titanium oxide on the optical properties of lithium potassium borate glass. J. Mol. Struct. 1026, 159– 167. Balaji Rao, R., Krishna Rao, D., Veeraiah, N., 2004. The role of titanium ions on structural, dielectric and optical properties. Mater. Chem. Phys., 87, 357–369. Balaji, R., Naga Raju G., Veeraiah, N., 2005. Catalyzed crystallization and some physical properties of Li2O-MgO-B2O3:TiO2 glasses. Indian J. Pure Appl. Phys., 43, 192-202. Bos, A.J.J., 2007. Theory of thermoluminescence. Radiat. Meas. 41, S45–S56. Chung, K.S., Park, C.Y., Lee, J.I., Kim, J.L., 2010. Development of a new curve deconvolution algorithm for optically stimulated luminescence. Radiat. Meas. 45, 320. El-Faramawy, N. A., El-Kameesy S.U., El-Agramy A., 2000. The dosimetric properties of in-house prepared copper doped lithium borate examined using the TLtechnique. Radiat. Phys. Chem., 58, 9－13. Elkholy, M.M., 2010. Thermoluminescence of B2O3–Li2O glass system doped with MgO. J. Lumin., 130, 1880–1892. Fukuda, Y., Takeuchi, N., 1985. Thermoluminescence of sodium borate compounds containing copper. J. Mater. Sci. Lett. 4, 94. Fukuda, Y., Mizuguchi, K., Takeuchi, N., 1986.Thermoluminescence in sintered CaB4O7:Dy and CaB4O7:Eu. Radiat. Prot. Dosim. 17, 397. Fukuda, Y., Tomita, A., Takeuchi, N., 1984. Thermoluminescence and thermally stimulated exoelectron emission in glass and sintered CaB4O7:CuCl2. Phys. Status Solidi, A 85, K141. Furetta, C., Prokic, M., Salamon, R., Prokic, R., 2001. Dosimetric characteristics of tissue equivalent thermoluminescent solid TL detectors based on lithium borate. Nucl. Instrum. Methods Phys. Res. A, 456, 411－417. Lakshmanan, A.R., Bhuwan Chandra, R.C., 1982. Dosimetric characteristics of Li2B4O7:Cu. Radiat. Prot. Dosim., 2, 231.

Liu, L.Y., Zhang, H.L., Hao, J.Q., Li, C.Y., Tang, Q., Zhang, C.X., Su, Q., 2005. Spectroscopic properties of inorganic and organometallic compounds. Phys. Status Solidi A, 202, 2800-2805. Ignatovich, M., Holovey, V., Watterich, A., Vidoczy. T., Baranyai, P., Kelemen, A., Chuiko, O., 2004. Luminescence characteristics of Cu- and Eu-doped Li2B4O7. Radiat. Meas. 38, 567 – 570. Martini, M., Furetta, C., Sanipoli, C., Scacco, A. Somaiah, K., 1995. Spectrally resolved thermoluminescence of Cu and Eu doped Li2B4O7. Radiat. Eff. Def. Solids 135, 133–136. McKeever, S.W.S., Moskovitch, M., Townsend, P.D. (1995). Thermoluminescence Dosimetry Materials: Properties and Uses. Nuclear Technology Pub., Ashford (UK), 204 pp. ISBN 1-87096-519-1. Nageswara Rao, P., Laxmi Kanth, C., Krishna Rao, D., Veeraiah, N., 2005. Influence of titanium ions on optical properties of AF–PbO–B2O3 glasses. J. Quant. Spectrosc. Radiative Transfer 95, 373–386. Pekpak, E., Gülhan, O., Aysen, Y. Thermoluminescent characteristics of lithium tetraborate. In: Proc. IV International Boron Symposium, 15-17 October, 2009. Eskişehir, Turkey, p. 103-110. ISBN: 978-9944-89-790-7. Prokic, M., 2002. Dosimeteric charetceristics of Li2B4O7:Cu,Ag,P solid TL detectors. Radiat. Prot. Dosim. 100, 265–268. Puppalwar, S.P., Dhoble, S.J., Dhoble, N.S., Animesh K., 2012. Luminescence characteristics of Li2NaBF6:Cu phosphor. Nucl. Instrum. Methods B, 74, 167-171. Schulman, J. H., Kirk, R. D., West, E. J., 1967. Use of lithium borate for thermoluminescence dosimetery. In: Luninescence Dosimetry, Proceedings of the International Conference on Luminescence Dosimetery, Stanford, June 1965. CONF650637, Clearinghouse, Springfield, p. 113–118. OCLC 841357796. Srivastava, J. K., Supe, S. J., 1989. The thermoluminescence characterization of Li2B4O7 doped with Cu. J. Phys. D. Appl. Phys. 22, 1537–1543. Takenaga, M., Yamamoto, O., Yamashita, T., 1980. Preparation and characteristics of Li2B4O7:Cu phosphor. Nucl. Instrum. Methods 175, 77–78. Takenaga, M., Yamamoto, O., Yamashita, T., 1983. A new phosphor Li2B4O7:Cu for TLD. Health Phys. 44, 387–393.

Venkateswara Rao, G., Reddy, P.Y., Veeraiah, N., 2002. Thermoluminescence studies on Li2O–CaF2–B2O3 glasses doped with manganese ions. Mater. Lett., 57, 403–408. Wall, B.F., Driscoll, C.M., Strong, J.C., Fisher, E.S., 1982. The suitability of different preparations of thermoluminescent lithium borate for medical dosimetry. Phys. Med. Biol., 27, 1023-1034.

Table 1. The compositions and thermal properties of the glass samples. Glass Sample 0 (S0) Sample 1 (S1) Sample 2 (S2) Sample 3 (S3) Sample 4 (S4) Sample 5 (S5) Sample 6 (S6) Sample 7 (S7) Sample 8 (S8)

Li2CO3 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00

Composition (mol%) H3BO3 K2CO3 TiO2 70.00 10.00 69.70 10.00 0.30 69.50 10.00 0.50 69.30 10.00 0.70 69.00 10.00 1.00 69.45 10.00 0.50 69.40 10.00 0.50 69.25 10.00 0.50 69.00 10.00 0.50

MgO 0.05 0.10 0.25 0.50

Thermal characteristics, °C Tg Tc Tm 490 633 900 497 628 910 505 625 913 512 620 920 510 645 927 515 635 936 520 632 928 530 627 913 540 620 915

Table 2. Thermoluminescence parameters of the glass LKB:(0.5)Ti,(0.25)Mg (mol%) obtained with the TolAnal deconvolution. Peak

Kinetic Order

Tm, K

Activation energy, eV

Frequency factor, s(s-1)

1

2nd

500

0.63 ± 0.04

8.55E+08

2

2nd

509

0.66 ± 0.03

8.05E+08

3

1st

519

0.71 ± 0.04

7.82E+09

4

2nd

588

0.74 ± 0.05

7.31E+08

5

2nd

654

0.78 ± 0.03

7.22E+09

Table 3. The fading factors for the proposed dosimeters at room temperature. Storage time (days) Fading factor (% / d)

1

7

10

30

50

70

90

4.24

1.67

1.16

0.45

0.30

0.27

0.23

Figure Captions Fig. 1. DTA curves of LKB:Ti with MgO in various concentrations. See Table 1 for sample designations. Fig. 2. Thermoluminescence glow curves of the LKB samples doped with TiO2 in various concentrations and irradiated to 2 Gy. Fig. 3 Intensity of the thermoluminescence of LKB:Ti,Mg irradiated to various doses as a function of the MgO concentration. Fig. 4 Deconvolution of the thermoluminescence glow curve of LKB glass co-doped with TiO2 and MgO. Gy.

Fig. 5. Fading of the LKB glass co-doped with TiO2 and MgO after irradiation to 10 Fig. 6 Thermoluminescence response of LKB:Ti,Mg to the 60Co dose.

Figures Fig.1

Fig.2

Fig.3

Fig.4

Fig. 5

Fig.6

Highlights • • • •

Lithium potassium borate glass doped with Ti and Mg was prepared. The material is close to soft tissues in terms of Zeff. The radiation sensitivity is about 12 times lower than that of TLD-100. The signal fades about 8% in 10 days and 17% in 3 months.