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On discrimination of HTTL peaks in TLD100 glow curves by a two steps heating readout
Radiation Measurements 45 (2010) 1491e1494
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
On discrimination of HTTL peaks in TLD100 glow curves by a two steps heating readout A. Abraham a, *, B. Magoz b, M. Weinstein a, O. Pelled a, U. German a, Z.B. Alfassi b a b
Nuclear Research Centre Negev, P.O.B 9001, Beer Sheva 84190, Israel Ben Gurion University of the Negev, Beer Sheva 84105, Israel
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 November 2009 Received in revised form 8 May 2010 Accepted 17 May 2010
The discrimination between the high temperature thermoluminescent peaks (HTTL) and the dosimetry peaks is not a simple process due to their overlapping. The application of the two steps heating method for this purpose was studied. If the heating is performed in the first step only to about 220e250 C, the dosimetry peaks are emptied, but the HTTL peaks are only partially affected. Performing a second reading to 300 C provides information attributed solely to HTTL peaks. The results of optimization of the two steps readout process for routine (high rate heating) readout are presented. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: TLD100 HTTL Neutron Gamma Readout
1. Introduction LiF:Mg,Ti is the most widespread material used for thermoluminescence dosimetry (TLD). In order to increase the throughput in routine dosimetry, fast heating rates of about 25 C s1 are applied. Mostly, in routine dosimetry TLD cards are used, which contain 3 or 4 chips of TLD100 held between Teflon foils. The use of Teflon limits the maximum temperature to 300 C, in order to prevent damage to the Teflon. The present work was performed within those limitations, as the purpose was to check the application of the two readout steps to routine dosimetry. The main peaks used for dosimetry are peaks 4 and 5 (the dosimetry peaks). Peak 5 appears at w205 C at heating rates of w1 C s1, but it shifts to about 230e250 C if a fast heating rate of about 25 C s1 is applied. At higher temperatures other peaks appear, which are usually referred to as the high temperature peaks (HTTL). The most important are the first peaks (6 and 7). At heating rates of w1 C s1, the maximum intensity of the HTTL is at about 270 C. When applying the heating rate of 25 C s1, they appear at about 300 C, which is the temperature limit for the cards readout. The intensity of the HTTL peaks is negligible for low gamma doses which are encountered in personal or environmental dosimetry, due to their low LET. However, for higher LET particles
* Corresponding author. Tel.: þ972 507678295; fax: þ972 86568877. E-mail address: [email protected] (A. Abraham). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.05.030
(heavy charged particles or neutrons which produce alpha particles) the intensity of the HTTL becomes significant. For thermal neutrons the relative intensity of the HTTL peaks in TLD100 is higher by about one order of magnitude relative to gamma irradiation (Weinstein, 2005, 2006). This is the basis for possible evaluation of gamma and neutron doses in a mixed field by using one TLD100 chip. In order to use the sensitivity difference of the HTTL peaks to high and low LET radiations, their discrimination from the dosimetry peaks must be performed. In most cases, it was done by mathematical analysis of the glow curve, either by peaks deconvolution (as by Horiuchi et al., 1992 and Gambarini and Roy, 1997) or by applying the regions of interest (ROI) method (as by Liu and Sims, 1991 and Weinstein et al., 2005). However, mathematical separation of HTTL peaks from the dosimetric peaks may be problematic, even for slow heating rates, due to the overlapping of the peaks. The Region of Interest method may be dependent on the mathematical procedure applied, therefore, the method of heating in two steps which was mentioned also in the past (Busuoli et al., 1970; Chernov et al., 1999) was investigated. This method is attractive, and was applied also recently (Pradhan et al., 2009). Its main advantage is that a physical separation of the HTTL peak from the dosimetric peaks can be achieved, without the need of mathematical analysis. The maximal temperature of the first step must be considerably lower than the HTTL temperature in order to assure that a minimal portion of the HTTL peak is readout, but it must be enough to ensure full readout of the dosimetry
1492
A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
Fig. 1. The ratio of the second to the first readout as a function of the first readout maximum temperature and the corresponding dosimetry peaks residuals.
peaks. The second readout is a normal routine readout to 300 C. As in the first readout the traps of the dosimetry peaks were emptied, the second readout will contain only information from the HTTL peaks. The purpose of the present work was to optimize the readout temperature of the first stage to obtain full readout of the dosimetry peaks with minimum loss of information from the HTTL peaks.
2. Materials and methods The experiments were performed with LiF: Mg,Ti Harshaw/ Thermo 1110 cards containing three 3 3 0.38 mm TLD100 chips. The readout of the irradiated cards was performed by a 6600 TLD reader (Harshaw/Thermo). Each chip was calibrated individually by a 90Sre90Y source, built in the reader. The heating of the TLD chips is
Fig. 2. The glow curve of the first readout at 220 C (upper curve) and the second readout at 300 C (lower curve) of a TLD100 chip irradiated by gamma rays.
A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
by a hot nitrogen gas jet, delivering pre-defined heating profiles. The glow curve of each chip is digitized to a 200-channel spectrum and stored on a PC computer. Due to the temperature lag when applying a high heating rate, in order to make sure that the chip temperature will reach the intended temperature, the heating must be continued for several seconds at this temperature. The readout process was split into two phases. In the first step, a preheat to 50 C (less than 0.5 s) and a linear heating at a rate of 25 C s1 was applied up to a predetermined temperature in the range from 220 C to 250 C and then kept at this temperature, for a total time of 20 s. The second readout consisted of a preheat to 50 C (less than 0.5 s) and a linear heating at a rate of 25 C s1 up to the temperature of 300 C and the kept at this temperature, for a total time of 30 s. No annealing was performed, except for the usual reader annealing. Gamma irradiations to a dose of 5 mSv were carried out using a 137Cs source. The neutron irradiations were performed using thermalized neutrons from a 81 MBq (at 1.1.2008) shielded 252Cf source. The source was placed in a graphite block equipped with a polypropylene coated irradiation hole. The neutrons were thermalized by layers of polypropylene. The thermal neutron dose was calibrated by gold foils and its rate at the irradiation location was 0.30 mSv/h (at 1.1.2008). The TLD chips were irradiated to a neutron dose of about 3.5 mSv. The contribution not originated by thermal neutrons, as measured by the light output from 7LiF chips relative to the light output from 6LiF chips, was negligible (up to about 2%). No glow curve spectra analysis was performed. The full glow curve
1493
integrals were calculated and assumed to represent the dosimetry peaks area (first readout) and HTTL area (second readout). 3. Results and discussion The readout temperature at the first stage is the main parameter which determines the separation quality between the dosimetry peaks and the HTTL peaks. If a temperature higher than the dosimetry peaks temperature would be applied (e250 C for a 25 C/s heating rate) the dosimetry peaks traps would be totally emptied, but a significant portion from the HTTL peaks would be also emitted. German et al. (2009) found that after a first readout at 250 C about 20% from the HTTL peaks were lost. Therefore, lower temperatures were applied and the dosimetry peaks were emptied by isothermal decay. It was shown (German et al., 2009) that the dosimetry peaks can be readout almost completely when applying temperatures down to 220 C (for a heating rate of 25 C/s and a total readout time of 20 s). Lower readout temperatures leave a residual dose in the dosimetry peaks, which may be significant. The ratio between the HTTL readout (second stage readout) and the first stage readout as a function of the first step maximal temperature after thermal neutrons irradiation is presented in Fig. 1. It can be seen that there is a constant improvement in the readout efficiency of the HTTL peaks when lowering the readout temperature. Also shown in Fig. 1 is the residual of the dosimetry peaks after gamma irradiation as a function of the first step maximal temperature in percents from the complete readout (at 300 C). At 230 C a very small residual of
Fig. 3. The glow curve of the first readout at 220 C (upper curve) and the second readout at 300 C (lower curve) of a TLD100 chip irradiated by thermal neutrons.
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A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
about 1.7% was obtained, but the HTTL to dosimetry peaks ratio is significantly lower relative to the 220 C value (12.4% compared to 18.6%), indicating a high loss of HTTL information. At 220 C the ratio is acceptable (close to about 20% obtained by the Region of Interest method e See Weinstein et al., 2005, 2006) and the residual percent is higher by only about 3%, therefore the readout temperature at the first stage was chosen 220 C. The first readout glow curves (for a maximum heating temperature of 220 C) and the second readout glow curves (for a maximum heating temperature of 300 C) obtained after gamma and thermal neutron irradiations are presented in Figs. 2 and 3. As can be seen from the second readout curves, their shape is similar after gamma and neutron irradiations, and there is no contribution from the dosimetric peaks. The shapes of the first readouts are different to some extent. Most of peak 5 seems to be read in the time interval between about 10 s and 15 s. The contribution of peak 5 is smeared, as it is obtained by isothermal decay. The lower part of the glow curve contains mainly the contribution of peaks 3 and 4. It has been already mentioned in the past by Horowitz and Yossian (1995) that the glow curve below peak 5 is significantly altered following alpha particle irradiation compared to gamma irradiation. It was observed that after alpha irradiation peak 4 appears at a lower temperature than after gamma irradiation, almost coinciding with peak 3, which seems to be the cause for the difference in the shape of the glow curves presented in Figs. 2 and 3. The neutron-gamma discrimination in a mixed field when employing the two peaks method is based on the different ratios of the HTTL peaks area to the dosimetry peaks area for the two radiations. This value must be stable and redundant to obtain an acceptable accuracy. The ratio of the HTTL peaks area to the dosimetry peaks area (the ratio of the glow curve areas from the second and first readout) obtained in the present work by the two steps method was 0.0164 0.0001 for gamma rays and 0.186 0.004 for thermal neutrons. Several cycles of repeated experiments gave results within the uncertainty range. The ratios between the HTTL peak area and the dosimetry peak area obtained by the two steps readout are not much different from previous results obtained by using the ROI analysis method (Weinstein, 2005, 2006). The HTTL to dosimetry peaks ratios are almost identical: 11.34 in the present work compared to 11 and 11.94 in the previous works using the ROI method.
4. Conclusions The results obtained in the present work indicate that it is possible to separate the dosimetric peaks from the HTTL peaks applying a two steps heating profile with a similar efficiency as by the regions of interest method. The main advantage of the two steps procedure is that it discriminates physically, in two separate measurements, the information related to the dosimetry and the HTTL peaks, without inducing mathematic errors which may be dependent on the neutron to gamma rays ratio and the analysis method. However, the two steps heating method has also some shortcomings. The readout time is doubled as two readings are needed, and there is some loss of efficiency for the readout of the HTTL peaks, as some of its information is lost in the first step readout. Further work is needed to characterize the limitations of the two steps heating method in a mixed gammaneutron field. Its practical advantage relative to the Region of Interest method will be checked by field experiments with mixed gamma-neutron doses. References Busuoli, G., Cavallini, A., Fasso, A., Rimondi, O., 1970. Mixed radiation dosimetry with LiF (TLD-100). Phys. Med. Biol. 15, 673e681. Chernov, V., Mironenko, S., Minaev, E., Alekseev, I., 1999. TL dosimetry of radon by the two peaks method. Rad. Prot. Dosim 85, 329e332. Gambarini, G., Roy, M.S., 1997. Dependence of TLD thermoluminescence yield on absorbed dose in a thermal neutron field. Appl. Radiat. Isot. 48, 1467e1475. German, U., Weinstein, M., Abraham, A., Alfassi, Z.B., 2009. On the readout of HT peaks in LiF: Mg, Ti by applying high rate gas heating. Nucl. Instr. Meth. A 600, 683e688. Horiuchi, N., Sato, T., Morimoto, H., 1992. Simultaneous evaluation of the neutron and gamma dose with a single TLD. Nucl. Instr. Meth. A 317, 542e552. Horowitz, Y.S., Yossian, D., 1995. Computerized glow curve deconvolution: application to thermoluminescence dosimetry. Rad. Prot. Dosim. 60, 1e114. Liu, J.C., Sims, C.S., 1991. Mixed field personnel dosimetry, Part I: high temperature peak characteristics of the reader-annealed TLD-600 SLAC-PUB-5340. Pradhan, A.S., Lee, J.I., Kim, J.L., 2009. Further studies on higher temperature TL glow peaks of 7LiF: Mg, Ti. Appl. Rad. Isotop. 67, 1078e1083. Weinstein, M., German, U., Abraham, A., Dubinsky, S., Alfassi, Z.B., 2005. On the linearity of the high temperature peaks of LiF: Mg, Ti. Radiat. Meas. 39, 489e494. Weinstein, M., German, U., Alfassi, Z.B., 2006. On neutronegamma mixed field dosimetry with LiF: Mg, Ti at radiation protection dose levels. Rad. Prot. Dosim. 119 (1e4), 314e318.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
On discrimination of HTTL peaks in TLD100 glow curves by a two steps heating readout A. Abraham a, *, B. Magoz b, M. Weinstein a, O. Pelled a, U. German a, Z.B. Alfassi b a b
Nuclear Research Centre Negev, P.O.B 9001, Beer Sheva 84190, Israel Ben Gurion University of the Negev, Beer Sheva 84105, Israel
a r t i c l e i n f o
a b s t r a c t
Article history: Received 15 November 2009 Received in revised form 8 May 2010 Accepted 17 May 2010
The discrimination between the high temperature thermoluminescent peaks (HTTL) and the dosimetry peaks is not a simple process due to their overlapping. The application of the two steps heating method for this purpose was studied. If the heating is performed in the first step only to about 220e250 C, the dosimetry peaks are emptied, but the HTTL peaks are only partially affected. Performing a second reading to 300 C provides information attributed solely to HTTL peaks. The results of optimization of the two steps readout process for routine (high rate heating) readout are presented. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: TLD100 HTTL Neutron Gamma Readout
1. Introduction LiF:Mg,Ti is the most widespread material used for thermoluminescence dosimetry (TLD). In order to increase the throughput in routine dosimetry, fast heating rates of about 25 C s1 are applied. Mostly, in routine dosimetry TLD cards are used, which contain 3 or 4 chips of TLD100 held between Teflon foils. The use of Teflon limits the maximum temperature to 300 C, in order to prevent damage to the Teflon. The present work was performed within those limitations, as the purpose was to check the application of the two readout steps to routine dosimetry. The main peaks used for dosimetry are peaks 4 and 5 (the dosimetry peaks). Peak 5 appears at w205 C at heating rates of w1 C s1, but it shifts to about 230e250 C if a fast heating rate of about 25 C s1 is applied. At higher temperatures other peaks appear, which are usually referred to as the high temperature peaks (HTTL). The most important are the first peaks (6 and 7). At heating rates of w1 C s1, the maximum intensity of the HTTL is at about 270 C. When applying the heating rate of 25 C s1, they appear at about 300 C, which is the temperature limit for the cards readout. The intensity of the HTTL peaks is negligible for low gamma doses which are encountered in personal or environmental dosimetry, due to their low LET. However, for higher LET particles
* Corresponding author. Tel.: þ972 507678295; fax: þ972 86568877. E-mail address: [email protected] (A. Abraham). 1350-4487/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2010.05.030
(heavy charged particles or neutrons which produce alpha particles) the intensity of the HTTL becomes significant. For thermal neutrons the relative intensity of the HTTL peaks in TLD100 is higher by about one order of magnitude relative to gamma irradiation (Weinstein, 2005, 2006). This is the basis for possible evaluation of gamma and neutron doses in a mixed field by using one TLD100 chip. In order to use the sensitivity difference of the HTTL peaks to high and low LET radiations, their discrimination from the dosimetry peaks must be performed. In most cases, it was done by mathematical analysis of the glow curve, either by peaks deconvolution (as by Horiuchi et al., 1992 and Gambarini and Roy, 1997) or by applying the regions of interest (ROI) method (as by Liu and Sims, 1991 and Weinstein et al., 2005). However, mathematical separation of HTTL peaks from the dosimetric peaks may be problematic, even for slow heating rates, due to the overlapping of the peaks. The Region of Interest method may be dependent on the mathematical procedure applied, therefore, the method of heating in two steps which was mentioned also in the past (Busuoli et al., 1970; Chernov et al., 1999) was investigated. This method is attractive, and was applied also recently (Pradhan et al., 2009). Its main advantage is that a physical separation of the HTTL peak from the dosimetric peaks can be achieved, without the need of mathematical analysis. The maximal temperature of the first step must be considerably lower than the HTTL temperature in order to assure that a minimal portion of the HTTL peak is readout, but it must be enough to ensure full readout of the dosimetry
1492
A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
Fig. 1. The ratio of the second to the first readout as a function of the first readout maximum temperature and the corresponding dosimetry peaks residuals.
peaks. The second readout is a normal routine readout to 300 C. As in the first readout the traps of the dosimetry peaks were emptied, the second readout will contain only information from the HTTL peaks. The purpose of the present work was to optimize the readout temperature of the first stage to obtain full readout of the dosimetry peaks with minimum loss of information from the HTTL peaks.
2. Materials and methods The experiments were performed with LiF: Mg,Ti Harshaw/ Thermo 1110 cards containing three 3 3 0.38 mm TLD100 chips. The readout of the irradiated cards was performed by a 6600 TLD reader (Harshaw/Thermo). Each chip was calibrated individually by a 90Sre90Y source, built in the reader. The heating of the TLD chips is
Fig. 2. The glow curve of the first readout at 220 C (upper curve) and the second readout at 300 C (lower curve) of a TLD100 chip irradiated by gamma rays.
A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
by a hot nitrogen gas jet, delivering pre-defined heating profiles. The glow curve of each chip is digitized to a 200-channel spectrum and stored on a PC computer. Due to the temperature lag when applying a high heating rate, in order to make sure that the chip temperature will reach the intended temperature, the heating must be continued for several seconds at this temperature. The readout process was split into two phases. In the first step, a preheat to 50 C (less than 0.5 s) and a linear heating at a rate of 25 C s1 was applied up to a predetermined temperature in the range from 220 C to 250 C and then kept at this temperature, for a total time of 20 s. The second readout consisted of a preheat to 50 C (less than 0.5 s) and a linear heating at a rate of 25 C s1 up to the temperature of 300 C and the kept at this temperature, for a total time of 30 s. No annealing was performed, except for the usual reader annealing. Gamma irradiations to a dose of 5 mSv were carried out using a 137Cs source. The neutron irradiations were performed using thermalized neutrons from a 81 MBq (at 1.1.2008) shielded 252Cf source. The source was placed in a graphite block equipped with a polypropylene coated irradiation hole. The neutrons were thermalized by layers of polypropylene. The thermal neutron dose was calibrated by gold foils and its rate at the irradiation location was 0.30 mSv/h (at 1.1.2008). The TLD chips were irradiated to a neutron dose of about 3.5 mSv. The contribution not originated by thermal neutrons, as measured by the light output from 7LiF chips relative to the light output from 6LiF chips, was negligible (up to about 2%). No glow curve spectra analysis was performed. The full glow curve
1493
integrals were calculated and assumed to represent the dosimetry peaks area (first readout) and HTTL area (second readout). 3. Results and discussion The readout temperature at the first stage is the main parameter which determines the separation quality between the dosimetry peaks and the HTTL peaks. If a temperature higher than the dosimetry peaks temperature would be applied (e250 C for a 25 C/s heating rate) the dosimetry peaks traps would be totally emptied, but a significant portion from the HTTL peaks would be also emitted. German et al. (2009) found that after a first readout at 250 C about 20% from the HTTL peaks were lost. Therefore, lower temperatures were applied and the dosimetry peaks were emptied by isothermal decay. It was shown (German et al., 2009) that the dosimetry peaks can be readout almost completely when applying temperatures down to 220 C (for a heating rate of 25 C/s and a total readout time of 20 s). Lower readout temperatures leave a residual dose in the dosimetry peaks, which may be significant. The ratio between the HTTL readout (second stage readout) and the first stage readout as a function of the first step maximal temperature after thermal neutrons irradiation is presented in Fig. 1. It can be seen that there is a constant improvement in the readout efficiency of the HTTL peaks when lowering the readout temperature. Also shown in Fig. 1 is the residual of the dosimetry peaks after gamma irradiation as a function of the first step maximal temperature in percents from the complete readout (at 300 C). At 230 C a very small residual of
Fig. 3. The glow curve of the first readout at 220 C (upper curve) and the second readout at 300 C (lower curve) of a TLD100 chip irradiated by thermal neutrons.
1494
A. Abraham et al. / Radiation Measurements 45 (2010) 1491e1494
about 1.7% was obtained, but the HTTL to dosimetry peaks ratio is significantly lower relative to the 220 C value (12.4% compared to 18.6%), indicating a high loss of HTTL information. At 220 C the ratio is acceptable (close to about 20% obtained by the Region of Interest method e See Weinstein et al., 2005, 2006) and the residual percent is higher by only about 3%, therefore the readout temperature at the first stage was chosen 220 C. The first readout glow curves (for a maximum heating temperature of 220 C) and the second readout glow curves (for a maximum heating temperature of 300 C) obtained after gamma and thermal neutron irradiations are presented in Figs. 2 and 3. As can be seen from the second readout curves, their shape is similar after gamma and neutron irradiations, and there is no contribution from the dosimetric peaks. The shapes of the first readouts are different to some extent. Most of peak 5 seems to be read in the time interval between about 10 s and 15 s. The contribution of peak 5 is smeared, as it is obtained by isothermal decay. The lower part of the glow curve contains mainly the contribution of peaks 3 and 4. It has been already mentioned in the past by Horowitz and Yossian (1995) that the glow curve below peak 5 is significantly altered following alpha particle irradiation compared to gamma irradiation. It was observed that after alpha irradiation peak 4 appears at a lower temperature than after gamma irradiation, almost coinciding with peak 3, which seems to be the cause for the difference in the shape of the glow curves presented in Figs. 2 and 3. The neutron-gamma discrimination in a mixed field when employing the two peaks method is based on the different ratios of the HTTL peaks area to the dosimetry peaks area for the two radiations. This value must be stable and redundant to obtain an acceptable accuracy. The ratio of the HTTL peaks area to the dosimetry peaks area (the ratio of the glow curve areas from the second and first readout) obtained in the present work by the two steps method was 0.0164 0.0001 for gamma rays and 0.186 0.004 for thermal neutrons. Several cycles of repeated experiments gave results within the uncertainty range. The ratios between the HTTL peak area and the dosimetry peak area obtained by the two steps readout are not much different from previous results obtained by using the ROI analysis method (Weinstein, 2005, 2006). The HTTL to dosimetry peaks ratios are almost identical: 11.34 in the present work compared to 11 and 11.94 in the previous works using the ROI method.
4. Conclusions The results obtained in the present work indicate that it is possible to separate the dosimetric peaks from the HTTL peaks applying a two steps heating profile with a similar efficiency as by the regions of interest method. The main advantage of the two steps procedure is that it discriminates physically, in two separate measurements, the information related to the dosimetry and the HTTL peaks, without inducing mathematic errors which may be dependent on the neutron to gamma rays ratio and the analysis method. However, the two steps heating method has also some shortcomings. The readout time is doubled as two readings are needed, and there is some loss of efficiency for the readout of the HTTL peaks, as some of its information is lost in the first step readout. Further work is needed to characterize the limitations of the two steps heating method in a mixed gammaneutron field. Its practical advantage relative to the Region of Interest method will be checked by field experiments with mixed gamma-neutron doses. References Busuoli, G., Cavallini, A., Fasso, A., Rimondi, O., 1970. Mixed radiation dosimetry with LiF (TLD-100). Phys. Med. Biol. 15, 673e681. Chernov, V., Mironenko, S., Minaev, E., Alekseev, I., 1999. TL dosimetry of radon by the two peaks method. Rad. Prot. Dosim 85, 329e332. Gambarini, G., Roy, M.S., 1997. Dependence of TLD thermoluminescence yield on absorbed dose in a thermal neutron field. Appl. Radiat. Isot. 48, 1467e1475. German, U., Weinstein, M., Abraham, A., Alfassi, Z.B., 2009. On the readout of HT peaks in LiF: Mg, Ti by applying high rate gas heating. Nucl. Instr. Meth. A 600, 683e688. Horiuchi, N., Sato, T., Morimoto, H., 1992. Simultaneous evaluation of the neutron and gamma dose with a single TLD. Nucl. Instr. Meth. A 317, 542e552. Horowitz, Y.S., Yossian, D., 1995. Computerized glow curve deconvolution: application to thermoluminescence dosimetry. Rad. Prot. Dosim. 60, 1e114. Liu, J.C., Sims, C.S., 1991. Mixed field personnel dosimetry, Part I: high temperature peak characteristics of the reader-annealed TLD-600 SLAC-PUB-5340. Pradhan, A.S., Lee, J.I., Kim, J.L., 2009. Further studies on higher temperature TL glow peaks of 7LiF: Mg, Ti. Appl. Rad. Isotop. 67, 1078e1083. Weinstein, M., German, U., Abraham, A., Dubinsky, S., Alfassi, Z.B., 2005. On the linearity of the high temperature peaks of LiF: Mg, Ti. Radiat. Meas. 39, 489e494. Weinstein, M., German, U., Alfassi, Z.B., 2006. On neutronegamma mixed field dosimetry with LiF: Mg, Ti at radiation protection dose levels. Rad. Prot. Dosim. 119 (1e4), 314e318.