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Thermoluminescence characteristics of BaSO4:Eu
Appl. Radial. Isot. Vol. 42, No. 9, pp. 861-863, ht. J. Radial. Appt. Insfrm. Part A
1991
0883-2889191
S3.00 + 0.00
Copyright 0 1991 Pergamon Press plc
Printed in Great Britain. All rights reserved
Thermoluminescence Characteristics of BaSO, : Eu JUAN AZORiN’,
CLAUDIO FURETTA’, ALICIA GUTIkRREZ** and PEDRO GONZALEZ’
degli Studi di Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italia and *Institute National de Investigaciones Nucleares, Carretera Mtxico, Toluca Km. 36.5 Salazar, 52045 Mexico, MCxico
‘UniversitL
(Received
I1 June 1990; in revised form 30 November 1990)
A new detector based on a thermoluminescence (TL) sheet of barium sulphate doped with europium embedded in polytetrafluoroethylene (BaSO,: Eu + PTFE) has been developed to study hadronic and electromagnetic cascade showers. TL characteristics of BaSO,: Eu + PTFE discs cut from a TL sheet were determined. This material has a TL glow curve with one peak at 540 K-which follows approximately first order kinetics; its TL response is linear from 4 mGy to 50 Gy and is 34 times more sensitive than CaSO,:Dy to @Co gamma radiation. Results suggest that BaSO,:Eu + PTFE discs can be used successfully as TL dosemeters.
gamma radiation using a Victoreen 64-764 irradiator of 2.79 GBq and with beta particles from “Sr/90Y In the last several years the number of different phos-k using a PTB beta secondary standard. TL readings phors suitable for radiation dosimetry has increased were made in a Harshaw 2000A TL analyser congreatly, especially CaSO, doped with rare earths nected to a Harshaw 2080 picoprocessor to analyse because of its very high thermoluminescence (TL) the glow curves. TL response was determined by intesensitivity and negligible fading (Azorin et al., 1984; gration of the glow curve between room temperature Azorin and Gutierrez, 1989). (-293 K) and 573 K at a heating rate of 7.1 K.s-‘. A new detector, a TL sheet of BaSO,: Eu has been The TL was read immediately after irradiation in each developed to study hadronic and electromagnetic case except in those instances where fading was being cascade showers (Okamoto et al., 1986; Yamamoto et determined. Each experimental data point represents al., 1984). the mean of at least five dosemeters. With the aim of using BaSO,: Eu as a TL dosemeter For this study, 500 discs were cut and irradiated at we studied the TL characteristics of BaSO, : Eu discs the same specified dose of 10 mGy with @‘Cogamma cut from a TL sheet. Results suggest that BaSO,:Eu radiation. The evaluated dose was determined for each + PTFE (polytetrafluoroethylene) discs can be used dosemeter and the dosemeters which deviated more to measure absorbed doses in cases in which lack than 55% from the average were rejected. of quantum equivalence of the detector material is Glow curves were recorded at a heating rate of without importance. 7.1 K’s_’ using an x-y recorder connected to the picoprocessor. Effect of pre-irradiation thermal treatment on TL Experimental sensitivity and fading was studied for temperature up Discs of 4.6 mm dia were cut from a 400km to 763 K because of the melting point of PTFE is thickness BaSO,:Eu mixed with PTFE sheet, proabout 700 K. Samples contained in Pt crucibles were vided to us by the Department of Physics, Okayama maintained at various temperatures for 1 h each and University, to be used as TL dosemeters. then cooled suddenly to room temperature in air. A Irradiations were made with @‘Cogamma radiation test dose of 100 mGy of @‘Cogamma radiation was using a Vickard 200 unit of 6.16TBq, with 13’Cs given at room temperature for determining the TL sensitivity and fading. *Author for correspondence at: Instituto National de InvesTL response as a function of dose and the detection tigaciones Nucleares, Apartado Postal 18- 1027, 11801 threshold were determined by irradiating samples of Mtxico, D.F., MCxico.
Introduction
861
JUAN AZOR~Net al.
862
BaSO,: Eu + PTFE disc with different doses of 6oCo and Ws gamma radiation and with beta particles of WSr/90Y. Fading was determined by storing the irradiated samples protected from the light at room temperature and reading them at different time intervals up to 150 days. The TL parameters: order of kinetics (1), activation energy (E) and frequency factor (s) were determined by means of isothermal decay and by glow curve shape methods (Azorin, 1986). To determine the order of the kinetics by isothermal decay, samples were irradiated at a dose of 100 mGy and placed in an oven at controlled temperatures T, = 473 + 1 K and T, = 483 k 1 K for times from 1 to 10 min. By measuring the TL intensity and plotting (Z, /Z)” “‘1 as a function of t, various values of I were tried, choosing as the correct value the one giving a straight line plot (May and Partridge, 1964; Partridge and May, 1965). The symmetry factor (pg) the glow peak was obtained from the glow curves and the corresponding 1 value determined according to the method proposed by Chen (1969). Once the order of the kinetics was determined, the Halperin-Braner and Luschik methods, both modified by Chen (1984), and the Chen (1984) method were applied to obtain the activation energy (E) and frequency factor (s) values. The three methods are summed up as: E, = c,(kT’m/c()
400
300
Fig.
Halperin-Braner c,= 1.51 +3.O(pg-0.42); b, = 1.58 + 4.2 (pg - 0.42) Luschik cg = 0.976 + 7.3 (pg - 0.42); b, = 0 Chen c,,, = 2.52 + 10.2 (pg - 0.42); b,,, = 1 Chen where pg = b/w is the symmetry factor and k is the Boltzmann’s constant. Fittings were made using the least squares method considering an uncertainty of +e for E values.
Results TL glow curve obtained discs irradiated with @Co in Fig. 1. This glow curve glow peak at around 540
for the BaSO, : Eu + PTFE gamma radiation is shown exhibits essentially a single K.
700
600 (K)
I. TL glow curve of BaSO,: Eu irradiated gamma 10'
with “Co
radiation.
r
104
=
10
L_ 10-3
I
1
1o-2 Id’ Dose
Fig. 2. TL response
I
IO0
10’
/
I
IO2
IO3
(Gy)
of BaSO,: Eu + PTFE dose.
- b,(2kTm)
were u stands for 6, r or u. The values of c, and b, for the three methods are given by:
500 Temperature
as a function
of
Figure 2 shows the TL response of BaSO,: Eu discs as a function of dose which is linear from 4 mGy to 50 Gy beyond which it is sublinear and the response saturates around 1 kGy. The response of the BaSO,: Eu + PTFE discs to “Co gamma radiation, on the integration of light basis, is around 3-4 times that of CaSO,: Dy f PTFE discs and around 10 times when irradiated with 30 keV photons. However, the detection threshold remains as high as 100 pGy for “Co gamma radiation. Fading at room temperature is about 20% when stored for 30 days but hardly changes thereafter during 150 days reaching the drop 30%. The integrated TL output per unit irradiation dose increases two-fold when thermal treatment of 673 K during 1 h is applied; no effect of thermal treatment on the fading was observed. The order of the kinetics determined by Chen’s method was 1.08 f 0.01 and the best value of 1 to Table
I. TL
parameters of &SO,: Eu + PTFE determined by means of isothermal decay and glow curve shape methods Kinetics order
Method Isothermal
decay
Glow curw shape Halperin-Braner Luschik (8) Chen (to)
(I
Activation energy E(eV)
Frequency factor s(s-‘)
1.09 + 0.03
1.15 k 0.04
(2.7 + 0.2) x IO9
1.08 kO.01
1.17 co.05 I.13 kO.02 l.l6+0.02
(2.6&0.01)x
)
IO9
TL characteristics of BaSO, :Eu yield a straight line of the plot (1,/I)” - ‘I’)vs t was 1.09 f 0.03. Hence, it can be considered that BaSO,:Eu follows first order kinetics. Table 1 shows the TL parameters obtained by means of the methods applied.
Conclusions It follows from the above results that BaSO.,:Eu exhibits the greatest sensitivity among the known TL phosphors. The main shortcoming of this phosphor is its high Z,, value which inevitably implies a high energy dependence of the sensitivity. This shortcoming will not always be an obstacle for its application because when long-wave radiation is measured in a narrow interval of radiation energies the strong energy dependence of BaSO,: Eu may have the advantage of additionally increasing the sensitivity over other TL phosphors. Hence, BaSO.,: Eu + PTFE TL discs can be used to measure absorbed doses in cases in which lack of quantum equivalence of the detector material is without importance. The TL parameters of BaS04: Eu, determined by different methods, are in good agreement among the different methods. Acknowledgement-The
authors wish to express their thanks to Dr Tomonori Wada, Department of Physics,
863
Okayama University, Japan, for providing the BaSO,:Eu TL sheets.
References Azorin J. (1986) Determination of thermoluminescence parameters from glow curves--I. A review. Nucl. Trucks 11, 159. Azorin J. and Gutierrez A. (1989) Preparation and performance of a CaSO,: Dy, Tm TL phosphor for long-term gamma measurements. Health Phys. 56, 551. Azorin J., Gonzalez G., Gutierrez A. and Salvi R. (1984) Preparation and dosimetric properties of a highly sensitive CaSO,:Dy TL dosimeter. Health Phys. 46, 269. Chen R. (1969) Glow curves with general order kinetics. J. Electrochem. Sot. 116, 1047.
Chen R. (1984) Kinetics of thermoluminescence glow peaks. In Thermoluminescence and Thermoluminescent Dosimetry (Ed. Horowitz Y. S.), Chap. 3, pp. 49-88. CRC Press, Boca Raton. May C. E. and Partridge J. A. (1964) Thermoluminescent kinetics of alpha irradiated alkali halides. J. Chem. Phys. 42, 797.
Okamoto Y., Kawaguchi S., Kino S., Miono S., Kitajima T., Misaki A. and Saito T. (1986) Thermoluminescent sheets for the detection of high energy hadronic and electromagnetic showers. Nucl. Instrum. Methocis Phys. Res. A243, 219. Partridge J. A. and May C. E. (1965) Anomalous thermoluminescent kinetics of irradiated alkali halides. J. Chem. Phys. 42, 797.
Yamamoto I., Tomiyama T., Miyai H., Wada T., Yamashita Y. (1984) Screening out obstructive radiation from thermoluminescence sheets (BaSO,: Eu) exposed to cosmic rays. Nucl. Instrum. Methodr Phys. Res. 224, 573.
1991
0883-2889191
S3.00 + 0.00
Copyright 0 1991 Pergamon Press plc
Printed in Great Britain. All rights reserved
Thermoluminescence Characteristics of BaSO, : Eu JUAN AZORiN’,
CLAUDIO FURETTA’, ALICIA GUTIkRREZ** and PEDRO GONZALEZ’
degli Studi di Roma “La Sapienza”, Piazzale Aldo Moro 2, 00185 Roma, Italia and *Institute National de Investigaciones Nucleares, Carretera Mtxico, Toluca Km. 36.5 Salazar, 52045 Mexico, MCxico
‘UniversitL
(Received
I1 June 1990; in revised form 30 November 1990)
A new detector based on a thermoluminescence (TL) sheet of barium sulphate doped with europium embedded in polytetrafluoroethylene (BaSO,: Eu + PTFE) has been developed to study hadronic and electromagnetic cascade showers. TL characteristics of BaSO,: Eu + PTFE discs cut from a TL sheet were determined. This material has a TL glow curve with one peak at 540 K-which follows approximately first order kinetics; its TL response is linear from 4 mGy to 50 Gy and is 34 times more sensitive than CaSO,:Dy to @Co gamma radiation. Results suggest that BaSO,:Eu + PTFE discs can be used successfully as TL dosemeters.
gamma radiation using a Victoreen 64-764 irradiator of 2.79 GBq and with beta particles from “Sr/90Y In the last several years the number of different phos-k using a PTB beta secondary standard. TL readings phors suitable for radiation dosimetry has increased were made in a Harshaw 2000A TL analyser congreatly, especially CaSO, doped with rare earths nected to a Harshaw 2080 picoprocessor to analyse because of its very high thermoluminescence (TL) the glow curves. TL response was determined by intesensitivity and negligible fading (Azorin et al., 1984; gration of the glow curve between room temperature Azorin and Gutierrez, 1989). (-293 K) and 573 K at a heating rate of 7.1 K.s-‘. A new detector, a TL sheet of BaSO,: Eu has been The TL was read immediately after irradiation in each developed to study hadronic and electromagnetic case except in those instances where fading was being cascade showers (Okamoto et al., 1986; Yamamoto et determined. Each experimental data point represents al., 1984). the mean of at least five dosemeters. With the aim of using BaSO,: Eu as a TL dosemeter For this study, 500 discs were cut and irradiated at we studied the TL characteristics of BaSO, : Eu discs the same specified dose of 10 mGy with @‘Cogamma cut from a TL sheet. Results suggest that BaSO,:Eu radiation. The evaluated dose was determined for each + PTFE (polytetrafluoroethylene) discs can be used dosemeter and the dosemeters which deviated more to measure absorbed doses in cases in which lack than 55% from the average were rejected. of quantum equivalence of the detector material is Glow curves were recorded at a heating rate of without importance. 7.1 K’s_’ using an x-y recorder connected to the picoprocessor. Effect of pre-irradiation thermal treatment on TL Experimental sensitivity and fading was studied for temperature up Discs of 4.6 mm dia were cut from a 400km to 763 K because of the melting point of PTFE is thickness BaSO,:Eu mixed with PTFE sheet, proabout 700 K. Samples contained in Pt crucibles were vided to us by the Department of Physics, Okayama maintained at various temperatures for 1 h each and University, to be used as TL dosemeters. then cooled suddenly to room temperature in air. A Irradiations were made with @‘Cogamma radiation test dose of 100 mGy of @‘Cogamma radiation was using a Vickard 200 unit of 6.16TBq, with 13’Cs given at room temperature for determining the TL sensitivity and fading. *Author for correspondence at: Instituto National de InvesTL response as a function of dose and the detection tigaciones Nucleares, Apartado Postal 18- 1027, 11801 threshold were determined by irradiating samples of Mtxico, D.F., MCxico.
Introduction
861
JUAN AZOR~Net al.
862
BaSO,: Eu + PTFE disc with different doses of 6oCo and Ws gamma radiation and with beta particles of WSr/90Y. Fading was determined by storing the irradiated samples protected from the light at room temperature and reading them at different time intervals up to 150 days. The TL parameters: order of kinetics (1), activation energy (E) and frequency factor (s) were determined by means of isothermal decay and by glow curve shape methods (Azorin, 1986). To determine the order of the kinetics by isothermal decay, samples were irradiated at a dose of 100 mGy and placed in an oven at controlled temperatures T, = 473 + 1 K and T, = 483 k 1 K for times from 1 to 10 min. By measuring the TL intensity and plotting (Z, /Z)” “‘1 as a function of t, various values of I were tried, choosing as the correct value the one giving a straight line plot (May and Partridge, 1964; Partridge and May, 1965). The symmetry factor (pg) the glow peak was obtained from the glow curves and the corresponding 1 value determined according to the method proposed by Chen (1969). Once the order of the kinetics was determined, the Halperin-Braner and Luschik methods, both modified by Chen (1984), and the Chen (1984) method were applied to obtain the activation energy (E) and frequency factor (s) values. The three methods are summed up as: E, = c,(kT’m/c()
400
300
Fig.
Halperin-Braner c,= 1.51 +3.O(pg-0.42); b, = 1.58 + 4.2 (pg - 0.42) Luschik cg = 0.976 + 7.3 (pg - 0.42); b, = 0 Chen c,,, = 2.52 + 10.2 (pg - 0.42); b,,, = 1 Chen where pg = b/w is the symmetry factor and k is the Boltzmann’s constant. Fittings were made using the least squares method considering an uncertainty of +e for E values.
Results TL glow curve obtained discs irradiated with @Co in Fig. 1. This glow curve glow peak at around 540
for the BaSO, : Eu + PTFE gamma radiation is shown exhibits essentially a single K.
700
600 (K)
I. TL glow curve of BaSO,: Eu irradiated gamma 10'
with “Co
radiation.
r
104
=
10
L_ 10-3
I
1
1o-2 Id’ Dose
Fig. 2. TL response
I
IO0
10’
/
I
IO2
IO3
(Gy)
of BaSO,: Eu + PTFE dose.
- b,(2kTm)
were u stands for 6, r or u. The values of c, and b, for the three methods are given by:
500 Temperature
as a function
of
Figure 2 shows the TL response of BaSO,: Eu discs as a function of dose which is linear from 4 mGy to 50 Gy beyond which it is sublinear and the response saturates around 1 kGy. The response of the BaSO,: Eu + PTFE discs to “Co gamma radiation, on the integration of light basis, is around 3-4 times that of CaSO,: Dy f PTFE discs and around 10 times when irradiated with 30 keV photons. However, the detection threshold remains as high as 100 pGy for “Co gamma radiation. Fading at room temperature is about 20% when stored for 30 days but hardly changes thereafter during 150 days reaching the drop 30%. The integrated TL output per unit irradiation dose increases two-fold when thermal treatment of 673 K during 1 h is applied; no effect of thermal treatment on the fading was observed. The order of the kinetics determined by Chen’s method was 1.08 f 0.01 and the best value of 1 to Table
I. TL
parameters of &SO,: Eu + PTFE determined by means of isothermal decay and glow curve shape methods Kinetics order
Method Isothermal
decay
Glow curw shape Halperin-Braner Luschik (8) Chen (to)
(I
Activation energy E(eV)
Frequency factor s(s-‘)
1.09 + 0.03
1.15 k 0.04
(2.7 + 0.2) x IO9
1.08 kO.01
1.17 co.05 I.13 kO.02 l.l6+0.02
(2.6&0.01)x
)
IO9
TL characteristics of BaSO, :Eu yield a straight line of the plot (1,/I)” - ‘I’)vs t was 1.09 f 0.03. Hence, it can be considered that BaSO,:Eu follows first order kinetics. Table 1 shows the TL parameters obtained by means of the methods applied.
Conclusions It follows from the above results that BaSO.,:Eu exhibits the greatest sensitivity among the known TL phosphors. The main shortcoming of this phosphor is its high Z,, value which inevitably implies a high energy dependence of the sensitivity. This shortcoming will not always be an obstacle for its application because when long-wave radiation is measured in a narrow interval of radiation energies the strong energy dependence of BaSO,: Eu may have the advantage of additionally increasing the sensitivity over other TL phosphors. Hence, BaSO.,: Eu + PTFE TL discs can be used to measure absorbed doses in cases in which lack of quantum equivalence of the detector material is without importance. The TL parameters of BaS04: Eu, determined by different methods, are in good agreement among the different methods. Acknowledgement-The
authors wish to express their thanks to Dr Tomonori Wada, Department of Physics,
863
Okayama University, Japan, for providing the BaSO,:Eu TL sheets.
References Azorin J. (1986) Determination of thermoluminescence parameters from glow curves--I. A review. Nucl. Trucks 11, 159. Azorin J. and Gutierrez A. (1989) Preparation and performance of a CaSO,: Dy, Tm TL phosphor for long-term gamma measurements. Health Phys. 56, 551. Azorin J., Gonzalez G., Gutierrez A. and Salvi R. (1984) Preparation and dosimetric properties of a highly sensitive CaSO,:Dy TL dosimeter. Health Phys. 46, 269. Chen R. (1969) Glow curves with general order kinetics. J. Electrochem. Sot. 116, 1047.
Chen R. (1984) Kinetics of thermoluminescence glow peaks. In Thermoluminescence and Thermoluminescent Dosimetry (Ed. Horowitz Y. S.), Chap. 3, pp. 49-88. CRC Press, Boca Raton. May C. E. and Partridge J. A. (1964) Thermoluminescent kinetics of alpha irradiated alkali halides. J. Chem. Phys. 42, 797.
Okamoto Y., Kawaguchi S., Kino S., Miono S., Kitajima T., Misaki A. and Saito T. (1986) Thermoluminescent sheets for the detection of high energy hadronic and electromagnetic showers. Nucl. Instrum. Methocis Phys. Res. A243, 219. Partridge J. A. and May C. E. (1965) Anomalous thermoluminescent kinetics of irradiated alkali halides. J. Chem. Phys. 42, 797.
Yamamoto I., Tomiyama T., Miyai H., Wada T., Yamashita Y. (1984) Screening out obstructive radiation from thermoluminescence sheets (BaSO,: Eu) exposed to cosmic rays. Nucl. Instrum. Methodr Phys. Res. 224, 573.