ARTICLE IN PRESS
Radiation Physics and Chemistry 76 (2007) 1523–1526
www.elsevier.com/locate/radphyschem
Effect of post-irradiation thermal treatments on the
stability of gamma-irradiated glass dosimeter
K. Faraha,, A. Kovácsb, A. Mejria, H. Ben Ouadac
a
Laboratoire de Radiotraitement, Centre National des Sciences et Technologie Nucléaires, 2020 Sidi-Thabet, Tunisia
Departement of Radiation Safety, Institute of Isotopes, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, 1121 Budapest, Hungary
c
Département de Physique, Laboratoire de Physique et Chimie des Interfaces, Faculté des Sciences de Monastir, 5000 Monastir, Tunisia
b
Abstract
A commercial window glass has been investigated as a routine high dose dosimeter for gamma irradiation. The irradiated samples
showed rapid fading at room temperature immediately after irradiation. This short-term rapid fading was followed by a slow fading at
long-term. This strong initial fading is a problem for dosimetry purposes. However, when the dosimeter is measured at the same time
interval after irradiation, it maintains proportionality to dose. Calibration curves have to be used for different time intervals after
irradiation. In order to improve post-irradiation stability dosimeters were submitted to different post-irradiation thermal treatments
from (20) up to 150 1C. After that, optical absorbance measurements were carried out up to 2 months at room temperature. The
heating at 150 1C for 20 min was found to be the most suitable procedure for the removal of unstable entities responsible for the initial
rapid fading. Due to these heat treatments, variation of response was found almost negligible 24 h after irradiation for several months.
Calibration curves demonstrated the applicability of this glass as routine dosimeter in the dose range of 0.5–90 kGy.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: Window glass dosimeter; Post-irradiation thermal treatments; Fading behaviour
1. Introduction
The ionizing radiation produces electron–hole pairs
which individually become trapped at various defect sites
in the glass structure. Consequently, new optical absorption bands may appear. The ionizing radiation-induced
colour centres in some commercial glasses have been found
suitable for certain applications in radiation processing
dosimetry (Zheng et al., 1988; Engin et al., 2006). Their use
does not require special preparation. These dosimeters are
recyclable, rigid, chemically inert, cheap and independent
of humidity and dose rate (Zheng et al., 1988; Engin et al.,
2006). The main difficulty presented by glass dosimeters is
the undesirable strong initial fading. Many authors overcame this problem by taking measurements for the most
adequate time intervals after irradiation (Rodrigues Jr. et
al., 2002; Engin et al., 2006). In order to solve this problem
in our work, the glass dosimeters were submitted to
Corresponding author. Tel.: +216 22 25 70 98; fax: +216 71 53 74 10.
E-mail address: k.farah@cnstn.rnrt.tn (K. Farah).
0969-806X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.radphyschem.2007.02.065
different post-irradiation thermal treatments from 20
up to 150 1C and the effect of this treatments on the fading
behaviour of the dosimeters was studied up to 2 months
after irradiation at room temperature.
2. Materials and methods
The glass samples were obtained from the same glass
sheets purchased from the local market and were cut into
pieces of 11 30 3 mm dimensions for optical measurements. The chemical composition of the glass samples was
determined by using the Prompt Gamma Activation
Analysis technique (Anderson et al., 2004) at the Budapest
Neutron Centre resulting in wt%: 68.52 SiO2, 13.77 Na2O,
8.19 CaO, 4.34 MgO, 1.003 Al2O3, 0.588 K2O, 0.105 Fe2O3
and about 3.5% of other components.
The irradiations were made at the Tunisian semiindustrial 60Co gamma irradiation facility at a dose rate:
2 kGy/h. Calibration was carried out at the 60Co
calibration facility of the Egyptian Reference High Dose
Laboratory at the dose rate of 4.78 kGy/h at controlled
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temperature of 34 1C. The traceability was established with
alanine/EPR dosimetry system in terms of absorbed dose
to water traceable to the National Physical Laboratory,
UK.
Optical absorption spectra were taken with a Perkin
Elmer spectrophotometer (Lambda 20) in the range of
350–800 nm. Genesis 5 spectrophotometer and Käfer MFT
30 thickness gauge were used to measure the specific
absorbance (i.e. absorbance of the dosimeter divided by the
thickness of the dosimeter) changes produced in glass.
An electrical furnace and a freezer were used to reach the
desired post-irradiation storage temperatures.
45 kGy
31 kGy
15 kGy
13 kGy
10 kGy
7 kGy
3 kGy
0.8 kGy
0.133 kGy
Absorbance (a.u.)
0.6
0.4
0.0
400
450
500
550
600
3.1. Optical absorption spectra of gamma-irradiated window
glass
Optical absorption spectra of the irradiated glass
samples were measured against nonirradiated sample in
order to obtain the net-induced changes of absorption.
Fig. 1 shows the effect of increasing doses between 0.13 and
45 kGy on the absorption spectra of glass dosimeter in the
region from 350 to 800 nm. The radiation-induced colour
was brown and two optical absorption bands were found at
410 and 600 nm. The intensities of the overall absorption
spectra increased progressively with increasing doses.
3.2. Thermal stability
0.2
350
3. Results and discussion
650
700
750
800
Wavelength (nm)
Fig. 1. Optical absorption spectra for the gamma-irradiated glass samples
in the dose range 0.13–45 kGy.
3.2.1. Fading characteristics at room temperature
Five replicate glass dosimeters were irradiated with 60Co
gamma rays to 30 kGy. The absorbance changes were
followed up to 535 days. After each measurement glass
samples were stored in the dark at room temperature.
Fig. 2 presents the fading behaviour of the 410 nm
absorption band at room temperature for the long-term
and the short-term period. A strong fading can be observed
in the first 9 days followed by a slow fading up to 535 days.
The 600 nm absorption band showed similar behaviour.
The data in Fig. 2. were fitted using first-order kinetics
based on the data measured after the first 10 days storage.
The coefficient of correlation (R2) was 0.99. The stability of
radiation-induced colour centres at room temperature
was mainly controlled by the initial strong fading process.
This initial fading process seems to follow neither a simple
8
Experimental data
First order decay kinetic fit on data after 9 days
Specificabsorbance at 410 nm(cm-1)
Specific absorbance at 410 nm (cm-1)
7
6
5
4
3
2
8
Experimental data for the first 9 days
Combination of second and first order decay kinetic fit
Second order decay kinetic fit
First order decay kinetic fit
7
6
5
4
3
2
0
1
2
4
6
8
10
12
Post-irradiation time(days)
0
200
400
600
800
1000
Post-irradiation time (days)
Fig. 2. Post-irradiation fading and kinetics of room temperature response of glass samples irradiated at 30 kGy. Inset: kinetics of the fading behaviour at
room temperature for the short-term period. (Specific absorbance: absorbance of the dosimeter divided by the thickness of the dosimeter).
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first-order nor second-order kinetics, but it can be well
described by the sum of second- and first-order decay
kinetics fit (y ¼ aebx+c/(1+cdx), where b is the firstorder and c is the second-order decay rate constant. Sheng
et al. (2002) gave evidence that the long-term fading
process of colour centres induced by X-rays in soda-lime
silicate glass was dominated by first-order kinetics, while
both the first- and the second-order kinetics played role in
the short-term fading process.
effective for the removal of unstable entities responsible for
the initial strong fading. The standard deviation of glass
dosimeters response measurements is about 0.5% (1s)
within the first 2 h after irradiation. After the heat
treatment performed at 150 1C, the response decay of
irradiated glass dosimeters is about 8% between the first
24 h and 20 days. This means that glass dosimeters can be
evaluated either within the first 2 h or just after 1 day after
irradiation and heating.
3.2.2. Effect of post-irradiation heat treatments on the room
temperature fading
The effect of post-irradiation heat treatments on the
glass response fading was studied in the temperature range
of 60–150 1C using sets of three glass samples. After
gamma irradiation with 30 kGy absorbed dose, dosimeter
sets were immediately submitted to the different heat
treatments for 20 min, which was found to be the best
treatment time, and stored after irradiation in the dark at
room temperature. Optical absorbance measurements were
carried out up to 2 months. The specific absorbance values
were normalized to the first measurements taken 5 min
after the heat treatments. The results are presented in Fig. 3
and Table 1. The best results have been obtained with heat
treatments at 150 1C (20 min). This procedure is very
3.2.3. Effect of low-temperature storage on the thermal
fading
Fig. 4. shows the thermal fading of glass samples stored
at low temperature. Two sets of three glass samples were
irradiated to 30 kGy and then kept in the freezer
immediately after irradiation. One set was stored at
(5) 1C and the other one at (20) 1C. Measurements
were taken up to 70 days. After the first 24 h an
approximate 5% reduction of response was observed for
the two sets (Table 1).
3.2.4. Effect of thermal treatments on the fading behaviour
The first- and second-order kinetics fading rate constants
were calculated for each storage temperature to fit the
short-term fading of the experimental data (Table 2). The
results show that the fading behaviour of the glass samples
is remarkably different for the various conditions of
No heat treatment
60 °C
80 °C
100 °C
120 °C
150 °C
0.8
0.6
0.4
0.2
40
Room temperature
104
102
100
98
96
0
0
0
1.2
Normalized specific absorbance
1
Relative specific absorbance (%)
Normalized specific absorbance
1.2
80
0.5
1
1.5
2
Post-irradiation time (hours)
120
2.5
160
Post-irradiation time (days)
- 5 °C
- 20 °C
1
0.8
0.6
0.4
0.2
0
0
Fig. 3. Post-irradiation fading at room temperature of glass samples after
30 kGy irradiation and different heat treatments for 20 min. Inset:
behaviour of glass samples, heated at 150 1C for 20 min, within the first
2 h after the heat treatment.
20
40
60
Post-irradiation time (days)
80
100
Fig. 4. Thermal fading of glass samples stored at room and low
temperature (5 and 20 1C) up to 70 days after an irradiation of 30 kGy.
Table 1
Effect of thermal treatments on fading of glass samples after an irradiation of 30 kGy with gamma rays
Storage time
24 h
20 days
60 days
Reduction of relative specific absorbance (%)
Room temperature
5 1C
20 1C
60 1C
80 1C
100 1C
120 1C
150 1C
25
54
65
5
40
66
5
39
65
17
49
60
16
45
54
15
35
45
12
29
31
7
15
19
*The samples heated in the temperature range of 60–150 1C were kept in the furnace for 20 min.
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Table 2
Fading time constants for temperature range from 20 to 150 1C
T (1C)
First-order kinetics t
(h)
Second-order
kinetics k (h)
Room temperature
5
20
60
80
100
130
150
189.6
1128
2184
169.5
168
110.4
6.25
3.15
30.9
60
117
7.5
0.43
0.024
0.0006
0
4. Conclusions
The observations of our study indicate, that the postirradiation heating (150 1C for 20 min) of the commercial
window glass reduces the radiation-induced absorbance
and accelerates the recombination of the entities responsible for the initial strong fading. Therefore, the evaluation
of the window glass dosimeters is suggested to be
performed either within the first 2 h or 1 day after
irradiation and heat treatment. This procedure does not
affect the useful dose range and the reproducibility of
measurements.
This study demonstrated the necessity of heat treatment
of window glass after irradiation and thus their applicability for routine dosimetric purposes with acceptable
post-irradiation stability.
0.16
Specific absorbance (cm-1)
glass dosimeters. In fact, by comparing the data obtained
from a similar batch of samples irradiated to the same
dose, but not heat treated, and measured at fixed time
(24 h) after irradiation resulted in a 3% (1s) overall
coefficient of variation.
0.14
0.12
0.1
0.08
0.06
0.04
Acknowledgements
0.02
0
0
20
40
60
80
100
120
Dose (kGy)
Fig. 5. Dose response curve of glass dosimeters (410 nm; heated at 150 1C
for 20 min) in the dose range of 0.5–90 kGy fitted with power law function.
storage and thermal treatments. Post-irradiation heat
treatments led to fast fading by accelerating the recombination of defects and the impurities diffusing into the glass
matrix, while post-irradiation storage at low temperatures
(5 and 20 1C) slows down the recombination processes.
3.3. Dose response curve
The heating at 150 1C for 20 min was found to be the
most suitable procedure to stabilize the irradiated glass
dosimeter. The dose response curve taken after this
procedure for the dose range of 0.5–90 kGy is shown in
Fig. 5. This procedure did not affect the metrological
properties (reproducibility and useful dose range) of the
The authors wish to thank Dr. T. Belgya and Dr. Zs.
Révay for the PGAA glass analysis and Dr. F. AbdelRehim for the calibration of the glass dosimeters. The
authors wish also to thank Dr. P.G. Fuochi for his useful
discussions and suggestions.
References
Anderson, D.L., Belgya, T., Firestone, R.B., Kasztovsky, Zs., Lindstom,
R.M., Molnár, G.L., Révay, Zs., Yonezawa, C., 2004. Handbook of
Prompt Gamma Activation Analysis. Kluwer Academic Publishers,
Dordrecht, The Netherlands.
Engin, B., Aydas, C., Demirtas, H., 2006. ESR dosimetric properties of
window glass. Nucl. Instrum. Methods B 243, 149–155.
Rodrigues Jr., Ary de, A., Caldas, L.V.E., 2002. Commercial plate
window glass tested as a routine dosimeter at a gamma irradiation
facility. Radiat. Phys. Chem. 63, 765–767.
Sheng, J., Kadona, K., Yazawa, T., 2002. Fading behaviour of X-ray
induced color centers in soda-lime silicate glass. Appl. Radiat. Isot. 57,
813–817.
Zheng, Z., Hoenggui, D., Jie, F., Daochuan, Y., 1988. Window glass as a
routine dosimeter for radiation processing. Radiat. Phys. Chem. 31,
419–423.