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Effect of gamma irradiation on some optical properties of sodium tetraborate glasses containing iron
Journal of Non-Crystalline Solids 104 (1988) 31-37 North-Holland, A m s t e r d a m
31
E F F E C T O F GAMMA IRRADIATION ON S O M E OPTICAL P R O P E R T I E S OF S O D I U M T E T R A B O R A T E G L A S S E S CONTAINING IRON A.A. K U T U B A N D M.S. E L M A N H A R A W Y Department of Physics, Umm Al-Qura University, Makkah Al-Mukarramah, Saudi Arabia Received 13 January 1988
A series of glass samples were prepared from admixtures of N a z B 4 0 7 and Fe203. The prepared glasses were irradiated for 12 h and 24 h using a gamma-ray dose rate of 206.4 Gy h 1 The optical absorption spectra were recorded for unirradiated and irradiated glass samples. It is found that g a m m a irradiation shifts the optical absorption edges towards longer wavelengths and introduces a new absorption band at 550 n m for the iron-free N a 2 B 4 0 v glass. This induced band disappears on doping with Fe203 at high concentration. The doping of Na2B407 with Fe203 produces the iron characteristic band at 440 n m which increases in intensity when gamma-irradiated. Thermoluminescence of irradiated Na2B407 shows two peaks around 393 K and 550 K and a linear dose-response over the dose range of 100 to 500 Gy which offers a possibility for use as a radiation dosemeter.
1. Introduction The interaction of nuclear radiation with glass was reviewed by Lell et al. [1]. Irradiating the glass by radiation such as gamma rays produced changes in their physical and chemical properties. These changes depend on the composition of the glass and on conditions of preparation [2]. When the glass is exposed to gamma radiation intrinsic defects are formed which are trapped in the network. Any transition metal impurities in the glass will compete with the intrinsic defects to trap electrons and holes produced by irradiation [3]. Transition metals, which can be introduced as impurities in glass, are present in different quantities, various valencies and unlike coordinations. It is well known that transition metals may easily change their valency under the action of irradiation [3-5]. A great deal of work has been carried out on many glass systems containing iron oxide [6-9]. The effect of irradiation on glass systems has been reported by many researchers [2,10,11]. Bishay [12] studied the effect of gamma rays on the optical absorption band of lead borate glasses. Ahmed et al. [13] studied the effect of irradiation 0022-3093/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
on (CaO-B203-A1203) glass containing copper. Morsi et al. [5] reported the effect of neutron and gamma irradiation on some properties of borate glasses containing uranium. Sanad et al. [14] investigated the effect of heat treatment and irradiation on the infrared spectra of barium borate glass containing iron oxide. In this work, the effect of gamma irradiation on the optical absorption spectra of sodium tetraborate glasses containing iron oxide is studied. Thermoluminescence of the glass is also measured.
2. Experimental
2.1. Sample preparation The glass samples were prepared for this study by mixing an appropriate amount of sodium tetraborate (e.g. N a z B 4 0 7 ) with Fe203 in an alumina crucible as shown in table 1. Before weighing, the borates were placed in a drying oven at 400 o C for 1 h and then transferred to a vacuum desiccator and allowed to cool. The crucible containing the mixture was placed into a closed high-temperature furnace where it was held for 1 h under atmo-
A.A. Kutub, M.S. Elmanharawy /Opticalproperties of sodium tetraborate glasses
32
Table 1 Composition data for sodium tetraborate glasses containing iron oxide Glass
1 2 3 4 5
Composition (mol%) (Na2B407)
(Fe203)
100.0 99.5 98.0 97.0 95.0
0.0 0.5 2.0 3.0 5.0
spheric conditions at a temperature of about 1000 ° C. During this time the melt was occasionally stirred with an alumina rod. By slow heating, it was hoped to reduce mechanical and volatilization losses. Bulk samples were prepared by pouring the melt on a massive stainless steel plate and cast into a disc of 1.5 cm in diameter and about 2 m m thick on a stainless steel plate maintained at 400 ° C and introduced into a furnace which was already at this temperature. The furnace was maintained at this temperature for 1 h and was then switched off to cool down to room temperature. The glass samples were polished using diamond paste down to a minimum grit size of 0.1 btm. Samples having thicknesses in the range 0.95 to 1.27 m m were obtained.
2.2. Spectrophotometric and irradiation studies The optical absorption measurements were carried out before and after irradiation at room temperature in the wavelength range from 185 to 900 nm using a Varian model C A R Y 2390 spectrophotometer. The samples were irradiated for 12 and 24 h using gamma-rays at a dose of 206.4 G y per hour using a cobalt-60 irradiation unit. The output was measured using a substandard Farmer dosemeter (Nuclear Enterprises Type 2570 A) fitted with a 0.03 cc ionization chamber, this calibration was checked with a FeSO4 chemical dosemeter. The absorption spectra of irradiated glasses were recorded immediately within about 5 min after termination of irradiation and also after different periods of time ranging from a few hours to as long as 125 days (3000 h) at room temperature.
2.3. Thermoluminescence measurements The thermoluminscence of a gamma-irradiated glass sample was measured immediately after irradiation. The Harshaw 3000 A T L D system was used, where the sample was heated using reproducible controlled temperature cycles (from room temperature to 400 o C); a linear heating of 3 ° C / s was employed. The detected thermoluminescence of the sample was recorded as a function of temperature on an external X - Y recorder. The Harshaw T L D system is also capable of integrating a thermoluminescence signal between any two present temperature limits and the measured thermoluminescence emitted during the heating cycle is digitally displayed.
3. Results and discussion
3.1. Glass without iron 3.1.1. The unirradiated glass The N a 2 B 4 0 7 glass sample used in the present investigation was colorless. Its absorption spectrum showed no characteristic bands in the ultraviolet or the visible range. The wavelength of its absorption edge was 201.0 nm. 3.1.2. The irradiated glass On subjecting the sample to g a m m a radiation, the color changed to faint violet then to violet at high radiation dose. Fig. 1 shows absorption spectra recorded at room temperature for both unirradiated and irradiated N a z B 4 0 7 glass samples. The spectra reveal a shift in the wavelength of the absorption edge from 201.0 nm to 203.5 nm on dosage with 206.4 G y h -a for 12 h (fig. la) and to 208.5 nm on irradiation for 24 h (fig. lb). The observed shift of the absorption edge to longer wavelength indicates a transfer of boron atoms from the tetrahedral BO 4 group to trianguler BO 3. Increasing irradiation dose is known to break the B - O in borate glasses forming non-bridging oxygen. Moreover, g a m m a irradiation also induced a new broad peak around 550 nm; its position remaining unchanged with increasing radiation dose.
33
A.A. Kutub, M.S. Elmanharawy / Optical properties of sodium tetraborate glasses
2.o (a)
Ii
(b)
1,5
~3
0.5
0,0
Wove[ength [nm)
~uu
t.ou
Wavelength (nmbjOo
800
Fig. 1. The optical absorption spectra of Na2B40v glass (sample 1) before and after irradiation for: (a) 12 h; (b) 24 h. A before irradiation, B - directly after irradiation, C - 6 h after irradiation, D - 24 h after irradiation, E - 120 h after irradiation, F - 500 h after irradiation, G - 3000 h after irradiation.
The induced visible absorption of alkali borate glasses was at first attributed to electrons trapped by oxygen vacancies neighboring alkali ions [15]. Bishay [16,17] attributed the induced band to positive hole centers formed by the loss of electrons from the oxygen during irradiation. Thus, the absorption of a gamma ray photon by the defect in glass leads to the creation of a positive hole and the release of an electron. The stability of the glass sample irradiated for 12 and 24 h was studied by remeasuring its spectral absorption at room temperature after different periods of time ranging from a few hours to as long as 125 days (3000 h). As it is obvious from fig. 1 (a and b), the wavelength of the absorption edge shifts back to shorter wavelengths with time; this is summarised in table 2. In addition, the intensity of the newly-induced peak around 550 nm decreased gradually with time. These observations could be due to a reversible transformation from BO 3 to BO4 which is assisted by the presence of non-bridging oxygen; a view which needs further quantitative elaboration. It is interesting to mention that Ahmed et al. [13] observed two absorption bands as a result of the irradiation of a (CaO-BzO3-A1203) glass sample. The first was around 550 nm and shifted to longer wavelength around 600 nm with increasing irradiation. The other band was observed at about 400 nm and its position did not show any change
with irradiation. Morsi et al. [18] noticed that gamma irradiation produced an appreciable change in the spectra of alkali borate glasses, particularly in the visible region. Bishay [12,16] reported an absorption band induced at 825 nm by gamma irradiation in lead borate glasses and at 550 nm in (A1203-B203-BaO) glass. 3.2. Glass containing iron 3.2.1. The unirradiated glass The inclusion of Fe203 in the originally colorless NazB407 glass produces changes in color ranging from pale brown at 0.5 mol% Fe203 to brown at 5 mol%. The effect of doping Na 213407 glass with Fe203 is shown in figs. 2 to 5, where absorption spectra recorded at room temperature are presented. By increasing the Fe203 content, the absorption edges shift towards longer wavelengths which range from 201 to 408 nm. It is also noticed that doping of iron in the NazB407 glass produced a characteristic band at 440 nm. Its intensity increases with increasing Fe203 concentration. It is known that the absorption spectra of ferric iron Fe 3+ are three weak absorption bands at 380, 420 and 435 nm. The absorption due to ferrous iron Fe 2+ is the well-known single broad deep absorption band centered at 1050 nm. In alkali borate glasses, no discrete ferric absorption spectra have been re-
A.A. Kutub, M.S. EImanharawy / Optical properties of sodium tetraborate glasses
34
Table 2 The relation between time of irradiation and absorption edge wavelengths after irradiation. Fe203 (mol%)
Time of irradiation
Before irradiation
(h)
Zero
0.5
2
3
5
0 12 24 0 12 24 0 12 24 0 12 24 0 12 24
Absorption edge wavelength (nm) Time elapsed after irradiation 6
24
120
500
3000
203.5 208.5
203.5 205.5
203.5 204.0
203.0 202.0
202.0 202.0
201.5
363.0 364.0
362.0 362.0
359.0 359.0
357.0 355.0
355.0 352.0
350.0
386.0 394.0
384.0 392.0
381.0 386.0
376.0 383.0
372.0 379.0
373.0
409.0 412.0
405.0 411.0
402.0 402.0
397.0 398.0
392.0 395.0
388.0
456.0 463.0
452.0 461.0
447.0 454.0
436.0 445.0
425.5 431.0
426.0
201
347.0
364.0
380.0
408.0
solved. Ferric iron in such glasses gives a brown coloration identified with a shift in the optical cut-off wavelength of the glasses into the blue spectral region. This shift has been attributed by Bamford [19] to the formation of colloidal Fe203 precipitated in the glass on cooling. His conclusion was based on optical and magnetic measurements of quenched and annealed glasses.
2.0
(h)
0
tl
(a)
1.5 5 6
3.2.2. The irradiated glass Gamma-irradiation of (Na2B4OT-Fe203) glass samples causes the original faint brownish color to become darker. Figs. 2 to 5 show absorption spectra recorded at room temperature for irradiated Na2B407 doped with various amounts of FezO 3. It is interesting to note that the irradiation of (NazBaO7-Fe203) causes the wavelength of the
2.0
•
(b)
"-'I !1'5 ~I.0
BCDEF
ABCDEF6
o
o.5l-
0.5
0'0200
"133 600 Wavelength (nm)
800
o.% ,
400 Wavelength (nm)
800
Fig. 2. The optical absorption spectra of sample 2 before and after irradiation for; (a) 12 h; (b) 24 h. A - before irradiation, B directly after irradiation, C - 6 h after irradiation, D - 24 h after irradiation, E - 120 h after irradiation, F - 500 h after irradiation, G - 3000 h after irradiation.
A.A. Kutub, M.S. Elmanharawy / Opticalproperties of sodium tetraborate glasses 2.0j
2.C
(a) 1.5
i/////
A BC D E F
<
ll
I
A00
K
ABC
-~'~----~"
I
600 Wavelength [nm)
800
DE
FG
////!//
O.C.
0.5
0£
(b)
1.5
i
~1.C
)
]
l .
g
35
I
0.~
I
40(3
~
I
'
,
500 Wavelength {nm)
800
Fig. 3. The optical absorption spectra o f sample 3 before and after irradiation for: (a) 12 h; (b) 24 h. A - before irradiation, B directly after i r r a d i a t i o n , C - 6 h after irradiation, D - 24 h a f t e r irradiation, E - 120 h a f t e r irradiation, F - 500 h a f t e r irradiation, G - 3000 h a f t e r irradiation.
152° t
' '
00
~
0%0 Wavelength (nm)
,
J
4OO
6O0 Wavelength (nm)
8OO
Fig. 4. The optical absorption spectra of sample 4 before and after irradiation for: (a) 12 h; (b) 24 h. A - before irradiation, B directly a f t e r i r r a d i a t i o n , C - 6 h after i r r a d i a t i o n , D - 24 h a f t e r i r r a d i a t i o n , E - 120 h a f t e r irradiation, F - 500 h a f t e r i r r a d i a t i o n , G - 3000 h a f t e r irradiation. 2£ r
'
(~)
17-
°/
1////
6 31.0 o
ABC
o
!i
DE F
<
/\\\\\
/!:: ((/
0.5
0,0 200
h
I 400
, Wavelength
I 600 (nm)
,
I 800
Fig. 5. T h e optical a b s o r p t i o n s p e c t r a o f s a m p l e 5 b e f o r e a n d a f t e r i r r a d i a t i o n for: (a) 12 h; (b) 24 h. A - b e f o r e i r r a d i a t i o n , B directly a f t e r i r r a d i a t i o n , C - 6 h after i r r a d i a t i o n , D - 24 h a f t e r i r r a d i a t i o n , E - 120 h a f t e r irradiation, F - 500 h a f t e r i r r a d i a t i o n , G - 3000 h a f t e r irradiation.
36
A.A. Kutub, M.S. Elmanharawy / Optical properties of sodium tetraborate glasses
absorption edge to shift to longer values. This shift is increased when the dosage time is increased and becomes more pronounced at high Fe203 content. The iron characteristic band observed at 440 n m is found to disappear at low iron concentration under the effect of irradiation while its intensity is increased at high iron concentration. This phenomenon is related to changes in the coordination number of iron from tetrahedral to octahedral structure; i.e. from glass former to glass modifier. With an Fe203 concentration of 0.5 mol%, the induced absorption peak around 550 nm, which appeared in the irradiated Na2BaO 7 glass, showed very little absorption around 550 nm (fig. 2) which disappeared with a further increase in Fe203 content (figs. 3 to 5). It seems that the inclusion of iron in low concentration in Na2B407 glass has little effect on the radiation-induced peak at 550 nm in Na2B407 glass. At high iron concentration, the (Na2B407-Fe203) glass is expected to behave differently from Na2B407 glass and the disappearance of the induced band is therefore understood. Fe203 is known to enhance the formation of tetrahedral BO 4 at the expense of the triangular B O 3. Ahmed et al. [13] noticed a band at 550-580 nm in (CaO-B203-AI203) glass containing copper which increased in intensity with irradiation dose but decreased with increasing CuO content. 3.3. Thermoluminescence
Thermoluminescence of irradiated Na2B407 glass samples was measured within the temperature range from room temperature to 673 K. The gamma dose ranged from 100 G y to 500 Gy. It is clear from fig. 6 that each thermoluminescence curve subsumes two peaks around 393 K and 550 K. This thermoluminescence arises obviously from the recombination of irradiation-formed trapped electrons or holes with luminescent centers [20]. It is difficult to assign with certainty the reaction which gives rise to thermoluminescence to the recombination of a given type of center. The present results show that this glass composition exhibits relatively stable thermoluminescence trap
'
I
I
I
'
"~90
E I
'
A: 100 Oy
~
/
2
\
/
--
B:200 Gy /
C: 300 Oy
61
~3c
L
~ 0~
~- 250
350
z,50 550 Temperature {K)
650
750
Fig. 6. Thermoluminescence curves for Na2B407 glass (sample 1) irradiated with gamma-rays.
centers when gamma irradiated. The systematic increase in the absorbed gamma dose gradually increases the glow peak height and area without any appreciable shift in the glow peak position or trap destruction. It is also found that this glass type exhibits when gamma irradiated a linear gamma-dose response. When the glow curve area per 100 mg of sample was plotted as a function of the gamma dose through a useful range of 100 G y to 500 Gy, a straight line was obtained. This is illustrated in fig. 7 and points to the possibility of using this glass composition in radiation dosimetry. Attempts were made to study the thermoluminescence of irradiated (Na 2B4Ov-Fe203) glass samples. It was found that in addition to the previous peaks of irradiated Na2B407, new peaks started to appear around 673 K but unfortunately
8
20
~1°t ~-o
o
100
200
300J
DOSE (6y)
I &00
500
Fig. 7. The relation between integrated glow curve area per 100 mg of sample as a function of radiation dose (for sample 1).
A.A. Kutub, M.S. Elmanharawy / Opticalproperties of sodium tetraborate glasses
we were unable to detect them fully because of the limited temperature range of the T L D equipment (0-400 ° C). In a very recent study, Henaish et al. [21] reported the thermoluminescence characteristics of Na2B407 glass containing neodymium, which showed two glow peaks caused by gamma irradiation. The peaks increased in intensity with increasing gamma dose; a trend which is similar to the presently-reported thermoluminescence characteristics.
4. Conclusion From the foregoing results and discussion the following conclusions can be drawn: (1) Irradiation of NazB407 glass shifts absorption edge wavelengths to longer values due to the transfer of the boron atoms from the tetrahedral BO 4 group to the triangular B O 3 with the formation of non-bridging oxygen. (2) A new band is also induced at 550 nm by gamma irradiation. Its position remains unchanged irrespective of increasing irradiation dose. This illustrates the stability of the centers created by radiation in this glass. (3) The inclusion of iron in the Na2B407 glass produces a characteristic band at 440 nm. Its intensity increases with increasing FezO 3 content. This is associated with a change in the role of iron from a glass former to a glass modifier. (4) The doping with Fe203 in low concentrations has little effect on the radiation-induced band at 550 nm in Na2B407 glass. This band disappears at high Fe203 concentrations due to the formation of BOa at the expense of B O 3. (5) The thermoluminescence centers created by radiation are found to be stable and show no
37
destruction with increasing radiation dose. The linear dose-response of Na2B407 glass over the used dose range of 100-500 Gy offers the possibility for using this glass for radiation dosimetry.
References [1] E. Lell, N.J. Kreidl and J.R. Hensler, Progress in Ceramic Science 4 ed., J. Burke (Pergamon Press, Oxford, 1966) p.l. [2] N.J. Kreidl and J.R. Hensler, J. Am. Ceram. Soc. 38 (1955) 423, [3] A. Bishay, J. Non-Cryst. Solids 3 (1970) 54. [4] F. Assabghy, S. Arafa, E. Boulos, A. Bishay and N.J. Kreidl, J. Non. Cryst. Solids 23 (1977), 81. [5] M.M. Morsi and A.M. Nassar, J. Non-Cryst. Solids 27 (1978) 181. [6[ A.M. Sanad, 1. Kashif, A.M. Abou-Al-Azm, M.A. Khaled and H. Farouk, J. Mat. Sci. 21 (1986) 230. [7] E.E. Khawaja, M. Sakhawat Hussain and M.N. Khan, J. Non-Cryst. Solids 79 (1986) 275. [8] E.E. Shaisha, A.A. Bahgat, A.I. Sabry and N.A. Eissa, Phys. Chem. Glasses 26 No.4 (1985) 91. [9] J.W. Park and H. Chen, J. Non-Cryst. Solids 40 (1980) 515. [10] G. Kordas and H.J. Oel, Phys. Chem. Glasses 25 (3) (1984) 76. [11] A.F. Abbas, A.A. Ahmed, M.A. E1-Fiki and H.M. Eissa, Phys. Chem. Glasses 26 (4) (1985) 97. [12] A. Bishay, J. Am. Ceram. Soc. 43 (8) (1960) 417. [13] A.A. Ahmed, A.F. Abbas and F.M. Ezz El-Din, Phys, Chem. Glasses 25 (1) (1984) 22. [14] A.M. Sanad, I. Kashif, A.A. El-Sharkawy, A.A. EI-Saghier and H. Farouk, J. Mat. Sci. 21 (1986) 3483. [15] R. Yokota, Phys. Rev. 95 (1954) 1145. [16] A. Bishay, Phys. Chem. Glasses 2 (5) (1961) 169. [17] A. Bishay, J. Am. Ceram. Soc. 45 (1962) 389. [18] M.M. Morsi, S. El-Konsol and M.A. Adawi, J. Non-Cryst, Solids 58 (1983) 187. [19] C.R. Bamford, Phys. Chem. Glasses l (1960) 159. [20] C. Bettinali and P. Granati, Rend. Sc. Fis. Mat. e Nat. Lincei XLIV (1968) 669. [21] B.A. Henaish, M.A. Kenawy, A.F, Abbas and L.R. Salem, The First Egyptian-British Conference on Bio-Physics, Cairo University, October 1987.
31
E F F E C T O F GAMMA IRRADIATION ON S O M E OPTICAL P R O P E R T I E S OF S O D I U M T E T R A B O R A T E G L A S S E S CONTAINING IRON A.A. K U T U B A N D M.S. E L M A N H A R A W Y Department of Physics, Umm Al-Qura University, Makkah Al-Mukarramah, Saudi Arabia Received 13 January 1988
A series of glass samples were prepared from admixtures of N a z B 4 0 7 and Fe203. The prepared glasses were irradiated for 12 h and 24 h using a gamma-ray dose rate of 206.4 Gy h 1 The optical absorption spectra were recorded for unirradiated and irradiated glass samples. It is found that g a m m a irradiation shifts the optical absorption edges towards longer wavelengths and introduces a new absorption band at 550 n m for the iron-free N a 2 B 4 0 v glass. This induced band disappears on doping with Fe203 at high concentration. The doping of Na2B407 with Fe203 produces the iron characteristic band at 440 n m which increases in intensity when gamma-irradiated. Thermoluminescence of irradiated Na2B407 shows two peaks around 393 K and 550 K and a linear dose-response over the dose range of 100 to 500 Gy which offers a possibility for use as a radiation dosemeter.
1. Introduction The interaction of nuclear radiation with glass was reviewed by Lell et al. [1]. Irradiating the glass by radiation such as gamma rays produced changes in their physical and chemical properties. These changes depend on the composition of the glass and on conditions of preparation [2]. When the glass is exposed to gamma radiation intrinsic defects are formed which are trapped in the network. Any transition metal impurities in the glass will compete with the intrinsic defects to trap electrons and holes produced by irradiation [3]. Transition metals, which can be introduced as impurities in glass, are present in different quantities, various valencies and unlike coordinations. It is well known that transition metals may easily change their valency under the action of irradiation [3-5]. A great deal of work has been carried out on many glass systems containing iron oxide [6-9]. The effect of irradiation on glass systems has been reported by many researchers [2,10,11]. Bishay [12] studied the effect of gamma rays on the optical absorption band of lead borate glasses. Ahmed et al. [13] studied the effect of irradiation 0022-3093/88/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
on (CaO-B203-A1203) glass containing copper. Morsi et al. [5] reported the effect of neutron and gamma irradiation on some properties of borate glasses containing uranium. Sanad et al. [14] investigated the effect of heat treatment and irradiation on the infrared spectra of barium borate glass containing iron oxide. In this work, the effect of gamma irradiation on the optical absorption spectra of sodium tetraborate glasses containing iron oxide is studied. Thermoluminescence of the glass is also measured.
2. Experimental
2.1. Sample preparation The glass samples were prepared for this study by mixing an appropriate amount of sodium tetraborate (e.g. N a z B 4 0 7 ) with Fe203 in an alumina crucible as shown in table 1. Before weighing, the borates were placed in a drying oven at 400 o C for 1 h and then transferred to a vacuum desiccator and allowed to cool. The crucible containing the mixture was placed into a closed high-temperature furnace where it was held for 1 h under atmo-
A.A. Kutub, M.S. Elmanharawy /Opticalproperties of sodium tetraborate glasses
32
Table 1 Composition data for sodium tetraborate glasses containing iron oxide Glass
1 2 3 4 5
Composition (mol%) (Na2B407)
(Fe203)
100.0 99.5 98.0 97.0 95.0
0.0 0.5 2.0 3.0 5.0
spheric conditions at a temperature of about 1000 ° C. During this time the melt was occasionally stirred with an alumina rod. By slow heating, it was hoped to reduce mechanical and volatilization losses. Bulk samples were prepared by pouring the melt on a massive stainless steel plate and cast into a disc of 1.5 cm in diameter and about 2 m m thick on a stainless steel plate maintained at 400 ° C and introduced into a furnace which was already at this temperature. The furnace was maintained at this temperature for 1 h and was then switched off to cool down to room temperature. The glass samples were polished using diamond paste down to a minimum grit size of 0.1 btm. Samples having thicknesses in the range 0.95 to 1.27 m m were obtained.
2.2. Spectrophotometric and irradiation studies The optical absorption measurements were carried out before and after irradiation at room temperature in the wavelength range from 185 to 900 nm using a Varian model C A R Y 2390 spectrophotometer. The samples were irradiated for 12 and 24 h using gamma-rays at a dose of 206.4 G y per hour using a cobalt-60 irradiation unit. The output was measured using a substandard Farmer dosemeter (Nuclear Enterprises Type 2570 A) fitted with a 0.03 cc ionization chamber, this calibration was checked with a FeSO4 chemical dosemeter. The absorption spectra of irradiated glasses were recorded immediately within about 5 min after termination of irradiation and also after different periods of time ranging from a few hours to as long as 125 days (3000 h) at room temperature.
2.3. Thermoluminescence measurements The thermoluminscence of a gamma-irradiated glass sample was measured immediately after irradiation. The Harshaw 3000 A T L D system was used, where the sample was heated using reproducible controlled temperature cycles (from room temperature to 400 o C); a linear heating of 3 ° C / s was employed. The detected thermoluminescence of the sample was recorded as a function of temperature on an external X - Y recorder. The Harshaw T L D system is also capable of integrating a thermoluminescence signal between any two present temperature limits and the measured thermoluminescence emitted during the heating cycle is digitally displayed.
3. Results and discussion
3.1. Glass without iron 3.1.1. The unirradiated glass The N a 2 B 4 0 7 glass sample used in the present investigation was colorless. Its absorption spectrum showed no characteristic bands in the ultraviolet or the visible range. The wavelength of its absorption edge was 201.0 nm. 3.1.2. The irradiated glass On subjecting the sample to g a m m a radiation, the color changed to faint violet then to violet at high radiation dose. Fig. 1 shows absorption spectra recorded at room temperature for both unirradiated and irradiated N a z B 4 0 7 glass samples. The spectra reveal a shift in the wavelength of the absorption edge from 201.0 nm to 203.5 nm on dosage with 206.4 G y h -a for 12 h (fig. la) and to 208.5 nm on irradiation for 24 h (fig. lb). The observed shift of the absorption edge to longer wavelength indicates a transfer of boron atoms from the tetrahedral BO 4 group to trianguler BO 3. Increasing irradiation dose is known to break the B - O in borate glasses forming non-bridging oxygen. Moreover, g a m m a irradiation also induced a new broad peak around 550 nm; its position remaining unchanged with increasing radiation dose.
33
A.A. Kutub, M.S. Elmanharawy / Optical properties of sodium tetraborate glasses
2.o (a)
Ii
(b)
1,5
~3
0.5
0,0
Wove[ength [nm)
~uu
t.ou
Wavelength (nmbjOo
800
Fig. 1. The optical absorption spectra of Na2B40v glass (sample 1) before and after irradiation for: (a) 12 h; (b) 24 h. A before irradiation, B - directly after irradiation, C - 6 h after irradiation, D - 24 h after irradiation, E - 120 h after irradiation, F - 500 h after irradiation, G - 3000 h after irradiation.
The induced visible absorption of alkali borate glasses was at first attributed to electrons trapped by oxygen vacancies neighboring alkali ions [15]. Bishay [16,17] attributed the induced band to positive hole centers formed by the loss of electrons from the oxygen during irradiation. Thus, the absorption of a gamma ray photon by the defect in glass leads to the creation of a positive hole and the release of an electron. The stability of the glass sample irradiated for 12 and 24 h was studied by remeasuring its spectral absorption at room temperature after different periods of time ranging from a few hours to as long as 125 days (3000 h). As it is obvious from fig. 1 (a and b), the wavelength of the absorption edge shifts back to shorter wavelengths with time; this is summarised in table 2. In addition, the intensity of the newly-induced peak around 550 nm decreased gradually with time. These observations could be due to a reversible transformation from BO 3 to BO4 which is assisted by the presence of non-bridging oxygen; a view which needs further quantitative elaboration. It is interesting to mention that Ahmed et al. [13] observed two absorption bands as a result of the irradiation of a (CaO-BzO3-A1203) glass sample. The first was around 550 nm and shifted to longer wavelength around 600 nm with increasing irradiation. The other band was observed at about 400 nm and its position did not show any change
with irradiation. Morsi et al. [18] noticed that gamma irradiation produced an appreciable change in the spectra of alkali borate glasses, particularly in the visible region. Bishay [12,16] reported an absorption band induced at 825 nm by gamma irradiation in lead borate glasses and at 550 nm in (A1203-B203-BaO) glass. 3.2. Glass containing iron 3.2.1. The unirradiated glass The inclusion of Fe203 in the originally colorless NazB407 glass produces changes in color ranging from pale brown at 0.5 mol% Fe203 to brown at 5 mol%. The effect of doping Na 213407 glass with Fe203 is shown in figs. 2 to 5, where absorption spectra recorded at room temperature are presented. By increasing the Fe203 content, the absorption edges shift towards longer wavelengths which range from 201 to 408 nm. It is also noticed that doping of iron in the NazB407 glass produced a characteristic band at 440 nm. Its intensity increases with increasing Fe203 concentration. It is known that the absorption spectra of ferric iron Fe 3+ are three weak absorption bands at 380, 420 and 435 nm. The absorption due to ferrous iron Fe 2+ is the well-known single broad deep absorption band centered at 1050 nm. In alkali borate glasses, no discrete ferric absorption spectra have been re-
A.A. Kutub, M.S. EImanharawy / Optical properties of sodium tetraborate glasses
34
Table 2 The relation between time of irradiation and absorption edge wavelengths after irradiation. Fe203 (mol%)
Time of irradiation
Before irradiation
(h)
Zero
0.5
2
3
5
0 12 24 0 12 24 0 12 24 0 12 24 0 12 24
Absorption edge wavelength (nm) Time elapsed after irradiation 6
24
120
500
3000
203.5 208.5
203.5 205.5
203.5 204.0
203.0 202.0
202.0 202.0
201.5
363.0 364.0
362.0 362.0
359.0 359.0
357.0 355.0
355.0 352.0
350.0
386.0 394.0
384.0 392.0
381.0 386.0
376.0 383.0
372.0 379.0
373.0
409.0 412.0
405.0 411.0
402.0 402.0
397.0 398.0
392.0 395.0
388.0
456.0 463.0
452.0 461.0
447.0 454.0
436.0 445.0
425.5 431.0
426.0
201
347.0
364.0
380.0
408.0
solved. Ferric iron in such glasses gives a brown coloration identified with a shift in the optical cut-off wavelength of the glasses into the blue spectral region. This shift has been attributed by Bamford [19] to the formation of colloidal Fe203 precipitated in the glass on cooling. His conclusion was based on optical and magnetic measurements of quenched and annealed glasses.
2.0
(h)
0
tl
(a)
1.5 5 6
3.2.2. The irradiated glass Gamma-irradiation of (Na2B4OT-Fe203) glass samples causes the original faint brownish color to become darker. Figs. 2 to 5 show absorption spectra recorded at room temperature for irradiated Na2B407 doped with various amounts of FezO 3. It is interesting to note that the irradiation of (NazBaO7-Fe203) causes the wavelength of the
2.0
•
(b)
"-'I !1'5 ~I.0
BCDEF
ABCDEF6
o
o.5l-
0.5
0'0200
"133 600 Wavelength (nm)
800
o.% ,
400 Wavelength (nm)
800
Fig. 2. The optical absorption spectra of sample 2 before and after irradiation for; (a) 12 h; (b) 24 h. A - before irradiation, B directly after irradiation, C - 6 h after irradiation, D - 24 h after irradiation, E - 120 h after irradiation, F - 500 h after irradiation, G - 3000 h after irradiation.
A.A. Kutub, M.S. Elmanharawy / Opticalproperties of sodium tetraborate glasses 2.0j
2.C
(a) 1.5
i/////
A BC D E F
<
ll
I
A00
K
ABC
-~'~----~"
I
600 Wavelength [nm)
800
DE
FG
////!//
O.C.
0.5
0£
(b)
1.5
i
~1.C
)
]
l .
g
35
I
0.~
I
40(3
~
I
'
,
500 Wavelength {nm)
800
Fig. 3. The optical absorption spectra o f sample 3 before and after irradiation for: (a) 12 h; (b) 24 h. A - before irradiation, B directly after i r r a d i a t i o n , C - 6 h after irradiation, D - 24 h a f t e r irradiation, E - 120 h a f t e r irradiation, F - 500 h a f t e r irradiation, G - 3000 h a f t e r irradiation.
152° t
' '
00
~
0%0 Wavelength (nm)
,
J
4OO
6O0 Wavelength (nm)
8OO
Fig. 4. The optical absorption spectra of sample 4 before and after irradiation for: (a) 12 h; (b) 24 h. A - before irradiation, B directly a f t e r i r r a d i a t i o n , C - 6 h after i r r a d i a t i o n , D - 24 h a f t e r i r r a d i a t i o n , E - 120 h a f t e r irradiation, F - 500 h a f t e r i r r a d i a t i o n , G - 3000 h a f t e r irradiation. 2£ r
'
(~)
17-
°/
1////
6 31.0 o
ABC
o
!i
DE F
<
/\\\\\
/!:: ((/
0.5
0,0 200
h
I 400
, Wavelength
I 600 (nm)
,
I 800
Fig. 5. T h e optical a b s o r p t i o n s p e c t r a o f s a m p l e 5 b e f o r e a n d a f t e r i r r a d i a t i o n for: (a) 12 h; (b) 24 h. A - b e f o r e i r r a d i a t i o n , B directly a f t e r i r r a d i a t i o n , C - 6 h after i r r a d i a t i o n , D - 24 h a f t e r i r r a d i a t i o n , E - 120 h a f t e r irradiation, F - 500 h a f t e r i r r a d i a t i o n , G - 3000 h a f t e r irradiation.
36
A.A. Kutub, M.S. Elmanharawy / Optical properties of sodium tetraborate glasses
absorption edge to shift to longer values. This shift is increased when the dosage time is increased and becomes more pronounced at high Fe203 content. The iron characteristic band observed at 440 n m is found to disappear at low iron concentration under the effect of irradiation while its intensity is increased at high iron concentration. This phenomenon is related to changes in the coordination number of iron from tetrahedral to octahedral structure; i.e. from glass former to glass modifier. With an Fe203 concentration of 0.5 mol%, the induced absorption peak around 550 nm, which appeared in the irradiated Na2BaO 7 glass, showed very little absorption around 550 nm (fig. 2) which disappeared with a further increase in Fe203 content (figs. 3 to 5). It seems that the inclusion of iron in low concentration in Na2B407 glass has little effect on the radiation-induced peak at 550 nm in Na2B407 glass. At high iron concentration, the (Na2B407-Fe203) glass is expected to behave differently from Na2B407 glass and the disappearance of the induced band is therefore understood. Fe203 is known to enhance the formation of tetrahedral BO 4 at the expense of the triangular B O 3. Ahmed et al. [13] noticed a band at 550-580 nm in (CaO-B203-AI203) glass containing copper which increased in intensity with irradiation dose but decreased with increasing CuO content. 3.3. Thermoluminescence
Thermoluminescence of irradiated Na2B407 glass samples was measured within the temperature range from room temperature to 673 K. The gamma dose ranged from 100 G y to 500 Gy. It is clear from fig. 6 that each thermoluminescence curve subsumes two peaks around 393 K and 550 K. This thermoluminescence arises obviously from the recombination of irradiation-formed trapped electrons or holes with luminescent centers [20]. It is difficult to assign with certainty the reaction which gives rise to thermoluminescence to the recombination of a given type of center. The present results show that this glass composition exhibits relatively stable thermoluminescence trap
'
I
I
I
'
"~90
E I
'
A: 100 Oy
~
/
2
\
/
--
B:200 Gy /
C: 300 Oy
61
~3c
L
~ 0~
~- 250
350
z,50 550 Temperature {K)
650
750
Fig. 6. Thermoluminescence curves for Na2B407 glass (sample 1) irradiated with gamma-rays.
centers when gamma irradiated. The systematic increase in the absorbed gamma dose gradually increases the glow peak height and area without any appreciable shift in the glow peak position or trap destruction. It is also found that this glass type exhibits when gamma irradiated a linear gamma-dose response. When the glow curve area per 100 mg of sample was plotted as a function of the gamma dose through a useful range of 100 G y to 500 Gy, a straight line was obtained. This is illustrated in fig. 7 and points to the possibility of using this glass composition in radiation dosimetry. Attempts were made to study the thermoluminescence of irradiated (Na 2B4Ov-Fe203) glass samples. It was found that in addition to the previous peaks of irradiated Na2B407, new peaks started to appear around 673 K but unfortunately
8
20
~1°t ~-o
o
100
200
300J
DOSE (6y)
I &00
500
Fig. 7. The relation between integrated glow curve area per 100 mg of sample as a function of radiation dose (for sample 1).
A.A. Kutub, M.S. Elmanharawy / Opticalproperties of sodium tetraborate glasses
we were unable to detect them fully because of the limited temperature range of the T L D equipment (0-400 ° C). In a very recent study, Henaish et al. [21] reported the thermoluminescence characteristics of Na2B407 glass containing neodymium, which showed two glow peaks caused by gamma irradiation. The peaks increased in intensity with increasing gamma dose; a trend which is similar to the presently-reported thermoluminescence characteristics.
4. Conclusion From the foregoing results and discussion the following conclusions can be drawn: (1) Irradiation of NazB407 glass shifts absorption edge wavelengths to longer values due to the transfer of the boron atoms from the tetrahedral BO 4 group to the triangular B O 3 with the formation of non-bridging oxygen. (2) A new band is also induced at 550 nm by gamma irradiation. Its position remains unchanged irrespective of increasing irradiation dose. This illustrates the stability of the centers created by radiation in this glass. (3) The inclusion of iron in the Na2B407 glass produces a characteristic band at 440 nm. Its intensity increases with increasing FezO 3 content. This is associated with a change in the role of iron from a glass former to a glass modifier. (4) The doping with Fe203 in low concentrations has little effect on the radiation-induced band at 550 nm in Na2B407 glass. This band disappears at high Fe203 concentrations due to the formation of BOa at the expense of B O 3. (5) The thermoluminescence centers created by radiation are found to be stable and show no
37
destruction with increasing radiation dose. The linear dose-response of Na2B407 glass over the used dose range of 100-500 Gy offers the possibility for using this glass for radiation dosimetry.
References [1] E. Lell, N.J. Kreidl and J.R. Hensler, Progress in Ceramic Science 4 ed., J. Burke (Pergamon Press, Oxford, 1966) p.l. [2] N.J. Kreidl and J.R. Hensler, J. Am. Ceram. Soc. 38 (1955) 423, [3] A. Bishay, J. Non-Cryst. Solids 3 (1970) 54. [4] F. Assabghy, S. Arafa, E. Boulos, A. Bishay and N.J. Kreidl, J. Non. Cryst. Solids 23 (1977), 81. [5] M.M. Morsi and A.M. Nassar, J. Non-Cryst. Solids 27 (1978) 181. [6[ A.M. Sanad, 1. Kashif, A.M. Abou-Al-Azm, M.A. Khaled and H. Farouk, J. Mat. Sci. 21 (1986) 230. [7] E.E. Khawaja, M. Sakhawat Hussain and M.N. Khan, J. Non-Cryst. Solids 79 (1986) 275. [8] E.E. Shaisha, A.A. Bahgat, A.I. Sabry and N.A. Eissa, Phys. Chem. Glasses 26 No.4 (1985) 91. [9] J.W. Park and H. Chen, J. Non-Cryst. Solids 40 (1980) 515. [10] G. Kordas and H.J. Oel, Phys. Chem. Glasses 25 (3) (1984) 76. [11] A.F. Abbas, A.A. Ahmed, M.A. E1-Fiki and H.M. Eissa, Phys. Chem. Glasses 26 (4) (1985) 97. [12] A. Bishay, J. Am. Ceram. Soc. 43 (8) (1960) 417. [13] A.A. Ahmed, A.F. Abbas and F.M. Ezz El-Din, Phys, Chem. Glasses 25 (1) (1984) 22. [14] A.M. Sanad, I. Kashif, A.A. El-Sharkawy, A.A. EI-Saghier and H. Farouk, J. Mat. Sci. 21 (1986) 3483. [15] R. Yokota, Phys. Rev. 95 (1954) 1145. [16] A. Bishay, Phys. Chem. Glasses 2 (5) (1961) 169. [17] A. Bishay, J. Am. Ceram. Soc. 45 (1962) 389. [18] M.M. Morsi, S. El-Konsol and M.A. Adawi, J. Non-Cryst, Solids 58 (1983) 187. [19] C.R. Bamford, Phys. Chem. Glasses l (1960) 159. [20] C. Bettinali and P. Granati, Rend. Sc. Fis. Mat. e Nat. Lincei XLIV (1968) 669. [21] B.A. Henaish, M.A. Kenawy, A.F, Abbas and L.R. Salem, The First Egyptian-British Conference on Bio-Physics, Cairo University, October 1987.