Gamma radiation shielding and optical properties measurements of zinc bismuth borate glasses

Annals of Nuclear Energy 68 (2014) 4–9

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Gamma radiation shielding and optical properties measurements of zinc bismuth borate glasses P. Yasaka a, N. Pattanaboonmee a, H.J. Kim b, P. Limkitjaroenporn c, J. Kaewkhao c,⇑ a

Department of Physics, Faculty of Science, King Mongkut’s University of Technology Thonburi, Bangkok 10140, Thailand Department of Physics, Kyungpook National University, Deagu 702-701, Korea c Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom 73000, Thailand b

a r t i c l e

i n f o

Article history: Received 14 August 2013 Received in revised form 15 December 2013 Accepted 24 December 2013 Available online 21 January 2014 Keywords: Mass attenuation coefficient Effective atomic number Electron density Glass

a b s t r a c t In this work, the zinc bismuth borate (ZBB) glasses of the composition 10ZnO:xBi2O3:(90x)B2O3 (where x = 15, 20, 25 and 30 mol%) were prepared by the melt quenching technique. Their radiation shielding and optical properties were investigated and compared with theoretical calculations. The mass attenuation coefficients of ZBB glasses have been measured at different energies obtained from a Compton scattering technique. The results show a decrease of the mass attenuation coefficient, effective atomic number and effective electron density values with increasing of gamma-ray energies; and good agreements between experimental and theoretical values. The glass samples with Bi2O3 concentrations higher than 25 mol% (25 and 30 mol%) were observed with lower mean free path (MFP) values than all the standard shielding concretes studied. These results are indications that the ZBB glasses in the present study may be developed as a lead-free radiation shielding material in the investigated energy range. Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, there has been an increasing interest in the synthesis and characterization of structure and physical properties of heavy metal oxide (HMO) glasses due to their high refractive index, high density, high nonlinear optical susceptibility, high infrared transparency and good radiation shielding for c-rays. Heavy metal oxide (HMO) based glasses such as bismuth oxide based glasses have attracted the scientific community due to its important applications of thermal and mechanical sensors, reflecting windows, glass ceramics’ etc. (Stehle et al., 1998; Luciana et al., 2000; Cheng et al., 2008; Ali and Shaaban, 2008). Bi2O3 possess high refractive index, and exhibit high optical basicity, large polarizability and large optical susceptibility values (Dimitrov and Komatsu, 1999; Sindhu et al., 2005; Zhao et al., 2007) which make them ideal candidates for applications as infrared transmission components, ultra fast optical switches, and photonic devices. Moreover, the HMO such as lead or bismuth oxide containing glasses shows extremely high radioactive resistance because of their high density and atomic number. Currently lead oxide glasses have been restricted in various applications as it is hazardous to health and environment (Singh et al., 2010). In this context, bismuth oxide has been a suitable substitution of lead oxide in glass preparation for its high refractive index, non-toxicity, bismuth oxide alone cannot be

⇑ Corresponding author. Tel./fax: +66 34261065.

considered as network former due to small field strength of Bi3+ ion (Volf, 1984). However, in combination with other glass formers, the glass formation is possible in a relatively larger composition range (Gerth and Russel, 1997). Due to their ideal combination of high c-ray absorption coefficient and good glass forming ability as oxides, Bi is useful in c-ray absorbing windows in the nuclear industry and high energy physics (Brekhovskikh, 1957; Singh and Singh, 2004; El Batal, 2007; El Batal et al., 2007; Sharma et al., 2007; Kaewkhao et al., 2010; Ou et al., 2010). Boric acid (B2O3) is one of the most popular and excellent glass formers known to form glass at lower melting point with good transparency, high chemical durability, and thermal stability (Varshnaya, 1994). Because of its higher bond strength, smaller cation size and heat of fusion, so the structural investigation of boron in borate glass and related doped systems is one of the most attractive points. Zinc oxide (ZnO) is one of the important constituents and known for large amounts of ZnO can lower the melting temperatures in the formation of oxide glasses. The previous widely used constituent for lowering the melting temperature of glasses, PbO, is now unfavorable from the environment concerns point of view. This gives rise to the importance of lowering the melting temperature of glasses with large amounts of ZnO instead of PbO. Indeed for instance, ZnO–B2O3 glasses with high ZnO contents have been used as a sintering aid for the fabrication of low temperature eco-fired ceramics. Glasses with high ZnO contents; therefore, are very attractive materials (Inoue et al., 2010). From above reviews, the zinc bismuth borate (ZBB) glasses are preferred

E-mail address: [email protected] (J. Kaewkhao). 0306-4549/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.anucene.2013.12.015

P. Yasaka et al. / Annals of Nuclear Energy 68 (2014) 4–9

as they possess a low melting temperature (easy to synthesis), a large refractive index, and good physical and chemical properties (large glass forming region, high thermal stability, good rare earth ions solubility and a large window transmission) (Pal et al., 2012). Several studies on ZBB glass samples have been published so far. (Shanmugavelu and Ravi Kanth Kumar, 2012) studied on crystallization and phase transformation of the ZBB glasses heated at intermediate temperatures of the exothermic peaks to exhibit both the b-BiB3O6 and Bi2ZnOB2O6 phases which indicating the presence of surface and bulk crystallizations. (Nam Jin et al., 2009) studied the effect of ZnO on physical and optical properties of bismuth borate glasses and found the systematic variation in density and molar volume of these glasses with ZnO content. Differential thermal analysis (DTA) studies showed that the glass transition temperature (Tg) decreases from 423 °C to 390 °C as the content of ZnO increases. (Koushik et al., 2013) studied on electrical transport characteristics of ZBB glasses. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined by the imaginary parts of modulus peaks was 2.54 eV. The obtained value was close to the DC conduction which implying the involvement of similar energy barriers in both the processes. (Feng et al., 2010) studied on structure of ZBB system low-melting sealing glass. The results show that with the increase of B2O3 content, the transition temperature and softening temperature of ZBB glass system low-melting sealing glasses are increased, which leads to the increasing of liquid phase precipitation temperature and promotes the structure stability in the glass. (Shashidhar et al., 2008) reported on the effects of Bi2O3 content on physical, optical and vibrational studies in ZBB glasses. The variations in density and molar volume of the glasses with Bi2O3 content indicate that the glass structures are depended on Bi2O3 concentration. In the optical absorption analysis, it is observed that the optical band gap is decreased with increasing of bismuth content; this is corresponding with the increasing of optical basicity. Raman and infrared spectra analysis of ZBB glasses revealed that Bi3+ cations are incorporated in the glass network as [BiO3] pyramidal and [BiO6] octahedral units. Although the ZBB is a high density glass system and can be applied as radiation shielding materials, from literatures, there has been no report on radiation shielding properties of ZBB glass system. This work is therefore the first to report on radiation shielding properties of ZBB glass at different gamma-rays energies based on Compton scattering technique.

collision is inelastic in the sense that one photon is absorbed and another of different frequency and momentum is emitted. 2.2. Mass attenuation coefficient and effective atomic number The mass attenuation coefficient is written as follows (Limkitjaroenporn et al., 2011):

lm ¼

lm ¼

Ec0 ¼

Ec 1 þ ð1  cos hÞEc =mc2

ð1Þ

where Ec0 is the scattered gamma-ray energy, Ec is the incident gamma-ray energy, h is the scattering angle, and m is the electron rest mass. This formula is easily derived by assuming a relativistic collision between the gamma-ray and an electron initially at rest. Certainly, under normal circumstances, all the electrons in a medium are not free but bound. If the energy of the photon, however, is of the order of keV or more, while the binding energy of the electron is of the order of eV, the electron may be considered at rest. The

ð2Þ

X wi ðlm Þi

ð3Þ

i

where wi is weight fraction of element in an alloy, (lm)i is mass attenuation coefficient for individual element in alloy. The value of mass attenuation coefficients can be used to determine the total atomic cross-section (rt,a) by the following relation (Limkitjaroenporn et al., 2011):

ðlm Þalloy n X NA ðwi =Ai Þ

rt;a ¼

ð4Þ

i

where NA is Avogadro’s number, Ai is atomic weight of constituent element of alloy. The total electronic cross-section (rt,el) for the element is also expressed by the following formula (Limkitjaroenporn et al., 2011):

rt;el ¼

n 1 X f i Ai ð lm Þ i NA i Zi

ð5Þ

where fi is the number of atoms of element i relative to the total number of atoms of all elements in alloy, Zi is the atomic number of the ith element in alloy. Total atomic cross-section and total electronic cross-section are related to effective atomic number (Zeff) of the compound through the formula (Limkitjaroenporn et al., 2011):

Z eff ¼

rt;a rt;el

ð6Þ

The electron density can be defined as the number of electrons per unit mass, and it can be mathematically written as follows (Kaewkhao et al., 2008):

Nel ¼

The inelastic scattering of X-ray and gamma-ray from electrons had been known for a decade when the American researcher Compton (Trousfanidis, 1983) showed a mathematical relationship between incident and scattered gamma-ray energies as follows:

lnðI0 =IÞ qt

where q is the density of material (g/cm3), I0 and I are the incident and transmitted intensities and t is the thickness of absorber (cm).Theoretical values of the mass attenuation coefficients of mixture or compound have been calculated by WinXCom, based on the rule of mixture (Gerward et al., 2004):

2. Theoretical backgrounds 2.1. Compton scattering

5

lm rt;el

ð7Þ

3. Experimental setup and procedure The ZBB glasses of the composition 10ZnO:xBi2O3:(90x)B2O3 (where x = 15, 20, 25 and 30 mol%) were prepared by the melt quenching technique. All chemicals; ZnO, Bi2O3 and H3BO3, used in the present work were of high purity (Fluka, 99.99%). Appropriate amounts of the raw materials were thoroughly mixed and ground in a pestle and mortar for half an hour. The prepared mixture was then heated in a high purity alumina crucible at 1100 °C inside an electric furnace for about 3 h to ensure complete melting of all components. The melt was then quickly poured into a preheated stainless steel mold and annealed at 500 °C for 3 h before left it to cool down slowly to room temperature. The amount of the glass batch is about 30 g/melts. The chemical compositions of the glasses, prepared in the present work, are summarized in Table 1.

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P. Yasaka et al. / Annals of Nuclear Energy 68 (2014) 4–9 Table 1 Chemical compositions of the glasses (in mol%) prepared in the present work. [Bi2O3] in (mol%)

Glass system

15 20 25 30

10ZnO:15Bi2O3:75B2O3 10ZnO:20Bi2O3:70B2O3 10ZnO:25Bi2O3:65B2O3 10ZnO:30Bi2O3:60B2O3

The density of the glass is calculated according to the following formula:

q

¼

Wa  qb Wa  Wb

ð8Þ

where Wa and Wb are the weights of samples in air and xylene, respectively, and qb is the density of xylene (qb = 0.863 g/cm3). All weight measurements were conducted on a sensitive microbalance. The optical spectra of the prepared glass samples in the UV–VIS region from 400 to 700 nm were recorded at room temperature using a double-beam spectrophotometer (Variance, Cary-50). The schematic of the Compton scattering technique for mass attenuation coefficient measurement is shown in Fig. 1. The source system was mounted on a composite of adjustable stands. This setup can move in the transverse direction for proper beam alignment. The 137Cs radioactive source of 15 mCi (555 MBq) strength was obtained from the Office of Atom for Peace (OAP), Thailand. The aluminum rod was used as the scattering rod. The Compton scattered c-rays were measured on a rotatable 200  200 NaI(Tl) scintillator detector in the scattering plane having an energy resolution of 8% at 662 keV (BICRON model 2M2/2), with CANBERRA photomultiplier tube base model 802-5. The optimum set up distances between the source to the scatterer and from scatterer and detector were found equally at 20 cm. The spectra were recorded using a CANBERRA PC-based multi-channel analyzer (MCA). The spectrum on the MCA of detector gave instance counts in each of 1024 bins divided by voltage. To measure the angular dependence of Compton scattering, we first performed a calibration on the relating channel number of the MCA spectrum with the known energy of gamma-ray sources and varied the angle of the scatter detector. The scattering angles (h) were used to produce gamma-ray of

Fig. 2. Densities of ZBB glasses of different Bi2O3 concentrations.

different energies (Limkitjaroenporn et al., 2013). Kaewkhao et al. (2012) was the first group to apply the Compton scattering technique for measuring mass attenuation coefficient and has confirmed the validity and energy calibration of the system. The procedure for measuring mass attenuation coefficients of glass samples at different gamma-ray energies are described in our previous work (Limkitjaroenporn et al., 2013; Kaewkhao et al., 2012).

4. Results and discussions The density variation of the glass with Bi2O3 concentration is shown in Fig. 2. The density is seen to increase with additional content of Bi2O3 into the network. This indicates the replacing of B2O3 by Bi2O3; a relatively higher molecular weight, in the network and as the result increases the average density of the glass. The mass attenuation coefficients of ZBB glass of different Bi2O3 concentration measured at different gamma-ray energies are shown in Table 2. The experimental values of mass attenuation coefficients were evaluated from intensities of incident (I0) and transmitted (I) gamma-ray at a selected energy level. The

Fig. 1. Schematic of the Compton scattering technique for mass attenuation coefficient measurement.

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P. Yasaka et al. / Annals of Nuclear Energy 68 (2014) 4–9 Table 2 The mass attenuation coefficients of ZBB glasses of different Bi2O3 concentrations at different gamma-ray energies. Energy (keV)

[Bi2O3] = 15 mol%

lm(th) 223.02 ± 12.2 252.98 ± 14.2 287.28 ± 15.6 340.83 ± 16.1 398.97 ± 16.0 481.59 ± 20.7 562.68 ± 27.8 662.00 ± 18.1

lm(ex)

[Bi2O3] = 20 mol%

[Bi2O3] = 25 mol%

[Bi2O3] = 30 mol%

(102 cm2/g) (102 cm2/g)

%RD lm(th) %RD lm(th) %RD lm(th) %RD lm(ex) lm(ex) lm(ex) (102 cm2/g) (102 cm2/g) (102 cm2/g) (102 cm2/g) (102 cm2/g) (102 cm2/g)

44.73 34.81 27.54 20.72 16.44 12.95 10.92 9.332

0.92 1.49 1.74 1.59 1.40 0.93 0.64 0.89

44.32 ± 2.25 34.29 ± 2.02 28.02 ± 1.48 21.05 ± 1.01 16.67 ± 0.67 12.83 ± 0.53 10.99 ± 0.35 9.415 ± 0.287

49.87 38.49 30.17 22.39 17.55 13.62 11.36 9.614

49.32 ± 2.37 38.95 ± 1.98 30.25 ± 1.62 22.58 ± 1.14 17.29 ± 0.85 13.54 ± 0.62 11.58 ± 0.34 9.588 ± 0.276

1.10 1.20 0.27 0.85 1.48 0.59 1.94 0.27

53.85 41.34 32.20 23.69 18.40 14.14 11.70 9.832

54.12 ± 2.43 40.87 ± 2.04 32.71 ± 1.72 23.28 ± 1.11 18.17 ± 0.73 14.32 ± 0.72 11.75 ± 0.39 9.798 ± 0.311

0.50 1.14 1.58 1.73 1.25 1.27 0.43 0.35

56.97 43.58 33.80 24.71 19.07 14.55 11.97 10.00

56.77 ± 2.51 43.88 ± 1.99 34.14 ± 1.63 24.78 ± 1.07 18.86 ± 0.81 14.63 ± 0.77 11.82 ± 0.42 10.07 ± 0.362

0.35 0.69 1.01 0.28 1.10 0.55 1.25 0.70

Fig. 3. Experimental and theoretical values of the total mass attenuation coefficients of ZBB glasses at different energies. Fig. 5. Experimental and theoretical values of the effective atomic numbers of ZBB glasses at different energies.

Fig. 4. Experimental and theoretical values of the total mass attenuation coefficients of ZBB glasses of different Bi2O3 concentrations.

theoretical values of mass attenuation coefficients for all glass compositions and energies were calculated from WinXCom program. It has been found that the total mass attenuation coefficients of all the ZBB glasses were decreased exponentially with the increasing of gamma-ray energy, which indicates the increasing of total interaction. These trends were observed in the glasses for all Bi2O3 concentrations. In the following figures, line-style followed by number mol% (th) will be used to signify the theoretical values while point-style followed by number mol% (ex) signifies the

Fig. 6. Experimental and theoretical values of the effective electron densities of ZBB glasses at different energies.

experimental values. There are good agreements on the mass attenuation coefficients obtained experimentally and theoretically as shown in Fig. 3. The errors between the experimental and theoretical values could mainly be attributed to the non-stoichiometry in the glass formula as a result of high melting temperature. In Fig. 4, the total mass attenuation coefficients of the glasses are

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P. Yasaka et al. / Annals of Nuclear Energy 68 (2014) 4–9

Fig. 7. The photon mean free path of ZBB glasses at different energies compared with WinXCom results on some standard shielding materials.

tially toward high energy. This indicates there are more interactions of ZBB glasses with gamma-rays of low energies than high energies and hence more electrons as the results are generated at low energy. The Ne results are observed with similar trends to Zeff, both values are decreased exponentially toward high energies. Fig. 7. shows the photon mean free path (MFP) values of ZBB glasses at different energies compared with WinXCom results on some standard shielding materials. The compositions and densities of standard shielding materials were obtained from literature (Basher, 1997). The compositions were used for lm calculation by WinXCom. The linear attenuation coefficients (l) was obtained from l = lm q. Finally, the MFP were calculated using relation MFP = 1/u. The MFP represents the averaged travel distance between two successive photo interactions. The shorter MFP indicates more interaction of photons to material and hence posses the better shielding properties (Chanthima and Kaewkhao, 2013). In this work, MFP is longer with increasing of gamma-ray energies, reflecting that more penetrating power of gamma-rays at higher energy. In order to test for practical usage, it is necessary to compare the MFP of the glasses to some standard shielding concretes. It can be seen from Fig. 7, the steel-magnetite concrete performs the best as standard shielding material in the studied energy range. The ZBB glasses developed in this work with Bi2O3 content in the glass samples higher than 25 mol% (25 and 30 mol%) show lower MFP values against all the standard shielding concretes over the entire energy range. These results are good indications that the ZBB glasses in the present study may be developed as radiation shielding materials. For the glasses containing Bi2O3 of 15 and 20 mol%, they exhibit better shielding properties than steel-magnetite concrete only at energy below 398 keV and 481 keV; respectively. In addition, the optical absorption spectra of the ZBB glasses are shown in Fig. 8. The cut off wavelengths for ZBB glasses with increasing Bi2O3 concentration are found to shift toward longer wavelengths. 5. Conclusions

Fig. 8. Optical absorption spectra of the ZBB glasses of different Bi2O3 concentrations.

observed over Bi2O3 concentrations for the Compton scattering energies. The total mass attenuation coefficients are increased with the increase of Bi2O3 concentrations for all energies. The effect of Bi2O3 concentration on the total mass attenuation coefficients can easily be observed at lower energy; e.g. higher slope for the low energy line at 223.02 keV than the high energy line at 662 KeV. This result is due to different partial interactions contributed by different Bi2O3 concentrations in the glass samples. The effective atomic number (Zeff) of the ZBB glasses were calculated using Eq. (6) and the results are shown in Fig. 5. It is seen that the value of the Zeff were decreased with the increasing of gamma-ray energies. There are good agreements between experimental and theoretical values. Several experimental results published had found similar findings on the dependent of Zeff on the photon energy such are thermoluminescence materials (Shivalinge et al., 2004), alloy (Kaewkhao et al., 2008; Limkitjaroenporn et al., 2013), superconductor (Baltas et al., 2007), semiconductor (Erzeneoglu et al., 2006) and biological materials (Demet and Ahmet, 2012). The variation of effective electron densities (Ne) of ZBB glasses at different gamma-ray energies is shown in Fig. 6. The ZBB glasses show with higher Nel values at low energy then decrease exponen-

The zinc bismuth borate glasses (ZBB) were prepared at various Bi2O3 concentrations and characterized for their radiation shielding and optical properties. The results can be concluded as follows: – The measured values of mass attenuation coefficients, effective atomic number and effective electron density of the glasses decrease toward higher energy of gamma-rays and are in good agreements with theoretical values. – The ZBB glasses with Bi2O3 composition higher than 25 mol% (25 and 30 mol%) show lower values of MFP than all the standard shielding concretes in this studied. These results are good indications that the ZBB glasses in the present study can be used as radiation shielding materials. – For the glasses containing Bi2O3 of 15 and 20 mol%, they exhibit better shielding properties than steel-magnetite concrete at energies below 398 keV and 481 keV; respectively. The study results are useful for design a lead-free radiation shielding glass in the appropriate energy range. Acknowledgements The present work was partially supported by the National Research Council of Thailand (NRCT). The authors would like to thank Prof. L. Gerward for WinXCom software.

P. Yasaka et al. / Annals of Nuclear Energy 68 (2014) 4–9

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