Interaction of 662 kev Gamma-rays with Bismuth-based Glass Matrices

Transcription

1 Journal of the Korean Physical Society, Vol. 59, No. 2, August 2011, pp Interaction of 662 kev Gamma-rays with Bismuth-based Glass Matrices J. Kaewkhao Center of Excellence in Glass Technology and Materials Science (CEGM), Nakhon Pathom Rajabhat University, Nakhon Pathom 73000, Thailand and Thailand Center of Excellence in Physics, Commission of Higher Education, Ministry of Education, Bangkok 10400, Thailand K. Kirdsiri and P. Limkitjaroenporn Science Program, Faculty of Science and Technology, Nakhon Pathom Rajabhat University, Nakhon Pathom 73000, Thailand P. Limsuwan Department of Physics, Faculty of Science, King Mongkut s University of Technology Thonburi, Bangkok 10400, Thailand and Thailand Center of Excellence in Physics, Commission of Higher Education, Ministry of Education, Bangkok 10400, Thailand Jeongmin Park and H. J. Kim Department of Physics, Kyungpook National University, Daegu , Korea (Received 11 November 2010, in final form 21 March 2011) In this work, the Bi 2O 3-SiO 2 glass system was synthesized by using the melt-quenching method. The radiation shielding properties of the glass samples at various levels of bismuth content were measured at 662 kev by usage a 137 Cs radioactive source, and comparisons were made with values theoretically calculated by usage WinXCom. The experimentally obtained values were generally in good agreement with the theoretical ones. Furthermore, a comparison was made to a lead-borate glass system with the same level of additive. The radiation shielding properties were found to be improved with increasing Bi 2O 3 concentration. The different values of Compton scattering yielded a higher total mass attenuation coefficient for the bismuth-silicate glass than for the bismuth-borate glass. These results reflect the potential usefulness of bismuth-based glasses as new materials for lead-free radiation-shielding glasses. PACS numbers: Bh, a, g, Dm Keywords: Glass, Mass attenuation coefficient, Effective atomic number, Shielding DOI: /jkps I. INTRODUCTION Glass materials are possible alternatives for radiation shielding materials with two advantages brought by their transparency to visible light, and their properties can be modified by using composition and preparation techniques. In general, two conventional glass formers, silicate and borate glasses, are used in a variety of fields for glass production because of their suitable characteristic properties. Silicate glasses are the most commonly available commercial glasses due to ease of fabrication and excellent transmission of visible light [1]. In addition, the very high viscosity allows the glass to be formed, cooled and annealed without crystallizing. This makes mink110@hotmail.com; Fax: the material particularly useful for optical windows in various industries. During the last two decades, borate glasses have been investigated extensively, yet there is still a great interest in developing new glasses to suit the demands of both industry and technology. Boric oxide, B 2 O 3, acts as one of the most important glass formers and flux materials. Melts that are B 2 O 3 rich in compositions exhibit rather high viscosity and tend to form a glass structure. Good reviews on the radiation shielding properties of silicate and borate glasses have been published recently by several authors [1 4]. These results show that silicate and borate glasses can be used in radiation shielding materials. The toxicity of lead has become more apparent in recent years, so alloy and composite materials using bis

2 -662- Journal of the Korean Physical Society, Vol. 59, No. 2, August 2011 Table 1. Total mass attenuation coefficients at 662 kev of silicate and borate glass systems containing Bi 2O 3. Silicate glass (This work) Borate glass (taken from Ref. 10) % composition (µ of Bi m) th 10 2 (µ m) ex 10 2 (µ 2O 3 % RD. m) th 10 2 (µ m) ex 10 2 % RD. (cm 2 /g) (cm 2 /g) (cm 2 /g) (cm 2 /g) ± ± ± ± ± ± ± ± ± ± *RD = Relative difference of µ m between experiment and theory. Fig. 1. Experimental arrangement for the mass attenuation coefficients measurement. muth as a replacement for lead are increasingly assuming commercial importance. Bismuth oxide, Bi 2 O 3, is a promising gamma-ray shielding materials due to its high effective atomic number and strong absorption of gamma rays. Moreover, the toxicity of Bi and its biological effects have been estimated to be much less than those of Pb and Sb [5]. In the present study, bismuth silicate glass system were synthesized by using a meltquenching method, and a comparison study of the shielding parameters such as mass attenuation coefficients, effective atomic numbers and half value layer (HVL) was performed. The shielding parameters of bismuth-silicate and bismuth-borate glasses containing the same levels of bismuth concentration were comparatively studied. Furthermore, the comparison study was extended to leadborate glass so as to explore the potential of replacing lead in radiation shielding glass. II. EXPERIMENTS The xbi 2 O 3 :(100-x)SiO 2 glass samples for the composition range of x from 30 to 70 (weight %) were prepared by using the melt-quenching technique. The highpurity starting materials used in the preparation were 99.9% pure Bi 2 O 3 (Sigma-Aldrich) and 99.9% pure SiO 2 (Fluka). All chemicals were weighed accurately using an electrical balance, ground to fine powder and mixed thoroughly. The mixed powder batches, about 50 g, in an alumina crucible were melted at 1,250 C by placing them in an electrical furnace for an hour. The melts were then poured into polished stainless-steel molds. The quenched glasses were annealed at 500 C for 3 h to reduce the thermal stress and were then cooled to room temperature. At room temperature, the densities (ρ) of all glass samples were measured by using Archimedes s method with xylene as the immersion liquid. The arrangement for measuring the mass attenuation coefficients of the glass samples is shown in Fig. 1. The thickness selection and the error analysis are described in our previous works [6,7]. The theoretical mass attenuation coefficients of samples were calculated by using the WinXCom program, which provided the total mass attenuation coefficient and total attenuation cross section data for about 100 elements, as well as partial cross sections for incoherent and coherent scattering, photoelectric absorption and pair production, at energies from 1 kev to 100 GeV [8, 9]. The obtained values of the mass attenuation coefficients were then used to calculate the total interaction cross sections, and the effective atomic numbers of the glass samples. III. RESULTS AND DISCUSSION 1. Glass Density The densities of the prepared Bi 2 O 3 -SiO 2 glass system and the Bi 2 O 3 -B 2 O 3 glass system were in the ranges of 4.89 ± 0.03 to 5.69 ± 0.01 g/cm 3 and 4.21 ± 0.02 to 5.01

3 Interaction of 662 kev Gamma-rays with Bismuth-based Glass Matrices J. Kaewkhao et al Table 2. Photoelectric and coherent attenuation coefficients at 662 kev of silicate and borate glass systems containing Bi 2O 3. Photoelectric attenuation coefficient Coherent attenuation coefficient % of Bi 2O (cm 2 /g) 10 2 (cm 2 /g) Bi 2O 3-SiO 2 Bi 2O 3- B 2O 3 Bi 2O 3-SiO 2 Bi 2O 3- B 2O Fig. 2. Densities of the Bi 2O 3-SiO 2 and the Bi 2O 3-B 2O 3 glass systems. Fig. 3. Compton scattering interaction of silicate and borate glass systems containing Bi 2O 3 at 662 kev. ± 0.09 g/cm 3, respectively. The densities of both glass systems increased with increasing Bi 2 O 3 concentration. The Bi 2 O 3 -SiO 2 glasses prepared in our work gave higher densities than the Bi 2 O 3 -B 2 O 3 glasses over all ranges of Bi 2 O 3 content. Figure 2 shows density plots of the glass for both systems with equal Bi 2 O 3 concentrations. Note that, as labeled in the graph, the densities of the borate glasses were obtained from literature [10]. 2. Total and Partial Interactions Table 1 shows the experimental and the theoretical values of total mass attenuation coefficients of the silicate and borate glass systems. In general, the experimental values agreed with the theoretical values calculated using WinXCom. The Bi 2 O 3 -based silicate glass showed higher total mass attenuation coefficients than borate glass, implying that the photons are attenuated more in the silicate glass. This can be explained by the differences in Compton scattering in the glass matrices, as shown in Fig. 3. The total mass attenuation coefficients of the two systems increased with increasing of Bi 2 O 3 concentration. This is due to the increasing photoelectric absorption interaction of glass samples, calculated using WinXCom, as the values of photoelectric absorp- tion and other partial interactions in both glass systems are comparable when the content of Bi 2 O 3 is at the same level (Table 2). The data in Table 1 show systematic differences between the experimental and the theoretical values, which may caused by the non-stoichiometry of the glass after melting at high temperature. The decreases of Compton scattering for the two glass systems with increasing Bi 2 O 3 concentration are shown in Fig. 3. Moreover, Compton scattering was found to be the main interaction process in this work for all glass systems. This result can explain the differences in total mass attenuation values for the two glass systems. Meanwhile, in this work, the coherent scattering was found to have a smaller effect on the total mass attenuation coefficients for all glass systems (Table 2). Similar finding for various glass systems, such as PbO-B 2 O 3 glasses [6], PbO-SiO 2 glasses [1], ZnO-PbO-B 2 O 3 glasses [11], PbO- BaO-B 2 O 3 glasses, BaO-B 2 O 3 glasses [10], PbO-P 2 O 5 glasses, Bi 2 O 3 -P 2 O 5 glasses, and BaO-P 2 O 5 glasses [12], have been published in the literature. 3. Effective Atomic Numbers The effective atomic numbers are shown in Fig. 4. The results show that the effective atomic numbers of both

4 -664- Journal of the Korean Physical Society, Vol. 59, No. 2, August 2011 Fig. 4. Effective atomic numbers at 662 kev for silicate and borate glass systems containing Bi 2O 3. Fig. 6. Half value layer (HVL) of Bi 2O 3-SiO 2 glasses compared with those of some shielding glasses and some types of concrete at 662 kev. PbO-B 2 O 3 glass. Thus, adding Bi 2 O 3 in silicate glass may make the silicate glass a potential candidate, better than lead for a radiation shielding glass. IV. CONCLUSION Fig. 5. Effect of effective atomic number and density on the mass attenuation coefficient of Bi 2O 3-SiO 2 glasses at 662 kev. glass systems increased with increasing of Bi 2 O 3 concentration, corresponding with the increasing total mass attenuation coefficients in the glasses. These results are due to increasing photoelectric absorption, as shown in Table 2. We can conclude that atomic number has a greater effect on the mass attenuation coefficient than on the density as show in Fig. 5. From the theoretical approach, the photoelectric absorption is related to more the atomic number than Compton scattering; which depends more on the density of the glass, is [6]. Moreover, the effective atomic number of borate glass is lower than that of silicate glass, indicating a lower atomic cross section. Figure 6 shows a comparison of the half value layer of Bi 2 O 3 -SiO 2 glasses (this work) with those of some shielding glasses and some types of concrete [1]. The glass samples in this work show better shielding properties with the lower HVL values than ordinary, barite, and chromite concrete do, with another important advantage of being transparent with concrete being opaque. Moreover, the glass samples in this work gave better HVL results than In this work, the Bi 2 O 3 -SiO 2 glass system was synthesized, their radiation shielding parameters were investigated, and comparison studies were done. The experimentally obtained values were generally in good agreement with the values theoretically calculated using WinXCom. The radiation shielding properties were found to be improved with increasing Bi 2 O 3 concentration. The higher Compton scattering in the bismuthsilicate glass than in the bismuth-borate glass resulted in a higher total mass attenuation coefficient. The better shielding properties of the glasses, compared to some standard shielding concrete, suggest smaller size requirements with a strong advantage for transparency in the visible region. The comparison studies suggested that the Bi 2 O 3 -B 2 O 3 glass could be a better shielding material and could replace lead, a high-toxicity material of globally concern. ACKNOWLEDGMENTS The authors gratefully acknowledge Professor L. Gerward for providing the WinXCom program. J. Kaewkhao and P. Limkitjaroenporn give special thanks to the National Research Council of Thailand (NRCT) and the Commission of Higher Education (CHE) under the SP2 project. P. Limsuwan would like to thank King Mongkut s University of Technology Thonburi for partial funding under the National Research University project.

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