A study on the investigation of gamma shielding properties of some metal borides

Progress in Nuclear Energy 115 (2019) 107–114

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A study on the investigation of gamma shielding properties of some metal borides

T

Hasan Gülbiçima,∗, M. Nureddin Türkanb, Mecit Aksuc, Sefa Durmuşc a

Department of Radiological Science, Institute of Health Science, Ondokuz Mayis University, 55139, Samsun, Turkey Department of Engineering Physics, Istanbul Medeniyet University Faculty of Engineering and Natural Sciences, 34720, Istanbul, Turkey c Department of Chemistry, Duzce University Faculty of Science and Arts, 81620, Duzce, Turkey b

ARTICLE INFO

ABSTRACT

Keywords: Gadolinium Gamma radiation Monte-Carlo Neodymium Samarium Shielding

In this study, the gamma radiation absorption capabilities of some metal borides were studied by using Monte Carlo simulation method. So, the mass attenuation coefficients, μm, the half value layer, HVL, the tenth value layer, TVL and the mean free path, MFP values of the NdB6, SmB6 and GdB6 were calculated by means of EGSnrc particle transport code and XCOM program theoretically within the energy range 0.125–5 MeV. It was seen that there is a quite successful consistency (t = 0.00049, p = 0.99961) between the simulated results and calculated values obtained by NIST's XCOM photon cross-section database. Those computational results for the synthesized compounds have also been compared with lead and vermiculite which have concluded that NdB6, SmB6, and GdB6 are good candidates for gamma shielding applications. These materials were sythesized by magnesiothermic reduction in open air. Stoichiometric amounts of M2O3, B2O3 and Mg (20% excess) were mixed, where MIII is a lanthanide metal (NdIII, SmIII and GdIII) ion. Mixture was heated to 700 °C, 800 °C and 900 °C. Optimum reaction temperature and reaction time were found by X-Ray Diffraction (XRD) analysis and Scannning Electron Microscopy (SEM). By fixing the reaction temperature, reaction time has changed as 1, 2, 3, 4 and 5 h to obtain nano crystals with homogeneous morphology. It was found that optimum reaction temperature and reaction time of NdB6 is 700 °C and 3 h, for SmB6 700 °C and 1 h for GdB6 900 °C.

1. Introduction Since the use of radioactive sources in different areas of science (such as radiation biophysics and shielding, nuclear industry, space research applications and agriculture, etc.) has been increasing day by day, the study of photon interactions with matter has attained a significant importance. Since modeling the photon attenuation through materials in computer environment gives flexibility and ease of use, instead of performing an experimental determination of mass attenuation of different composite materials, there are some attempts of Monte Carlo calculations (Dong et al., 2017a,b; Medhat, 2015; Ozyurt et al., 2018; Sardari et al., 2009; Singh et al., 2013, 2015; Tarim et al., 2013, 2017; Tekin and Manici, 2017; Tekin et al., 2017; Yang et al., 2017) that are guiding us to get a theoretical conclusion for further shielding experiments. This work covers two main parts; the first part contains the theoretical calculations for gamma shielding properties of such synthesized materials using Monte Carlo method and the second one covers the experimental studies discussing the optimization of synthesis of some

∗

metal borides with the help of magnesiothermic reduction method. Metal borides are divided into two groups, first is metal rich (MxBy, x > y) group, the latter is a boron rich group (M x By, y > x). Metal borides have geometries that determine their physical and chemical behavior as material. So they may have a variety of geometries depending upon the group that it belongs to. For example, metal rich ones are cluster compounds that have more metal when compared to boron. This type of compounds have high surface hardness and corrosion resistances. Boron rich compounds comprise different cluster compounds with different geometries. Increase in boron content results in increase of thermionic properties and decrease of work function. There are many ways to synthesize rare earth borides which have tendency to form boron rich compounds, such as MB4 and MB6 where M denotes lanthanide metal ion (Aksu and Aydin, 2013, 2010; Aprea et al., 2013; Novikov et al., 2016a,b; Sonber et al., 2014; Zou et al., 2006). Most of the ways for production of rare earth borides are not feasible for mass production since methods require vacuum conditions, high temperature and expensive chemicals. In this work, we synthesized MB6 (M: Gd, Sm and Nd) by

Corresponding author. E-mail address: [email protected] (H. Gülbiçim).

https://doi.org/10.1016/j.pnucene.2019.03.022 Received 7 July 2018; Received in revised form 3 February 2019; Accepted 17 March 2019 0149-1970/ © 2019 Published by Elsevier Ltd.

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magnesiothermic reduction in the open air, for the reaction scheme given by:

6B2 O3 + M2 O3 + 21MG

them pass through the third region without doing any interaction and deflection along their paths. The linear attenuation coefficients of the samples are calculated by using Beer-Lambert law (I = I0e−μx), where I0 is the total photon number simulated, I is the transmitted photons to the third region without scattering, μ is the linear attenuation coefficient and t is the thickness of material. The mass attenuation coefficients are obtained by dividing μ to ρ, which is the density of matter. The half value layer, HVL, the tenth value layer, TVL and the mean free path, MFP are other significant parameters used to compare materials against each other in terms of revealing their shielding abilities. These parameters are generated from the linear attenuation coefficients by using the exponential absorption law. If the number of transmitted photons is half of the incoming photons, HVL is calculated as 0.693/μ. If the number of transmitted photons is one tenth of the incoming photons, TVL is calculated as 2.3026/μ. MFP is calculated by taking the inverse of the linear attenuation coefficient (1/μ).

2MB6 + 21MgO

The effects of reaction parameters (temperature, time) on synthesized compounds are illustrated in Section 2.3. 2. Theoretical and experimental studies 2.1. Monte Carlo calculations In recent years, Monte Carlo (MC) technique has been commonly used to solve physical problems by simulation. Especially, because of its cost effectiveness and the design of difficult experiments, this method is preferred to model radiation-matter interactions in the field of industry, radiation and medical physics. Dose calculations, detector and radiation shielding material designs having complex geometry are main application area of this technique. The EGS (Electron Gamma Shower) is a general-purpose software toolkit for the MC simulation of coupled electron and photons in an arbitrary three dimensional geometry with the energies above a few keV up to hundreds of GeV (Kawrakow and Rogers, 2000). In this study, enhanced version called EGSnrc program code was used for calculation of the radiation shielding parameters, μ/ρ of samples. For MC calculations, firstly main required parameters such as photon energy, material and geometry definitions were defined to execute correctly the modified user code completed in the user area of EGSnrc. For determination of material data, PEGS4 code which is the sub-module of EGSnrc was used to produce the cross-sections of the selected samples in the appropriate format. The energy ranges for particle transport were chosen to be AE = 0.521, UE = 1.511, AP = 0.001 and UP = 10 MeV in PEGS4 data sets. AE and AP are the lower and upper energy limits of the electron to be transported respectively. UE and UP are the lower and upper energy limits for the photons, respectively. Particle transport cannot be performed outside these ranges. Note that the electron rest-mass energy (0.511 MeV) is also added to the energy limit values of the electrons. In other words, when the electron lower limit energy is written as 0.521 MeV, this means that the electrons below 10 keV cannot be simulated. The total geometry model for particle transport is shown in Fig. 1. In this simulation, three volumetric regions on xyz axes are defined to assign media and to determine material thickness. The first and third region are composed of vacuum and the second region has the features of selected materials. Narrow beam photons which are parallel to the zaxis are initiated for the simulation from the first region (in front of the relevant material) towards the third region. These photons are absorbed completely or scattered with low energy at different angles as they pass through matter in the second region by some physical processes such as photoelectric effect, Compton scattering, and pair production. Knockon electrons and Bremsstrahlung photons can also be created in this process and they are included in the simulation if they occur. Some of

2.2. XCOM calculations In addition, the mass attenuation coefficients of the aforementioned samples are calculated by using XCOM program theoretically. This program has the ability to generate mass attenuation coefficients of different types of material structures such as element, compound and mixture in the wide photon energy range from 1 keV up to 100 GeV (Berger et al., 2010). In this software, the entries to be used for elements can be used as atomic numbers or atomic symbols. For compounds, chemical formulas should be entered as standard chemical notation. Elemental or compound components may be available inside mixtures. So, for mixtures, the user must specify the chemical symbol or formula by a fraction by weight for each component. 2.3. Synthesis and optimization of metal borides Borontrioxide (B2O3) was obtained by heating boric acid (H3BO3) at 900 °C (Scheme 2).

2H3 BO3 (s )

B2 O3 (s ) + 3H2 O (g )

To illustrate the effect of reaction temperature three reactions were employed at 700 °C, 800 °C and 900 °C. Reaction times were determined by the reaction temperature and used as 1, 2, 3, 4 and 5 h. Stoichiometric amounts of reactants were used according to Scheme 1. 2.3.1. Reduction of Nd2O3 1 mmol Nd2O3, 6 mmol B2O3 and 25 mmol Mg (excess 20%) mixed in a porcelain crucible. Crucible was heated in a muffle furnace. To determine the temperature parameter, three experiment were run at 700 °C, 800 °C and 900 °C. Resultant mixture was put in concentrated nitric acid solution for 4 h. Filtered two times with distilled water, then dried at 120 °C in oven. A scan rate, step size and 2θ range of the samples was 0.1°/s, 0.013° and 10-90°, respectively. According to XRD analyses 700 °C is suitable reaction temperature (Fig. 2). By setting the reaction temperature as 700 °C, five experiments were set by changing the time as 1, 2, 3, 4 and 5 h. SEM images of NdB6 are given in Figs. 3–7. 2.4. Reduction of Sm2O3 1 mmol Nd2O3, 6 mmol B2O3 and 25 mmol Mg (excess 20%) mixed in a porcelain crucible. Crucible was heated in a muffle furnace. To determine the temperature parameter three experiment were run at 700 °C, 800 °C and 900 °C. Resultant mixture was put in concentrated nitric acid solution for 4 h. Filtered two times with distilled water, then

Fig. 1. Total geometry for Monte Carlo simulation.

Scheme 1. Reaction of Magnesiothermic reduction. 108

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Scheme 2. Dehydration of boric acid.

Fig. 2. XRD patterns of NdB6. Fig. 5. SEM image of NdB6 obtained at 700 °C and 3 h reaction time.

Fig. 3. SEM image of NdB6 obtained at 700 °C and 1 h reaction time. Fig. 6. SEM image of NdB6 obtained at 700 °C and 4 h reaction time.

Fig. 4. SEM image of NdB6 obtained at 700 °C and 2 h reaction time. Fig. 7. SEM image of NdB6 obtained at 700 °C and 5 h reaction time.

dried at 120 °C in oven. According to XRD analyses, 700 °C is suitable reaction temperature (Fig. 8). By setting the reaction temperature as 700 °C, five experiment were set by changing the time as 1, 2, 3, 4, and 5 h. SEM images of GdB6 are given in Figs. 15–19.

in a porcelain crucible. Crucible was heated in a muffle furnace. To determine the temperature parameter three experiment were run at 700 °C, 800 °C and 900 °C. Resultant mixture was put in concentrated nitric acid solution for 4 h. Filtered two times with distilled water, then dried at 120 °C in oven. According to XRD analyses, 900 °C is suitable reaction temperature (Fig. 14).

2.4.1. Reduction of Gd2O3 1 mmol Gd2O3, 6 mmol B2O3 and 25 mmol Mg (excess 20%) mixed 109

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Fig. 8. XRD patterns of SmB6.

Fig. 11. SEM image of SmB6 obtained at 700 °C and 3 h reaction time.

Fig. 9. SEM image of SmB6 obtained at 700 °C and 1 h reaction time.

Fig. 12. SEM image of SmB6 obtained at 700 °C and 4 h reaction time.

Fig. 10. SEM image of SmB6 obtained at 700 °C and 2 h reaction time.

By setting the reaction temperature as 700 °C, five experiment were set by changing the time as 1, 2, 3, 4, and 5 h. SEM images of GdB6 are given in Figs. 15–19.

Fig. 13. SEM image of SmB6 obtained at 700 °C and 5 h reaction time.

3. Results and discussion

of X-Ray Diffraction patterns (Fig. 2). Setting the temperature to 700 °C, reaction times were changed as 1, 2, 3, 4, and 5 h. Effect of reaction time on morphologies of the samples were investigated. Surface analysis of the samples were done via Scanning Electron Microscopic images (Fig. 3). SEM images of the sample obtained for 1 h reaction time show that

Melting point of magnesium is 650 °C, so it is liquid at reaction temperature. Due to the loss and oxidation of Mg may appear by vaporisation at reaction temperature, excess amount of it (20%) was used in all experiments. Borides of lanthanides are insoluble in nitric acid, to get rid of MgO formed after the reaction concentrated nitric acid was used. 700 °C is optimum temperature for synthesis of NdB6 by analysis 110

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Fig. 14. XRD patterns of GdB6.

Fig. 17. SEM image of GdB6 obtained at 700 °C and 3 h reaction time.

Fig. 15. SEM image of GdB6 obtained at 700 °C and 1 h reaction time.

Fig. 18. SEM image of GdB6 obtained at 700 °C and 4 h reaction time.

Fig. 16. SEM image of GdB6 obtained at 700 °C and 2 h reaction time.

crystalline samples have semi cubic and semi spherical shapes. They are also heterogeneous (Fig. 4). When the reaction time is 2 h, sample has cubic and prismatic shape with sharp lines with micro sizes (Fig. 5). Products with heterogeneous morphology and nano sizes were obtained when the reaction time was kept as 3 h. A mixture of nano and micro sized products was obtained when the reaction time was adjusted to 4 h (Fig. 6). It has mainly cubic shape, but there seem to be spherical shapes as well because of sinterization. Product obtained when the reaction time is 5 h has heterogeneous morphology and microsized rod structures (Fig. 7). 700 °C is optimum temperature for synthesis of SmB6 by analysis of

Fig. 19. SEM image of GdB6 obtained at 700 °C and 5 h reaction time.

X-Ray Diffraction patterns (Fig. 7). Setting the temperature to 700 °C, reaction times were changed as 1, 2, 3, 4, and 5 h. Effect of reaction time on morphologies of the samples were investigated. Surface analysis of the samples were carried out via Scanning Electron Microscopic images. (Figs. 9–13). All of the products obtained by changing the reaction time gave microsized structures with heterogeneous 111

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morphology. It was found that 900 °C is suitable reaction temperature for synthesis of GdB6 by analysis of XRD patterns (Fig. 14) Reaction time parameter was adjusted as 1, 2, 3, 4, and 5 h by keeping the temperature constant. SEM images of all samples were analysed. Nano sized GdB6 was obtained when reaction time is 1, 2 and 3 h (Figs. 15–17). Samples have heterogeneous morphology with no significant geometrical shape. By adjusting the reaction time as 4 and 5 h nanosized GdB6 were obtained with homogeneous morphology (Fig. 18). Spherical shapes were observed. Nano sized products changed their geometrical shape to spherical because of sinterization effect. It seems to be rather agglomerized when the reaction time is 5 h (Fig. 19). It was decided that the optimum reaction conditions for production of GdB6 are 900 °C reaction temperature and 4 h reaction time. Agglomeration appearing because of Van der Waals forces has an effect on quality of products. This effect resulted with different reaction times. Variation of density takes place during sinterization. This resulted with broken crystal growth. The mass attenuation coefficients obtained by both EGS and XCOM for the synthesized materials as well as lead and vermiculite were given in Table 1 in the energy range 0.125–5.00 MeV. The μm variations of the relevant materials were also plotted as a function of incident photon energy in Fig. 20 in order to show difference between them clearly. The comparison of HVL, TVL and MFP values of the samples and the accuracy of these parameters were presented in Tables 2–4. It is clearly seen from the figure that there is a good agreement between the simulated results and the theoretical ones (σ ≤ 0.001). Ttest analysis was performed on the obtained results to make statistical evaluation. The t-value and the p-value obtained according to the t-test analysis result were 0.00049 and 0.99961, respectively. The mass attenuation coefficients are exponentially decreasing with increasing photon energy. The μm values of the samples are rapidly decreasing at low energies below 0.5 MeV. The main reason of this rapid decrease is because of the fact that the photoelectric absorption is more dominant in this energy region in terms of the interaction process carrying out between photon and matter. However, it is also observed from the figure that there are a few discontinuous jumps for some specimens in this region. This may be attributed to the absorption edges of elements called as K, L and M. The decrease of μm values is varied slightly in the energy range between 0.5 and 3.0 MeV, where the Compton scattering is more dominant interaction process in this region known as intermediate energy region. At higher energies above 3 MeV, the μm values increase a little bit and then remain constant, where the pair production process is more dominant in proportion to the others. Although density is an important parameter for gamma ray shielding, lightness and some other parameters (eg. weight, cost, storage, health effect, etc.) are also required for the materials to be

Fig. 20. Variations of the mass attenuation coefficients of the investigated samples calculated by XCOM and EGS.

investigated and evaluated in this area. Vermiculite, for example, is a very light-weight material studied by (Gulbicim et al., 2017) as an alternating shielding material for gamma rays, both experimentally and theoretically. Therefore, the synthesized materials were compared with lead and vermiculite in terms of shielding efficiency. Because one of them, lead (known as standard material), is very dense and the other is very light-weight. The synthesized materials have less in weight than half of the lead (GdB6: 5.31 g/cm3, NdB6: 4.93 g/cm3, SmB6: 5.04 g/ cm3, Lead: 11.34 g/cm3 and Vermiculite: 2.5 g/cm3). Even if the new synthesized NdB6, SmB6, and GdB6 have advantages, they also have disadvantages of having slightly more cost and more heaviness when compared to lead. In many practical applications of gamma radiation in medicine and industry, the energy range of gamma rays are between 0.08 and 1 MeV. In diagnostic nuclear medicine mostly used radionuclide is Tc-99m and it emits about 0.14 MeV gamma rays. Technicians use lead panel placed between them and patient for protecting from gamma radiation. If NdB6, SmB6 and GdB6 are used as the materials for protection they are needed to have heavier panel when compared to lead because of their lower gamma attenuation values than the those of lead. Some chemical and physical properties of such synthesized metal borides are given in Table 5. Their molecular linear formula and atomic weights were obtained as a result of XRD analysis. Their density values are retrieved from https://www.americanelements.com/ rare-earths.html (American Elements Advanced Materials Data Sheet) to be used in simulations. Theoretical results of lead and vermiculite are taken from the study published by (Gulbicim et al., 2017). As can be understood from the obtained data, it is observed that

Table 1 The mass attenuation coefficients μm (cm2/g) calculated by XCOM and EGS for relevant materials. Energy

GdB6

NdB6

SmB6

(MeV)

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

0.125 0.200 0.300 0.384 0.500 0.662 0.800 1.000 1.250 1.500 2.000 3.000 5.000

1.204 0.396 0.186 0.132 0.099 0.078 0.068 0.059 0.052 0.047 0.042 0.037 0.034

1.204 0.395 0.185 0.131 0.099 0.078 0.068 0.059 0.052 0.047 0.042 0.037 0.034

1.018 0.343 0.169 0.123 0.095 0.077 0.068 0.059 0.052 0.047 0.042 0.037 0.034

1.018 0.343 0.169 0.123 0.095 0.077 0.068 0.059 0.052 0.047 0.042 0.037 0.034

1.111 0.368 0.177 0.127 0.097 0.078 0.068 0.059 0.052 0.047 0.042 0.037 0.034

1.111 0.369 0.177 0.127 0.097 0.076 0.068 0.059 0.052 0.047 0.042 0.037 0.034

3.042 0.936 0.373 0.231 0.150 0.103 0.084 0.068 0.057 0.051 0.045 0.042 0.043

3.023 0.936 0.373 0.231 0.150 0.104 0.084 0.068 0.057 0.051 0.045 0.042 0.043

0.153 0.126 0.107 0.097 0.088 0.077 0.070 0.064 0.057 0.052 0.045 0.036 0.029

0.153 0.125 0.107 0.097 0.088 0.077 0.071 0.064 0.057 0.052 0.045 0.037 0.029

112

Lead

Vermiculite

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Table 2 Variations of the half value layer (HVL) calculated by EGS and XCOM codes. Energy

GdB6

NdB6

SmB6

Lead

Vermiculite

(MeV)

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

0.125 0.200 0.300 0.384 0.500 0.662 0.800 1.000 1.250 1.500 2.000 3.000 5.000

0.108 0.330 0.704 0.992 1.317 1.670 1.909 2.205 2.524 2.771 3.144 3.555 3.814

0.108 0.330 0.703 0.993 1.318 1.669 1.908 2.205 2.520 2.771 3.137 3.547 3.794

0.138 0.410 0.833 1.142 1.476 1.833 2.082 2.390 2.721 2.980 3.382 3.833 4.151

0.138 0.410 0.834 1.143 1.478 1.833 2.079 2.423 2.708 2.978 3.371 3.830 4.147

0.123 0.371 0.773 1.074 1.408 1.765 2.007 2.317 2.639 2.896 3.280 3.725 3.989

0.123 0.370 0.772 1.074 1.408 1.764 2.007 2.313 2.634 2.896 3.278 3.714 3.997

0.020 0.065 0.164 0.265 0.409 0.592 0.727 0.900 1.078 1.203 1.351 1.456 1.436

0.020 0.065 0.164 0.265 0.408 0.590 0.727 0.899 1.076 1.201 1.349 1.455 1.435

1.813 2.209 2.589 2.846 3.165 3.586 3.936 4.341 4.852 5.366 6.180 7.626 9.583

1.815 2.215 2.583 2.846 3.167 3.581 3.904 4.338 4.854 5.320 6.174 7.574 9.591

Table 3 Variations of the tenth value layer (TVL) calculated by EGS and XCOM codes. Energy

GdB6

NdB6

SmB6

Lead

Vermiculite

(MeV)

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

0.125 0.200 0.300 0.384 0.500 0.662 0.800 1.000 1.250 1.500 2.000 3.000 5.000

0.360 1.096 2.338 3.297 4.377 5.549 6.343 7.342 8.388 9.206 10.446 11.811 12.674

0.360 1.096 2.336 3.297 4.380 5.545 6.340 7.325 8.371 9.206 10.424 11.784 12.606

0.459 1.362 2.767 3.795 4.904 6.092 6.917 7.940 9.040 9.902 11.236 12.736 13.791

0.459 1.361 2.771 3.797 4.911 6.089 6.909 8.052 8.999 9.895 11.201 12.726 13.778

0.409 1.234 2.569 3.570 4.677 5.863 6.669 7.698 8.768 9.620 10.897 12.378 13.253

0.409 1.231 2.566 3.568 4.677 5.860 6.669 7.685 8.751 9.622 10.891 12.341 13.279

0.067 0.217 0.544 0.880 1.358 1.967 2.417 2.993 3.582 3.996 4.490 4.839 4.770

0.067 0.217 0.544 0.879 1.354 1.961 2.413 2.985 3.573 3.988 4.480 4.832 4.764

6.025 7.338 8.604 9.455 10.517 11.915 13.077 14.423 16.123 17.828 20.534 25.337 31.842

6.031 7.362 8.584 9.456 10.526 11.900 12.972 14.414 16.130 17.678 20.513 25.165 31.869

Table 4 Variations of the mean free path (MFP) calculated by EGS and XCOM codes. Energy

GdB6

NdB6

SmB6

(MeV)

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

EGS

XCOM

0.125 0.200 0.300 0.384 0.500 0.662 0.800 1.000 1.250 1.500 2.000 3.000 5.000

0.156 0.476 1.015 1.432 1.901 2.410 2.755 3.189 3.643 3.998 4.537 5.129 5.504

0.156 0.476 1.015 1.432 1.902 2.408 2.753 3.181 3.636 3.998 4.527 5.118 5.475

0.199 0.592 1.202 1.648 2.130 2.646 3.004 3.449 3.926 4.300 4.880 5.531 5.989

0.199 0.591 1.203 1.649 2.132 2.645 3.001 3.497 3.908 4.298 4.864 5.527 5.984

0.178 0.536 1.116 1.550 2.031 2.546 2.896 3.343 3.808 4.178 4.732 5.376 5.756

0.178 0.534 1.114 1.549 2.031 2.545 2.896 3.337 3.800 4.179 4.730 5.360 5.767

0.029 0.094 0.236 0.382 0.590 0.854 1.050 1.300 1.556 1.736 1.950 2.101 2.072

0.029 0.094 0.236 0.382 0.588 0.852 1.048 1.296 1.552 1.732 1.946 2.099 2.069

2.617 3.187 3.737 4.106 4.567 5.175 5.679 6.264 7.002 7.743 8.918 11.004 13.829

2.619 3.197 3.728 4.106 4.571 5.168 5.634 6.260 7.005 7.678 8.909 10.929 13.840

Weight (%) Metal B

Exact Mass (g/mol)

Density (g/cm3)

GdB6 NdB6 SdB6

70.976 68.979 69.945

222.984 209.108 217.976

5.31 4.93 5.07

29.203 31.021 30.054

Vermiculite

lead and harmless to health, easier to process than vermiculite, and also they can be produced in abundant quantities. So, some concluded results are as follows;

Table 5 Chemical composition and the density of samples. Molecular Formula

Lead

• Optimum reaction condition of solid state reaction for the synthesis of Lanthanide (Gd, Sm, Nd) hexa borides was obtained. • Changing reaction time has little effect on crystal formation. • The results of studying the attenuation coefficient for such materials

there is a good agreement between the XCOM and the simulation results. In addition, these materials have significant advantages in terms of shielding properties due to the fact that they are much lighter than

• 113

are in very good agreement with the previous results of shielding materials (lead, vermiculite). At the end, it was seen that synthesized NdB6, SmB6, and GdB6 have

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the properties of a good absorber for gamma radiation and it is very reasonable to think that those materials may be accepted as alternating shielding materials in industrial area.

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4. Conclusion Interest to the boron rich lanthanide borides having peculiar properties has been increasing from day to day. In this study, the synthesis of such borides (GdB6, NdB6 and SmB6) was experimentally performed by magnesiothermic reduction technique firstly, and then the optimum reaction temperature and reaction time of these synthesized materials were also determined by XRD and SEM analyzes. In addition, the gamma shielding capability of the synthesized materials was studied by Monte-Carlo simulation method. This is a well accepted method producing more sensitive results for the last decades. To do this, the EGSnrc code was used to determine the mass attenuation coefficients of the synthesized materials. The energy ranges of the simulated gamma photons have been changed from 0.125 to 5 MeV. The mass attenuation coefficient values obtained were compared with the WinXCom results. The obtained results showed that there were statistical deviations of less than 0.1%. The same simulation process were performed for lead and vermiculite due to understanding of the shielding capabilities of the synthesized materials. It is concluded from the obtained results that such materials are a good candidate for gamma ray shielding in those areas such as nuclear medicine, industry and nuclear power plant. Although they have particularly the density as much as half of the lead, the synthesized such materials have the almost same radiation shielding capability to compete with the lead. Acknowledgement This work was performed within the projects partially supported by İstanbul Medeniyet University under grand F-GAP-2018-1289 and by Düzce University under grand DÜBAP:2012.05.03.098. Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.pnucene.2019.03.022. References Aksu, M., Aydin, E., 2013. Nano and microsized EuB6 via magnesiothermic reduction. J. Ceram. Process. Res. 14 (1), 47. Aksu, M., Koyuncu, U., Erol, M., 2010. Fast and low cost synthesis of lab4 and LaB6 nanowires. Middle East J. Sci. Res. 5 (2), 101106. Aprea, A., Maspero, A., Masciocchi, N., Guagliardi, A., Albisetti, A.F., Giunchi, G., 2013. Nanosized rare-earth hexaborides: low temperature preparation and microstructural analysis. Solid State Sci. 21, 3236. https://doi.org/10.1016/j.solidstate sciences. 2013.04.001. Berger, M., Hubbell, J., Seltzer, S., Chang, J., Coursey, J., Sukumar, R., Zucker, D., Olsen, K., 2010. Xcom: Photon Cross Sections Database, Nist Standard Reference Database (Xgam). Dong, M., El-Mallawany, R., Sayyed, M., Tekin, H., 2017a. Shielding properties of 80teo25tio2(15x) wo3xanom glasses using winxcom and mcnp5 code. Radiat. Phys. Chem. 141, 172178. https://doi.org/10.1016/j.rad physchem.2017.07.006 http:// www.sciencedirect.com/science/article/pii/S0969806X17301391. Dong, M., Sayyed, M., Lakshminarayana, G., Celikbilek Ersundu, M., Ersundu, A., Nayar,

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