characterization and radiation shielding properties of

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Characterization and Radiation Shielding Properties of Philippine Natural Bentonite and Zeolite

Mon Bryan Z. Gili*, and Frederick C. Hila

Department of Science and Technology–Philippine Nuclear Research Institute (DOST-PNRI) Commonwealth Avenue, Diliman, Quezon City 1101 Philippines

In this paper, the investigation of the structural and radiation shielding characteristics of natural bentonite and zeolite was presented. XRD (X-ray diffraction) and SEM (scanning electron microscopy) were used to examine the structural properties and morphologies of the minerals. The Electron-Photon Interaction Cross Sections 2017 (EPICS2017) library through EpiXS software was used to obtain the photon shielding properties – including mass attenuation coefficients, mean free paths, half-value and tenth-value layers, effective atomic numbers, and buildup factors for energy absorption and exposure. The ESTAR web program and SRIM code were used to obtain electron and ion stopping powers and ranges. The neutron removal cross-sections and the fast and thermal attenuation factors were obtained using the Phy-X/PSD, MRCsC, and NGCal software. The results showed that the zeolite grain sizes were typically smaller than 50 µm, while the bentonite grain sizes were larger reaching 100 µm. It was found that both materials were significantly composed of mordenite and montmorillonite. The photon shielding quantities for both materials showed similar MFP, HVL, and TVL values with different buildup factor values at large penetration depths. The high-energy charged particle range within both materials described similar trends and values. The range of alpha particles was significantly smaller than the average grain sizes for both materials. The fast neutron removal cross-sections of zeolite and bentonite were significantly higher than for typical soil values. Both natural materials may be suitable candidate ingredients for radiation shielding composites, especially due to their natural abundance and unique properties.

Keywords: bentonite, electron, EpiXS, mass attenuation, neutron, zeolite

*Corresponding Author: [email protected]

INTRODUCTION

Ionizing radiation is a serious concern in nuclear power plants, nuclear research reactors, particle accelerators, space research, medical radiography and radiotherapy facilities, and large-scale irradiation facilities. Containing radiation and preventing it from causing physical harm to living organisms and their environment is an important part of any facility emitting potentially hazardous rays (Puišo et al. 2013). Protection against external radiation

depends on three important aspects: 1) the distance from the source of radiation, 2) the time of exposure to ionizing radiation, and 3) the shield between the source and the body to be protected. Among the three, the most controllable – especially when working with radioactive isotopes – is the use of shielding material. The design of radiation shielding depends on the type of source and its characteristics, installation type, and shielding materials characteristics (Puišo et al. 2013). The selection of material for shielding purposes is crucial as different kinds of radiation interact differently with these materials.

Philippine Journal of Science150 (6A): 1475-1488, December 2021ISSN 0031 - 7683Date Received: 23 Jun 2021

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To find material candidates for radiation shielding, one must consider several properties: heat diffusivity, heat resistance, gamma-ray and/or x-ray attenuation coefficients, cost-effectiveness, ability to mold, etc.

The radiation attenuation parameters such as mass attenuation coefficient, linear attenuation coefficient, half-value layer, mean free path, etc. provide a wide variety of information about radiation penetration and energy deposition in biological shielding and other dosimetric materials. Lead and concrete are conventional X-rays and gamma-ray shielding materials. It is important to look for cheap and locally available innovative alternate shielding material. The new material should be cost-effective, eco-friendly, abundant, and possibly have unique characteristics. In previous years, several relevant studies for the measurement of linear and mass attenuation coefficients for different materials such as building materials (Damla et al. 2011), soils (Hila et al. 2021b; Taqi and Khalil 2017), clays (Gili and Hila 2021; Mann et al. 2016), concretes (Gaikwad et al. 2018), cement (Türkmen et al. 2008), ceramics (Sayyed et al. 2021a), polymers (Hasan et al. 2019; Indrajati et al. 2015), marble (Akkurt et al. 2004), alloys (Almuqrin et al. 2021; Ekinci et al. 2021), and glasses (Al-Harbi et al. 2021; Sayyed et al. 2019, 2020, 2021b) have been carried out. Other important materials being studied are zeolites and bentonites, which both can filter radioactive waste (Kubota et al. 2012). Aside from being a potential shielding material, bentonite is commonly employed as a buffer for high-level nuclear waste (Galamboš et al. 2011).

Zeolites and bentonites are abundant natural materials with adsorption characteristics. Zeolites are a group of soft, mostly white aluminosilicate minerals of tectosilicate type of interconnected tetrahedra composed mostly of aluminum (Al), silicon (Si), and oxygen (O) atoms (Jha and Singh 2016). Zeolites occur as low-temperature (generally less than 200 °C) alteration products of volcanic and feldspathic rocks. They are known to crystallize in cavities of basalt as a result of diagenetic or hydrothermal alteration (Wise 2013). On the other hand, bentonite clay consists chiefly of crystalline clay minerals belonging to the smectite group, which are hydrous aluminum silicates containing Fe and Mg as well as either Na or Ca. Bentonite forms from the alteration of volcanic glass to clay minerals, which requires hydration (combination or taking up of water) and a loss of alkalis, bases, and possibly silica while preserving the textures of the original glass (Britannica, The Editors of Encyclopaedia 2021). Bentonite is mainly composed of montmorillonite (Uddin 2008) and other minor non-clay minerals where it has an overall negative charge, either in tetrahedral sheet or octahedral sheet form.

Several studies regarding the use of zeolites and bentonites

as shielding materials have been reported in recent years. Natural clinoptilolite-rich zeolite has been previously studied by Kurudirek et al. (2010), and cement containing zeolite aggregates have been studied by Türkmen et al. (2008) and Akkurt et al. (2010). In these studies, although zeolite did not exceed cement in shielding photons, zeolites can be easily enhanced as was reported by Puišo et al. (2013) wherein the adsorption of heavy ions (i.e. Pb, etc.) can have significant effects on radiation shielding characteristics. Furthermore, Indrajati et al. (2015) showed that the rubber composites containing zeolite had different properties such as swelling ratio and crosslink density, which depended on the zeolite content. On the other hand, bentonite-polymer composites have been studied by Hasan et al. (2019), Sallam et al. (2020), and Hager et al. (2019). It was emphasized by Hager et al. (2019) that the shielding characteristics of bentonite clays can be improved by mechanical compression. Bentonite-based ceramics were also studied by Asal et al. (2021), who emphasized that the abundance of bentonite and toxicity of other shielding alternatives could make bentonite ceramics a desirable radiation shielding material.

This present study characterizes the structure and radiation shielding parameters of Philippine natural zeolite (PNZ) and Philippine natural bentonite (PNB). The crystal structure and morphology of the samples were obtained via XRD and SEM. The photon shielding quantities were evaluated using the EPICS2017 library, which was interpolated using the EpiXS software. The photon shielding quantities included the mass attenuation coefficient, half-value layer, mean free path, effective atomic number, and buildup factors for energy absorption and exposure. The electron, proton, and alpha-particle shielding characteristics were obtained using the ESTAR web program and SRIM code. The fast neutron removal characteristics were obtained using the Phy-X/PSD and MRCsC software, and the neutron attenuation for fast and thermal neutrons was calculated using the NGCal software.

THEORETICAL ASPECTA useful concept in describing the attenuation of photon radiation in the matter is called photon cross-section, � (in barns atom–1). It is a measure of the probability that photons interact with matter by a particular process. The photon cross-section in a multi-element material can be taken as a weighted sum of the constituent elements’ cross-sections as shown in Equation 1, where 𝑓� is the atom fraction of the 𝑖�� element.

(1)

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Gili et al.: Characterization and Radiation Shielding

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The total atomic cross-section, , is the sum of partial cross sections given in Equation 2. Here, , ,

, , and are the cross-sections for the photoelectric, coherent scattering, incoherent scattering, pair production in the nuclear field, and pair production in electron field (or triplet production), respectively (Hila et al. 2021a).

(2)

The cross-section is related to the mass attenuation coefficient (μ𝑚, in cm2 g-1), as shown in Equation 3 where

is Avogadro’s number and is the corresponding atomic mass of the 𝑖�� element. The μ𝑚 is a measure of the probability of the interaction that occurs between incident photons and matter in unit area per unit mass. The two quantities 𝜎 and μ𝑚 both measure photon interaction probabilities and are, hence, directly proportional as follows.

(3)

The μ𝑚 is also the quotient of the linear attenuation coefficient (μ) to the density of the material (�) given by Equation 4. This is to avoid the effects of variations in the density of material for reference purposes (Kaplan 1989).

(4)

The linear attenuation coefficient (μ, in cm–1) or the probability of a photon interacting in a particular way with a given material, per unit length, can be computed using the Beer-Lambert’s Law given by:

(5)

where I is the intensity of the transmitted photon (i.e. X-ray, γ-ray), 𝐼₀ is the intensity of the incident photon, and 𝑥 is the thickness of the absorbing medium. The mean free path (MFP, in cm), or the average distance traveled by a photon between two successive interactions, is just the inverse of the linear attenuation coefficient (μ) (Javier-Hila et al. 2021).

(6)

The effectiveness of the shielding capability of a material to a photon can be described by the half-value layer (HVL, in cm), as given in Equation 7, or the thickness of the material, which reduces the intensity of a photon by half.

(7)

The effective atomic number (𝑍��) is a quantity used for multi-element materials. It quantifies the photon attenuation capabilities of the material in terms of atomic number. It is described by Equation 8, where 𝜎 ₁ and 𝜎 ₂ are elemental cross-sections of two consecutive elements 𝑍₁ and 𝑍₂. The 𝜎 ₁ and 𝜎 ₂ are chosen such that 𝜎 � of the material lies in-between.

(8)

The buildup factor (𝐵) can account for the effects of scattering, which are otherwise neglected by the simple Beer-Lambert law in Equation 5. The buildup factor is a convenient multiplier to the Beer-Lambert law, as described in Equation 9. It is a function of penetration depth and energy. The two most practical types of buildup factors are those for energy absorption (𝐸𝐴𝐵𝐹) and exposure (𝐸𝐵𝐹). These can be obtained through the G-P fitting method in the standard ANSI/ANS-6.4.3-1991.

(9)

The mass stopping power (𝑀𝑆𝑃, in MeV cm2 g–1), denoted as −𝑑𝐸/�𝑑𝑥 relates the energy loss of a charged particle per unit distance traversed, normalized to the density of the medium. The continuous-slowing-down approximation 𝐶𝑆𝐷𝐴 range gives the average path length traveled by a charged particle, and the projected range is the distance traveled along the initial particle direction (Grimes et al. 2017).

The neutron removal cross-section (𝛴�) is a pseudo-cross section that characterizes the material’s effectiveness to remove the fast neutron group by scattering. This quantity is valid in systems where sufficient moderation is present (Wood 1982). Furthermore, it assumes that the starting or source neutrons are from U-235 fission. On the other hand. the neutron macroscopic cross-section or attenuation factor (𝛴��) (Gökçe et al. 2021) is an energy-dependent quantity related to the probability of neutron interaction.

METHODOLOGY

MaterialThe PNZ and PNB used in this study were supplied by LITHOS Manufacturing, OPC. It was mined from Mangatarem, Pangasinan on the island of Luzon, Philippines. The chemical composition of the PNZ and



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PNB, according to the supplier’s chemical analysis report from an independent laboratory (Chemistry Laboratory of the Mines and Geosciences Bureau, Department of Environment and Natural Resources, North Ave., Diliman, Quezon City, Philippines) is given in Appendix Table I. Various chemical analyses such as gravimetric method, flame-atomic absorption spectrometry, and titration were done to determine the components of PNB and PNZ and their respective % composition. For both minerals, the most abundant components were silica (SiO2) and alumina (Al2O3), which comprise 47.90 and 14.02% respectively of the total weight of bentonite while 55.29 and 12.63% for zeolite. It is worthy to mention that these two components determine the number of Si and Al present in the minerals. Si/Al ratio affects the efficiency of the material to adsorb cation or its cation exchange capacity (CEC) (Gili and Conato 2019). Normally, the lower the Si/Al ratio, the greater the CEC, the higher the maximum adsorption capacity. This means that the material might be a good candidate adsorbent of heavy metals and other positively charged molecules as one of its many applications. Other compounds present in the samples were ferric oxide (Fe2O3), magnesia (MgO), lime (CaO), soda (Na2O), and potash (K2O). The bentonite and zeolite absorb a substantial amount of moisture comprising 10.71 and 7.04%, respectively. The loss of ignition is around 12.27 and 14.71% for bentonite and zeolite, respectively. This is probably due to the organic matter, which burns at elevated temperatures.

CharacterizationThe materials used in the study were characterized using a scanning electron microscope (SEM SU1510, Hitachi High Technologies, Japan) to observe the morphology of the particles that make up the powder samples. The materials were also subjected to XRD (SHIMADZU, XRD-7000 Maxima) analysis using Cu 𝐾𝛼 (1.5406Å) radiation at a voltage of 40.0 kV and a current of 30.0 mA to determine its mineral components. A continuous scan was conducted with a speed of 2.00° min–1 from 3–70° 2θ. Crushed rock samples were analyzed for true specific gravity using the gravimetric method.

Shielding Parameter CalculationThe samples were evaluated for photon, electron, proton, alpha particle, and neutron attenuation characteristics. The X-ray and gamma shielding quantities of the materials were determined using a windows-based interpolation software called EpiXS (Hila et al. 2021a). This software is based on the Monte Carlo transport library known as EPICS2017 (Cullen 2018) of the ENDF/B-VIII (Brown et al. 2018). The photon shielding quantities included �𝑚, 𝐻𝑉𝐿, 𝑇𝑉𝐿, 𝑀𝐹𝑃, 𝑍��, and buildup factors 𝐸𝐴𝐵𝐹 and 𝐸𝐵𝐹. In interpolating and computing for the gamma

photon attenuation parameters, the chemical compositions of the materials are entered together under their respective weight percentages. The actual density of the material is also provided and entered into the program. The interpolation scheme of EpiXS follows the recommended law for the EPICS2017 (i.e. linear spline in Linear-Linear axes). This is following the linearization of the EPICS2017, as opposed to the Log-Log interpolable older Monte Carlo transport libraries.

For electrons, the 𝑀𝑆𝑃 and 𝐶𝑆𝐷𝐴 range were obtained using ESTAR (Berger et al. 2005). The ESTAR is an online web program specifically designed for calculating electron stopping power and range tables. For protons and alpha particles, 𝑀𝑆𝑃 and projected range were obtained using the SRIM code (Ziegler et al. 2010). SRIM is a Monte Carlo transport code that simulates the passage of ions into a material or layers of different materials; this code can also be used to obtain stopping power and range tables for different materials. The 𝛴� were calculated using the Phy-X/PSD (Şakar et al. 2020) and the MRCsC (El-Samrah et al. 2021). The Phy-X/PSD uses the mass removal cross sections tabulated in Chilton et al. (1984) and Kaplan (1989) to calculate data. In contrast, the MRCsC is based on the empirical approximation that the 𝛴� is equal to 2/3 , where was taken from the ENDF/B-VIII (Brown et al. 2018) averaged at 2–10 MeV. Lastly, the NGCal (Gökçe et al. 2021) is a photon and neutron attenuation software; this was used to calculate the 𝛴�� for both fast and thermal neutrons.

RESULTS AND DISCUSSION

SEMThe powder particles that make up the PNZ, as shown in Figures 1a and b, are comprised of particles with irregular shapes and sizes. Due to the wide particle size distribution of the particles, no average size was obtained. However, most particles are less than 50 µm. The surface of each particle appears to be porous. Bigger particles seem to be an aggregate of smaller particles.

On the other hand, the particles that make up the PNB are much larger with particle size reaching 100 µm, as can be seen in Figure 1c. Smaller particles tend to coalesce forming bigger particles. Similar to the PNZ, the morphological structure of PNB is porous, as shown in Figure 1d.

X-ray Diffractometry and Specific GravityThe PNZ is composed mainly of mordenite, clinoptilolite, and montmorillonite – as shown in Figure 2a. A minor amount of calcite is also seen in the sample, as indexed in



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the XRD pattern. The amount of each mineral is difficult to ascertain as the peaks of each component are very close to each other. The results agree well with the composition of PNZ based on previous studies (Gili et al. 2019, 2020; Gili and Olegario 2020).

Figure 2b shows the X-ray diffractogram of the PNB. It can be observed that the sample is primarily composed of hectorite and montmorillonite from the smectite group and mordenite from the zeolite family. However, the amount of each component is difficult to ascertain as the peaks of each component overlap each other. Small amounts of nontronite and other minerals such as kaolinite, feldspar, and mica are also present in the sample. The results agree well with the XRD patterns of the Philippine bentonite in previous studies (Olegario-Sanchez and Felizco 2017; Taaca et al. 2019).

Thru the gravimetric method, the true specific gravity of the crushed Philippine zeolite rock sample was determined to be equal to 2.16. This translates to a density of 2.16 g cm–3. On the other hand, the true specific gravity of pulverized Philippine bentonite rock sample is equal to 2.19, which translates to a density of 2.19 g cm–3.

Radiation Shielding CharacteristicsThe photon shielding quantities of PNB and PNZ were obtained based on the EPICS2017 collection of ENDF/B-VIII. The EPICS2017 was extracted using the EpiXS interpolation program. The mass attenuation coefficients derived are displayed in Appendix Figure I. It describes the partial and total coefficients for both mineral samples. Notably, the photoelectric effect is the dominant mechanism for low-energy photons; this mode has a probability (per atom) approximately proportional to Z4-5/E3.5. In both mineral samples, the photoelectric effect is dominant below ~ 50 keV. Higher than this, the incoherent scattering becomes the predominant mode with a probability of Z/E. At much higher energies, pair production becomes possible with threshold energy of E’ = 1.022 MeV in the nuclear field and E’ = 2.044 MeV in the electron field. This mode has a probability proportional to Z2(E-E’) and becomes predominant above ~ 18 MeV for both samples. On the other hand, coherent scattering never predominates at any energy range and can be neglected. A comparison of mass attenuation coefficients is given in Appendix Table II, from different natural and construction materials in literature. This data shows that the mass attenuation coefficients for bentonites and zeolites are

Figure 1. SEM images of PNZ at magnifications of a) 270x and b) 4000x and PNB at magnifications of c) 270x and d) 4000x.



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similar to other building materials. This is due to the similarities in chemical compositions.

The 𝑀𝐹𝑃, 𝐻𝑉𝐿, and 𝑇𝑉𝐿 for bentonite and zeolite are obtained using mass attenuation coefficients and density; these three are considered practical radiation shielding quantities. The 𝑀𝐹𝑃, 𝐻𝑉𝐿, and 𝑇𝑉𝐿 are illustrated in Figure 3 in a broad energy range. The 𝑀𝐹𝑃 is the distance between two consecutive photon interactions and is crucial for radiation transport simulations. On the other hand, the 𝐻𝑉𝐿 and 𝑇𝑉𝐿 are the thicknesses of a material required to reduce the radiation intensity by factors of 2 and 10, respectively. At 100 keV, the 𝑀𝐹𝑃, 𝐻𝑉𝐿, and 𝑇𝑉𝐿 are 2.67, 1.85, and 6.15 cm for zeolite and 2.55, 1.77, and 5.87 cm for bentonite. At 1 MeV, they are 7.25, 5.03, and 16.69

cm for zeolite and 7.14, 4.95, and 16.44 cm for bentonite. This denotes that the PNB is only slightly advantageous to PNZ, and both have similar practical photon attenuation characteristics.

The effective atomic number (𝑍��) for bentonite and zeolite is described in Figure 4. This quantity reflects the radiation shielding capability (per atom) of the material. The results show higher values for zeolite in most of the photon energy range, except at low energies between 10–90 keV; this minor exception is due to the larger amount of Fe atoms in the bentonite sample. The Fe atoms in the sample increased the photoelectric probability above the 7.117 keV K-edge, as expected from the added possibility of the K-shell photoionization. On the other hand, for

Figure 2. X-ray diffractogram of the a) PNZ and b) PNB.



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most of the energy range, the zeolite sample is better than the bentonite sample at attenuating photon radiation (per mol of material). At the constant region where Compton scattering is predominant, the 𝑍�� values for zeolite and bentonite were 8.16 and 7.82, respectively. At high energies, close values were obtained at around 9.10 and 9.00, respectively.

The photon buildup factors are described in Figure 5 at several penetration depths from 15 keV to 15 MeV. The values were obtained using the G-P fitting method, considering the EPICS2017 Compton and total (without coherent scattering) photon cross-sections. Both 𝐸𝐴𝐵𝐹 and 𝐸𝐵𝐹 show the least values at the photoelectric predominated region, and the largest values at the Compton scattering

Figure 3. Photon mean free path, half-value and tenth-value layer of PNB and PNZ using EPICS2017 data library interpolation.

Figure 4. Photon effective atomic number of PNB and PNZ using EPICS2017 data library interpolation.

Figure 5. Photon buildup factors of PNB and PNZ using EPICS2017 data (a and b) and G-P fitting method (c and d).



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predominated region. Photoelectric absorptions reduce the number of photons scattering within the material. Photoelectric-dominated regions typically contain the least values of buildup factors, except at energies slightly above a K-edge of a material, wherein X-ray cascades would be an issue (Shultis and Faw 2010). In both materials, since the highest K-edge comes from Fe K-edge (7.117 keV), which is significantly below the photon energy range, no sharp peaks in 𝐸𝐴𝐵𝐹 or 𝐸𝐵𝐹 are illustrated in the photoelectric region. As the photon energy reaches the Compton predominated region, the buildup factors have incurred maximum values. This is due to the nature of Compton scattering, which essentially produces scattered radiation. On the other hand, pair production is an absorption mechanism that also gives rise to the annihilation of radiation and X-rays. Hence, buildup factor values are also significant in this region. At 10 𝑀𝐹𝑃, the maximum 𝐸𝐴𝐵𝐹 and 𝐸𝐵𝐹 are 98.0 and 55.5 for zeolite and 85.8 and 46.8 for bentonite. At 40 𝑀𝐹𝑃, the maximum 𝐸𝐴𝐵𝐹 and 𝐸𝐵𝐹 are 2351 and 1262 for zeolite and 1788 and 940 for bentonite. The large difference between zeolite and bentonite (at large penetration depths) shows the importance of taking into account the buildup of scattered radiation in shielding applications. It is worth noting that the zeolite has significant heavy metal adsorption capacities, which may potentially decrease buildup factors and lead to increased gamma shielding characteristics, as shown by Puišo et al. (2013).

The 𝑀𝑆𝑃 and range of electrons, protons, and alpha particles are described in Figure 6. The 𝑀𝑆𝑃 is the rate of energy loss of a charged projectile per cm2/g of the traversed material, the 𝐶𝑆𝐷𝐴 range is the output of ESTAR and gives the average path length traversed by the electron, and lastly, the projected range can be obtained using SRIM and is the average depth traveled by the particle with respect to its initial direction. It can be seen that the charged particle attenuation properties of zeolite and bentonite are very similar. For electrons, the total 𝑀𝑆𝑃 in both samples is largely due to the collision stopping power, except at very high energies where the contribution of radiative stopping power exponentially increases, and there is an uptrend in 𝑀𝑆𝑃. For protons and alpha particles, the total 𝑀𝑆𝑃 is mostly from electronic stopping power with only small contributions from nuclear stopping power. It is also seen that the range of high-energy electrons in zeolite and bentonite is in macroscopic scales. The range of 5 MeV protons (~ 200 µm) is larger than the particle sizes of both materials, especially the finer particle zeolite, as described in the SEM results (in Figure 1). In contrast, the range of 5 MeV alpha particles (~ 20 µm) is smaller than the particle sizes of both materials.

The neutron shielding properties are typically characterized by its 𝛴� and 𝛴�� (El-Samrah et al. 2021; Gökçe et al. 2021). These neutron shielding quantities are described

in Table 1 for bentonite and zeolite and with comparative values for water and typical soil composition (McConn et al. 2011). The 𝛴� is a pseudo-cross section that quantifies fast neutron shielding characteristics of materials (Wood 1982); this quantity is valid for a shielding material if it is adjacent to another material layer with enough hydrogen content (e.g. > 50 cm of light water) (Shultis and Faw 2010; Wood 1982). Since this is the case in typical reactors and shielding containers, this quantity is of great utility. On the other hand, for single-layered shielding configurations (following Beer-Lambert law), the 𝛴�� gives the probability of interaction at certain neutron energy. The 𝛴� values for bentonite were shown to be higher than zeolite. Moreover, the 𝛴� for bentonite was comparable with water. Also, both bentonite and zeolite minerals were shown to be significantly higher than typical soil. This denotes that both bentonite and zeolite have significant neutron shielding characteristics when used as a primary shielding layer, followed by a moderator for fission neutrons. However, as a single layer of shielding material, the typical soil composition (McConn et al. 2011) is shown to have higher values of 𝛴��, essentially because of the moisture content. Nonetheless, bentonite could potentially be increased by absorption of water or by its use in a clay-polymer matrix composite. On the other hand, the zeolite may also be potentially improved by adsorption of metal ions with higher 𝛴� than water (e.g. Fe, Ni, Cu, etc.).

CONCLUSIONThis study characterizes the microstructure and photon, electron, proton, alpha, and neutron shielding properties of PNB and PNZ. The SEM and XRD characterization methods were used to study the microstructure including crystallinity, grain size, and texture. The EPICS2017 of ENDF/B-VIII was utilized through the EpiXS interpolation software for quantifying photon attenuation characteristics. The SRIM and ESTAR software were applied for obtaining the stopping power and range by high-energy electrons and ions. The Phy-X/PSD, MRCsC, and NGCal were used to characterize the neutron attenuation properties. The results showed that the zeolite grain sizes were typically smaller than 50 µm, and the bentonite grain sizes were larger – reaching approximately 100 µm. It was found that both materials were significantly comprised of mordenite and montmorillonite minerals. The zeolite is additionally composed of clinoptilolite, while the bentonite is also composed of hectorite, mordenite, nontronite, and other minerals such as kaolinite, feldspar, and mica. The photon shielding quantities for both materials showed similar 𝑀𝐹𝑃, 𝐻𝑉𝐿, and 𝑇𝑉𝐿 values. However, they sustained



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Figure 6. Electron and ion (H1+ and He2+) mass stopping power and range within PNB and PNZ obtained with ESTAR and SRIM.

Table 1. Fast neutron removal cross-section 𝛴� (cm-1) and neutron attenuation factor 𝛴�� (cm–1) of selected materials, PNB and PNZ obtained using Phy-X/PSD, MRCsC, and NGCal.

Sample 𝛴�(cm–1) 𝛴��(cm–1)

Phy-X/PSD MRCsC NGCal (25.4 meV)

NGCal (4 MeV)

PNZ 0.08975 0.09717 0.82155 1.25848

PNB 0.09499 0.10275 0.82425 1.26396

Soil, typical (McConn et al. 2011) 0.07542 0.07984 1.74680 1.73732

Water 0.10270 0.11100 5.37846 5.35627



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significantly different buildup factor values at large penetration depths. The range of high-energy charged particles was similar between both natural materials. The range of high-energy electrons and protons was beyond the average particle sizes of both materials, while the range of alpha particles was shown to be smaller than the average particle sizes. The fast neutron removal cross-sections of zeolite and bentonite showed significantly higher values than typical western soil. Both natural bentonite and zeolite may present a suitable ingredient for radiation shielding composites, especially due to their abundance in nature and unique physical and chemical properties.

REFERENCESAKKURT I, AKYILDIRIM H, MAVI B, KILINCARSLAN

S, BASYIGIT C. 2010. Radiation shielding of concrete containing zeolite. Radiat Meas 45(7): 827–830.

AKKURT I, KILINCARSLAN S, BASYIGIT C. 2004. The photon attenuation coefficients of barite, marble and limra. Ann Nucl Energy 31(5): 577–582.

ALAM MN, MIAH MMH, CHOWDHURY MI, KAMAL M, GHOSE S, RAHMAN R. 2001. Attenuation coefficients of soils and some building materials of Bangladesh in the energy range 276–1332keV. Appl Radiat Isot 54(6): 973–976.

AL-HARBI N, SAYYED MI, KUMAR A, MAHMOUD KA, OLARINOYE OI, ALHUTHALI AMS, AL-HADEETHI Y. 2021. A comprehensive investigation on the role of PbO in the structural and radiation shielding attribute of P2O5-CaO-Na2O-K2O-PbO glass system. J Mater Sci: Mater Electron 32(9): 12371–12382.

ALMUQRIN AH, JECONG JFM, HILA FC, BALDERAS CV, SAYYED MI. 2021. Radiation shielding properties of selected alloys using EPICS2017 data library. Prog Nucl Energy 137: 103748.

ASAL S, ERENTURK SA, HACIYAKUPOGLU S. 2021. Bentonite based ceramic materials from a perspective of gamma-ray shielding: preparation, characterization and performance evaluation. Nucl Eng Technol 53(5): 1634–1641.

AWADALLAH MI, IMRAN MMA. 2007. Experimental investigation of γ-ray attenuation in Jordanian building materials using HPGe-spectrometer. J Environ Radioact 94(3): 129–136.

BERGER MJ, COURSEY JS, ZUCKER MA, CHANG J. 2005. ESTAR, PSTAR, and ASTAR: computer programs for calculating stopping-power and range tables for electrons, protons, and helium ions (version

1.2.3). National Institute of Standards and Technology, Gaithersburg, MD. Retrieved on 05 Jun 2021 from http://physics.nist.gov/Star

BRITANNICA, THE EDITORS OF ENCYCLOPAEDIA. 2021. Bentonite (Encyclopaedia Britannica). Retrieved on 05 Jun 2021 from https://www.britannica.com/science/bentonite

BROWN DA, CHADWICK MB, CAPOTE R, KAHLER AC, TRKOV A, HERMAN MW, SONZOGNI AA, DANON Y, CARLSON AD, DUNN M, …, ZHU Y. 2018. ENDF/B-VIII.0: the 8th major release of the nuclear reaction data library with CIELO-project cross sections, new standards and thermal scattering data. Nucl. Data Sheets 148: 1–142.

CHILTON AB, FAW RE, SHULTIS JK. 1984. Principles of radiation shielding. Englewood Cliffs: Prentice-Hall.

CULLEN DE. 2018. A survey of photon cross section data for use in EPICS2017, IAEA-NDS-225, rev.1. International Atomic Energy Agency.

DAMLA N, CEVIK U, KOBYA AI, CELIK A, CELIK N, VAN GRIEKEN R. 2010. Radiation dose estimation and mass attenuation coefficients of cement samples used in Turkey. J Hazard Mater 176(1–3): 644–649.

DAMLA N, BALTAS H, CELIK A, KIRIS E, CEVIK U. 2011. Calculation of radiation attenuation coefficients, effective atomic numbers and electron densities for some building materials. Radiat Prot Dosim 150(4): 541–549.

EKINCI N, EL-AGAWANY FI, MAHMOUD KA, KARABULUT A, AYGÜN B, YOUSEF E, RAMMAH YS. 2021. Synthesis, physical properties, and gamma-ray shielding capacity of different Ni-based super alloys. Radiat Phys Chem 186: 109483.

EL-SAMRAH MG, EL-MOHANDES AM, EL-KHAYATT AM, CHIDIAC SE. 2021. MRCsC: A user-friendly software for predicting shielding effectiveness against fast neutrons. Radiat Phys Chem 182: 109356.

GAIKWAD DK, OBAID SS, SAYYED MI, BHOSALE RR, AWASARMOL VV, KUMAR A, SHIRSAT MD, PAWAR PP. 2018. Comparative study of gamma ray shielding competence of WO3-TeO2-PbO glass system to different glasses and concretes. Mater Chem Phys 213: 508–517.

GALAMBOŠ M, ROSSKOPFOVÁ O, KUFČÁKOVÁ J, RAJEC P. 2011. Utilization of Slovak bentonites in deposition of high-level radioactive waste and spent nuclear fuel. J Radioanal Nucl Chem 288(3): 765–777.

GILI MBZ, OLEGARIO EM. 2020. Effects of γ-irradiation on the Cu2+ sorption behaviour of NaOH-modified



1485

Philippine natural zeolites. Clay Miner 55(3): 248–255.

GILI MB, OLEGARIO-SANCHEZ L, CONATO M. 2019. Adsorption uptake of Philippine natural zeolite for Zn2+ ions in aqueous solution. J Phys Conf Ser 1191: 012042.

GILI MBZ, PARES FA, NERY ALG, GUILLERMO NRD, MARQUEZ EJ, OLEGARIO EM. 2020. Changes in the structure, crystallinity, morphology and adsorption property of gamma-irradiated Philippine natural zeolites. Mater Res Express 6(12): 125552.

GILI MBZ, CONATO MT. 2019. Adsorption uptake of mordenite-type zeolites with varying Si/Al ratio on Zn2+ ions in aqueous solution. Mater Res Express 6(4): 045508.

GILI MBZ, HILA FC. 2021. Investigation of gamma-ray shielding features of several clay materials using the EPICS2017 library. Philipp J Sci 150(5): 1017–1026.

GÖKÇE HS, GÜNGÖR O, YILMAZ H. 2021. An online software to simulate the shielding properties of materials for neutrons and photons: NGCal. Radiat Phys Chem 185: 109519.

GRIMES DR, WARREN DR, PARTRIDGE M. 2017. An approximate analytical solution of the Bethe equation for charged particles in the radiotherapeutic energy range. Sci Rep 7(1).

HAGER IZ, RAMMAH YS, OTHMAN HA, IBRAHIM EM, HASSAN SF, SALLAM FH. 2019. Nano-structured natural bentonite clay coated by polyvinyl alcohol polymer for gamma rays attenuation. J Theor Appl Phys 13(2): 141–153.

HASAN WK, MAHDI JT, HAMEED AS. 2019. Measurement technique of linear and mass attenuation coefficients of polyester-bentonite composite as gamma radiation shielding materials. AIP Conf Proc 2144, 030018.

HILA FC, ASUNCION-ASTRONOMO A, DINGLE CAM, JECONG JFM, JAVIER-HILA AMV, GILI MBZ, BALDERAS CV, LOPEZ GEP, GUILLERMO NRD, AMORSOLO JR AV. 2021a. EpiXS: a Windows-based program for photon attenuation, dosimetry and shielding based on EPICS2017 (ENDF/B-VIII) and EPDL97 (ENDF/B-VI.8). Radiat Phys Chem 182: 109331.

HILA FC, JAVIER-HILA AMV, SAYYED MI, ASUNCION-ASTRONOMO A, DICEN GP, JECONG JFM, GUILLERMO NRD, AMORSOLO JR AV. 2021b. Evaluation of photon radiation attenuation and buildup factors for energy absorption and exposure in some soils using EPICS2017 library. Nucl Eng Technol.

INDRAJATI I, DEWI I, GUSRIZAL D, SYIFA A. 2015. Zeolite-filled natural rubber latex for gamma rays radiation shielding application. Prosiding Seminar Nasional Kulit, Karet, dan Plastik ke-4, Yogyakarta, Indonesia.

JAVIER-HILA AMV, JAVIER BCV, HILA FC, GUILLERMO NRD. 2021. Photon attenuation parameters of non-essential amino acids using EPICS2017 library interpolations. SN Appl Sci 3(5).

JHA B, SINGH DN. 2016. Basics of zeolites. In: Fly ash zeolites. Advanced structured materials, Vol. 78. Singapore: Springer.

KAPLAN MF. 1989. Concrete radiation shielding. New York: John Wiley and Sons Inc.

KUBOTA T, FUKUTANI S, OHTA T, MAHARA Y. 2012. Removal of radioactive cesium, strontium, and iodine from natural waters using bentonite, zeolite, and activated carbon. J Radioanal Nucl Chem 296(2): 981–984.

KURUDIREK M, ÖZDEMIR Y, TÜRKMEN İ, LEVET A. 2010. A study of chemical composition and radiation attenuation properties in clinoptilolite-rich natural zeolite from Turkey. Radiat Phys Chem 79(11): 1120–1126.

MANN HS, BRAR GS, MANN KS, MUDAHAR GS. 2016. Experimental investigation of clay fly ash bricks for gamma-ray shielding. Nucl Eng Technol 48(5): 1230–1236.

MANN KS, KAUR B, SIDHU GS, KUMAR A. 2013. Investigations of some building materials for γ-rays shielding effectiveness. Radiat Phys Chem 87: 16–25.

MCCONN JR R, GESH C, PAGH R, RUCKER R, WILLIAMS III R. 2011. Compendium of material composition data for radiation transport modeling. Technical Report PNNL-15870, Rev 1. Pacific Northwest National Laboratory, Richland, WA.

OLEGARIO-SANCHEZ E, FELIZCO JC. 2017. Investigation of the structural properties of amorphous Philippine bentonite clay and its potential use for topical applications. Key Eng Mater 737: 401–406.

PUIŠO J, JAKEVIČIUS L, VAIČIUKYNIENĖ D, VAITKEVIČIUS V, KANTAUTAS A, BALTUŠNIKAS A. 2013. X-ray shielding zeolite containing lead. Proceedings of International Conference “Medical Physics in the Baltic States,” Kaunas, Lithuania.

SAHADATH MH, BISWAS R, HUQ MF, MOLLAH AS. 2016. Calculation of gamma-ray attenuation parameters for locally developed ilmenite-magnetite (I-M) concrete. J Bangladesh Acad Sci 40(1): 11–21.



1486

ŞAKAR E, ÖZPOLAT ÖF, ALIM B, SAYYED MI, KURUDIREK M. 2020. Phy-X / PSD: Development of a user friendly online software for calculation of parameters relevant to radiation shielding and dosimetry. Radiat Phys Chem 166: 108496.

SALLAM FH, HAGER IZ, RAMMAH YS, OTHMAN HA, IBRAHIM EM, HASSAN SF, AHMED Z. 2020. Evaluation of gamma rays shielding competence for bentonite clay /PVA polymer matrix using MCNPX code. Arab J Nucl Sci Appl 53(2): 177–188.

SAYYED MI, JECONG JFM, HILA FC, BALDERAS CV, ALHUTHALI AMS, GUILLERMO NRD, AL-HADEETHI Y. 2021a. Radiation shielding characteristics of selected ceramics using the EPICS2017 library. Ceram Int 47(9): 13181–13186.

SAYYED MI, KAKY KM, GAIKWAD DK, AGAR O, GAWAI UP, BAKI SO. 2019. Physical, structural, optical and gamma radiation shielding properties of borate glasses containing heavy metals (Bi2O3/MoO3). J Non-Cryst Solids 507: 30–37.

SAYYED MI, KUMAR A, ALBARZAN B, JECONG JFM, KURTULUS R, ALMUQRIN AH, KAVAS T. 2021b. Investigation of the optical, mechanical, and radiation shielding features for strontium-borotellurite glass system: fabrication, characterization, and EPICS2017 computations. Optik 243: 167468.

SAYYED MI, TEKIN HO, TAKI MM, MHAREB MHA, AGAR O, ŞAKAR E, KAKY KM. 2020. Bi2O3-B2O3-ZnO-BaO-Li2O glass system for gamma ray shielding applications. Optik 201: 163525.

SHULTIS JK, FAW RE. 2010. Radiation shielding and radiological protection. In: Handbook of nuclear engineering. Cacuci DG ed. Boston, MA: Springer. p. 1313–1448.

TAACA KLM, DAHONOG LA, OLEGARIO EM. 2019. Cell viability and bacterial reduction activity of Ag-modified bentonite. Mater Today: Proc 16: 1782–1788.

TAQI AH, KHALIL HL. 2017. Experimental and theoretical investigation of gamma attenuation of building materials. J Nucl Part Phys 7(1): 6-13.

TÜRKMEN İ, ÖZDEMIR Y, KURUDIREK M, DEMIR F, SIMSEK Ö, DEMIRBOĞA R. 2008. Calculation of radiation attenuation coefficients in Portland cements mixed with silica fume, blast furnace slag and natural zeolite. Ann Nucl Energy 35(10): 1937–1943.

UDDIN F. 2008. Clays, nanoclays, and montmorillonite minerals. Metall Mater Trans A 39(12): 2804–2814.

WISE WS. 2013. MINERALS | Zeolites. In: Reference module in earth systems and environmental sciences.

Elsevier.

WOOD JI. 1982. Computational methods in reactor shielding. Pergamon Press.

YASMIN S, KHANDAKER MU, BARUA BS, MUSTAFA MN, CHOWDHURY F-U-Z, RASHID MA, BRADLEY DA. 2018. Ionizing radiation shielding effectiveness of decorative building materials (porcelain and ceramic tiles) used in Bangladeshi dwellings. Indoor Built Environ 28(6): 825–836.

YESMIN S, SONKER BARUA B, UDDIN KHANDAKER M, TAREQUE CHOWDHURY M, KAMAL M, RASHID MA, MIAH MMH, BRADLEY DA. 2017. Investigation of ionizing radiation shielding effectiveness of decorative building materials used in Bangladeshi dwellings. Radiat Phys Chem 140: 98–102.

ZIEGLER JF, ZIEGLER MD, BIERSACK JP. 2010. SRIM – the stopping and range of ions in matter. Nucl Instrum Methods Phys Res, Sect B 268(11–12): 1818–1823.



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Table II. Comparison of mass attenuation coefficients μ𝑚 (cm2 g–1) of selected materials.

MaterialEnergy (keV) Ref.

59.5 356 662 1173 1332

Silica fume 0.263 0.100 – – – Türkmen et al. (2008)

Zeolite 0.264 0.123 – – – Türkmen et al. (2008)

Brick – – – 0.055 0.051 Alam et al. (2001)

Soil – – – 0.057 0.054 Mann et al. (2013)

Cement – – – 0.057 0.052 Damla et al. (2010)

Concrete – – – 0.060 0.055 Sahadath et al. (2016)

Marble stone – – – 0.078 0.081 Yesmin et al. (2017)

Tiles – – – 0.144 0.138 Yasmin et al. (2018)

Clay – – 0.0778 0.058 0.0542 Mann et al. (2016)

Clay w/ 50% fly ash – – 0.0762 0.0566 0.0529 Mann et al. (2016)

Concrete – – 0.0730 0.0660 0.0600 Awadallah and Imran (2007)

Bentonite/PVA – – 0.076 0.059 0.056 Sallam et al. (2020)

Bentonite – – 0.0788 0.0600 0.0566 Hager et al. (2019)

Lead 5.0794 0.2870 0.1099 0.0615 0.0559 EpiXS, Hila et al. (2021a)

PNZ 0.2742 0.1009 0.0775 0.0589 0.0552 This study

PNB 0.3020 0.1012 0.0777 0.0591 0.0553 This study

APPENDICES

Table I. Chemical components of the PNB and PNZ based on chemical tests.

Component PNZ (wt%) PNB (wt%) Analytical method

SiO2 55.29 47.90 Gravimetric

Al2O3 12.63 14.02 TitrationaFe2O3 3.43 7.54 Flame-AASc

CaO 4.69 4.83 Titration

MgO 1.49 1.59 Titration

K2O 0.58 0.46 Flame-AAS (by computation)

Na2O 0.62 0.33 Flame-AAS (by computation)

H2O 7.04 10.71 GravimetricbLOI 14.71 12.27 Gravimetric

Total 100.48 99.65aComputed from Feγ; bloss on ignition, C; catomic adsorption spectrometry



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Figure I. Photon mass attenuation coefficients of a) PNB and b) PNZ using EPICS2017 data library interpolation.



characterization and radiation shielding properties of

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