Feasibility of polymer-based composite materials as radiation shield
Introduction
As the use of ionizing radiation increases across scientific disciplines, the risk of serious injuries and health hazards such as radiation poisoning and burning has also increased. Consequently, the need to carefully control radiation has increased (Almurayshid et al., 2017). In clinical oncology, the absorbed dose in human beings during radiation procedures is reduced by following radiation protection techniques like shielding (Salehi et al., 2015). Protecting human beings and the environment from the harmful effect of neutron and photon radiation (i.e. gamma or X-rays) is a major consideration in establishing a radiation facility. Lead (Pb) is widely used as X-ray and gamma radiation shields because of its high atomic number (Z), high density and high linear and mass attenuation coefficients (Soylu et al., 2015; AbuAlRoos et al., 2020). However, the drawbacks of Pb include weight and cost. Furthermore, special handling is required for Pb shielding during manufacturing and installation. Metallic Pb, or materials contaminated with it, could be transported via tiny particles that stick to hands or accumulated as dust in an environment, and it would be hazardous when ingested or inhaled. As a result, it is not ideal for critical and clean environments such as hospitals (AbuAlRoos et al., 2019). Moreover, Pb is rather ineffective in attenuating neutron radiation due to the uncharged nature of neutrons that allows them to penetrate through dense materials (Kaçal et al., 2019).
Therefore, discovering a non-toxic, environment friendly, Pb-free X-ray shielding system with low weight and high radiation shielding efficiency for healthcare applications is the need of the hour (Singh et al., 2017). Considering this, researchers have been attempting to replace Pb-based materials for radiation protection with non-toxic, flexible, lightweight, low-cost radiation shielding materials. Several facilities are utilizing low-energy X-rays, such as in diagnostic radiology and the gamma radiation used in research laboratories and industries. This trend may pave the way for the development of inexpensive Pb-free materials that absorb low-energy beams. Compared with heavy metals, polymers doped with Pb-free heavy minerals or metals such as W, or their oxides or salts, could have potential as radiation shields because of their low weight, high corrosion resistance and plasticity, simple and low-cost processing methods, and high neutron absorption ability (Gorjiara et al., 2011; Singh et al., 2017; Soylu et al., 2015; Wang et al., 2020).
Polymers as matrices and fillers as reinforcements are drawing research interest in the field of radiation protection. Many published studies have attempted to develop new polymer composites as ionizing radiation shields based on high-atomic-number materials or elements other than Pb. A majority of the studies dealt with high-energy photon beams using Cs-137 and Co-60 gamma radiation (Körpınar et al., 2020). Few studies have investigated polymer composites in low-energy photon beam radiation. For example, Noor-Azman et al. (2013) in their experiment with a mammography unit, infused 5 wt% of WO3 in an epoxy polymer sample and tested the latter using 25–49 kVp X-rays. They recorded an attenuation of approximately 78% of the initial beam at 49 kV, which was further enhanced at lower tube voltages (Noor-Azman et al., 2013). In another study, a lead-free PVC-based X-ray shield was tested. The results showed that the composite demonstrated good X-ray attenuation ability with a 100-kVp source. This indicates that Pb-free PVC-composite-weave garments such as aprons and gloves can safeguard the user from X-rays and result in a weight that is 25% lighter than a conventional Pb-based apron (Singh et al., 2017).
Certain studies suggested investigating the attenuation property of proposed composites at different doses and energies (neutron, X-ray or gamma rays) before commercializing them (Mirji and Lobo, 2017). Potential shielding materials can be characterized by calculating various parameters. The most common method for studying the performance of a shield is by studying its effect on the mass attenuation coefficient (μm), half value layer (HVL), mean free path (MFP), and equivalent atomic number (Zeq) (AbuAlRoos et al., 2020; Alavian and Tavakoli-Anbaran, 2019; Gülbiçim et al., 2019). Although previous studies have investigated the attenuation property of different polymer composites, to the best of the authors’ knowledge, no study has experimentally synthesized and tested high-density polyethylene (HDPE) composites filled with different weight percentages of Mo, MoC, W, or WC using X-ray beams in an energy range similar to that used in whole diagnostic radiology departments. In addition, most studies characterizing radiation shielding properties are simply focused on employing Monte Carlo simulation toolkits or accumulating calculated values of the studied samples from the available databases (Alavian and Tavakoli-Anbaran, 2019; Mann et al., 2015).
We prepared and investigated empirically the potential use of low-weight shielding materials, which are safer and easier to handle, based on mixtures of HDPE polymer and 5, 10, or 15 wt% of Mo, MoC, W, or WC, by analyzing the attenuation properties in terms of μm, HVL, MFP, and Zeq in a low-energy X-ray application (60–300 kVp).
Section snippets
Experimental materials and methods
The attenuation characteristics of a shielding material can be evaluated by calculating the mass attenuation coefficient , which is a measure of the fraction of the residual radiation intensity (I) and initial intensity (I0), after passing through a layer (x) in the material (Akkurt et al., 2010; Kaçal et al., 2019). The mass attenuation coefficient (cm2 g−1), in terms of mass per unit area of the material (X), can be determined using an exponential law (Lambert–Beer) and by
Results
Table 3 summarizes the measured values of the mass attenuation coefficient μm for the present polymer composites (Table 1) measured under an applied voltage of 60–300 kV using a narrow beam X-ray (Table 2). In addition, the table below illustrates the measured and computed results of the mass attenuation coefficient μm values taken from the XCOM database for the present samples, for the verification of the experimental results. The uncertainty of measurement was assessed by measuring the
Discussion
In this study, the mass attenuation coefficient μm was used to quantify the radiation shielding efficiency of selected polymer composites in attenuating 60–300 kV X-rays. Shielding materials based on the HDPE polymer were proposed and developed and mixed with different concentrations (5%, 10%, and 15%) of four elements/compounds. The shielding materials proposed were synthesized and cut into disks. They had the advantage of being light relative to Pb. Fig. 4, Fig. 5 illustrate the plots of mass
Conclusion
Despite the widespread use of polymers in the last decade, little data is available of the shielding properties of the wide range of polymer composites doped with different high atomic-number constituents. The use of polymer composites for ionizing radiation attenuation and shielding applications requires empirical investigation before it can achieve commercial viability. This study evaluated the potential of HDPE polymer composites doped in Mo, MoC, W, and WC as a shield against kilovoltage
Author Statement
Mansour Almurayshid and Sultan Alsagabi: Conceptualization, Methodology, Data curation, Writing- Original draft preparation, Investigation, Supervision and Writing- Reviewing and Editing. Yousif Alssalim, Zayed Alotaibi and Rashed Almsalam: Data curation and Validation.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors thank Haitham Algothmi for his assistance in the preparation of the polymer composite samples and Saeed Almalki for his help during the experimental set-up and irradiation procedures.
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