2012 polymer-composite materials for radiation protection

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  • Polymer-Composite Materials for Radiation ProtectionShruti Nambiar, and John T. W. Yeow*,,

    Department of Systems Design Engineering and Waterloo Institute for Nanotechnology, University of Waterloo, Ontario, CanadaN2L 3G1

    ABSTRACT: Unwanted exposures to high-energy or ionizingradiation can be hazardous to health. Prolonged oraccumulated radiation dosage from either particle-emissionssuch as alpha/beta, proton, electron, neutron emissions, orhigh-energy electromagnetic waves such as X-rays/ rays, mayresult in carcinogenesis, cell mutations, organ failure, etc. Toavoid occupational hazards from these kinds of exposures,researchers have traditionally used heavy metals or theircomposites to attenuate the radiation. However, protectivegear made of heavy metals are not only cumbersome but alsoare capable of producing more penetrative secondaryradiations which requires additional shielding, increasing thecost and the weight factor. Consequently, signicant research eorts have been focused toward designing ecient, lightweight,cost-eective, and exible shielding materials for protection against radiation encountered in various industries (aerospace,hospitals, and nuclear reactors). In this regard, polymer composites have become attractive candidates for developing materialsthat can be designed to eectively attenuate photon or particle radiation. In this paper, we review the state-of-the-art of polymercomposites reinforced with micro/nanomaterials, for their use as radiation shields.

    KEYWORDS: reinforced polymers, polymer nanocomposites, radiation shielding, space radiation, particle shielding, X-ray protection,gamma-ray protection

    1. INTRODUCTION

    High-energy radiations such as alpha/ particle emissions, X-ray or gamma ray electromagnetic radiation, or neutron particleemissions are often employed or encountered (as a byproduct)in a wide range of industries that includes nuclear power plants,healthcare industry, and aerospace. Unwanted exposure/s toany of these radiations may be hazardous to life. However, theimplications of such exposures are related to a number offactors that include the type of radiation and the energyassociated with it, the amount of dose administered (absorbeddose), exposure time, etc. Table 1 summarizes dierent types ofradiation encountered in the spacecraft industries, hospitals,and nuclear reactors. Cosmic radiation imposes importantsafety concerns for space exploration missions. Several studieshave speculated the radiation risks associated with exposure toboth galactic cosmic rays (GCR) and solar particle events(SPE).1,2 The radiation-induced health risks include carcino-genesis, cardiac problems, cataracts, and other acute radiationsyndromes.1 Damage to neuronal system has been a potentialconcern related especially to the heavy ions present in theGCR.2

    In medical radiation applications, radiotherapy is a commontechnique used to treat cancer patients. High-energy ionizingradiations (up to tens of MeV) are used to control tumorgrowth as part of cancer treatment. It is also used to treatnonmalignant conditions such as severe thyroid eye disease,abnormal growth of mucousal tissue (pterygium) or bone(heterotopic ossication), aggressive joint lesions such as

    pigmented villonodular synovitis, etc. The tissues near theregion of treatment often get exposed to the penetrative X-raysleading to harmful side eects to both internal and supercialorgans. One such side-eect that occurs in patients treated forhead and neck cancer is xerostomiaa condition that reducessaliva secretion, alters speech and taste, and induces othersecondary nutritional deciencies.3 X-rays with energies in keVrange are often employed in interventional procedures (X-rayimage-guided procedures), and in diagnostic radiology such ascomputed tomography (CT) examinations.Neutrons are uncharged particles commonly used in nuclear

    reactors for producing nuclear energy. They readily passthrough most materials and interact with the nuclei of thetarget atom. Many of the sources that emit X-rays and raysalso tend to emit neutrons. Exposure to neutron radiation isparticularly hazardous to body tissues since they are capable ofgenerating a much denser ion path as they lose/deposit theirenergy within the target material (in this case, body tissues).Interactions with biological matter may also result in theproduction of other radiations such as rays, protons and alphaparticles. Nuclear plant workers and aircraft crew are mostsusceptible to occupational exposure of neutrons.4 Hence, thereis a signicant demand for eective, durable radioprotectivegear in applications related to potential health hazards from

    Received: May 4, 2012Accepted: September 25, 2012Published: September 25, 2012

    Review

    www.acsami.org

    2012 American Chemical Society 5717 dx.doi.org/10.1021/am300783d | ACS Appl. Mater. Interfaces 2012, 4, 57175726

  • dierent types of radiation. In this paper, we focus on radiationsthat have high energy and/or high charge (referred to as HZE,where Z stands for atomic number), or have charge-inducingcapability when they traverse through a medium.Numerous experimental investigations and theoretical studies

    have reported the use of a variety of shielding materials (e.g.,concrete, polymer composites, heavy metals such as lead,composites of lead oxide/tungsten/tin, etc.) for attenuation orabsorption of the undesired radiations.710 The shieldingeectiveness of a given material largely depends on the type ofradiation and the range of energies associated with theradiation.11 Lead and other high Z materials have beenemployed to attenuate high-energy radiations such as X-raysand rays. However, high Z elements may not always be able toblock all types of radiations, particularly the emissions ofneutron particles in space or nuclear laboratories. Moreover,the radio-protective gear made from these materials are heavyand bulky, both of which often are unwanted features for mostapplications. For example, in mobile nuclear devices andmanned spacecrafts, radioprotective materials that are light-weight and have less volume are preferred due to the space andmaneuverability constraints imposed by the vehicles/devices.12

    There is an increasing demand to develop new shieldingmaterials that can be customized according to specicapplication (or radiation type). In the past two decades, severalstudies have reported application of nano- and microcompositematerials to attenuate/absorb high energy radiation. Because ofthe large surface-area-to-volume ratio, the nanoparticles havebeen reported to show enhanced ability to absorb photons.13

    Micro- or nanomaterials (also known as llers in this context)dispersed in a polymer matrix can be used to design eectiveradiation shields. The attenuation is obtained by a combinationof the ller/s and the structural material/s. Polymer-basedcomposites are particularly interesting candidates as radiation-shielding materials for varied reasons. First, they oer geometricconformability and can be used as a structural material likemetals or alloys commonly used in air-/space-craft industries.Second, they are lighter than their metal counterparts, andtherefore utilize lesser fuel to get to high altitudes or orbits.14

    Finally, they can be processed to achieve eective shielding forradiations associated with specic industry.In this paper, the state-of-the-art polymer composites with

    micro- or nanomaterials used as radiation-shielding materialsare reviewed. In section 2, an overview of the basic interactionsbetween the incident radiation and the target (shieldingmaterial) are presented. In section 3, the polymer compositesare broadly categorized based on the structure of the micro/nanomaterials used and a brief literature review is presented.The use of new polymer-based shielding materials and somepointers relevant for eective shielding are outlined in section4.

    2. RADIATION AND TARGET INTERACTIONS

    In order to design or select an eective radioprotective material,it is important to consider the following: (i) the type ofradiation (photons or particles) to be attenuated (or absorbed),and (ii) the type of interaction of the radiation with the targetmaterial. In this section, radiation-target interactions arecategorized into 2 subsections according to the type ofradiation: (i) high-energy photonmatter interactions, and(ii) particlematter interactions. In each of these subsections, abrief overview of the basic mechanisms of interactions, andT

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