# Electromagnetic Radiation Shielding Using Carbon Nanotube and Nanoparticle Composites
## 7 Mechanisms for Small Particles to Block Radiation
Polymers reinforced with clay platelets were also investigated. Sheets approximately 1 nm thick to 30 nm thick and up to several microns wide provided enhanced resistance from high-energy radiation such as gamma rays. Styrene-butadiene-styrene/organophilic clay nanocomposites could have undergone crosslinking and main chain scission when exposed to gamma radiation. This is another effect of nanoparticles integrated into polymers. The composition of the material may change due to the radiation. A comparison of polymer composite based shielding materials and conventional materials is given in ([48],reference Table 2). The increased gelation and increased molecular weight of nanocomposites at higher fluences indicate that exposure to swift heavy ions mainly induced chain scission in pure hexafluoropropylene, whereas crosslinking was the major phenomenon in nanocomposites. It was also reported that other composites can have increased radiation resistance due to crosslinking mechanisms in a parallel chain conformation of molecules on the surface of layered nanoclay. Crosslinking may change the durability in the radiation shielding of materials. The radiation-resistant properties of nanomaterials still need to be fully understood especially for different types (energy levels) of radiation. The size effects of nanoparticles versus microparticles on the X-ray-attenuation properties of copper oxide embedded into bees wax were reported. The copper oxide nanoparticles showed enhanced attenuation characteristics at low X-ray energies compared to microparticles. The selective enhancement of radiation attenuation by the nanomaterials at lower energies was attributed, in the paper, to the increased number of particles per gram and grain size effects. These investigations need to be extended to other high-atomic-number materials to fully understand and take advantage of the new properties offered by nanosized materials. These new polymer nanocomposites may offer a lead-free approach for shielding against the low-energy radiation used in diagnostic applications. But there are many issues related to secondary particles and long-term stability of the nanocomposite. High-energy particles in space can also degrade composites. Further research is needed to investigate their reliability over the long term. The current trend is toward exploiting the properties of nanoscale structures for effective lightweight and durable radiation-resistant materials. Radiation dosimetry is discussed in [94]. An important investigation into the synthesis, characterization, and application of ultra-small nanoparticles was performed by [PERSON] and others [95]. Ultra-small nanoparticles in the one nanometer size range have a large surface area-to-volume ratio. This review paper focused on ultra-small nanoparticles. Sub nm aggregates consisting of less than 20 atoms were defined as clusters rather than particles or crystals. The clusters require different synthesis and characterization methods and have different properties than nanoparticles. Clusters are defined separately from atoms and particles. Clusters are not categorized as ultra-small nanoparticles. This paper focused on the properties of ultra-small nanoparticles defined to be in the range of one to three nanometers. Nine references are given that represent different investigations of ultra-small nanoparticles. When the size of a material decreases to one to three nanometers, the number of atoms contained in the material is less than 500. Thus, these ultra-small nanoparticles can be regarded as large molecules. If most of the component atoms are located at the interface with the environment, this means a greater number of atoms are exposed to the outer environment. A very important point in this paper is that the crystal structures of ultra-small nanoparticles are often significantly different from those of their bulk counterparts. An example is bulk gold.