If civilian and military equipment and personnel are to be effectively shielded in a high radiation environment- such as that found in space, or in a nuclear-powered naval vehicle, or in a nuclear-active battlefield environment- then protection against high-energy photons must be enhanced well beyond that currently delivered by existing materials. Materials that are highly effective in stopping the nuclear by-products before they encounter sensitive electronics or the war-fighter can mitigate the need to develop radiation-hard components or biological countermeasures following radiation exposure. Unfortunately, the current shielding modality, in which one adds more material-depth in order to increase the attenuation of any damaging quanta, is unattractive for deployed missions because of the weight and size of high-Z materials for photon shielding becomes operationally cumbersome. One must therefore modify the underlying material in order to elicit transformational improvements in current shielding materials. If one can make a material with multitudinous interfaces, such as provided by a combination of high-Z (e.g. Pb) nanoparticles potentially bonded to low-Z polymeric components, then the small interfacial loss per interaction can accumulate to dominate the attenuation characteristics. Our nanostructured gamma-ray shielding material has: (1) a transformative mechanism- distributed multitudinous interfacial scattering at nanoparticle surfaces- to enhance stopping power and neutral particle attenuation, (2) 1/10th to ½ the mass density of the equivalent bulk material, (3) a very high temperature resilience (up to 752 0F), (4) a low-cost solution-based synthesis, (5) a high thermal (and electrical) conductivity, (6) a flexibility and high-damping of mechanical vibration, and (7) a readily scalable production method. During Phase I, our goal is to demonstrate the feasibility of forming large-volume, nanostructured composite shielding with a gamma-ray linear attenuation coefficient at least twice that of the equivalent bulk material. Although solid nanoparticles, composed of lead for instance, can achieve this goal, our wave-mechanics modeling predicts that core-shell nanoparticles are substantially superior in exploiting gamma-ray redirection effects within a heavily loaded solid. We will therefore form PbO/Pb, CdS/PbS, and Pb hollow-core nanoparticles and form those into solids through either bottom-up self-assembly methods or through top-down milled-and-pressed methods. The advantage of the latter is that the organic constituents, which govern the self-assembly for bottom-up approached, are avoided and one can therefore make a more component-pure nanostructured solid from which to prove the feasibility of enhanced stopping. The advantage of the solution-based nanostructured composite approach is that the process is simple, scalable, and low-cost and therefore ultimately preferred for commercialization of the material.
