Radiation Shielding Using Micro Cavities Filled with Highly Pressurised Gas
Usually, hydrogen is stored under high pressure, in chemical compounds or in its liquid state requiring very low temperatures. Gaseous hydrogen can be stored in hollow glass microspheres (5 μm to 200μm diameters) under high pressure (350 bar to 700 bar). The sphere-wall is impermeable for hydrogen at ambient temperature; the heating of the spheres increases the diffusion of hydrogen through the wall. The Aerospace Engineering group of the FOTEC GmbH developed an innovative process for the European Space Agency that combines the storage concepts of hollow glass microspheres with chemical hydrogen storage. The combination of these two principles provides the advantages of both but cancels their respective drawbacks. Our analysis shows that such a system can reach hydrogen storage capacities of up to 10wt% in theory. This value depends on the sphere dimensions, the weight of the spheres, the hydrogen pressure, and the nature of the utilised hydride. The expertise gained in the course of the extensive research on gas storage in hollow microspheres lead to new applications for such a system. One of these applications is the use of microspheres filled with highly pressurized gas as radiation shielding material. Since hydrogen is very effective in absorbing the energy of highly energetic particles with minimal generation of secondary particles, it is particularly suitable for radiation shielding. Effective radiation shielding materials therefore often incorporate high concentrations of hydrogen. By using glass microspheres, it becomes possible to collect large amounts of hydrogen atoms with a relatively high gravimetric as well as volumetric density. It is also possible to store other light gases in the microspheres like deuterium or helium, in order to customize the absorption properties of the material. Preliminary calculations show that this technique can be used as radiation shielding with significant mass savings in respect to conventional materials. In comparison to aluminium for example, the hydrogen filled microspheres can shield high-energy protons and ions with 30% to 40 % increased efficiency. Also bremsstrahlung, secondary neutrons and gamma rays can be significantly reduced. Due to the fact that the material can be easily adapted to any given form, the possible terrestrial applications include: radiation shielding of aircrafts, shielding of computer and electronics, radiation shielding in research facilities as well as on medical sites, but also protective clothing for PCRs (Competent Person in Radioprotection). Considering the possibility to produce large amounts of such a material with relatively low cost, a broad industrial interest for such a light-weight and ultra-dense radiation shielding material can be expected. Also, the considered material is easy to handle with respect to safety and flexibility. Space technology could be used to protect the environment and the population against radiation. To make this technology available for terrestrial applications, the first step is the detailed assessment of the physical processes of gas-filled microspheres in a radioactive environment. It is then possible to investigate the best combination of gas species, microsphere properties, coating layer and support structure or binding material for different applications. The second step is the production of a prototype layer material based on filled microspheres and the testing of the radiation shielding properties of the new material. The Aerospace Engineering group is specialised in the development of micro propulsion and gas storage systems for space application. It has a long record of successful projects performed on behalf of the European Space Agency. As research and service provider of the University of Applied Sciences Wiener Neustadt, it is the ideal hub for educational, industrial and scientific projects. A test facility to test the catalyst efficiency and the thermal properties of the coated microspheres as well as filling the microspheres with different gases is available.