Advanced Carbon-based Material as Space Radiation Shields
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Advanced Carbon-based Material as Space Radiation Shields Sanju Gupta,∗ Rishi J. Patel, and Nathaniel D. Smith Department of Physics and Materials Science and Center of Applied Science and Engineering (CASE), Southwest Missouri State University, Springfield, MO 65804-0027, USA. ABSTRACT Carbon-based materials including microcrystalline diamond, nanocrystalline diamond, and carbon nanotubes films were prepared by microwave plasma-assisted chemical vapor deposition (MWCVD) technique. While the former were submitted to gamma radiation doses of 1, 5, and 20 Mrad, the latter to low energy electron beam of 30 keV or to 30 GeV/cm2) to study the radiation-induced structural transformation. The characterizations were performed prior to and after irradiation using Raman spectroscopy, scanning electron microscopy, and X-ray diffraction, techniques. Microcrystalline diamond showed a dramatic modification in the structural properties only after a cumulative dose of 26 Mrad (2 Grad/cm2), while nanocrystalline carbon showed a relatively small but systematic transformation with increasing gamma radiation dose. The results indicate that nanocrystalline carbon tends to reach a state of saturation when submitted to 26 Mrad doses of gamma radiation, suggesting the possibility of fabricating radiation buffer materials that would undergo internal sp3 ⇔ sp2 inter-conversion while absorbing ionizing radiation without changing their average microstructure and protecting the device/material underneath. Single- and multi-walled nanotubes exhibited structural modifications after 5.5-8 hrs of continuous exposure to electron beam. The variation in the characteristic X-ray peaks for multi-walled and single-walled corresponding to intertube spacing and the high frequency Raman band around 1580 cm-1 (G band) are reflected in their corresponding spectra. The results indicate that there is an increase in the intertube spacing for multi-walled nanotubes due to electron irradiation. While single-wall nanotubes tends to ‘collapse’ after > 8 hours of exposure forming multi-wall nanotubes analyzed using scanning electron microscopy and Raman spectroscopy. These C materials can be employed for preventing space radiation from reaching sensitive materials and electronic devices at least for short term experiments and entitled them as ‘space radiation shields’. INTRODUCTION Carbon-based materials continue to attract attention because of their unique combination of physical properties [1]. Included in this group of materials are microcrystalline diamond, nanocrystalline carbon, or nanostructured carbon, HPHT diamond, disordered tetrahedral carbon (DTC), and carbon nanotubes [2]. In addition to their technologically interesting electrical/electronic properties, these materials have many other attractive physical and chemical properties, such as chemical inertness, high thermal conductivity, mechanical robustness, and resilience to harsh environments. Diamond is reputed for being radiation hard and hence preferable over the other existing semiconductors
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