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Modular power systems intended for radiation-intense environments such as geosynchronous orbit must withstand total ionizing doses (TID) up to 300 krad without mechanical or electronic failure. Traditional aluminum shielding adds mass and may generate secondary Bremsstrahlung x-rays when struck by high-energy charged particles, increasing the internal radiation dose on electronics. To protect against these effects, three low-Z polymer materials (polypropylene (PP), polyethylene (PE), and Bakelite (BK)) were identified as candidates for outer shielding layers. Preliminary tests included degradation and radiation exposure experiments in which Nexperia Gallium Nitride (GaN) field-effect transistors (FETs) were subjected to 300, 1000, and 3000 krad of gamma radiation using a Co-60 source. Post-irradiation measurements showed considerable threshold voltage shifts and moderate increases in leakage current at higher doses. Thermogravimetric analysis (TGA) was performed at 90 °C and 150 °C under inert nitrogen flow to evaluate relative off-gassing behavior of PP, PE, and BK, with results indicating minimal mass loss in PE and PP (<0.2%) and significant mass loss in BK (>4%). Additional beta irradiation tests at 20 kGy were performed to evaluate polymer shielding durability and dose attenuation, using a linear accelerator (LINAC) as a monoenergetic 6 MeV electron source. Post-irradiation microscopy revealed dielectric breakdown in PP and discoloration in all polymers. Dosimetry measurements showed that BK was most effective per unit thickness at shielding the dosimeter from the electron stream. In conclusion, if off-gassing can be mitigated by pre-baking, Bakelite represents the most promising candidate for polymeric shielding against charged-particle radiation flux in modular power systems. Keywords: Radiation Hardening; Power Modular System; Thermogravimetric Analysis; Gamma Irradiation; Beta Irradiation

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Purdue University / 2025

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