Comparative analysis and experimental validation of gamma ray shielding performance of potential polymeric materials

This work reports the shielding performance of different potential polymer matrices for composite material based shield to attenuate gamma ray’s emitted as secondary radiation due to interaction of Protons and heavy ions with spacecraft structural as well as electronics materials.  The estimation of shielding effectiveness to determine Total Ionizing Dose (TID) deposited on Silicon (Si) sensor, the substrate material used for fabrication of semiconductor electronic devices is reported. The analyzed polymers include PolyDiMethylSiloxane (PDMS), PolymethylMethaAcrlate (PMMA), Ultra-High-Molecular-Weight PolyEthylene (UHMWPE), High-Density PolyEthylene (HDPE), Polyether ether ketone (PEEK), Polybenzimidazole (PBI), Polyetherimide (PEI), PolyImide (PI) and Epoxy. It was found that PMMA is more effective to attenuate gamma radiation at lower energies up to 1.0 KeV due to higher value of MAC whereas PDMS attenuates more gamma radiation than other analyzed polymers with energies up to 8.0 keV. For energies higher than 40 keV the computed value MAC for all the polymer matrices remains the same. Moreover, computed value of MAC for HDPE comes out to be better for gamma radiation energies of 1.173 and 1.332 MeV emitted by Cobalt-60 radioisotope. The 500 µm Si detector was selected to assess TID deposited by gamma radiation in MULASSIS online resource, so that the dose rating of COTS devices to be deployed aboard satellite could be estimated.

Mass Attenuation Coefficient (µm) of shielding compositions were determined using NIST WinXCOM online software for gamma radiation peak energies of Co60 radioisotope i.e. 1.17 MeV and 1.33 MeV. Based on µm values determined using WinXCOM and Phy-x online tools for given energies, calculation of radiation shield effectiveness parameters such as Linear Attenuation Coefficient (µ), Half Value Layer (HVL), Tenth value layer (TVL) and Mean Free Path (λ) were theoretically deduced. The gamma radiation energies/TID deposition after passing through TVL, HVL thicknesses were estimated with Space Environment Information System (SPENVIS)- Multilayer Shielding Simulation Software (MULASSIS) which is integrated as GEANT4 tool in SPENVIS online resource developed by European Space Agency (ESA). The co-relation was established between variation in shield parameters and attenuation of gamma radiations absorption by polymer composite shield model and TID deposition on Si sensor, the substrate material used for VLSI microelectronics components fabrication. Finally, comparative analysis of TID deposition on Si sensor was analyzed for different shield configurations and its corresponding dose-depth curves were determined.

The experimental results revealed good agreement with the theoretical values obtained using the WinXCOM program, Phy-X PSD and SPENVIS software.  The research output will be helpful to optimize hybrid composite based shielding for protection of microelectronic devices against TID deposition by secondary gamma radiation in space environment.

Keywords: Polymer matrix; Gamma radiation; Mass Attenuation Coefficient; Radiation shielding parameters; Space environment: shielding effectiveness

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