Temperature Dependent Density of States Models and Compiled Data for Radiation Induced Conductivity

Radiation Induced Conductivity (RIC) is the change in conductivity of a material due to bombardment from incident high energy radiation. RIC has consistently been found to follow a standard power law relation, 𝜎𝑅𝐼𝐶(𝑇) = 𝑘𝑅𝐼𝐶(𝑇)Ḋ∆(𝑇), between conductivity, 𝜎𝑅𝐼𝐶 and adsorbed dose rate, Ḋ. 𝑘𝑅𝐼𝐶(𝑇) and ∆(𝑇) are material dependent parameters. Previous RIC models were developed in the 𝑇 → 0 limit. Now expanded models are developed in the low temperature limit (within a few 𝑘𝐵𝑇 of the effective Fermi level) by approximating the Fermi-Dirac equation within a few 𝑘𝐵𝑇 of the effective Fermi level. Derivations are based on seven density of states (DOS) models for highly disordered insulating materials: three monotonically decreasing models within the bandgap (exponential, power law, and linear) and two symmetric peaked models within the bandgap (Gaussian and delta function), plus a limiting case with a uniform DOS for each type. In addition, temperature dependent RIC data is compiled from literature for five polymeric materials used commonly in spacecraft: KaptonTM (polyimide or PI), polyethylenes (PE, low density polyethylene or LDPE, high density polyethylene or HDPE), TeflonTM (polytetrafluoroethylene or PTFE), MylarTM (polyethylene terephthalate or PET), and fluorinated ethylene propylene (FEP). Comparisons are made between compiled data from the literature and Utah State University RIC data, along with pertinent discussion of the results with a focus on the relevance of structural phase transition temperatures on measured RIC values. The second part of this work addresses the serious dearth of pertinent RIC data available needed to make critical design decisions for spacecraft, namely for the current NASA Europa Clipper and Lander missions.