Time-Dependent Radiation Induced Conductivity of Polyimide: Effects of Dose Rate and Temperature on Dynamic RIC

Radiation induced conductivity (RIC) can impact charge dissipation within highly insulating materials used in spacecraft in harsh space plasma environments. Previous Utah State University (USU) research analyzed only the equilibrium portions of an extensive RIC database for polymeric materials, including Kapton HN (Trademark). This confirmed that equilibrium RIC follows a standard theoretical model that is temperature and dose rate dependent. The current study provides a new analysis of RIC’s time-dependent behavior of the Kapton HN data from this database. With the onset of radiation, the material response is characterized by an exponential increase in conductivity, while a hyperbolic inverse time-dependent decline characterizes the decay of delayed RIC. A model with dual fast and slow time constants, representing the capture and release of charges from shallow and deep traps, respectively, produces the best fits to time-dependent RIC from successive dosing cycles at fixed temperatures. This dual-defect model provides information about the dose rate and temperature dependence of material properties in response to dynamic (time-dependent) RIC and helps infer relative trap state distributions and occupancy of the material.