Temperature Dependence of Radiation Induced Conductivity in Insulators

This study measures Radiation Induced Conductivity (RIC) of Low Density Polyethylene (LDPE) over temperatures ranging from ~110 K to ~350 K. RIC occurs when incident ionizing radiation deposits energy and excites electrons into the conduction band of insulators. Conductivity was measured when a voltage was applied across vacuum-baked, thin film LDPE polymer samples in a parallel plate geometry. RIC was calculated as the difference in sample conductivity under no incident radiation and under an incident ~4 MeV electron beam at low incident fluxes of 10-4-10-1 Gr/sec. The steady-state RIC was found to agree well with the standard power law relation, sRIC = kRIC*DD between conductivity, s and adsorbed dose rate, '. Both the proportionality constant, kRIC, and the power, d, were found to be temperature dependant above ~250 K, with behavior consistent with photoconductivity models developed for localized trap states in disordered semiconductors. Below ~250 K, kRIC and D exhibited little change. The observed difference in temperature dependence might be related to a structural phase transition seen at Tb~256 K in prior studies of mechanical and thermodynamic properties of LDPE.