Population kinetics of localized states in nanocomposite materials under exposure to radiation

We simulated the population of localized states in nanocomposite materials using Rouse-Fowler model. The following radiation effects were considered: prolonged irradiation (over 3 s) with the low absorbed dose rate (0,002 W/kg) and pulsed irradiation (100 ns) with the high absorbed dose rate (over 105 W/kg) of ionizing radiation. We investigated the role of localized states in electrical conductive properties of nanocomposite materials on the example of nanocomposite materials with hole conductivity (polymathimethacrilate (PMMA) + CdS) and electron conductivity ($\alpha$-Al$_2$O$_3$+SrO), as well as in pure PMMA and $\alpha$-Al$_2$O$_3$. Our results indicate that the small traps influence the speed of relaxation to the equilibrium radiation induced electrical conductivity, while the deep traps, the depth of which is much greater than $kT$, have an impact on the sensitivity to an absorbed dose of ionizing radiation. Moreover, pure PMMA and nanocomposite materials based on it are unsuitable for dosimetry due to a large share of the small traps in the spectrum of intrinsic localized states. On the contrary, aluminum oxide is an almost perfect material for the accumulation of the information about the ionizing radiation, since its spectrum of localized states includes only deep traps. On the whole, the most interesting materials from the dosimetry viewpoint are nanocomposites based on aluminum oxide, where the concentration of impurity centers does not exceed the concentration of intrinsic states, and the nanoparticle radius is no more than 2 nm in case of small share of the small traps in impurity spectrum.