Activation Energy Distributions for Electron Traps in Polystyrene

A new form of analysis of thermally stimulated luminescence data is presented, enabling the form of the (concentration capture cross-section) vs. activation energy distribution function of the electron traps in a dielectric to be deduced. At the end of the irradiation the trapped electrons are divided into four groups; namely, the fraction of fo not re-trapped, and the fractions f1, f2, and f3 re-trapped once, twice, and three times, respectively, before recombining with a luminescent center. A distribution consisting of one or more sections of the form n(E) dE∝exp[ai(E-Ei)] dE is assumed, where n(E) dE is the concentration of traps with activation energies between E and E+dE multiplied by their electron capture cross-sections and ai and Ei are constants. A temperature-dependent frequency factor s(T) given by log s(T)= a+b(T-Tirr) is also assumed, where Tirr is the irradiation temperature and a and b are constants; s(T) applies to all traps, independent of E. The paraments ai, Ei, fi a, and b are adjusted to yield best agreement between experimental and synthesized data. Results are presented for polystyrene X-irradiated at liquid nitrogen temperature.