F-aggregate colour centres in LiF crystals with divalent impurities (M = Ni, Co, Be, Mg) are investigated by optical and thermally stimulated depolarization current (TSDC) spectroscopy methods. The F+2 centres accumulation in the LiF:M2+ crystals is similar to the F+2 centres accumulation in undoped LiF. Accumulation of F+2-like colour centres was observed only in the LiF:Mg2+ crystals at the first stage of low temperature irradiation with radiation doses exceeding 107 R. F+2-like centres are not formed in LiF with Ni, Be and Co impurity ions. The difference between the properties of the magnesium on one hand and the nickel, beryllium or cobalt doped crystals on the other is discussed in terms of the Hayes-Nickols mechanism with extra anion vacancy generation in the case of the LiF:Mg2+ crystal. The absence of the mechanism in LiF:Ni2+ and LiF:Be2+ is connected to the reduction of the impurity Ni2+ and Be2+ ion valence state and in LiF:Co2+ to the small concentration of single Co2+V-c dipoles as a result of extensive dipole aggregation. The destruction of the F+2 and F+2-like centres takes place in LiF:Mg2+ crystals at the second stage of aggregation, at which other F-aggregated centres are formed, with the impurity-vacancy (IV) dipoles included in their composition. The two-band structure of the TSDC curve of irradiated LiF:Mg2+, with relaxation parameters close to those of single IV dipole reorientation bands, is in accordance with the above mechanism of aggregation. The creation mechanisms and models of laser active colour centres (F+2-like and F3Mg2+V-c `red' colour centres) are discussed.

The dielectric relaxation of bovine serum albumin (BSA) aqueous solution was studied in various stages of urea denaturation by means of the thermally stimulated depolarization currents (TSDC) technique. A large variation of urea concentration was utilized (0-4 M). Special attention was given for concentrations between 0.006 and 0.050 M, which are comparable to those measured in normal and uremic human serum. The TSDC spectrum consists of two main bands in the temperature range 100-300 K: (1) a broad low-temperature band (A) with two maxima at about 128 and 142 K, which are attributed to the (re)orientation mechanisms of bulk and hydration water molecules, respectively, and (2) an intense band (B), whose position varies in the range between 230 and 245 K and which is attributed to the (re)orientation of protein macromolecules. Two peaks of lower intensity (B 1 and B 2 ) are resolved in the rising part of band B and are most likely due to relaxation mechanisms of the side chains of BSA. The activation energies for the last three mechanisms depend on urea concentration, and this fact might be attributed to the conformational changes of BSA upon denaturation. It is of interest to note that the macromolecules' activation energies depend drastically on the concentration of urea up to 0.05 M. Abstract published in AdVance ACS Abstracts, December 15, 1995.

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The dielectric relaxation spectra of dye containing silica gel-PMMA and bulk PMMA composites, recorded by means of the TSDC dielectric technique in the temperature range 10-320 K, have demonstrated a variety of overlapping thermally-induced current bands associated with different modes of dielectric relaxation, which are rather characteristic of the polymeric component. Molecular interactions between the inorganic (SO2) and polymeric (PMMA) phases have been shown to reflect in the activation energies of the polymer's @-relaxation mode. In the present study, the effect is unambiguously illustrated in the energy spectrum analysis of the partial discharge curves and the mathematical analysis based upon the varying heating rates procedure introduced by Solunov and Ponevsky.