On the melting-crystallization criterion and the energy of activation processes for nanocrystals

It is shown that the localization criterion for the crystal-liquid phase transition introduced earlier for macrostructures is also valid for nanocrystals. The variation of the parameters of activation processes (formation of vacancies and self-diffusion) with a decrease in the nanocrystal size is investigated. It is shown that the lattice of a nanocrystal is more perfect than that of a macrocrystal at low temperatures, while at high temperatures, the nanocrystal is activated by mobile vacancies to a greater extent than the macrocrystal.

     

On the determination of thermal ionization energy of deep centers from ESR data

It is shown that the skin effect due to thermal generation of free carriers may affect the ESR signal more than deep center depopulation. Experimental results for 0.33 eV deep Eu²⁺ donor in CdF₂ crystals are presented, to show the way in which the thermal energy of deep centers is deduced from the ESR data.     

Anomalous thermal bleaching of color centers in calcium fluorapatite

A study has been made of the radiation-induced paramagnetic color centers in calcium fluorapatite on annealing. It is found that there is an anomalous increase in the center concentration during isothermal annealing. An explanation is given via a model for diffusion of point defects and groups involving charge redistribution. It is found that the dislocation structure affects the thermal bleaching of the color centers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 34–37, April, 1975.     

The mechanism of disintegration of color centers and the non-stationary recombination luminescence of NaCl-Ag phosphor crystal. I

A combined method has been used to study the disintegration processes of the 355, 465, and 720 color centers of NaCl-Ag phosphor in the temperature range 100–550 ° K. The emission spectra of thermostimulated and photostimulated recombination luminescence of NaCl-Ag excited by X-rays at various temperatures were also studied. The possibility of ion-electron and ion-hole disintegration mechanisms of the color centers in the phosphor crystal at low temperatures is examined.The authors thank Doctor of Physical and Mathematical Sciences Ch. B. Lushchik for discussion of the subjects touched upon in the present paper, and also Yu. N. Evstifeev for assistance in performing the experiment.     

Determination of the activation energy for complicated relaxation processes

Different methods are considered for analyzing the temperature dependence of the relaxation rate in the Arrhenius form. It is emphasized that the possible changes in the barrier to elementary acts with variations in temperature should be taken into account in order to determine the relaxation activation energy correctly. Changes in the barrier to elementary acts are illustrated using experimental data on the temperature-frequency dependence of the dielectric relaxation in polymers. A theoretical approach offering realistic activation energies is proposed.     

On the complex energy eigenvalue theory of alpha decay

We have developed a method to compute alpha decay widths in the theoretical frame of the complex energy eigenvalue. We apply it to 102 alpha decays of even-even nuclei. The theoretical values reproduce reasonably well the experimental results and they also show that there is a structure which depends on the orbital angular momentum of decay.     

Investigation into the processes of thermal and photothermal destruction of F-color centers in alkali-halide crystal phosphors

Using the concept of thermal and photothermal destruction of color centers in alkali-halide phosphors as an ion mechanism, certain formulas are examined which represent these processes. The phenomenon of thermal and photothermal destruction of F-color centers is investigated experimentally for the case of NaCl-Ag. A comparison of the experimental results obtained with the theory enabled an estimate to be made of a number of kinetic characteristics of the processes in question.The results obtained confirm the usefulness of the idea of ion processes in explaining the phenomena of relaxation in alkali-halide crystal phosphors.     

Irradiation effect on the activation energy of thermal decomposition of polymers

The present work looks into the aspect of thermal modifications induced in polymers by proton irradiation. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived.     

Effect of electron energy on the accumulation of color centers in reflective coatings based on ZnO

We have made the first studies of the effect of electron energy in the range of tens of keV on the intensity changes of the intrinsic absorption bands of color center point defects (F⁺ and F centers, V _Zn ⁻ , V _Zn ²⁻ , (V _Zn ⁻ — Zn _i ⁰ )-, etc.) and temperature-control coatings (TCC) for space equipment based on it, obtaining an expansion of the integral induced absorption band into components. It was established that the intensity grows in the region 10–100 keV up to an energy of about 15 keV and then it decreases. An explanation is proposed for the behavior seen. It has been established that the free electron concentration increases by a power law with increasing electron acceleration energy. Tomsk Polytechnical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 85–90, April, 1998.     

On Ulam's redistribution of energy problem

We continue the work on Ulam's redistribution of energy problem started by D. Blackwell and R. D. Mauldin (Lett. Math. Phys. 10, 149–153 (1985)). We prove that for any initial distribution with the first moment finite, its images under iteration of Ulam transformation weakly converge. Some properties of the limit measure (especially its absolute continuity) are examined.     

Low energy activation processes in amorphous polymers - the case of selenium

We present an internal friction experiment in amorphous selenium at low frequency (30 kHz) and low temperature (4 K < T). Our results prove that, below the glass transition, there exists in amorphous selenium only one kind of thermal activated processes involving internal friction. We suggest that the underlying microscopic mechanisms are closely related to the polymeric amorphous structure and so should exist in any amorphous polymers.     

Ordering processes and activation energy in Ni3Fe-based ternary alloys

The measurement of electrical resistance () has been used, to study the kinetics of isothermal ordering in the range 200 °–545 ° C in Ni₃(FeMn) alloy quenched from 970 ° C, and the kinetics of ordering at 390 ° C in the alloy quenched from various temperatures in the 600 °–800 ° C range. The sections method and the gradient of the (t) curves were used to find the activation energy for migration and vacancy formation in this alloy on the assumption that the excess vacancies frozen in the alloy by quenching at temperatures above T_c are responsible for ordering. The activation energies for vacancy formation and migration were respectively U₀ = 33 ± 3 kilocal/mole and U_m = 39 ± 4 kilocal/mole, which in total give the activation energy for diffusion Q = 72 ± 7 kilocal/mole in the alloy studied; this approximates to the activation energy for diffusion in pure nickel.     

On the absence of energy transfer between F and M centers in KCl

M-centers, when excited in M₁ and M_F bands, show the same luminescence in the 79–263 K temperature range. No evidence of any energy transfer between F and M centers has been found. The measurements of other authors, involving such a process, are discussed. In addition an investigation of a possible change in the radiative lifetime, due to the presence of α centers, gives a negative result.     

A study of the activation energy of thermal decomposition of irradiated polymers

The ion irradiation of polymeric solids induces numerous modifications in the polymer properties thus increasing their applicability in various fields. The present work looks into the aspect of thermal modifications induced in the irradiated polymers. The kinetics of thermal decomposition of polymers is investigated by using the thermogravimetric (TG) technique. It has been observed that the degradation of polymers is a multi-step process that involves sequential and competing processes, and obeys the Arrhenius kinetics which allows us to connect the rate constant with the absolute temperature and the activation energy. The activation energy of thermal decomposition has been calculated from the TG curves, and its variation with different irradiation doses has been derived.     

The thermal activation energy of crystalline Sb2Se3

Crystalline Sb₂Se₃ exhibits intrinsic-like electrical conductivity behavior with varying thermal activation energies. An explanation is offered based on the incorporation of native defects during crystal growth.     

On the problem of vacuum energy in brane theories

We point out that modern brane theories suffer from a severe vacuum energy problem. To be specific, the Casimir energy associated with the matter fields confined to the brane, is stemming from the one and the same localization mechanism which forms the brane itself, and is thus generically unavoidable. Possible practical solutions are discussed, including in particular spontaneously broken supersymmetry, and quantum mechanically induced brane tension.