Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation

Rate theory of the radiation-induced precipitation in solids is modified with account of non-equilibrium fluctuations driven by the gas of lattice solitons (a.k.a. quodons) produced by irradiation. According to quantitative estimations, a steady-state density of the quodon gas under sufficiently intense irradiation can be as high as the density of phonon gas. The quodon gas may be a powerful driver of the chemical reaction rates under irradiation, the strength of which exponentially increases with irradiation flux and may be comparable with strength of the phonon gas that exponentially increases with temperature. The modified rate theory is applied to modelling of copper precipitation in FeCu binary alloys under electron irradiation. In contrast to the classical rate theory, which disagrees strongly with experimental data on all precipitation parameters, the modified rate theory describes quite well both the evolution of precipitates and the matrix concentration of copper measured by different methodsComment: V. Dubinko, R. Shapovalov, Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation. (Springer International Publishing, Switzerland, 2014

Effect of radiation-induced emission of Schottky defects on the formation of colloids in alkali halides

Formation of vacancy clusters in irradiated crystals is considered taking into account radiation-induced Schottky defect emission (RSDE) from extended defects. RSDE acts in the opposite direction compared with Frenkel pair production, and it results in the radiation-induced recovery processes. In the case of alkali halides, Schottky defects can be produced as a result of the interaction of extended defects with excitons, as has been suggested previously. We consider a model that takes into account excitonic mechanisms for the creation of both Frenkel and Schottky defects, and which shows that although the contribution of the latter mechanism to the production of primary defects may be small, its role in the radiation-induced evolution of microstructure can be very significant. The model is applied to describe the evolution of sodium colloids and the formation of voids in NaCl, which is followed by a sudden fracture of the material, presenting a potential problem in rock salt-based nuclear waste repositories. The temperature, dose rate and dose dependence of colloid growth in NaCl doped with different types of impurities is analyzed. We have found that colloid growth may become negative below a threshold temperature (or above a threshold dose rate), or below a certain impurity concentration, which is determined by the RSDE, that depends strongly on the type and concentration of the impurities. The results obtained with the model are compared with experimental observations.

Nucleation and growth of sodium colloids in NaCl under irradiation: theory and experiment

A mechanism of radiation-induced emission of Schottky defects from extended defects proposed originally for metals has recently been applied to ionic crystals, where it is based on interactions of excitons with extended defects such as dislocations and colloids. Exciton trapping and decay at colloids may result in the emission of F centers and consequent shrinkage of the colloid. In the present paper, the radiation-induced emission of F centers is taken into account in the modeling of nucleation and growth of sodium colloids and chlorine bubbles in NaCl exposed to electron or gamma irradiation. The evolution of colloid and bubble number densities and volume fractions with increasing irradiation dose is modeled in the framework of a modified rate theory and compared with experimental data. Experimental values of the colloid volume fractions and number densities have been estimated on the basis of latent heat of melting of metallic Na obtained with combined differential scanning calorimetry experiments and atomic force microscopy investigations of metallic clusters.

Modeling of the radiation-induced microstructural evolution in ionic crystals

Results of experimental and theoretical investigations are presented on heavily irradiated natural and synthetic NaCl crystals in the temperature range where anion defects are mobile. They give a strong evidence for the formation of vacancy voids, which cannot be explained by the Jain-Lidiard model used up to date for description of metal colloids and dislocation loops formed in ionic crystals during earlier stages of irradiation. We consider an additional set of reactions between experimentally observed extended defects (metal colloids, gas bubbles and voids) and point defects. The latter include F and H centers that are the primary defects produced by irradiation, and cation vacancies (with a trapped hole) that are secondary defects, produced in the process of dislocation climb due to absorption of extra H centers. We show that highly overpressurized bubbles of fluid halogen are strongly biased for absorption of H centers, which makes them grow via punching out interstitial dislocation loops. The loops grow and produce cation vacancies that are subsequently trapped at the incoherent colloids together with extra F centers giving rise to the colloid-void transition. Elastic interaction between extended defects and point defects is shown to play a major role, since it determines the bias factors of extended defects, which is a major driving force of the microstructural evolution under irradiation. A quantitative comparison of the new model for radiation damage in NaCl with experimental data is presented. Mean sizes and volume fractions of all types of observed defects are calculated. It is shown that voids formed due to agglomeration of F centers and cation vacancies can grow to the dimensions exceeding the mean distance between colloids and bubbles, eventually absorbing them, hence, bringing the halogen gas and metal to a back reaction. Impurities play a major role in the void development with increasing irradiation dose, which strongly affects the radiation stability of NaCl. (C) 1999 Elsevier Science B.V. All rights reserved

Influence of y-irradiation on optical properties of GaSe crystals

Performed in this work are low-temperature (T = 4.5K) investigations of exciton photoluminescence spectra in layered GaSe crystals both non-doped and doped with Zn and Sn in concentrations < 0.01 wt. %. The crystals were irradiated with y-quanta of the energy within the range 0 to 34 MeV with the doses up to 10^14 y/cm2. It has been shown that irradiation with the above doses results in improvement of quality in non-doped GaSe crystals: there disappears the “thin structure” of the emission line inherent to free excitons related with stacking fault defects of crystalline layers, observed is ordering the sets of bound exciton lines related with deep acceptors. As a consequence, there observed is an essential increase in the parameter S0 – integrated intensity of radiative recombination of free and bound excitons. Analogous changes related with healing of defects in GaSe crystalline lattice are observed after doping with Zn impurity. Irradiation of these crystals with y-quanta causes increasing S0, too. By contrast, doping with Sn impurity results in a sharp drop of S0 that begins to grow after irradiation with y-quanta. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2089

Synthesis of hydrogen storage materials in a Ti-Zr-Ni system using the hydride cycle technology during dehydrogenation by an electron beam in a vacuum

The synthesis of intermetallic material was carried out by means of dehydrogenating annealing of a (TiH₂)₃₀Zr₄₅Ni₂₅ sample in vacuum by an electron beam. The properties of the obtained material were studied for establishing the structural phase composition by scanning electron microscopy and X-ray structural analysis. It was found that prolonged exposure of an electron beam to a sample containing titanium hydride leads to a number of structural transformations in the material, accompanied by a redistribution of hydrogen from titanium to zirconium and culminating in the synthesis of a ternary alloy with characteristic growth structures. The processes of hydrogen sorption-desorption by a synthesized sample were studied, the temperature ranges of these processes and the absorption capacity of the obtained material were established. It was shown that the structure of the sample formed upon heating by an electron beam promotes the absorption of hydrogen at room temperature up to 1.41 wt.%.Проведено синтез інтерметалічного матеріалу за допомогою дегідруючого відпалу зразка (TiH₂)₃₀Zr₄₅Ni₂₅ у вакуумі електронним пучком. Методом скануючої електронної мікроскопії і рентгеноструктурного аналізу досліджені властивості отриманого матеріалу для встановлення структурно-фазового складу. Встановлено, що тривала дія електронного пучка на зразок, що містить гідрид титану, призводить до ряду структурних перетворень у матеріалі, що супроводжуються перерозподілом водню з титану в цирконій і завершуються синтезом потрійного сплаву з характерними структурами зростання. Досліджено процеси сорбціїдесорбції водню синтезованим зразком, встановлені температурні діапазони даних процесів і поглинальна здатність отриманого матеріалу. Показано, що сформована при нагріванні електронним пучком структура зразка сприяє поглинанню водню при кімнатній температурі до 1,41 ваг.%.Проведен синтез интерметаллического материала посредством дегидрирующего отжига образца (TiH₂)₃₀Zr₄₅Ni₂₅ в вакууме электронным пучком. Методом сканирующей электронной микроскопии и рентгеноструктурного анализа исследованы свойства полученного материала для установления структурнофазового состава. Установлено, что длительное воздействие электронного пучка на образец, содержащий гидрид титана, приводит к ряду структурных превращений в материале, сопровождающихся перераспределением водорода из титана в цирконий и завершающихся синтезом тройного сплава с характерными структурами роста. Исследованы процессы сорбциидесорбции водорода синтезированным образцом, установлены температурные диапазоны данных процессов и поглотительная способность полученного материала. Показано, что сформировавшаяся при нагреве электронным пучком структура образца способствует поглощению водорода при комнатной температуре до 1,41 вес.%