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[en] In this paper, soil samples collected in the Tartarugalzinho region, State of Amapa, were analyzed by instrumental neutron activation analysis. The concentration of about 24 elements such as As, Ba, Br, Ce, Co, Cr, Cs, Fe, Hf, K, La, Lu, Na, Rb, Sb, Sc, Se, Sm, Ta, Tb, Th, U, Zr e Zn could be determined. The soil samples collected near gold mining activities, were separated into fractions smaller than 2 mm and powdered to the granulometry of 200 mesh, and homogenized. Analysis of the reference materials Buffalo River Sediment (NIST SRM 2704) and Soil 7 (IAEA) showed the accuracy and precision of the method. (author). 7 refs., 3 figs., 4 tabs
[en] Solvent extraction and ion exchange have been the most widely used separation techniques in nuclear and radiochemistry since their development in the 1940s. Many successful separations processes based on these techniques have been used for decades in research laboratories, analytical laboratories, and industrial plants. Thus, it is easy to conclude that most of the fundamental and applied research that is needed in these areas has been done, and that further work in these ''mature'' fields is unlikely to be fruitful. A more careful review, however, reveals that significant problems remain to be solved, and that there is a demand for the development of new reagents, methods, and systems to solve the increasingly complex separations problems in the nuclear field. Specifically, new separation techniques based on developments in membrane technology and biotechnology that have occurred over the last 20 years should find extensive applications in radiochemical separations. Considerable research is needed in such areas as interfacial chemistry, the design and control of highly selective separation agents, critically evaluated data bases and mathematical models, and the fundamental chemistry of dilute solutions if these problems are to be solved and new techniques developed in a systematic way. Nonaqueous separation methods, such as pyrochemical and fluoride volatility processes, have traditionally played a more limited role in nuclear and radiochemistry, but recent developments in the chemistry and engineering of these processes promises to open up new areas of research and application in the future
[en] Sono-chemical reactions are known since a long period of time. Undoubtedly, the chemical effects of the ultrasound are related to the acoustic cavitation. However, the origin of the processes occurred within the cavitating bubbles are still unclear. Recent discovery of the single bubble sono-luminescence and the evidences for the sono-chemical activity of the single cavitating bubble offer the opportunity to obtain more detailed information about the cavitation events. However, many researches claim the lack of correlation between the processes in the single bubble and in the multi bubble cases. The fundamental aspects of the multi bubble and single bubble sono-chemistry and sono-luminescence will be reviewed during the presentation. Also the potentials of sono-chemistry for nano-chemistry and nuclear chemistry will be discussed. (author)
[en] Starting from the Breit–Wigner model, we present a generalized approach for calculating the electrical conductance of a one-atom metallic constriction with electrochemical-potential control. In addition, the corresponding current intensity is determined. On the one hand, the nanoconstriction is conceived as a dilute (degenerate) Fermi gas (relatively low electron concentrations are considered) and, on the other hand, non-dilute gas is considered. Under these conditions, the Fermi energy-level into the Breit–Wigner formula is replaced by the corresponding chemical-potential energy. We emphasize the role of the optical potential as significant ingredient of the chemical potential.
[en] The basic physical principles underlying electron transfer between metal ions and other well-localised centres are summarized. Recent experimental progress is reviewed, with particular reference to electron transfer in the gas phase-between large molecules; in solution - results of volume of activation studies; and in the solid phase-transfer between paramagnetic centres. The potential value of neutron scattering spectroscopy, as a probe of low-energy electronic transitions in mixed-value materials, and as a method of measuring rate processes in the range 1010-1012 s-1, is discussed. (author). 86 refs.; 6 figs
[en] We investigated the electrochemical properties of alkanethiol monolayers adsorbed on NPG surfaces by cyclic voltammetry and electrochemical impedance spectroscopy, and the results are compared to those on flat Au surfaces. The reductive desorption of alkanethiols on NPG surfaces is observed in more negative potential regions than that on flat Au surfaces due the stronger S-Au interaction on NPG surfaces. While the electron transfer through alkanethiol monolayers on flat Au surfaces occurs via a tunneling process through the monolayer films, the redox species can permeate through the monolayers on NPG surfaces to transfer the electrons to the Au surfaces. The results presented here will help to elucidate the intrinsic electrochemical properties of alkanethiol monolayers adsorbed on curved Au surfaces, particularly on the surface of AuNPs. Self-assembled monolayers (SAMs) of thiolate molecules on Au surfaces have been the subject of intensive research for the last few decades due to their unique physical and chemical properties. The well-organized surface structures of thiolate SAMs with various end-group functionalities can be further utilized for many applications in biology and nanotechnology. In addition to the practical applications, SAMs of thiolate molecules on Au surfaces also provide unique opportunities to address fundamental issues in surface chemistry such as self-organized surface structures, electron transfer behaviors, and moleculesubstrate interactions. Although there have been numerous reports on the fundamental physical and chemical properties of thiolate SAMs on Au surfaces, most of them were investigated on flat Au surfaces, typically on well-defined Au(111) surfaces
[en] The electrochemical decoration of Au and Pd nanoparticles by Pd and Au atoms respectively is discussed in a statistical mechanical framework. It is found that depending on precursor nanoparticle size and shape, controlled decoration may be achieved in undersaturation or oversaturation conditions. Multilayer deposition is also considered, with the finding that this phenomenon is also size dependent.
[en] The available models of charge transfer processes in electroactive polymer films are considered. Examples of interpretation of the data of electrochemical measurements using model approaches are given. The emphasis is placed on the interpretation of the results on the impedance of modified electrodes. On this basis, conclusions concerning the most topical research problems and the description of the processes in question are drawn.
[en] This glossary lists close to 400 terms and definitions commonly used in radiochemistry, with emphasis on radioanalytical chemistry. Part of the definitions have been taken, sometimes with minor modifications, from existing glossaries of such organizations as the International Organization for Standardization and the International Electrotechnical Commission. In cases where no acceptable definition could be found, a new definition is proposed. (author)