Search Results
Abstract
A new procedure to isolate carrier-free isotopes of Nb and Ta after a 12-MeV proton bombardment of a natural Hf foil has been considered. The cross section of the corresponding natHf(p,x)179Ta reaction has been estimated for the first time as 5.4 ± 0.5 mb. The isotopes that were produced were subsequently used for development of procedures for the chemical characterization of element 105 (Db). HF/HNO3 and HNO3/H2O2 media have been chosen and the parameters of the experiments have been optimized. Based on the results obtained in this work, off-line experimental procedures have been proposed for the evaluation of the chemical behavior of Db.
The reaction [Mn(NH3)2]Cl2+ 4NH3 ⇄ [Mn(NH3)6]Cl2, which is of potential use in chemical heat pumps, was studied by means of differential scanning calorimetry. The thermodynamic conditions, the enthalpy of the reaction, and the heat capacity values for MnCl2, [Mn(NH3)2Ch and [Mn(NH3)6Cl2 were measured. The influence of the reaction kinetics of the experimental procedure and some parameters such as sample temperature, ammonia pressure and scanning rate was examined.
Abstract
A computer program is described, which calculates the induced activities of isotopes after irradiation in a known neutron field, thermal and epithermal neutron fluxes from the measured induced activities and from nuclear data of 2–4 monitor nuclides as well as the element concentrations in samples irradiated together with the monitors. The program was developed for operation in Windows 3.1 (or higher). The application of the program for neutron activation analysis allows to simplify the experimental procedure and to reduce the time. The program was tested by measuring different types of standard reference materials at the FRJ-2 (Research Centre, Jülich, Germany) and Triga (University Mainz, Germany) reactors. Comparison of neutron flux parameters calculated by this program with those calculated by a VAX program developed at the Research Centre, Jülich was done. The results of testing seem to be satisfactory.
Abstract
Use of laboratory model experiments for analysis of interaction of radionuclides with surface water solids is connected with methodical problems concerning selection of solid phase, sampling, storage and pretreatment of solid phase, concentration of radionuclide, selection of liquid to solid ratio, adsorption of radionuclide on vessel walls, choice of experimental procedures and change in radionuclide speciation in the solid phase. These problems are discussed on the basis of literature data and of experiments with radiocobalt or radiocesium in a system river water-suspended solids or bottom sediments. Possible ways of solution of the problems are shown. Two modifications of batch method are described in detail and their merits or drawbacks evaluated. Comparison of the modifications shows their possible use as complementary methods for the study of radionuclide behaviour in surface waters.
Abstract
The sorption and desorption of thorium on a West Anatolian montmorillonite has been studied by application of a batch technique. Experimental procedures are outlined and results for thorium contacted with montmorillonite are reported and discussed. The thorium concentration range was between 200–4000 ppm (8.5×10–4–1.7×10–2M). The sorption and desorption coefficients varied between 1.586–0.216 ml g–1 and 0.829–0.168 ml g–1, respectively, and sorption was not fully reversible. The data could be fitted to Freundlich and Langmuir isotherms. The quantity of the sorbed thorium was much lower than its theoretical CEC. This was attributed to a blocking of montmorillonite's CEC by thorium islands in the interlayer.
Abstract
The thermal curves and the enthalpy changes of the interaction between some oral sustained release preparations (Contac, Fenbid and Benza sustained release capsules) and physiological saline have been measured at 298.15 K with a MS-80 standard Calvet microcalorimeter. The curves that recorded the changes of heat effect with time have clearly shown the sustained release action and process of the above preparations. A method for examining the sustained release action of sustained release preparations can be developed from the above experiments. The principle of application and the experimental procedure of this method have been expounded, and some results of the above experiments have also been discussed.
Summary
The influence of calcite, dolomite, pyrite and vaterite on the kinetics of uranium release from a natural rock under relevant, i.e., field conditions has been investigated. The time dependence of the U release has been studied in two different experimental procedures (open and closed systems) at laboratory temperature (21±2 °C). Performing batch experiments in tap water, the U release efficiency of a natural U-bearing rock was characterized in the presence of varying amounts of three different carbonate bearing minerals for experimental durations of up to 782 days. Another experiment was conducted for a period of 14 days in the presence of a pyrite mineral. The results demonstrate that the presence of carbonate minerals does not have any significant influence on U release in closed systems where the U concentration at saturation was ca. 54 mg/l. In contrast, in open systems, the U concentration was ca. 8 mg/l at saturation and the effects of all additives both on kinetics and saturation concentration of U were apparent.
Generosity seems to be a cross-culturally ubiquitous feature of life. Helping others is considered as a costly act through which the altruists gain popularity and reputation in their reference group and this elevated reputation will pay off for them in future social relationships. This costly signaling theory has been widely tested in pre-industrial societies. Our purpose was to examine if the assumptions of CST are verifiable in modern, industrial societies. Using a complex experimental procedure with four subsequent phases we could examine reputation-gaining in realistic conditions. We found that more people are willing to offer help to a charity organization when their group mates are aware of their altruistic intention than those whose offer was concealed from the rest of the group. In return, the offered charity service increased the altruist's reputation in the group; in the light of sociometric surveys they gained more popularity than the others. Finally, it turned out that whereas men are more likely to offer potentialhelp in the presence of others, women provide more actualhelp.
Abstract
At the irradiation sites in a research reactor where neutrons are well thermalized, the "bare" irradiation methods for a and f determinations that are incorporated in the KAYZERO®/SOLCOI® v4.0 package seem to be unworkable. It is a fact that when carrying out the determination of a and f at the PN-3 irradiation site of the JRR-3M research reactor (Tokai, Japan) using the KAYZERO software, unacceptable results were obtained from experiment to experiment for a ranging from 0.10 to 0.999 and f ranging from 70 to 9999. The "Cd ratio" for a gold monitor in the PN-3 site is about 300. These unacceptable results have indicated the need for the application of Cd methods that are based on "Cd-covered" irradiation and "Cd-ratio" measurements at certain suitable and available monitors. Such Cd methods have not been incorporated into the KAYZERO v4.0 software. Therefore, computational and experimental procedures of the "Cd-covered" method for a and the "Cd-ratio" method for f determination have been presented in this paper. The PN-2 irradiation site of the JRR-3M reactor where the neutron thermalization is not high has a Cd ratio for gold of about 26. The commonly used "bare" irradiation methods can be applied together with the Cd methods so that all results may be presented as comparable data. The results of a and f determinations that were carried out in the PN-2 and PN-3 irradiation sites are presented.
Abstract
The sorption and desorption of uranium on two different clay samples which are obtained from the deposit located in Turgutlu and Kula have been studied by application of a batch technique. The two types of clay materials are Ca-montmorillonite. The uranium concentration range was between 200–3000 ppm. Experimental procedures are outlined and results for uranium contacted with montmorillonite are reported and discussed. The sorption/desorption isotherms were reversible and non-linear for this concentration range. The relative importance of test parameters e.g., pH, clay particle size, temperature, ground water composition, contact — time, solid/water ratio which require definition in order to arrive at meaningful distribution coefficients were carried out. The sorption coefficients varied between 0.65–1.45 and 0.45–1.14 for Kula clay and for Turgutlu clay, respectively. The data could be fitted to Freundlich and Langmuir isotherms. The quantity of the sorbed and desorbed uranium ions was much lower than its theoretical CEC's. This was attributed to a blocking of montmorillonite's CEC by uranium islands sorbed in interlayer. The results have shown that the test parameters can have a marked effect on sorption and the present work provides further evidence of the need to take account of the presence of such materials in safety assessment modeling.
