Rapid surfactant-free synthesis of Mg(OH)2 nanoplates and pseudomorphic dehydration to MgO

Magnesium hydroxide nanoplates ca. 50 nm in thickness can be prepared over minute timescales via hydrothermal synthesis in a multimode cavity (MMC) microwave reactor. This approach allows ca. 1 g of single-phase Mg(OH)2 to be synthesised in under 3 minutes without the requirement of surfactants or non-aqueous solvents. The hydroxide nanomaterial dehydrates at temperatures >200 K below that of the equivalent bulk material and can be utilised as a precursor for the pseudomorphic synthesis of nanoplates of MgO as investigated by TG-DTA-MS, XRD and SEM measurements. Equally, the pseudomorphic synthesis can be performed by irradiating the Mg(OH)2 nanomaterial with microwaves for 6 minutes to produce single phase MgO

Impact of Modular Total Absorption Spectrometer measurements of β decay of fission products on the decay heat and reactor ν e flux calculation

We report the results of a β-decay study of fission products Br86, Kr89, Rb89, Rb90gs, Rb90m, Kr90, Rb92, Xe139, and Cs142 performed with the Modular Total Absorption Spectrometer (MTAS) and on-line mass-separated ion beams. These radioactivities were assessed by the Nuclear Energy Agency as having high priority for decay heat analysis during a nuclear fuel cycle. We observe a substantial increase in β feeding to high excited states in all daughter isotopes in comparison to earlier data. This increases the average γ-ray energy emitted by the decay of fission fragments during the first 10 000 s after fission of U235 and Pu239 by approximately 2% and 1%, respectively, improving agreement between results of calculations and direct observations. New MTAS results reduce the reference reactor νe flux used to analyze reactor νe interaction with detector matter. The reduction determined by the ab initio method for the four nuclear fuel components, U235, U238, Pu239, and Pu241, amounts to 0.976, 0.986, 0.983, and 0.984, respectively

A reference high-pressure CH₄ adsorption isotherm for zeolite Y: results of an interlaboratory study

This paper reports the results of an international interlaboratory study led by the National Institute of Standards and Technology (NIST) on the measurement of high-pressure surface excess methane adsorption isotherms on NIST Reference Material RM 8850 (Zeolite Y), at 25 °C up to 7.5 MPa. Twenty laboratories participated in the study and contributed over one-hundred adsorption isotherms of methane on Zeolite Y. From these data, an empirical reference equation was determined, along with a 95% uncertainty interval (Uk=2). By requiring participants to replicate a high-pressure reference isotherm for carbon dioxide adsorption on NIST Reference Material RM 8852 (ZSM-5), this interlaboratory study also demonstrated the usefulness of reference isotherms in evaluating the performance of high-pressure adsorption experiments

Nondestructive spectrometric study on a radioactive particle embedded in a marine sediment

A radioactive particle embedded in a sediment collected from the Irish Sea was examined with spectrometric methods to understand the potential bioavailability of its constituents. Images of the particle surface were acquired in the backscattering mode by scanning electron microscopy. The elemental composition of the particle surface layer was measured using energy dispersive ~SEM-EDX! and wavelength dispersive ~SEM-WDX! X-ray spectrometers. The investigation showed that the sample consists of a calcite matrix in which uranium is present in the form of separate inclusions. The diameter of U inclusions was less than 10 mm. Synchrotron radiation based X-ray fluorescence in confocal geometry ~confocal m-XRF! was used to determine the spatial distribution of elements in the particle. Three-dimensional reconstructions of the Ca, Cr,Mn, Fe, Zn, Sr, Ba, Pb, and U distributions were performed. The oxidation state of uranium in the different inclusions was determined by synchrotron radiation based X-ray absorption in confocal geometry ~confocal m-XANES!. The isotopic composition of uranium was measured by secondary ion mass spectrometry. The results revealed that uranium was depleted in 235U. Pu and other actinides were not detected.JRC.E.5-Nuclear chemistr

Confocal (micro)-XRF for 3D anlaysis of elements distribution in hot environmental particles

Studies on the fate and transport of radioactive contaminates in the environment are often constrained by a lack of knowledge on the elemental distribution and general behavior of particulate bound radionuclides contained in hot particles. A number of hot particles were previously isolated from soil samples collected at former U.S. nuclear test sites in the Marshall Islands and characterized using non-destructive techniques [1]. The present investigation at HASYLAB is a part of larger research program at ITU regarding the characterization of environmental radioactive particles different locations and source-terms. Radioactive particles in the environment are formed under a number of different release scenarios and, as such, their physicochemical properties may provide a basis for identifying source-term specific contamination regimes. Consequently, studies on hot particles are not only important in terms of studying the elemental composition and geochemical behavior of hot particles but may also lead to advances in assessing the long-term impacts of radioactive contamination on the environment. Six particles isolated from soil samples collected at the Marshall Islands were studied. The element distribution in the particles was determined by confocal {micro}-XRF analysis using the ANKA FLUO beam line. The CRL (compound refractive lens) was used to focus the exciting beam and the polycapillary half lens to collimate the detector. The dimensions of confocal spot were measured by 'knife edge scanning' method with thin gold structure placed at Si wafer. The values of 3.1 x 1.4 x 18.4 {micro}m were achieved if defined as FWHMs of measured L?intensity profiles and when the19.1 keV exciting radiation was used. The collected XRF spectra were analyzed offline with AXIL [2] software to obtain net intensities of element characteristic lines.Further data processing and reconstruction of element distribution was done with the software 'R' [3] dedicated for statistical calculations. In figure 1 the distributions of Pu, Fe and Ti obtained for one of the studied hot particles are presented. The strongest signal was recorded for plutonium; the signals from iron and titanium are respectively 14 and 38 times less. It means that Pu is the most abundant of the observed elements. However, since the light elements are not detectable with the applied measurement conditions, it cannot be definitely stated if plutonium is the main element present in the sample. The isosurfaces are calculated at 20 % of maximum intensity for each element. Please note that the isosurfaces on the drawing are transparent. Changes in the spatial distribution of Pu, Fe, and Ti within the particle are shown in Fig. 2a, 2b, and 2c. Distinct elemental patterns are clearly visible at the higher concentration levels. The distributions of Cr, Cu, and Pb were also reconstructed but the results are not presented here. As it is shown in Fig. 1, the correlation between elements is good at low concentrations but the maxima of concentrations are not strongly correlated (see Fig. 2.). In general, the particle is inhomogeneous in terms of its elemental composition. Similar inhomogeneities were found for other particles with Pu identified as a major element in three of the six particles examined

Anthropogenic changes of CO2, CH4, N2O, CFCI3, CF2Cl2, CCl2FCClF2, CHCl3, CH3CCI3, CCI4, SF6 and SF5CF3 mixing ratios in the atmosphere over southern Poland

An overview of long-term, sysiematic observations of trace gas composition of the atmosphere over southern Poland is given. Three major greenhouse gases (CO2, CH4, N2O) and selected halocarbons (freons F-11, F-12 and F-113; chloroform; 1,1,1-trichloroetane; carbon tetrachloride; sulphur hexafluoride and trifluoromethyl sulphur pentafuoride) were monitored. Measurements were performed at two locations of contrasting characteristics: (1) the high-mountain site Kasprowy Wierch, High Tatras, representing atmospheric conditions relatively free of local influences, and (2) two sites located in the Kraków agglomeration, representing a typical urban atmosphere. The data available for Kraków and Kasprowy Wierch were compared with the Mace Head data, representing a marine regional background. The impact of continental sources for some of the measured gases is clearly seen in the Kraków and Kasprowy Wierch records. The mean offset between CH4 concentrations recorded at Kasprowy Wierch and at Mace Head for the period 1998-2012 is 20.7 ppb and stems from continental emissions of this gas originating mainly from anthropogenic activities (leaks of natural gas distribution networks, landfills, livestock). For N2O, a similar offset of ca. 1 ppb for the period 2009-2012 was observed. Although the long-term concentration trends of selected halogenated compounds measured in Kraków coincide in general with the respective trends in Mace Head data, the Kraków records contain numerous spikes and periods of enhanced concentrations, reflecting the impact of local sources of these compounds. The impact of a legislative framework enforced in Poland in July 2002, regulating the trade, storage and disposal of ozone-depleting substances, is visible in the Kraków record of halogenated compounds

Ni/C/SiO2 nanostructured composites synthesized by carbonization of carboxymethyl cellulose

Ni/C/SiO2 porous composites were synthesized by one-pot approach by carbonization of sodium carboxymethyl cellulose/SiO2 xerogels containing NiCl2. Synthesized composites are mesoporous materials (average pore size 11.8 -15.1 nm) with the surface area 72.1 – 91.1 m2. Ni nanoparticles of 30-90 nm in diameter are evenly distributed within the volume of composites. The hydrogen sorption capacity at -196\ub0C and 20 bar measured for as-synthesized samples was up to 0,32%