Zsolt Varga

Silica-supported Au nanoparticles decorated by TiO2 : Formation, morphology, and CO oxidation activity

Au-TiO(2) interface on silica support was aimed to be produced in a controlled way by use of Au hydrosol. In method A, the Au colloids were modified by hydrolysis of the water-soluble Ti(IV) bis(ammoniumlactato)dihydroxide (TALH) precursor and then adsorbed on Aerosil SiO(2) surface. In method B, Au sol was first deposited onto the SiO(2) surface and then TALH was adsorbed on it. Regular and high-resolution transmission electron microscopy (TEM and HRTEM) and energy dispersive spectrometry (EDS) analysis allowed us to conclude that, in method A, gold particles were able to retain the precursor of TiO(2) at 1.5 wt % TiO(2) loading, but at 4 wt % TiO(2) content the promoter oxide appeared over the silica surface as well. With method B, titania was detected on silica at each TiO(2) concentration. In Au-TiO(2)/SiO(2) samples, the stability of Au particles against sintering was much higher than in Au/TiO(2). The formation of an active Au-TiO(2) perimeter was proven by the greatly increased CO oxidation activity compared to that of the reference Au/SiO(2).

Rapid sequential determination of americium and plutonium in sediment and soil samples by ICP-SFMS and alpha-spectrometry

An improved sample preparation method for the determination of americium and plutonium in sediment and soil samples by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) and alpha-spectrometry is described. The developed procedure involves a selective CaF2 co-precipitation for pre-concentration and matrix removal followed by a sequential extraction chromatographic separation. The average chemical recovery of sample preparation was between 81–94% for both americium and plutonium. The method development also focused on the elimination of possible interferences in mass spectrometric analysis caused by molecular ions (e.g.238U 1H+, 204Pb 36Ar+ or 208Pb 16O2+) employing the suitable matrix separation prior to ICP-SFMS analysis coupled with a desolvation sample introduction system. For 239Pu, 240Pu, 241Pu and 241Am limits of detection of 15, 9.2, 14 and 23 fg g-1 was achieved by ICP-SFMS, respectively. The applied sample preparation and measurement can be carried out within 6 h for one batch of samples. Results of certified reference materials (IAEA-384 and IAEA-385) analysed by the two different measurement techniques agreed well with the recommended or information values.

Application of laser ablation inductively coupled plasma mass spectrometry for the isotopic analysis of single uranium particles.

The paper describes the application of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for the isotopic analysis of individual uranium-oxide particles. The procedure developed is suitable for the accurate measurement of 234U, 235U, 236U and 238U isotopes in single actinide particles with lateral dimensions down to 10 microm. The 235U/238U isotope ratios can be obtained with a precision of a few percent relative standard deviation using a single collector ICP-MS instrument. The precision could be improved by the use of slow ablation and by taking several LA-ICP-MS replicate spectra on the same particle investigated. For the minor isotopes use of higher mass resolution (R=4000) was necessary in some cases to avoid spectral interferences. The technique developed offers a rapid and accurate possibility for the isotopic composition determination of uranium-containing individual particles in environmental and safeguards samples.

Origin assessment of uranium ore concentrates based on their rare-earth elemental impurity pattern

Abstract The rare-earth element pattern was used as an additional tool for the identification and origin assessment of uranium ore concentrates (yellow cakes) for nuclear forensic purposes. By this means, the source of an unknown material can be straightforwardly verified by comparing the pattern with that of a known or declared sample. In contrast to other indicators used for nuclear forensic studies, the provenance of the material can also be assessed in several cases even if no comparison sample is available due to the characteristic pattern. The milling process was found not to change the pattern and no significant elemental fractionation occurs between the rare-earth elements, thus the pattern in the yellow cakes corresponds to that found in the uranium ore.

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity

Silica-Supported Au Nanoparticles Decorated by CeO2: Formation, Morphology, and CO Oxidation Activity Anita Horv ath,* Andrea Beck, Gy€orgyi Stefler, Tímea Benk o, Gy€orgy S afr an, Zsolt Varga, Jen 00 o Gubicza, and L aszl o Guczi Department of Surface Chemistry and Catalysis and Department of Radiation Safety, Institute of Isotopes of HAS, P.O. Box 77, H-1525 Budapest, Hungary Research Institute for Technical Physics and Materials Science of HAS, P.O. Box 49, H-1525 Budapest, Hungary Department of Materials Physics, E€otv€os Lor and University, Budapest, P.O. Box 32, H-1518, Hungary

Characterization and classification of uranium ore concentrates (yellow cakes) using infrared spectrometry

Abstract In this work the applicability of Fourier-transform infrared spectrometry (FTIR) for nuclear forensic studies of uranium ore concentrates (UOC) are investigated. The technique was used for the identification of the type of uranium compound and various process-related impurities, which can give information on the production method of the material. The measured spectra were evaluated also by statistical means, using the soft independent modelling of class analogy (SIMCA) technique to reveal less apparent similarities between the measured UOC samples.

Detection of previous neutron irradiation and reprocessing of uranium materials for nuclear forensic purposes

The paper describes novel analytical methods developed for the detection of previous neutron irradiation and reprocessing of illicit nuclear materials, which is an important characteristic of nuclear materials of unknown origin in nuclear forensics. Alpha spectrometry and inductively coupled plasma sector-field mass spectrometry (ICP-SFMS) using solution nebulization and direct, quasi-non-destructive laser ablation as sample introduction were applied for the measurement of trace-level (232)U, (236)U and plutonium isotopes deriving from previous neutron irradiation of uranium-containing nuclear materials. The measured radionuclides and isotope ratios give important information on the raw material used for fuel production and enable confirm the supposed provenance of illicit nuclear material.

Interviewing a Silent (Radioactive) Witness through Nuclear Forensic Analysis

Nuclear forensics is a relatively young discipline in science which aims at providing information on nuclear material of unknown origin. The determination of characteristic parameters through tailored analytical techniques enables establishing linkages to the materials processing history and hence provides hints on its place and date of production and on the intended use.

Synthesis of the pentasaccharide hapten from the glycopeptidolipid antigen of Mycobacterium avium serovar 12

Effective synthesis of the pentasaccharide hapten from the glycopeptidolipid antigen of Mycobacterium avium serovar 17 in a p-aminophenyl linker-containing form, using 3+2 block synthesis strategy, is described. A 2+3 block synthesis could not be achieved, although different glycosyl donors (1-Br, 1-SPh, 1-O-C(NH)CCl3) were used.

Laser ablation assisted ICP-MS as a tool for rapid categorization of seized uranium oxide materials based on isotopic composition determination

The paper describes an analytical method for rapid categorization of nuclear forensic evidence based on uranium isotopic composition. The investigation of uranium-based nuclear materials seized in Hungary was carried out by inductively coupled plasma sector-field mass spectrometry (ICP-SFMS) applying laser ablation (LA) for sample introduction. The results obtained by the LA-ICP-SFMS method were compared with independent analytical techniques. The advantage and limitations of the method are discussed.