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[en] Complete text of publication follows. Speciation analyses are of increasing interest in environmental toxicological and analytical fields, as the toxicity and reactivity of trace elements depend strongly on the chemical forms in which they are involved. A simple electrodeposition-electrothermal atomic absorption spectroscopy (ED-ETAAS) method for speciation analysis of inorganic selenium species in some water samples has been developed. The method is based on the selective reduction of the Se(IV) at uncontrolled applied potential (1.5-2.0 V) on a mercury coated electrode. In acidic media (1.0M HCl solution) only Se(IV) was electrodeposited in mercury electrode surface after removal of the electrode, the separated Se(VI) was remained in solution. The spent electrolyte containing Se(VI) was measured by ETAAS under optimum conditions. Se(IV) was calculated as the difference between the measured total selenium and Se(VI) content. The spiked average recovery value varied between 98 to 103%. An experimental design was developed to investigate the effective parameters on selenium ETAAS measurement. Response surface methodology (RSM) and central composite face centered design (CCF) have been used as a strategy for evaluation of the effects of these parameters. Based on the analysis results, the optimal conditions were predicted as follows: modifier concentration 40(ppm), ashing temperature 500(deg C), atomization temperature 2400(deg C), drying time 20(s), ashing time 15(s) and atomization times 4(s). Under these conditions statistical assessment showed a good agreement between predicted and observed values. The performance of suggested method has been shown by characteristic mass mo=70 pg for Se (IV) and LOD = 0.9 μg L-1 for Se (VI) with RSD of 3.5% for measurement of 100 μg L-1 of Se (IV).
[en] Electron-impact double and triple ionization (TI) is investigated for the Se3+ ion by performing level-to-level calculations. It is demonstrated that ionization-autoionization, excitation double-autoionization, direct double ionization (DDI), and resonant-excitation triple-autoionization contribute to the total double ionization process. The ionization–ionization (II) branch plays the main role in the DDI process. The excitation-II part of DDI with subsequent autoionization dominates in the formation of the Se6+ ions. The contribution to the TI cross sections from the II process is not observed. The correlation effects considered for the 3p shell ionization open the way for the TI. (paper)
[en] It is found by Moessbauer and X-ray measurements on FeS0.985Se0.015 that the selenium impurities affect hardly the superexchange interaction of FeS while they change drastically both Morin and α-transitions. Measurements quadrupole shift confirm that the iron spins rotate by 90o upon the α-transition. The Morin transition temperature was measured at 429K, Which is 15K higher than the α-transition temperature. (Author)
[en] Spectra of germanium and selenium injected into the PLT tokamak plasma were observed in the 50 to 350 A region for GeXIV-XXV (KI to OI-like) and SeXVI-XXIV (KI to NaI-like). A number of 3p/sup k/-3p/sup k-1/3d transitions predicted by isoelectronic sequence extrapolation have been identified. Also, previously identified lines from ions in the AlI to OI-like and KI-like isoelectronic sequences have been observed in the tokamak plasma
[en] Theoretically selenium (Se) is expected to be present as Se/FeSe/FeSe2 under the reducing conditions implied by the pyrite (FeS2) presence in Boom clay. This theoretical equilibrium situation is experimentally investigated from over-saturation (starting from SeO42-/SeO32-) and from under-saturation (starting from Se0 and Se2- (FeSe precipitates). Upon introduction of SeO42- to Boom clay, no considerable sorption or reduction was seen to occur over short experimental measuring periods. Its migration behaviour is therefore assumed to be (initially) almost un-retarded. Association with Boom clay organic matter is highly unlikely. Upon reduction of SeO32- in the presence of FeS2, a precipitate with a solubility of approximately 3 x 10-9 M was observed (probably crystalline Se0). In the presence of organic matter or Boom clay minerals, the kinetics of reduction are decreased and an association with Boom clay organic matter was found to exist, probably attributable to a stabilisation of Se colloids (which are formed upon reduction of SeO32-) by the organic colloids present in solution. These colloids are not expected to be mobile within the clay formation. SeO32- migration is expected to be retarded, because of sorption onto FeS2 and clay minerals. Through chemical reduction and electro -deposition, different reduced Se solid phases (amorphous Se0, crystalline Se0, metal selenides) were formed with different experimental solubilities ranging from 10-10 M to 10-7 M. Upon equilibration with Boom clay organic matter, no interaction was observed. It remains unclear if HSe- species can interact with solid phases present in Boom clay. (authors)
[en] The oscillator strengths (and corresponding wavelengths) for stronger n = 3 to 2 and 3 transitions in F-like Selenium have been computed in both Coulomb gauge and length gauge using the Multi-Configurational Dirac-Fock (MCDF) code and the successive subroutines developed by ourselves for calculating electric dipole transition probability rates. For most n = 3 to 2 transitions, our results from both gauges are in good agreement with those of Hagelstein's, but for n = 3 to 3 transitions, only in length gauge, our results are close to his. It is shown that the discrepancies between our results from different gauges are large for n = 3 to 3 transitions. (orig.)
[en] Ion implantation is an alternative technique to the epitaxial growth of semiconductor material for device fabrication. In this work, Se+ ions have been implanted directly into bulk grown semi-insulating GaAs substrates to fabricate low noise MESFET devices. The device performance, when operated at dc and high frequencies, is shown to be dependent on the quality and technique and growth of the material. The basic principles of device operation have been outlined, followed by a review of previous studies of the assessment of GaAs and the influence of material and geometric parameters on device performance. Analysis of the different material types by secondary ion mass spectrometry has revealed high concentrations of donor impurities in the boat grown GaAs which have a significant influence on the ion implanted devices. In particular, large variations in saturation current, pinch off voltage and noise figure have been observed for materials implanted and fabricated under identical conditions. Cathodoluminescence has been used to gain further insight into the role of impurities in these materials and its potential as a technique for ingot selection assessed. The results have revealed the presence of acceptor impurities and native crystalline defect complexes, undetected by the chemical analysis which may account for some of the observed variations in material stability and device parameters. Measurements at the temperature of liquid helium have provided a further insight into the compensation mechanisms in the Cr doped and undoped semi insulating GaAs. (author)
[en] Complete text of publication follows. One of the principle problems in electrochemical generation of volatile compounds in the atomic spectral methods, used for ultra trace analysis, is difficult to achieve one hundred per cent of hydride generation efficiency. This efficiency significantly depends on the properties of the cathode surface and the cell construction. The key step of hydride forming process is transport of the analyte on the cathode surface where the analyte reduction and hydride forming take place. Therefore is necessary to ensure getting all analyte to the cathode surface. The aim of this work was to construct many types of electrolytic cells to achieve maximal hydride generation efficiency, nearly one hundred per cent, using different cathode forms and shapes. Selenium(IV) in aqueous solution was used as a model analyte. The efficiency of electrochemical hydride generation was at first obtained comparing sensitivity of Selenium determination with classical chemical hydride generation whose efficiency is about one hundred per cent. For cells with high generation efficiency the radiotracer experiments with 75Se were carried out. At first the electrolytic cells with lead wire as a cathode in the cathode chamber, without ion-exchange membrane, were constructed. These cells were not suitable for routine analysis, because considerable part of electrolyte often flowed away without any contact with cathode surface. The cells in other group contained ion-exchange membrane and they were very similar to classical thin-layer electrolytic cell but their cathode chambers were extensive and divided. High generation efficiency was observed with flow through cells with all-lead chamber as the cathode with maximal area and minimal inner volume. At last the tubular electrolytic cells were prepared. The generation efficiency was also high. Generally more than ten completely different electrolytic cells were constructed. Using last two types of electrolytic cell better than 95% of Selenium hydride generation efficiency was obtained. Simultaneously the limit of detection 0.4 μg.dm-3 for the Selenium determination in aqueous solution (drinking water) was reached. The authors thank to the Grant Agency of the ASCR (project: A400310507/2005) and MSMT CR (research project: MSM0021620857) for the financial support.
[en] The spectra of Se V and Br VI were photographed in the 2000 A-200 A and 1200 A-200 A regions on a variety of spectrographs using a triggered spark light source. The new observations have lead to revision and extension of earlier analyses. The 4s2, 4s4p, 4p2, 4s4d, 4s5s and 4s5p configurations have been confirmed in both Se V and Br VI. In addition, the 4s5d and 4s6s configurations have been established in Se V. Fifty-three lines have been classified in Se V and forty-nine lines have been classified in Br VI. (orig.)
[en] Double ionization of He and Ne by charged particle impact was explored in kinematically complete experiments measuring the final momenta of the 2 emerging electrons (Pe1f, Pe2f) and of the recoiling target ion PRf. The momentum transfer from the 3.6 MeV/u Se28+ projectile to the electrons is found to be negligibly small. Thus, distinct patterns observed in the Pe1f-versus-Pe2f spectra sensitively reflect the details of the electrons' correlated motion. Classical calculations reasonably describe the data only when the (e-e) interaction during the ionization reaction is included. (orig.)