Small Amounts Of Cs Research Articles

Chemical species of cesium and iodine in condensed vaporized microparticles formed by melting nuclear fuel components with concrete materials.

In this study, we report chemical species of Cs and I in condensed vaporized particles (CVPs) produced by melting experiments using nuclear fuel components containing CsI with concrete. Analyses of CVPs by SEM with EDX showed the formation of many round particles containing Cs and I of diameters less than ∼20 μm. X-ray absorption near-edge-structure and SEM-EDX analyses showed two kinds of particles: one containing large amounts of Cs and I, suggesting the presence of CsI, and the other containing small amounts of Cs and I with large Si content. When CVSs were placed in contact with deionized water, most of the CsI from both particles was dissolved. In contrast, some fractions of Cs remained from the latter particles and possessed different chemical species from CsI. In addition, the remaining Cs was concomitantly present with Si, resembling chemical components in the highly radioactive cesium-rich microparticles (CsMPs) released by nuclear plant accidents into the surrounding environments. These results strongly suggest that Cs was incorporated in CVSs along with Si by melting nuclear fuel components to form sparingly-soluble CVMPs.

Adsorbate-induced modification of electronic band structure of epitaxial Bi(111) films

Changes of the electronic band structure of Bi(111) films on Si(111) induced by Cs and Sn adsorption have been studied using angle-resolved photoemission spectroscopy and density functional theory calculations. It has been found that small amounts of Cs when it presents at the surface in a form of the adatom gas leads to shifting of the surface and quantum well states to the higher binding energies due to the electron donation from adsorbate to the Bi film. In contrast, adsorbed Sn dissolves into the Bi film bulk upon heating and acts as an acceptor dopant, that results in shifting of the surface and quantum well states upward to the lower binding energies. These results pave the way to manipulate with the Bi thin film electron band structure allowing to achieve a certain type of conductivity (electron or hole) with a single spin channel at the Fermi level making the adsorbate-modified Bi a reliable base for prospective spintronics applications.

In vitro intestinal degradation and absorption of chondroitin sulfate, a glycosaminoglycan drug.

Chondroitin sulfate (CAS 24967-93-9, CS) is a natural polymer of a disaccharide consisting of glucuronic acid and N-acetyl glucosamine which is sulfated either in the 4 or 6 position. It is administered orally as a slow acting drug to treat osteoarthritis, though there is much debate about its effectiveness and its mode of action, given that macromolecules are not normally absorbed in the gastrointestinal (GI) tract. Initially using a spectrophotometric assay, the stability of CS was tested in the presence of both tissues and lumenal contents of stomach, small intestine, cecum and colon. There was no degradation by the contents of the stomach or small intestine or in any of the tissues. Degradation only took place in the contents of the colon and particularly the cecum. Using 14C-radiolabelled CS it was shown that the cecum contents degraded CS down to the component disaccharides. The 14C-radiolabelled CS was also used to investigate the transport of CS across the different parts of the GI tract in vitro. The CS was transported across the small intestine in low amounts in the intact form, probably by the mechanism of endocytosis. In the colon and the cecum, higher amounts of radioactivity were transported, but most of the radioactivity was in the form of the degradation products, the disaccharides. This study shows that small amounts of CS may cross the upper intestine intact, but in the distal GI tract the molecule is effectively degraded, presumably by the enzymes in the intestinal flora.

Chemistry of Thiophene on ZnO, S/ZnO, and Cs/ZnO Surfaces: Effects of Cesium on Desulfurization Processes

The adsorption of thiophene (C4H4S) on clean ZnO and oxide surfaces precovered with S and Cs has been studied using synchrotron-based high-resolution photoemission and ab initio self-consistent-field (SCF) calculations. On polycrystalline ZnO, C4H4S is weakly chemisorbed, and most desorbs at temperatures below 250 K. A very small fraction of the adsorbed C4H4S (∼0.02 monolayer) that interacts with O-unsaturated Zn sites decomposes on the oxide surface. S adatoms weaken the bonding interactions of thiophene on ZnO, whereas Cs adatoms enhance the adsorption energy of the molecule by at least 5−10 kcal/mol and facilitate the cleavage of C−S bonds. Pure metallic Cs reacts vigorously with C4H4S, decomposing the molecule at very low temperatures (100−200 K). The Cs atoms supported on ZnO are in an ionic state (Csδ+), but they retain a large chemical affinity for thiophene. Small amounts of Cs (∼0.2 monolayer) are enough to activate the oxide surface. Results of ab initio SCF calculations indicate that the bonding interactions of thiophene with the (0001)-Zn and (0001̄)-O faces of ZnO are weak, and promotion with Cs adatoms considerably improves the energetics for C4H4S adsorption and C−S bond breaking. The Cs adatoms provide occupied states that are very efficient for bonding interactions with the frontier orbitals of C4H4S and other S-containing molecules. This should lead to an improvement in the performance of ZnO as a sorbent in desulfurization processes.

A photoelectron spectroscopy and x-ray absorption study of single crystal with adsorbed Cs: on the origin of the states affected by electron doping and evidence for spatially resolved electron doping

The influence of electron doping, via deposition of small amounts of Cs, on the electronic structure of has been studied by high-resolution photoelectron spectroscopy (PES) and x-ray absorption spectroscopy (XAS), utilizing synchrotron radiation. The changes in the electronic structure were monitored by PES of the valence band and of the O 1s, Bi 4f, Bi 5d, Ca 2p and Sr 3d core levels, and by XAS at the O 1s, Cu 2p and Ca 2p edges. The experimental data suggest that the loss of the Fermi edge and the loss of spectral intensity down to about 2 eV below the Fermi level, and the substantial loss of spectral intensity of the pre-edge structure in the O 1s XAS spectrum are mainly due to annihilation of states with O 2p character in the Cu - O layer. It is evident from bulk- and surface-sensitive XAS spectra that the electron doping by Cs affects the electronic structure more strongly close to the surface. This implies that the doping occurs locally and that the charge transfer between the different layers in the unit cell is not uniform. Thus it seems possible to alter the electronic properties of locally through spatially resolved electron doping. When larger amounts of Cs are deposited, a chemical reaction occurs which causes a disruption of the Bi - O layer. This deposition regime is characterized by the presence of caesium oxide and reduced (metallic) Bi.

Interaction of Silver, Cesium, and Zinc with Alumina Surfaces: Thermal Desorption and Photoemission Studies

Cs, Ag, and Zn behave in a different way when deposited on surfaces of ultrathin (15−20 A) films of alumina. In the case of Cs/Al2O3, the alkali atoms wet the oxide, forming strong chemisorption bonds. At small coverages of Cs, desorption of the alkali occurred between 600 and 1000 K. As the amount of Cs deposited increased, there was a reduction in the Cs desorption temperature to ∼350 K. This broad range of desorption temperatures reflects a continuous decrease in the Cs adsorption energy from 63 to 18 kcal/mol with increasing Cs coverage. The deposition of small amounts of Cs induced large (0.9−1.1 eV) positive shifts in the binding energies of the O KVV, O 1s, and Al 2p features of the alumina films. This is consistent with a transfer of electrons from Cs into surface states of alumina that produces a transformation similar to a change from p-type to n-type semiconductors. Ag and Zn do not wet the surface of alumina well and form three-dimensional clusters or particles. In these systems, the activatio...

Anomalous quenching of photoemission from bulk states by deposition of Cs on InAs(100).

The effect of angle-resolved valence-band photoelectron spectra from adsorption of small amounts of Cs on InAs(100)4\ifmmode\times\else\texttimes\fi{}2 has been studied. It is shown that a bulk interband transition is totally quenched at a coverage of Cs that leaves the 4\ifmmode\times\else\texttimes\fi{}2 reconstruction practically intact. The surface order was monitored by low-energy electron diffraction and photoemission from surface states. A shift of the surface Fermi level to well above the conduction-band minimum is also observed. It is proposed that the resulting development of a two-dimensional electron gas at the surface affects the bulk states probed in photoemission.

Interaction of oxygen with Si(111)7 × 7 and Si(100)2 × 1 surfaces modified with small amounts of Cs

The effect of small amounts of Cs (∼ 0.2 of the saturation Cs coverage at 300 K) on the oxidation of Si(111)7 × 7 and Si(100)1 × 2 at reaction temperatures of 300–700 K has been studied by means of Auger and electron energy loss (EEL) spectroscopies, thermal desorption and work function (WF) measurements. It has been found that at these low Cs coverages only the first stage of the oxidation process — the initial oxygen uptake — is affected. The result is: (i) an increase and temperature independence of the initial sticking coefficient, S 0; (ii) coverage independence of S upto certain (reaction temperature determined) oxygen coverages. EEL and WF data have shown that at 300 K oxygen occupies preferentially Cs promoted sites. The liberation of oxygen from this Cs influenced state in order to form usual Si-O bonding configurations takes place at temperatures exceeding 400 K as evidenced by the rise of sharp SiO related ∼ 5 and 7 eV loss peaks and reduction of the work function. Thermal desorption data showed that the oxidation of Si leads to an appearance of a higher temperature desorption state of Cs. Because of this oxygen induced stabilization of the Cs layer the removal of Cs requires annealing the mixed layer at 950 K. At oxygen coverages less than 1 ML this annealing procedure led also to complete SiO desorption.

Thermal Expansion Behavior of Pure and Doped Cordierite by Time-of-Flight Neutron Diffraction

AbstarctIn order to reveal the mechanism of the negative c-axis expansion in cordierite (4 MgO 4 Al2O3 10 SiO2), the thermal expansion of cordierite containing small amounts of Cs, Li, B, Ge, Sc and Ni-cations was investigated by time-of-flight neutron diffraction at temperatures between 22 and 750°C. The samples were prepared by melting the constituent oxides followed by quenching and devitrification to obtain the hexagonal form (Indialite). Using the neutron powder diffraction data, the atom positions in the space group P6/mcc were refined by Rietveld least squares analyses.The expansion behavior of the cordierite structure could be explained in terms of the various kinds of constraints and the interatomic bond strengths of the structure. It was found that cordierite doped with Cs-cations shows the largest volume expansion, followed by the Li-doped sample. So-doped cordierite has the lowest volume expansion. All cordierite samples show positive expansion along the a-axis and negative expansion along the c-axis, except the Cs-doped sample which has positive expansion in both directions.

Conductivity of Seeded Atmospheric Pressure Plasmas

The electrical conductivity is calculated for some typical seeded gases of magnetohydrodynamic interest. The electron density is obtained using Saha's equation. A method is developed for calculating electron mobility in gas mixtures, taking account of the variation of the scattering cross section with energy. Scattering by ions is also considered. Results are presented for several gases seeded with small amounts of Cs or K in the temperature range from 2000° to 4000°K.

INFLUENCE OF K AND CS ON RELEASE OF CS 137 FROM THREE SOILS

Experiments were conducted to study the influence of stable K and Cs amendments on the uptake of Cs/sup 137/ by Ladino clover upon prolonged cropping of contaminated soils. The addition of K to soils containing relatively high levels of K was ineffective in reducing Cs/sup 137/ uptake by plants but after the soil K was reduced to a low level by cropping, the addition of K to soils reduced Cs/sup 137/ uptake by plants. This implies that K added to a soil may reduce Cs/sup 137/ uptake by plants when the soil is low in K content but not when high in K. The Cs/sup 137 uptake by plants increased as the K concentration in the soil was reduced by cropping. The addition of small amounts of Cs to the soil markedly increased Cs/sup 137/ uptake by plants and reduced K uptake. The addition of Cs even at a level severely injurious to plants increased Cs/sup 137/ uptake rather than reduced it. The threshold level for producing injury to clover appeared to be around 4.5 x 10/sup -4/ me Cs per g soil in Vina loam. The toxic effect of Cs added in injurious amount to the soil was alleviatedmore » by the addition of K. K was, thus, antagonistic to Cs. The amount of Cs and K uptake by plants depended on the soil type. Uptake of Cs/sup 137/ by plants was in the order Hanford> Adken> Vina, and, concurrently, K uptake was in the reverse order. (auth)« less