Study of the electronic structures of oxygen doped in LiBaF3 crystal

The most likely substituting positions of impurity oxygen ions in LiBaF₃ crystals are studied using the general utility lattice program (GULP). The calculated results indicate that the main defect model is [] in the O:LiBaF₃ crystal. The electronic structures of the LiBaF₃ crystal with the defect [] are calculated using the DV-Xα method. It can be concluded from the electronic structures that the LiBaF₃ crystal with the defect [] will exhibit a 217-280 nm absorption band and the impurity oxygen will decrease core-valence luminescence yield.     

Tracer diffusion of Mn in alloy D9 in presence of sodium

The diffusivity of manganese in vacuum annealed and cold worked alloy D9 in presence of sodium was measured by the standard tracer technique. The lattice diffusion coefficient of manganese in vacuum annealed alloy D9 specimens in the temperature range 773-873 K is given by the expression and that in cold worked alloy D9 specimens is given by where R is in J K⁻¹ mol⁻¹. The activation energy for diffusion in cold worked specimens is less than that in vacuum annealed specimens. The activation energy for diffusion of manganese in presence of sodium is almost four times less than that in various austenitic stainless steels reported in the literature.     

Excitation energies, radiative and autoionization rates, dielectronic satellite lines, and dielectronic recombination rates for excited states of Na-like W from Ne-like W

Energy levels, radiative transition probabilities, and autoionization rates for and states in Na-like tungsten (W⁶³⁺) are calculated. Cowan’s relativistic Hartree-Fock method, the relativistic multiconfiguration method implemented in the Hebrew University Lawrence Livermore Atomic Code, and the relativistic many-body perturbation theory method, are used. Autoionizing levels above the threshold 1s²2s²2p⁶ are considered. It is found that configuration mixing plays an important role for all atomic characteristics. Also strong mixing between states with 2s and 2p holes (1s²2s²2p⁵3l₁nl₂+1s²2s2p⁶3l₃nl₄) occurs. Branching ratios relative to the first threshold and intensity factors are calculated for satellite lines, and dielectronic recombination (DR) rate coefficients are determined for the excited states. It is shown that the contribution of the highly excited states is very important for calculation of total DR rates. Contributions from the autoionizing states and to the DR rate coefficients are estimated by extrapolation of all atomic parameters. The orbital angular momentum (l) distribution of the rate coefficients shows a peak at l=2. The total DR rate coefficient is derived as a function of electron temperature. The dielectronic satellite spectra of W⁶³⁺ are important for L-shell diagnostics of very high-temperature laboratory plasmas such as future ITER fusion plasmas.     

Ga NMR and magnetic susceptibility in δ-phase of Pu1−xGax (x = 0.05, x = 0.08) alloys

⁶⁹Ga nuclear magnetic resonance spectra, line shifts (⁶⁹K) and nuclear spin-lattice relaxation rate have been measured in the 20 years aged Pu_0.95Ga_0.05 and in fresh prepared Pu_0.92Ga_0.08 alloys, stabilized δ-phase, at magnetic field of 9.4 T in the temperature range (10-500) K. The line shift and are determined correspondingly by the static and fluctuating-in-time parts of the local magnetic field that originates in transferred hyperfine coupling the Ga nuclear spin with the nearest f-electron environment of more magnetic Pu.Temperature behavior of the resonance properties is found the same in fresh Pu_0.92Ga_0.08 and aged Pu_0.95Ga_0.05 alloy. The NMR results are in favor that δ-phase of Pu_1−xGa_x alloys represents at T > 200 K the Kondo lattice, in which the localized electronic spins fluctuate independently from each other without any macroscopic coherence. The coherent state like in heavy-fermion liquids emerges in Pu_0.95Ga_0.05 below T^∗ = 200 K. A little bit higher estimate of crossover temperature T^∗ = 250 K was founded for Pu_0.92Ga_0.08.     

Oxygen potential of (U0.88Pu0.12)O2±x and (U0.7Pu0.3)O2±x at high temperatures of 1673-1873 K

The oxygen potential of (U_0.88Pu_0.12)O_2±x (−0.0119 < x < 0.0408) and (U_0.7Pu_0.3)O_2±x (−0.0363 < x < 0.0288) was measured at high temperatures of 1673-1873 K using gas equilibrium method with thermo gravimeter. The measured data were analyzed by a defect chemistry model. Expressions were derived to represent the oxygen potential based on defect chemistry as functions of temperature and oxygen-to-metal ratio. The thermodynamic data, and , at stoichiometric composition were obtained. The expressions can be used for in situ determination of the oxygen-to-metal ratio by the gas-equilibration method. The calculation results were consistent with measured data. It was estimated that addition of 1 wt.% Pu content increased oxygen potential of uranium and plutonium mixed oxide by 2-5 kJ/mol.     

Analysis of oxygen potential of (U0.7Pu0.3)O2±x and (U0.8Pu0.2)O2±x based on point defect chemistry

Stoichiometries in (U_0.7Pu_0.3)O_2±x and (U_0.8Pu_0.2)O_2±x were analyzed with the experimental data of oxygen potential based on point defect chemistry. The relationship between the deviation x of stoichiometric composition and the oxygen partial pressure P_O2 was evaluated using a Kröger-Vink diagram. The concentrations of the point defects in uranium and plutonium mixed oxide (MOX) were estimated from the measurement data of oxygen potentials as functions of temperature and P_O2. The analysis results showed that x was proportional to near the stoichiometric region of both (U_0.7Pu_0.3)O_2±x and (U_0.8Pu_0.2)O_2±x, which suggested that intrinsic ionization was the dominant defect. A model to calculate oxygen potential was derived and it represented the experimental data accurately. Further, the model estimated the thermodynamic data, and , of stoichiometric (U_0.7Pu_0.3)O_2.00 and (U_0.8Pu_0.2)O_2.00 as −552.5 kJ·mol⁻¹ and −149.7 J·mol⁻¹, and −674.0 kJ · mol^-1 and −219.4 J · mol⁻¹, respectively.     

First principle studies on the electronic structures and absorption spectra in KMgF3 crystal with fluorine vacancy

The experiments indicate that the perfect KMgF₃ crystal has no absorption in the visible range, however the electron irradiation induces a complex absorption spectrum. The absorption spectra can be decomposed by five Gaussian bands peaking at 2.5 eV (488 nm), 3.4 eV (359 nm), 4.2 eV (295 nm), 4.6 eV (270 nm) and 5.2 eV (239 nm), respectively. The purpose of this paper is to seek the origins of the absorption bands. The electronic structures and absorption spectra either for the perfect KMgF₃ or for KMgF₃: with electrical neutrality have been studied by using density functional theory code CASTEP with the lattice structure optimized. The calculation results predicate that KMgF₃: also exhibits five absorption bands caused by the existence of the fluorine ion vacancy and the five absorption bands well coincide with the experimental results. It is believable that the five absorption bands are related to in KMgF₃ crystal produced by the electron irradiation.     

Radiation synthesis of low swelling acrylamide based hydrogels and determination of average molecular weight between cross-links

A comparative analysis of determination of cross-link density (ν_e) of hydrogels by using swelling tests and mechanical measurements has been made. Poly(acrylamide/methacrylamide) P(AAm/MAAm) and poly(acrylamide/hydroxyethyl methacrylate) P(AAm/HEMA) hydrogels were prepared by using gamma rays and used as model hydrogel systems. The uniaxial compression test was applied to cylindrical gel samples in the swollen state at pH 7. Stress-strain curves of hydrogels were evaluated to calculate the shear modulus values. The average molecular weight between cross-links and ν_e obtained from mechanical measurements were significantly different than the values obtained from swelling experiments. Large differences were attributed to the uncertainty on the value of the χ parameter used in the Flory-Rehner equation. ±1% change in this parameter doubled or reduced the value of hydrogel to half value.     

Hydrogen influence on mechanical and fracture mechanics characteristics of zirconium Zr–2.5Nb alloy at ambient and elevated temperatures

This article deals with the investigation of the hydrogen concentration and temperature influence onto mechanical and fracture mechanics characteristics of RBMK-1500 Ignalina NPP unit 2 reactor fuel channel material—Zr–2.5Nb zirconium alloy (TMT-2) at temperatures from ambient up to 300 °C. The investigation of mechanical characteristics was performed on tensile specimens, fracture mechanics characteristics K_Q, , J_IC—on compact specimens (B = 4 mm) of hydrogen-free and saturated by hydrogen (52, 100 and 140 ppm) at 20, 170, 200 and 300 °C. The investigation showed that temperature increasing calls mechanical strength decreasing, whereas the reductions of area increase. Stronger influence of hydrogen concentration onto mechanical characteristics is noticed only at 20–170 °C temperature, however this influence diminishes as the temperature increases and weakest hydrogen influence is given at 300 °C. Fracture toughness characteristics K_Q, more depends on temperature than on hydrogen concentration. Critical J_IC integral values for the specimens containing hydrogen were given lowest at 20 °C, increases when temperature were raised up to 140 °C and were given highest when it reaches 300 °C.The analysis of and J_IC dependence due to the mechanical characteristics of zirconium alloy has showed that the modified plasticity Z_mod = (R_p0.2/R_m)Z satisfactorily approximates the influence of temperature and hydrogen concentration on variation of these characteristics.     

Luminescence from low-energy impact of and ions (n = 1,2,3) on a Tore Supra carbon tile

The hydrogen Balmer series was observed when beams of H⁺, , and D⁺, , ions impinged at 100–1000 eV on a carbon fiber composite tile (Tore Supra). The excitation functions of the H_β (D_β) lines demonstrate the validity of the independent particle model. The logarithmic plot of the H_β (D_β) line intensity versus the reciprocal projectile ion velocity can be well reproduced by a model in which the hydrogen ion projectiles are neutralized in the entrance phase and subsequently electronically excited in collisions with carbon atoms. Finally, the excited hydrogen atoms leave the solid and emit the observed photons, unless they are quenched in non-radiative processes.     

Linear free energy relationship applied to trivalent cations with lanthanum and actinium oxide and hydroxide structure

Linear free energy relationships for trivalent cations with crystalline M₂O₃ and, M(OH)₃ phases of lanthanides and actinides were developed from known thermodynamic properties of the aqueous trivalent cations, modifying the Sverjensky and Molling equation. The linear free energy relationship for trivalent cations is as , where the coefficients a_MvX, b_MvX, and β_MvX characterize a particular structural family of MvX, r_M³⁺ is the ionic radius of M³⁺ cation, is the standard Gibbs free energy of formation of MvX and is the standard non-solvation free energy of the cation. The coefficients for the oxide family are: a_MvX = 0.2705, b_MvX = −1984.75 (kJ/mol), and β_MvX = 197.24 (kJ/mol nm). The coefficients for the hydroxide family are: a_MvX = 0.1587, b_MvX = −1474.09 (kJ/mol), and β_MvX = 791.70 (kJ/mol nm).     

Development of secondary ion mass spectroscopy using medium energy C60 ion impact

In this paper, we report time-of-flight (TOF) secondary ion mass spectroscopy using primary C₆₀ ions with an energy range from several tens of keV to several hundreds of keV. Application of the spectroscopy to the analysis of a poly(amino acid) film revealed that characteristic peaks, necessary for identification of the amino acid in proteins, show higher intensities for medium energy C₆₀ (120 keV and 540 keV ) impacts than those for low energy C₆₀ (30 keV ) impacts. This finding demonstrates that medium energy C₆₀ ion impacts are useful for highly sensitive characterization of amino acids.     

Onset of water accumulation in the upper plenum with a perforated plate

This paper describes an experimental study on the onset of water accumulation above a perforated plate in a vertical air-water countercurrent flow. We experimentally investigate the effects of holes with the relatively large diameter (5 cm), the number of holes (4 holes and 12 holes), the thickness of plate (1 cm and 4 cm), asymmetric water injection, and the location of the air vent line on the onset of water accumulation. The present results indicate that the onset of water accumulation is promoted by a smaller diameter of hole, a smaller number of holes, and symmetric water injection whereas it has negligible dependence on the location of air vent line in the upper plenum. It turns out that the nondimensional superficial velocity, , fits the data better than either the Kutateladze number, K_k, or the interpolation parameter, . We develop a Wallis-type correlation for the onset of water accumulation when the diameter of the holes ranges between 0.7 and 5 cm, and the number of holes is greater than six.