Neutralization rate for slow Ar ions in front of KCl(0 0 1)

Charge state distributions of reflected ions are measured when 5 keV Ar^q+(q = 0−2) ions are incident on a clean KCl(0 0 1) surface at grazing angle, θ_i. Although the charge state distribution does not depend on the incident charge state at larger θ_i, significant dependence of the charge state distribution on incident charge state is observed at smaller θ_i. The ionization of Ar⁰ is completely suppressed at θ_i < 20 mrad, while large neutralization probability is observed for Ar⁺ incidence. These features allow us to derive the position-dependent neutralization rate of Ar⁺ in front of KCl(0 0 1). The obtained neutralization rate decreases exponentially with distance from the surface as it is usually assumed.     

Enthalpy and heat capacity of LiAlO2 between 298 and 1700 K by drop calorimetry

The enthalpy of γ-LiAlO₂ was measured between 403 and 1673 K by isothermal drop calorimetry. The smoothed enthalpy curve between 298 and 1700 K results in H⁰(T) − H⁰(298 K)=−37 396 + 93.143 · T + 0.00557 · T² + 2 725 221 · T⁻¹ J/mol. The standard deviation is 2.2%. The heat capacity was derived by differentiation of the enthalpy curve. The value extrapolated to 298 K is C_p,298=(65.8 ± 2.0) J/K mol.     

Investigation of in-reactor creep and irradiation growth of zirconium-2.5 wt% niobium channel tubes

We summarize the diametral creep results obtained in the MR reactor of the Kurchatov Institute of Atomic Energy on zirconium-2.5 wt% niobium pressure tubes of the type used in RBMK-1000 power reactors. The experiments that lasted up to 30 000 h cover a temperature range of 270 to 350°C, neutron fluxes between 0.6 and 4.0 ×10¹³ n/cm² · s (E > 1 MeV) and stresses of up to 16 kgf/mm². Diametral strains of up to 4.8% have been measured. In-reactor creep results have been analyzed in terms of thermal and irradiation creep components assuming them to be additive. The thermal creep rate is given by a relationship of the type ε_th = A₁ exp [(A₂ + A _3σt) T] and the irradiation component by ε_rad = A_4σtø(T − A₅), where T = temperature, σ_t = hoop stress, ø = neutron flux and a₁ to A₅ are constants. Irradiation growth experiments carried out at 280° C on specimens machined from pressure tubes showed a non-linear dependence of growth strain on neutron fluence up to neutron fluences of 5 × 10²⁰ n/cm². The significance of these results to the elongation of RBMK reactor pressure tubes is discussed.     

Co γ-ray irradiation effects on dielectric characteristics of tin oxide films of different thicknesses on n-type Si(1 1 1) substrates

We have tried to determine the effects of ⁶⁰Co gamma irradiation on properties of Au/SnO₂/n-Si (MOS) structures such as dielectric constant (ε′), dielectric loss (ε″), tangent loss (tan δ) and ac conductivity (σ_ac). Three samples were fabricated with different deposition time. The samples were irradiated using a ⁶⁰Co γ-ray source irradiation with the total dose range of 0–500 kGy at room temperature. Capacitance and conductance (C–G–V) measurements were performed at a frequency of 500 kHz in the dark and at room temperature before and after irradiation. The experimental data were analyzed using complex permittivity and electric modulus. The values of ε′, ε″, tan δ and σ_ac showed a strong dependence on the applied voltage and irradiation dose. The dielectric properties of MOS structures have been found to be strongly influenced by the presence of dominant radiation-induced defects. Experimental results show that the interfacial polarization contributes to the improvement of dielectric properties of Au/SnO₂/n-Si (MOS) Schottky diodes.     

Influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in PWR primary water

The influence of ageing heat treatment on alloy A-286 microstructure and stress corrosion cracking behaviour in simulated Pressurized Water Reactor (PWR) primary water has been investigated. A-286 microstructure was characterized by transmission electron microscopy for ageing heat treatments at 670 °C and 720 °C for durations ranging from 5 h to 100 h. Spherical γ′ phase with mean diameters ranging from 4.6 to 9.6 nm and densities ranging from 8.5 × 10²² m⁻³ to 2 × 10²³ m⁻³ were measured. Results suggest that both the γ′ phase mean diameter and density quickly saturate with time for ageing heat treatment at 720 °C while the γ′ mean diameter increases significantly up to 100 h for ageing heat treatment at 670 °C. Grain boundary η phase precipitates were systematically observed for ageing heat treatment at 720 °C even for short ageing periods. In contrast, no grain boundary η phase precipitates were observed for ageing heat treatments at 670 °C except after 100 h. Hardening by γ′ precipitation was well described by the dispersed barrier hardening model with a γ′ barrier strength of 0.23. Stress corrosion cracking behaviour of A-286 was investigated by means of constant elongation rate tensile tests at 1.5 × 10⁻⁷ s⁻¹ in simulated PWR primary water at 320 °C and 360 °C. In all cases, initiation was transgranular while propagation was intergranular. Grain boundary η phase precipitates were found to have no significant effect on stress corrosion cracking. In contrast, yield strength and to a lesser extent temperature were found to have significant influences on A-286 susceptibility to stress corrosion cracking.     

Surface morphology of the Ar ion-irradiated Ag/Si(1 1 1) system

In the present study, a 500 Å thin Ag film was deposited by thermal evaporation on 5% HF etched Si(1 1 1) substrate at a chamber pressure of 8×10⁻⁶ mbar. The films were irradiated with 100 keV Ar⁺ ions at room temperature (RT) and at elevated temperatures to a fluence of 1×10¹⁶ cm⁻² at a flux of 5.55×10¹² ions/cm²/s. Surface morphology of the Ar ion-irradiated Ag/Si(1 1 1) system was investigated using scanning electron microscopy (SEM). A percolation network pattern was observed when the film was irradiated at 200°C and 400°C. The fractal dimension of the percolated pattern was higher in the sample irradiated at 400°C compared to the one irradiated at 200°C. The percolation network is still observed in the film thermally annealed at 600°C with and without prior ion irradiation. The fractal dimension of the percolated pattern in the sample annealed at 600°C was lower than in the sample post-annealed (irradiated and then annealed) at 600°C. All these observations are explained in terms of self-diffusion of Ag atoms on the Si(1 1 1) substrate, inter-diffusion of Ag and Si and phase formations in Ag and Si due to Ar ion irradiation.     

Primary creep of UO2 and the effect of amorphous grain boundary phases

Creep experiments were conducted on nearly stoichiometric UO₂ helical springs from 1000 to 1600°C and 2.1 to 80 MPa. Entirely transient behaviour was measured in all experiments with the plastic strain,ε = (Aσ/d^1.5) exp(−Q/RT)t^m, where A is a constant that depends on purity, d is the grain size, σ is the applied stress, Q is the apparent activation energy, t is the time, m is a constant, and the other terms have their usual meaning. At T > 1200°C, Q 100 kcal mol⁻¹, but at T < 1200°C, Q increased dramatically and became strain dependent. The value of m for most experiments was 0.8, but at σ > 48 MPa, m decreased, and for d < 10 μm, it increased. Amorphous or glassy grain boundary phases were observed by transmission electron microscopy in all specimens: specimens containing the largest concentrations of Fe and Si sometimes had anomalously high creep rates. The phases existed as discontinuous, lenticular bodies on grain faces and a continuous network along triple grain junctions. Some instances of precipitation of UO₂ from the phase were observed. At T > 1200°C, glassy phases may accelerate Coble creep by providing short circuit diffusion paths along the grain boundaries or may accelerate superplastic deformation by diffusion along the continuous glassy phase triple line junctions. At low temperatures the glassy phase appears to control grain-boundary sliding.     

Measurements of the rate of the uranium-water vapour reaction

The rate of the uranium-water vapour reaction has been measured between 30 and 80°C. The measured reaction rate obeys the rate equation: k = 3.0 × 10⁹r^1/2 exp(−15.5 kcal/RT) mg U/cm ² H = 4.0 × 10⁸r exp(−15.5 kcal/RT) mg weight gain/cm² h, where r is the fractional relative humidity.

This rate equation agrees remarkably well with the literature equation which was derived from much more limited experimental evidence and so the present equation is preferred.     

Thermodynamic studies on Cs4U5O17(s) and Cs2U2O7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs₄U₅O₁₇(s)+Cs₂U₂O₇(s)+Cs₂U₄O₁₂(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δμ(O₂) (kJ/mol) (±0.5)=−272.0+0.207T (K). The differential thermal analysis showed that Cs₄U₅O₁₇(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs₄U₅O₁₇(s) was calculated from the above oxygen potentials and can be given by, Δ_fG⁰ (kJ/mol)±6=−7729+1.681T (K). The enthalpy measurements on Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, (H⁰_T−H⁰₂₉₈), in J/mol for Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) can be represented by, H⁰_T−H⁰_298.15 (Cs₄U₅O₁₇) kJ/mol±0.9=−188.221+0.518T (K)+0.433×10⁻³T² (K)−2.052×10⁻⁵T³ (K) (368 to 905 K) and H⁰_T−H⁰_298.15 (Cs₂U₂O₇) kJ/mol±0.5=−164.210+0.390T (K)+0.104×10⁻⁴T² (K)+0.140×10⁵(1/T (K)) (411 to 860 K). The thermal properties of Cs₄U₅O₁₇(s) and Cs₂U₂O₇(s) were derived from the experimental values. The enthalpy of formation of (Cs₄U₅O₁₇, s) at 298.15 K was calculated by the second law method and is: Δ_fH⁰_298.15=−7645.0±4.2 kJ/mol.     

Heavy ion irradiation effects in the rare-earth sesquioxide Dy2O3

Polycrystalline pellets of the rare-earth sesquioxide Dy₂O₃ with cubic C-type rare-earth structure were irradiated with 300 keV Kr²⁺ ions at fluences up to 5 × 10²⁰ Kr/m² at cryogenic temperature. Irradiation-induced microstructural evolution is characterized using grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). In previous work, we found a phase transformation from a cubic, C-type to a monoclinic, B-type (C2/m) rare-earth structure in Dy₂O₃ during Kr²⁺ ion irradiation at a fluence of less than 1 × 10²⁰ Kr/m². In this study, we find that the crystal structure of the top and middle regions of the implanted layer transform to a hexagonal, H-type (P6₃/mmc) rare-earth structure when the irradiation fluence is increased to 5 × 10²⁰ Kr/m²; the bottom of the implanted layer, on the other hand, remains in a monoclinic phase. The irradiation dose dependence of the C-to-B-to-H phase transformation observed in Dy₂O₃ appears to be closely related to the temperature and pressure dependence of the phases observed in the phase diagram. These transformations are also accompanied by a decrease in molecular volume (or density increase) of approximately 9% and 8%, respectively, which is an unusual radiation damage behavior.     

The kinetics and mechanism of the uranium-water vapour reaction — an evaluation of some published work

The published results of Grimes and Morris on the rate of the uranium-water vapour reaction which were obtained using interferometry have been recalculated using the best values derived from the literature for the complex refractive indices of uranium and uranium dioxide (3.1–3.91 for uranium and 2.2-0.51 for uranium dioxide). The kinetics have been described by Haycock's model and the linear rate constant is given by K₁ = 1.3 × 10⁴P^1/2_H2O exp( − 9.0 kcal/RT )mg U/cm² h, where P_H2O is the water vapour pressure in torr or K₁ = 3.48 × 10⁸r^1/2 exp( −14.1 kcal/RT)mg U/cm² h, where r is the fractional relative humidity, R is the gas constant and T is the absolute temperature.

A mechanism is described which accounts for the observed dependence of the rate of uranium-water vapour reaction on the square root of the water vapour pressure.     

Formation processes of nickel oxide nanoparticles in SiO2 by metal-ion implantation combined with thermal oxidation

Formation processes of nickel oxide (NiO) nanoparticles (NPs) in silica glass (SiO₂) by implantation of 60 keV Ni⁻ ions combined with thermal oxidation are studied using cross-sectional transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry. In as-implanted state, Ni metallic NPs form within the surface layer of 80 nm thick. The mean depth z and the standard deviation (Δz)^21/2 of Ni atom distribution determined by XTEM were 43 and 15 nm, respectively. After the oxidation at 800 °C for 1 h, z and (Δz)^21/2 became 47 nm and 20 nm, respectively, i.e. the distribution was almost the same except a small diffusional shift to the deeper region. Mean volume of Ni- and NiO-NPs after heat treatments at 800 °C were 27 and 43 nm³, respectively. The larger mean volume of NiO-NPs is explained from the fact that NiO-NPs include both Ni and O atoms, i.e. approximately 2N atoms, while Ni-NPs include Ni atoms only, i.e. N atoms. Both the Ni- and NiO-NPs include 2.4 × 10³ Ni atoms per NP in average. These results indicate that NiO-NPs are formed by oxidation of Ni-NPs without pronounced redistribution of Ni atoms.     

Dynamic response of target electrons upon low and medium energy ion impact

We found that differential scattering cross sections for medium and low energy He⁺ and Ne⁺ impact on high Z-atoms were significantly enhanced compared with those calculated from the inter-atomic potential based on the Hartree–Fock–Slater atomic model coupled with the bare nuclear charge of a projectile. The enhanced scattering cross sections determined experimentally are reproduced well by a simple model that the center of gravity of target electrons is shifted toward the projectile during a large-angle collision. The shift from the target nucleus is expressed as a function of inter-nuclear distance in terms of a dipole moment (Z₁ and Z₂: atomic numbers of projectile and target, : polarizability, e: electron charge). The effective polarizability β (≡Z₁/Z₂) is expressed as a function of ion velocity v [10⁷ cm/s], in the form β = 0.079 exp[−0.46v].     

Ion beam induced nucleation in amorphous GaAs layers during MeV implantation

To investigate the nonlinear dose dependence of the thickness of the recrystallized layer during ion beam induced epitaxial recrystallization at amorphous/crystalline interfaces GaAs samples were irradiated with 1.0 MeV Ar⁺, 1.6 MeV Ar⁺ or 2.5 MeV Kr⁺ ions using a dose rate of 1.4 × 10¹² cm⁻² s⁻¹ at temperatures between 50°C and 180°C. It has been found that the thickness of the recrystallized layer reaches a maximum value at T_max = 90°C and 135°C for the Ar⁺ and Kr⁺ implantations, respectively. This means that the crystallization rate deviates from an Arrhenius dependence due to ion beam induced nucleation and growth within the remaining amorphous layer. The size of the crystallites depends on the implantation dose. This nucleation and growth of the crystallites disturbes and at least blocks the interface movement because the remaining surface layer becomes polycrystalline. Choosing temperatures sufficiently below T_max the thickness of the recrystallized layer increases linearly with the implantation dose indicating that the irradiation temperature is too low for ion induced nucleation.     

Standard molar Gibbs free energy of formation of PbO(s) over a wide temperature range from EMF measurements

The EMF of the following galvanic cells,

(render)

Kanthal,Re,Pb,PbOCSZO₂ (1 atm.),Pt

(render)

Kanthal,Re,Pb,PbOCSZO₂(1 atm.),RuO₂,Pt

were measured as a function of temperature. With O₂ (1 atm.), RuO₂ as the reference electrode, measurements were possible at low temperatures close to the melting point of Pb. Standard Gibbs energy of formation, Δ_fG⁰_mβ-PbO was calculated from the emf measurements made over a wide range of temperature (612–1111 K) and is given by the expression: Δ_fG⁰_mβ-PbO±0.10 kJ=−218.98+0.09963T. A third law treatment of the data yielded a value of −218.08 ± 0.07 kJ mol⁻¹ for the enthalpy of formation of PbO(s) at 298.15 K, Δ_fH⁰_mβ-PbO which is in excellent agreement with second law estimate of −218.07 ± 0.07 kJ mol⁻¹.     

Contribution of uranium diffusion on creep behavior of uranium dicarbide

Compressive creep tests of uranium dicarbide (UC₂) have been conducted. The general equation best describing the creep rate over the temperature range 1200–1400°C and over the stress range 2000–15000 psi is represented by the sum of two exponential terms ge =A(σ/E)^0.9 exp(−39.6 ± 1.0/RT) + B(σ/E)^4.5 exp(−120.6 ± 1.7/RT), where pre-exponential factors are A(σ/E)^0.9 = 12.3/h at low stress region (3000 psi) and B(σ/E)^4.5 = 3.17 × 10¹³/h at high stress region (9000 psi), and the activation energy is given in kcal/mol. Each term of this experimental equation indicates that important processes occurring during the steady state creep are grain-boundary diffusion of the Coble model at low stress region and the Weertman dislocation climb model at high stress region. Both mechanisms are related to migration of uranium vacancies.     

Standard Gibbs energy of formation of Cs2CdI4

The vapor pressures of CdI₂ and Cs₂CdI₄ were measured below and above their melting points, employing the transpiration technique. The standard Gibbs energy of formation Δ_fG° of Cs₂CdI₄, derived from the partial pressure of CdI₂ in the vapor phase above and below the melting point of the compound could be represented by the equations Δ_fG°Cs₂CdI₄ (±6.7) kJ mol⁻¹=−1026.9+0.270 T (643 K≤T≤693 K) and Δ_fG°{Cs₂CdI₄} (±6.6) kJ mol⁻¹=−1001.8+0.233 T (713 K≤T≤749 K) respectively. The enthalpy of fusion of the title compound derived from these equations was found to be 25.1±10.0 kJ mol⁻¹ compared to 36.7 kJ mol⁻¹ reported in the literature from differential scanning calorimetry (DSC). The standard enthalpy of formation Δ_fH°_298.15 for Cs₂CdI₄ evaluated from these measurements was found to be −918.0±11.7 kJ mol⁻¹, in good agreement with the values −920.3±1.4 and −917.7±1.5 kJ mol⁻¹ reported in the literature from two independent calorimetric studies.     

Ion beam synthesis and recrystallization of amorphous SiGe/SiC structures

Si_1−xGe_x amorphous layers implanted with different doses of carbon (between 5 × 10¹⁵ and 2 × 10¹⁷ cm⁻² and annealed at 700°C and 900°C have been analyzed by Raman and Infrared spectroscopies, electron microscopy and Auger electron spectroscopy. The obtained data show the synthesis of amorphous SiC by implanting at the highest doses. In these cases, recrystallization only occurs at the highest annealing temperature (900°C). The structure of the synthesized SiC strongly depends on the implantation dose, in addition to the anneal temperature. For the highest dose (2 × 10¹⁷ cm⁻²), crystalline β-SiC is formed. Finally, a strong migration of Ge towards the Si substrate is observed from the region where SiC precipitation occurs.     

Influence de la pression sur le diagramme de phases Pu-Ga

The phase diagram (P, T) was determined for Pun at % Ga alloys (with n = 2, 4, 6, 8) from 20°C to 700°C in the 0–40 kbar pressure range.

From this work, a three-dimensional (P, T, c%) diagram was deduced. The main emphasis was put on the limits of the δ phase field.     

Power density effect on feasibility of water cooled thorium breeder reactor

Breeding is made possible by the high value of neutron regeneration ratio η for ²³³U in thermal energy region. The reactor is fueled by ²³³U–Th oxide and it has used the light water as moderator. Some characteristics such as spectrum, η value, criticality, breeding performance and number density are evaluated. Several power densities are evaluated in order to analyze its effect to the breeding performance. The η value of fissile ²³³U obtains higher value than 2 which may satisfy the breeding capability especially for thermal reactor for all investigated MFR. The increasing enrichment and decreasing conversion ratio are more significant for MFR < 0.3. The required enrichment and conversion ratio do not change significantly caused by power density change for very tight lattice cell (MFR < 0.3), however, its strongly depends on the power density change for higher MFR (MFR ≥ 0.3). Breeding condition of all investigated power densities can be achieved for burnup ≥ 30 GW d/t at MFR = 0.3 and it requires about 3.5% of required ²³³U enrichment. Number density of ²³³Pa decreases significantly with decreasing power density which leads the reactor has better breeding performance because lower capture rate of ²³³Pa.