Projectile charge and velocity effect on UO2 sputtering in the nuclear stopping regime

Angular distributions and yields of uranium sputtered by slow highly charged Xe^q+ ions (kinetic energy 1.5 keV ￡ E_k ￡ 811.5~{\rm keV}\le E_{k}\le 81  keV, charge state 1≤q≤25) from UO₂ were measured by means of the catcher technique. A charge state effect on the sputtering process is observed at 8 and 81 keV. A deviation from a Acosθ shape (the linear collision cascade theory) is observed in case of Xe^q+ impinging a UO₂ surface at E_k=8 keV. Yields increase linearly with projectile charge state q thus clearly revealing the contribution of potential energy to the sputtering process. In addition, as the kinetic energy of a Xe¹⁰⁺ projectile decreases from 81 keV to 1.5 keV, a velocity effect is clearly observed on the angular distribution.     

Reliability of stopping power tables and codes for heavy ions (8 ≤ Z ≤ 92) in gases

A comparative study of various stopping power tables and codes for heavy ions in gases has been made through comparison of computed values and the corresponding experimental data. Ten gaseous media: five monatomic rare gases (He to Xe), two diatomic gases (H₂, N₂) and three polyatomic gaseous compounds (CH₄, CF₄ and CO₂) have been chosen to study the stopping power investigations of heavy ions (8 ≤ Z ≤ 92) having energy ranges of ∼0.10–10.00 MeV/n and ∼20.00–57.00 MeV/n. We compare the experimental data of stopping power to values calculated using various tables and computer codes by ICRU-73, Ziegler et al (SRIM2003.26), Grande and Schiwietz (CasP3.1), Paul and Schinner (MSTAR3.12), and Bazin and Tarasov (LISE ++:2-ATIMA1.2). On the basis of statistical analysis, we estimate the reliability of these tables and codes. It has been observed that the MSTAR3.12 code shows the best agreement with the experimental data for projectile ions (8 ≤ Z ≤ 18) in the entire energy range. The SRIM2003.26 code provides good results except for some heavy projectiles (Xe, Pb and U). The values tabulated by CasP3.1 code underestimate especially at low energy region. No significant trend is observed in case of LISE++:2-ATIMA1.2 code and ICRU-73 report.     

Elastic, inelastic scattering and fusion of the 14N +59Co system at energies close to the coulomb barrier

Elastic and inelastic scattering differential cross sections were measured in the energy range 30 MeV ≤ E _lab ≤ 55 MeV, for the ¹⁴N +⁵⁹Co system. Ambiguities of the optical potential derived from the analysis of the elastic scattering data were removed by performing calculations at the radius of sensitivity and by comparison with the available fusion cross section data. A simultaneous analysis of the three mechanisms was performed by coupled channel calculations, and a unique energy independent nuclear potential was found to be able to fit the data. Discussions and comparisons concerning the optical model, the threshold anomaly, full and approximated coupled channel calculations are presented. Received: 6 February 1997 / Revised version: 1 August 1997     

Low temperature electrical conductivity and magnetoconductivity of Fe39Ni39Mo4Si6B12 and Co58Ni10Fe5Si11B16 metallic glass alloys

A detailed study on the weak localization phenomenon vis-a-vis electron-electron interaction effects in magnetic metallic glasses has been carried out. We measured the electrical conductivity and magnetoconductivity within the temperature range 1.8≤T≤300K. A maximum on the conductivity versus temperature curve exists atT=T _m. The conductivity was observed to follow aT ^1/2 law forT<T _m andT ² law forT>T _m. Magnetoconductivity data of these alloys indicate the prominence of electron-electron interaction at low temperatures. The authors have determined the inelastic scattering field and spin-orbit scattering field from the magnetoconductivity data. The inelastic scattering field obeys aT ^p law (p=2) at low temperatures.     

Search for cosmic γ-ray bursts in the (1÷50) GeV energy range

Summary A search for cosmic gamma-ray bursts in the GeV energy range has been performed by means of the EAS-TOP Extensive Air Shower array at Campo Imperatore (Gran Sasso Laboratories) during the period March–December 1990. In 2566.5 hours of measurement the obtained upper limit to the rate of bursts of amplitude >2% of the cosmic-ray intensity and time duration τ=1 s, isR≤7.9y⁻¹ (90% c.l.). Assuming for γ-rays a differential energy spectrumS(E ₀ )≈E ₀ ^−2.5 , the corresponding upper limit to the energy flux of γ-rays with energy >5 GeV in bursts of duration τ≤1 s is Φ<8.3·10⁻⁵erg cm⁻².     

Mass measurements of relativistic projectile fragments in the storage ring ESR

Two experimental methods of measuring masses of exotic nuclei in the storage ring ESR are presented. Bismuth and nickel fragments were produced via projectile fragmentation, separated and investigated with the combination of the fragment separator FRS and the ESR: (i) Direct mass measurements of relativistic projectile fragments were performed using Schottky mass spectrometry (SMS), i.e., exotic nuclei were stored and cooled in the ESR. Applying electron cooling, the relative velocity spread of circulating low intensity beams can be reduced below 10⁻⁶. Under this condition a mass resolving power of up to m/Δm=6.5·10⁵ (FWHM) was achieved in a recent measurement. Previously unknown masses of more than 100 neutron-deficient isotopes have been measured in the range of 60≤Z≤84. Using known Q _α values the area of known masses could be extended to more exotic nuclei and to higher proton numbers. The results are compared with mass models and extrapolations of experimental values. In a second experiment with ²⁰⁹Bi projectiles the area of the measured masses was extended to lower proton numbers. Due to various improvements at the ESR the precision of the measurements could be raised. (ii) Exotic nuclei with half-lives shorter than the time needed for SMS (present limit: T _1/2 ≈ 5 sec) can be investigated by time-of-flight measurements whereby the ESR is operated in the isochronous mode. This novel experimental technique has been successfully applied in first measurements with nickel and neon fragments where a mass resolving power of m/Δm=1.5·10⁵ (FWHM) was achieved.     

Real-gas properties of n-alkanes, O2, N2, H2O, CO, CO2, and H2 for diesel engine operation conditions

The objective of the research outlined in this paper was to develop the analytical approximations for calculating real-gas properties (p-v-T data, thermodynamic functions: internal energy, enthalpy, and entropy, and specific heats) of vapor-phase n-alkanes from C₁ (methane) to C₁₄ (normal tetradecane), O₂, N₂, H₂O, CO, CO₂, and H₂ within the range of pressure 0.05 MPa ≤ p ≤ 20 MPa and temperature 280 K ≤ T ≤ 3000 K aimed for implementation into computational fluid dynamics (CFD)-codes simulating the operation process in modern Diesel engines. The analytical approximations have been developed based on available literature data and on the new equation of state for moderately dense gases. The approximations reported are rather simple and therefore can be used directly in CFD codes. Approximations for mixing rules are also provided.     

A model for multiparticle production in high energy hadronic collisions

A model for multiparticle production process in high-energy hadronic collisions is proposed. In the centre of mass (CM) system of colliding particles the target and the projectile are assumed to pass through each other sharing energies allowed by kinematical constraints. Thus in app collision the energy associated with each is √S/2 (S being the square of the CM energy) which is taken to be the real variable that governs the number of particles produced. In the case of hadronnucleus collisions the projectile and the target ofv nucleons lying in a (Lorentz contracted) tube pass through each other sharing energies ⋍ √S _A2, whereS _A ⋍vS. Before the final state particles emerge from these systems, the constituents of the target, i.e.,v nucleons share equally (= √S _A2v) the total energy associated with the target and become the centres from which final state particles stem out. Several results have been discussed.     

Field theoretic calculation of energy cascade rates in non-helical magnetohydrodynamic turbulence

Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field, and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r _A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd ^1/3. For the normalized cross helicity σ_c →1, the cascade rates are proportional to (1 − σ_c)/(1 + σ_c , and the Kolmogorov’s constants vary significantly with σ_cc.     

Pion-nucleon scattering in the K-matrix approach

The K-matrix approach with effective Lagrangians is used to describe the S and P pion-nucleon partial-wave amplitudes in the energy range E _lab≤ 1 GeV. It is demonstrated, that treating the resonance as K-matrix a pole gives the natural way to separate the resonance and non-resonance parts of the πN amplitude. The model includes all the four-star πN resonances, the non-resonance contributions are calculated from relevant Feynman graphs without any phenomenological form factors. Different contributions to the inelastic π⁻ p→ηn amplitude are estimated. Received: 9 July 1998     

He-Na2体系低温下的冷碰撞研究

在已经拟合好的He-Na₂体系势能面上,根据原子-双原子分子的非反应性碰撞动力学的相关基本理论,在空间固定坐标系下,采用严格的密耦方法求解了He原子和Na₂分子的转动非弹性碰撞动力学方程.并对He-Na₂体系的微分散射截面、积分截面作了详细的分析,结果与实验符合得比较好.结果表明：（1）弹性散射（Δj=0）截面远大于非弹性截面;（2）较小Δj的跃迁主要产生前向散射,随着Δj的增加,后向散射的几率增加 关键词： 2体系')" href="#">He-Na₂体系 密耦方法 微分散射截面 积分截面     

Use of the wake of a small cylinder to Control unsteady loads on a circular cylinder

Simultaneous measurements of lift and drag forces have been performed in order to study passive control of unsteady loads induced on a circular cylinder. For this purpose, an aerodynamic balance has been developed. The balance, developed for a cylinder of 25.4 mm in diameter, was designed to operate in the subcritical regime (Re=32000). This instrument is characterized by its sensitive element that forms a small central part of the cylinder. The static and dynamic calibrations of the balance show the appropriateness of the present design. Moreover, qualification experiments carried out with a single cylinder gave results (mean and rms values of the lift and drag coefficients) that are in good agreement with those found in the literature. The purpose of this paper is to present a passive control experiment performed by means of the wake of a smaller cylinder interacting with a larger one. Firstly, a parametric study was performed by varying the following: i) the diameterdS of the small cylinder for one large cylinder diameterd (7 values in the range 0.047≤d _S /d≤0.125); ii) the center-to-center spacingS/d (11 values in the range 1.375≤S/d≤2.5); and iii) the stagger anglea(0≤a≤90 with a fine angular stepDa fora≤15). A maximum mean drag reduction of about 48% is achieved. Ata=4 to 8, one can observe a peak of mean lift coefficient. Then unsteady fluid forces, vortex shedding frequency and flow pattern were systematically investigated for the small cylinder having a diameterdS=2.4 mm (0.094d). Reductions of 78% and 56% of the rms lift and drag fluctuations respectively were obtained with the small cylinder placed at a slight stagger angle in the range 6<a<9. This leads to an instantaneous force vector that exhibits more steadiness both in angle and amplitude. Moreover, at these stagger angles, the energy of the lift fluctuations at the shedding frequency is significantly reduced compared to the single cylinder case.     

Thermal and optical analysis of Te-substituted Sn–Sb–Se chalcogenide semiconductors

Bulk amorphous samples of Te-substituted Sn₁₀Sb₂₀Se_70−X Te _X (0≤X≤12) were prepared using a melt quenching technique. Calorimetric studies of the samples were performed using differential scanning calorimetry (DSC) and the glass transition temperature and crystallization temperature were evaluated from DSC scans. The glass transition temperature T _g exhibits a sharp decrease for small Te substitution of X=2, thereafter increases with increase in Te content up to X=10, and then decreases for further Te substitution. The apparent activation energy for glass transition and the activation energy for crystallization were calculated using Kissinger, modified Kissinger, and Matusita equations. The change in glass transition temperature T _g has been explained based on the bond formation energy of different heteropolar bonds. The optical band gap of thermally evaporated thin films of Sn₁₀Sb₂₀Se_70−X Te _X (0≤X≤12) was calculated from reflectance and transmittance data. The optical band gap variation with tellurium content exhibits a sharp decrease for an initial tellurium substitution of X=2 similar to that of the glass transition temperature and thereafter a peak is observed in optical band gap around X=4 composition.     

Procedural analysis of a new method for determining the Gibbs energy and experimental data on thermodynamic properties of liquid-metal coolants based on alkali metal alloys

A detailed procedural analysis is given and results of implementation of the new version of the effusion method for determining the Gibbs energy (thermodynamic activity) of binary and ternary systems of alkali metals Cs-Na, K-Na, Cs-K, and Cs-K-Na are presented. The activity is determined using partial pressures of the components measured according the effusion method by the intensity of their atomic beams. The pressure range used in the experiment is intermediate between the Knudsen and hydrodynamic effusion modes. A generalized version of the effusion method involves the pressure range beyond the limits of the applicability of the Hertz-Knudsen equation. Employment of this method provides the differential equation of chemical thermodynamics; solution of this equation makes it possible to construct the Gibbs energy in the range of temperatures 400 ≤ T ≤ 1200 K and concentrations 0 ≤ x _i ≤ 1.     

Specific features of the structural states in Pb2CdWO6 in the temperature range 15 ≤ T ≤ 770°C

In the temperature range 15–770°C, a correlation between the dielectric and structural specific features of lead cadmium tungstate is established. When studying the structure of Pb₂CdWO₆ in the temperature range 15 ≤ T ≤ 770°C, the unit-cell parameters and atomic parameters of the orthorhombic phase with space group Pmc2₁ (15 ≤ T ≤ 380°C) and cubic phase with space group Fm3m (380 ≤ T ≤ 770°C) are determined. It is revealed that the antiferroelectric state observed in of Pb₂CdWO₆ in the orthorhombic phase is associated with antiparallel displacements of Pb atoms. In the cubic phase, the Cd atoms are found to have disordered static displacements along [100]-type directions.     

Amorphous-to-crystalline transition in Ge22Se78−x Bi x system

Summary Crystallization kinetics is studied in glassy Ge₂₂Se_78−x Bi _x (0≤x≤10) using isothermal annealing at various temperatures between the glass transition and melting. D.c. conductivity is taken as a parameter to estimate the extent of crystallization (α). The activation energy of crystallization (ΔE) and the order parameter (n) are calculated by fitting the values of α in Avrami’s equations of isothermal transformation. The results indicate that ΔE is highly composition dependent and decreases as the Bi concentration increases.     

Description of cross sections for photonucleon reactions on tin isotopes at photon energies in the range 2 ≤ <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">γ</Emphasis></Subscript> ≤ 140 MeV

A modified model of preequilibrium decay is considered. This model makes it possible to calculate cross sections for multiparticle photonucleon reactions with allowance for the impact of collective isospin effects. Features of the photodisintegration of 101 ≤ A ≤ 135 tin isotopes in the energy range 2 ≤ E _γ ≤ 140 MeV are studied on the basis of this model.     

Morphotropic phase boundary, weak ferromagnetism, and strong piezoelectric effect in Bi1 ? xCaxFeO3 ? x/2 compounds

The crystal structure and magnetic and piezoelectric properties of the Bi_{1 − x} Ca _x FeO_{3 − x/2} system (x ≤ 0.2) are studied. The crystal-structure transformations occur in the following sequence: rhombohedral (R3c) polar phase (x ≤ 0.06) → modulated polar phase (0.07 ≤ x ≤ 0.1) → modulated antipolar phase (0.11 ≤ x ≤ 0.14). The modulated polar and antipolar phases are weakly ferromagnetic with a spontaneous magnetization of 0.25 G cm³/g (x = 0.09). In the polar weak ferromagnet with x = 0.09, a uniform piezoelec- tric response 2.5 times stronger than in the initial BiFeO₃ compound is detected by the piezoelectric force microscopy.     

Effect of the aluminium doping on the microstructure and morphology of LiNi0.5Co0.5O2 oxides

LiCo_1−xNi_xO₂ materials having the layeredα-NaFeO₂-type structure are promising positive electrodes for advanced lithium-ion batteries. Their electrochemical performance is very much conditioned by the integrity of the lamellar structure that needs to be stable enough to stand many charge/discharge cycles. LiNi_0.5−xAl_xCo_0.5O₂ (0≤x≤0.3) samples have been prepared by a low-temperature route, the sol-gel method assisted by succinic acid as chelating agent. We study in detail their crystallographic structure by XRD, their chemical composition by ICP and their morphology by SEM. Their local cationic environment is also carried out by means of FTIR spectroscopy. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Precise model approximation of JINR (Dubna) data on nuclear level densities in the region 40 ≤ <Emphasis Type="Italic">A</Emphasis> ≤ 200 below <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>

The experimental nuclear level density below the neutron binding energy B _n in the mass region 40 ≤ A ≤ 200 is approximated to a high precision on the basis of the Strutinsky model combined with the assumption that the coefficient of collective enhancement of the level density for a given number of excited quasiparticles decreases exponentially with increasing excitation energy. This combination of model concepts makes it possible to reproduce faithfully not only the general trend revealed by the method developed at the Joint Institute for Nuclear Research (JINR, Dubna) in the change in the level density with increasing excitation energy in any nuclei but also the fine structure of this level density. Realistic experimental information about the change in the relationship between the densities of quasiparticle- and vibrational-type states was obtained for the first time for any nuclei virtually up to the neutron binding energy B _n .