Analysis of the dielectric behaviour of transition metal oxides

We present an analysis of the dielectric behaviour of MnO, CoO and NiO on the basis of the shell model of Dick and Overhauser. The electronic polarizability, ionic polarizability, the effective charge parameter and transverse optic mode frequency have been calculated for the crystals under study. A comparison of the results with experimental data reveals the necessity of considering the effect of exchange charge polarization in the theory of the shell model.     

Unified study of lattice dynamics of NiO

A unified study of lattice dynamics of paramagnetic NiO has been studied by correcting the basic equations of the three-body force shell model for the valency of the cations and anions. The shell charge and core charge parameters are also modified. This approach explains the complete lattice dynamics of NiO successfully only when both the ions are taken to be polarizable. There is good scope for fresh determination of positive ion polarizability and Debye temperature variation.     

Laser spectroscopy of the bismuth isotopes

Isotope shifts and hyperfine structures of the bismuth isotope chain have been studied on the 306.7 nm line in off-line measurements using gas cell laser spectroscopy and atomic beam spectroscopy. The changes in nuclear mean square charge radii and the nuclear magnetic and spectroscopic quadrupole moments have been deduced. The neutron-rich isotopes are the first isotones of Pb to be measured immediately above the N=126 shell closure. A remarkable correspondence between the nuclear charge radii of the Bi and Pb isotope chains is demonstrated by a King Plot analysis. The relationship between nuclear shapes and the charge radii can be understood in the framework of the spherical shell model using few-nucleon configurations. This revised version was published online in July 2006 with corrections to the Cover Date.     

可变形战斗部弹体变形型面研究

基于炸药瞬时爆轰理论,将战斗部变形阶段的结构简化为辅助装药,对等效圆柱壳体实施爆轰加载,并在等效壳体上的加载段引入若干个塑性铰,相应地将辅助装药划分成与塑性铰相对应的若干个独立微元。针对均匀加载下等效壳体的原始位移分布,采用具有能量分布梯度的辅助装药加载进行匹配,设计出能实现D型型面的辅助装药形状,最后通过数值模拟进行验证。结果表明,采用该形状的辅助装药能实现较理想的D型弹体变形型面。     

Dynamics of cylindrical conducting shells in a pulsed longitudinal magnetic field

A theoretical model is constructed for describing the motion of a cylindrical conducting shell in a pulsed longitudinal magnetic field generated by an external solenoid. The model takes into account the dynamics of the electric circuit (with the solenoid as its part), inertial and strength properties of the shell, magnetic field diffusion, and heating of the solenoid and shell materials. Difference schemes are constructed for the numerical solution of the system of the defining differential equations, and the criteria of their stability are analyzed. The model is used for studying magnetic-p ulse compression of hollow shells, as well as magnetic field compression in their inner cavity, and the effect of controlling parameters such as the starting charge voltage of the energy storage system and the size of the shell being compressed on the process dynamics is analyzed. Various approximations for calculating the shell heating (adiabatic approximation and uniform heating approximation) are analyzed in comparison with rigorous calculations. The possibility of conducting shell expansion due to magnetic field diffusion into the inner cavity is investigated.     

Dielectric properties of alkali halide and alkaline earth oxide crystals

The deviations of ionic charge and compressibility from their nominal values in alkali halides and alkaline earth oxide crystals have been discussed and explained in terms of a theory based on shell model and exchange charge interactions originally developed by Dick and Overhauser. The exchange charge polarization parameters have been evaluated in the present study using the appropriate values of overlap integrals. It has been concluded that the second neighbour short range forces have significnant magnitudes in alkaline earth oxides.     

Charge transfer in the shell model

the mechanism of charge transfer is incorporated into the shell model in an effort to better describe the lattice dynamics of crystals of the zincblende structure. The long-wavelength aspects of the resulting new model are treated in detail. A preliminary application is made to GaAs.     

Asymmetry of mass and charge division in spontaneous fission

The order-disorder model has been used to explain asymmetry of mass and charge division and related phenomena in fission. According to this model the fission process involves two steps consisting of charge polarisation into two ‘impending fragment clusters’ with beta stable neutron numbers and subsequent distribution of the balance neutrons between the two. Mode of elemental division of the fissioning nuclei is attributed to the charge polarisation in the first step. Theory of reaction rate has been applied to the system. The frequency term is obtained by applying the conditional stochastic process under charge polarisation constraint and the energy-dependent term is given by the condition of minimum in free energy of the system. Using this, the relative probability of polarisation into given charge pair is arrived at. The model uses stable neutron numbers for the charges as the only input. No explicit assumption or quantification on the preference of formation of shell closure species in fission is necessary. The statistics developed on the principle of equala priori probability of all charge polarisation is used. The shell effects come into play only in deciding a stable neutron number for the charges. The total isotopic yield distribution for a number of fission reactions shows asymmetry in the actinide region which reduces with increasing mass/charge of the fissioning nuclide and bunching of the higherz peaks. Although the mass yields obtained therefrom for a number of fission reactions agree with experimental results, the peaks of the distributions are slightly shifted away from the symmetric point and the distributions are somewhat narrower. Charge distribution parameters obtained from these results are also presented.     

A molecular dynamics study of uranyl hydration

Molecular dynamics calculations were carried out in order to investigate the hydration structure of uranyl in aqueous solution. The CF1 model of flexible water molecules is used. This model allows one to investigate a hydrolysis reaction for water molecules in the first uranyl hydration shell. Charge redistribution effects on hydrolysis products are also taken into account. We found five ligands in uranyl hydration shell, which is of bipyramidal pentacoordinated structure. The charge redistribution effects resulted in ligands of four water molecules and one hydroxyl, which was found closer to uranium than the other ligands.     

Effects of nuclear structure in double charge exchange reactions on 16O and 40Ca

The energy dependence of forward double charge exchange (DCX) reaction is studied for the doubly closed shell nuclei ¹⁶O and ⁴⁰Ca. A common characteristic of the two DCX reactions is a resonance-like peak around 50 MeV pion lab energy. While some authors have interpreted this peak as the evidence of a dibaryon resonance state, we show that it arises naturally in a two-step process in the conventional pion—nucleon system with proper handling of nuclear structure. The effects of nuclear structure are demonstrated through a comparison among different nuclear structure models: the symmetry model SU(4) ? SU(3), the single particle shell model and the «realistic” shell model.     

Electronic structure of Yb<Superscript>3+</Superscript> impurity centers in fluorites

The electronic structure and g factors of simple impurity centers and hexamer ytterbium clusters in fluorites have been calculated in terms of the exchange charge model. Preliminarily, their local crystal structures have been calculated in the framework of the shell model with the inclusion of lattice distortions near the impurity.     

Nuclear charge radii of (21-32)Mg

Charge radii of all magnesium isotopes in the sd shell have been measured, revealing evolution of the nuclear shape throughout two prominent regions of assumed deformation centered on (24)Mg and (32)Mg. A striking correspondence is found between the nuclear charge radius and the neutron shell structure. The importance of cluster configurations towards N=8 and collectivity near N=20 is discussed in the framework of the fermionic molecular dynamics model. These essential results have been made possible by the first application of laser-induced nuclear orientation for isotope shift measurements.     

Defect charge states for classical modeling of diffusion processes in insulators

Some point defect properties can be accurately modeled by describing the ions classically, in terms of the shell model. This is particularly the case for point-defect diffusion in strongly ionic crystals. First, we discuss the issue of what ionic charge should be attributed to shell-model ions, including the possibility of partly covalent materials. We then discuss the issue of what defect charge states are likely to be of experimental interest and at the same time amenable to classical modeling. Finally, we discuss the rather common case where the defect charge is not well localized at a single ionic site, and where the electronic charge distribution of the defect and its neighbors will not remain fixed throughout a diffusion step.     

Charge renormalization in quantum field theory by the unitary clothing transformation method

The clothing procedure in several lowest orders in the coupling constant has been implemented using the unitary clothing transformation method. Within a simple field theory model, including interaction of charged spinless nucleons and scalar mesons, an expression for the charge shift is obtained, which is determined by the operators beyond the energy shell.     

Calculation of charge vibration in fission with Strutinsky shell correction

The Strutinsky shell correction method has been applied to the two spheroid model to study charge vibrations in fission. The investigation is carried out by calculating the potential energy surface with respect to three degrees of freedom: charge vibration from the uniform value and the deformations of the two fragments. The results suggest that the effect of shells at Z = 50 and N = 82 do not cause large deviations from the liquid drop model charge density around mass 132; their effect is much more pronounced in the fragment excitation energy. The results also suggest that the fragment excitation and kinetic energies for a given mass ratio are markedly charge density dependent. Some features inherent to this treatment with respect to characteristic periods of individual degrees of freedom have been discussed.     

Electro-optic response of metal halide $$\hbox {CsPbI}_3$$: A first-principles study

In this work, we have obtained energy levels and charge radius for the β-stability line nucleus, in relativistic shell model. In this model, we considered a close shell for each nucleus containing double magic number and a single nucleon energy level. Here we have taken ⁴¹Ca with a single neutron in the ⁴⁰Ca core as an illustrative example. Then we have selected the Eckart plus Hulthen potentials for interaction between the core and the single nucleon. By using parametric Nikiforov–Uvarov (PNU) method, we have calculated the energy values and wave function. Finally, we have calculated the charge radius for ¹⁷O, ⁴¹Ca, ⁴⁹Ca and ⁵⁷Ni. Our results are in agreement with experimental values and hence this model can be applied for similar nuclei.     

Charge-drift and dispersion in deep inelastic collisions in an equilibrium model

First and second moments of the charge distribution for the reaction⁸⁶K +¹⁶⁶Er have been calculated assuming a thermal equilibrium model. The moments are calculated microscopically on the basis of a realistic two-center shell model as a function of distance as well as of excitation energy. The experimentally observed constancy of the first moments is reproduced.     

Theory of strain derivative of electronic dielectric constant of ionic crysts

A theoretical method for evaluating the strain derivative of the electronic dielectric constant of ionic crystals has been developed. The analysis presented here is based on the shell model and takes account of the exchange charge polarizations. Values of strain derivative of the electronic constant dielectric calculated for 6 alkali halides and MgO show a remarkable agreement with experimental data on photoelastic constants.