Electron Shells Of Atoms Research Articles

Computer representation of characteristics of atomic electron shells

A brief review on information systems that, with the help of databases, provide data on the structure of atomic electron shells in both tabular and graphical forms is given. The merits and drawbacks of such systems are indicated. The information system Electronic Structure of Atoms is presented for the first time.

Effect of beta-electron capture to a bound state on delayed-neutron emission from fission fragments

The effect of ionization of the atomic electron shell on beta decay is investigated. The change in the beta-decay probability is due primarily to the appearance of the channel involving beta-electron capture to a bound state. It is shown that the effect may be significant at low beta-transition energies. The magnitude of the effect was studied in the case of the emission of one to three delayed neutrons following the beta decay of fission fragments. In the calculations, use was made of the beta-decay strength function with allowance for the population of isobaric resonances in daughter nuclei. The effect proved to be maximal for fragments where the numbers of protons and neutrons approach those in closed shells and subshells, thereby illustrating the role of the shell structure of the nucleus in fission.

Rare decay modes of fission fragments

The experimental data on rare modes of radioactive decay of fission fragments is reviewed. These decay modes are due to a large excess of neutrons and a high energy of β decay fragments. They appear in delayed emission of various particles after the β decay (several neutrons, α particles, or heavy clusters) and excitation of unusual states (giant multipole resonances and shape isomers). The β decay and internal conversion of γ radiation into bound states of the atomic electron shell and their influence on the probability of secondary particle emission are considered. The possibility is discussed of observing decays that have not yet been experimentally detected, but theoretically predicted, as well as information on the nuclear structure obtained by studying such decay modes.

Energy losses of fast heavy multiply charged structural ions in collisions with complex atoms

A nonperturbatve theory of energy losses of fast heavy multiply charged structural ions in collisions with neutral complex atoms is elaborated with allowance for simultaneous excitations of ionic and atomic electron shells. Formulas for the effective deceleration that are similar to the well-known Bethe-Bloch formulas are derived. By way of example, the energy lost by partially stripped U q+ ions (10 ≤ q ≤ 70) colliding with argon atoms and also the energy lost by Au, Pb, and Bi ions colliding with various targets are calculated. The results of calculation are compared with experimental data.

Polaron shift for intercalation compounds of titanium dichalcogenides

The data available in the literature on the magnitude and character of the lattice deformation upon intercalation of transition metals and silver into titanium dichalcogenides are analyzed, and the stability condition for the localization of charge carriers in the form of polarons is determined. It is shown that the stability of polarons is determined by the competition between the gain in the free energy of the electronic subsystem and the quasi-elastic contribution associated with the interaction of filled electron shells of intercalant ions and atoms of the nearest environment.

Resonance conversion of gamma radiation in the radiative transitions between neutron resonances

The influence of the resonance conversion on the α-particle spectra in the reaction (n, α) in low-energy transitions between neutron resonances is discussed. Unusual α spectra from neutron resonances in the reaction 147Sm(n, α)144Nd are considered as an example of such influence. The calculation of resonance conversion coefficients was performed for the transitions from K shell in the free levels of P shell of Sm atom. The large effect of resonance in the radiative transitions for the nuclei and atomic electron shells is observed.

The mobility of positive and negative ions in liquid xenon

The mobility of defined positive and negative ions in liquefied xenon is discussed from a microscopic point of view. The effects of electrostriction and spatial variation of viscosity around the ion have a profound influence on the mobility. In the case of negative ions, in addition, the repulsive exchange interaction between the lone electron and the closed electron shells of the xenon atoms has to be taken into account. Generalization of these findings allows to explain qualitatively the difference between positive and negative ion mobility in non-polar dielectric liquids.

Single sub-fs soft-X-ray pulses: generation and measurement with the atomic transient recorder

The change from a zero transition to the maximum amplitude of the electric field of visible light lasts shorter than one femtosecond (1 fs = 10−15 s). By precisely controlling the hyperfast electric field oscillations in a short laser pulse we developed a measuring apparatus—the atomic transient recorder—like an ultrafast stopwatch. This apparatus is capable of measuring the duration of atomic processes with an accuracy of less than 100 as (1 as = 10−18 s), which is the typical duration of electronic processes (transients) deep inside atoms. A 250 as X-ray pulse initiates the atomic process to be measured and the attosecond stopwatch at the same time. For the first time it is now possible with this new measuring method to observe ultrafast processes in the electron shell of atoms.

Time-domain atomic dynamics with attosecond XUV pulses

The interaction of quasi-free electrons with intense laser fields gives rise to phenomena such as high harmonic generation upon rescattering with the parent ions or steering of the electron trajectories. Both effects can be utilized for the realization of time-resolved electron spectroscopy on free atoms. Extreme ultraviolet (XUV) pulses with photon energies exceeding 90 eV are sufficiently energetic to excite inner atomic electron shells and durations down to 250 as permit a time-based view of the extremely rapid relaxation processes that follow the creation of an atomic core-hole. To this end, a strong laser field serves as an ultrafast local probe for an escaping secondary electron by sampling the formation of its wave packet in real time. The capability of the technique was demonstrated in a time-domain study of the MNN Auger decay in krypton.

Calculation of the Equation of State of a Dense Hydrogen Plasma by the Feynman Path Integral Method

A method is developed for calculating the equation of state of a system of quantum particles at a finite temperature, based on the Feynman formulation of quantum statistics. A general analytical expression is found for the virial estimator for the kinetic energy of a system with rigid boundaries at a finite pressure. An effective method is developed for eliminating the unphysical singularity in the electrostatic potential between a discretized Feynman path of an electron and a proton. It is shown that the “refinement” of an expansion of a quantum-mechanical propagator by addition of high powers of time exacerbates, rather than eliminates, the divergence of a Feynman path integral. A brief summary of the current status of the problem is presented. The proposed new approaches are presented in relation to progress made in this field. Path integral Monte Carlo simulations are performed for nonideal hydrogen plasmas in which both indistinguishability and spin of electrons are taken into account under conditions preceding the formation of the electron shells of atoms. The electron permutation symmetry is represented in terms of Young operators. It is shown that, owing to the singularity of the Coulomb potential, quantum effects on the behavior of the electron component cannot be reduced to small corrections even if the system must be treated as a classical system according to the formal de Broglie criterion. Quantum-mechanical delocalization of electrons substantially weakens the repulsion between electrons as compared to protons. In relatively cold plasmas, many-body correlations lead to complex behavior of the potential of the average force between particles and give rise to repulsive forces acting between protons and electrons at distances of about 5 angstroms. Plasma pressure drops with decreasing plasma temperature as the electron shells of atoms begin to form, and the electron kinetic energy reaches a minimum at a temperature of about 31000 K. The minimum point weakly depends on plasma density. Owing to quantum effects, the electron component is “heated” well before electrons are completely bound in the field of protons.

Metallization of liquid iodine

Abstract The metallization of melted iodine observed above the temperature of 900 K and pressure of 3 GPa (V.V. Brazhkin et al., High Press. Res. 6 (1992) 363) has been interpreted using a percolation model of overlapping electron shells (classically accessible spheres) of virtual atoms in molecules. The percolation threshold density falls in the middle of normal densities of the melt and solid. At high temperatures, the pressure near the transition point has a thermal nature mainly caused by seven partially free valence electrons of virtual atoms. Due to a very steep potential within the outer 5s25p5 shell of iodine, the transition yields a sharp increase of the conductivity even at rather high temperatures. With a model of virtual atoms, we have calculated the permittivity, energy gap, and conductivity in the electron–hole and percolation channels which are compared with experimental data.

Radial electron-pair densities in momentum space and shell structure of atoms

The radial electron-pair intracule (relative motion) H(u) and extracule (center-of-mass motion) D(R) densities in position space were known to reveal four types of maxima which are related to the four inner electron shells, K, L, M, and N, of atoms. The corresponding radial electron-pair intracule H¯(v) and extracule D¯(P) densities in momentum space are studied for the 102 atoms from He (atomic number Z=2) to Lr (Z=103). The densities H¯(v) and D¯(P) are found to have either one maximum or two maxima, and the numbers of maxima in H¯(v) and D¯(P) are the same for 98 atoms. For these atoms, the locations υmax and Pmax and the heights H¯max and D¯max of the corresponding maxima satisfy the approximate relations υmax ≅ 2Pmax and H¯max≅D¯max/2. On the basis of their Z-dependence, the maxima in H¯(v) and D¯(P) of the 102 atoms are classified into five types. Shell-pair decompositions of the radial densities show that these maxima reflect five outer electron shells of atoms.

Structural transition and metallization in liquid selenium

The insulator-metal transitions of different kinds caused by heating above the melting temperature under pressure of tens kilobars and by compressing at the critical temperature to a pressure of about 1.1 kbar occur in liquid selenium. At tens kilobars, metallization is interpreted as the forbidden energy band vanishing due to a gradual structural transition (melting of polymer chains) described by the Clapeyron-Clausius equation. At supercritical temperatures, the insulator-metal transition is caused by percolation of overlapping electron shells (classically accessible spheres) of virtual atoms in molecules Se2 remaining when polymer chains decay. The percolation threshold in such a system has been found to increase due to coupling of virtual atoms. The thermally activated conductivity in the vicinity of percolation threshold has been calculated and compared with existing experimental data.

Space, time and entropy in quantum physics

The present paper is a contribution within the E (∞) Cantorian space theory. After a brief review of the historical development of length and time measurements, we consider conventional definitions and methods of calculation of vector and fractal dimensions. A definition of emptiness as zero entropy is discussed. Treating the `fabric' of space-time as non-permanent, we consider other possible ways of filling emptiness. This leads to a definition of range dimension ( p), the properties of which are then discussed. p=1/2 and p=1/4 range dimensions are linked to p=1 (conventional) range dimensions in fluid environments using differential velocities and accelerations. Applications of p=2 range dimensions to quantum events are also considered, and eclectic evidence for the existence of range dimensions is presented. The bijection relationship, defining space-filling fractal dimension ( d c, n ) is extended to cover the range 1< n<4 vector dimensions, and a physical interpretation in terms of a characteristic length ratio ( l n / l 0) is developed. The n-dimensional term ( l n / l 0) n is then closely correlated to the ratio ( l 1/ l 0) d c, n . The bijection relationship is extended to other range dimensions. An approximate empirical relationship is now presented, which provides a basis for defining conventional ( p=1) range dimensional space, by introducing N n , the number of elements needed to set up 1–4 vector dimensions. Two other ways of obtaining approximately the same number of elements are also given, one of which leads to the concept of a p=2 range dimensional substrate for conventional ( p=1) range dimensions. It is found that a single track in p=1 range dimensions needs nearly p=2 range dimensions to support it. The required value then falls as n increases, equaling approximately unity for n=3 vector dimensions. A second empirical equation defining the same value of N n for 3< n<4 vector dimensions, based on space-filling fractal dimensions for p=2 range dimensions is also presented. A fractal form for conventional space is then defined, characterised by tiny elements of negative entropy (in log space). This definition is then readily amalgamated with dynamically generated space, and the latter is shown to correlate with the classical gas equation and Hooke's law for solids. Based on the new definition of space, a proof of both the well-known inverse square law and Hubble's astronomical law is given. A relationship between the number of events in p=1 and p=2 range dimensions is next established, and the effect of `information loss' corresponding to the reduction in the required value of range dimension as vector dimension ( n) increases is tentatively linked to wave functions, for n=4 vector dimensions. The corresponding `useful' information is then shown to be contained in the exponent field, which is of the form {2 f( e−1) pd c,4 }, where f≈1, p=2 range dimensions, and e (within the exponent!) equals the numerical value of the exponent. This field is then sub-divided to various extents, and the corresponding entropies are used to determine sets of distinguishable arrangements N. These sets are successfully compared with `magic' numbers in atomic and nuclear physics, and with preferred sodium atom groupings. A prediction of the number of occupied energy levels in atomic electron shell theory is successfully carried out. Finally, combining `useful' and `hidden' information the p=2 range dimension substrate is re-created by allowing matter to collapse and `drain away' from its p=2 range dimensional space base. Light propagation through space having p=2 range dimensions is then discussed. The paper concludes with a discussion of various ideas implicit in the text, though not necessarily directly obvious. The interdependence of fractal, range and vector dimensions is first considered, followed by a review of the universal application of range dimensions. The paper ends with a study of the fractal nature of space and its justification.

Spin and orbital contributions to the magnetic scattering of neutrons

The current densities in partially filled electron shells of free atoms or ions, when analyzed in terms of multipole expansions, do not carry signatures that would distinguish orbital and spin currents. The same holds for the orbital and spin contributions to elastic neutron scattering amplitude, which are related to Fourier transforms of the respective current densities. The pitfalls of the so-called dipole approximation, which appears to enable a distinction, are pointed out and errors involved are calculated for some free-ion and crystal-field states.

Photoluminescence of composite ceramics derived from polysiloxanes and polycarbosilanes by ion irradiation

Polysiloxanes and polycarbosilanes films were irradiated with increasing fluences of C or Au ions and changes of their photoluminescence (PL) spectra were correlated to structural transformations, assessed by means of ion beam analyses, Raman, XPS and FTIR. They exhibit a strong yellow emission when the energy transferred by the ions to electron shells of target atoms is within the range of 20–60 eV/atom, due to the segregation of C into clusters embedded in an amorphous Si xO yC yH z matrix. For larger energy transfers and for pyrolized films, the photoluminescence shifts towards red then vanishes, because of the growth and percolation of the quantum dots.

Group of symmetry of the periodic system of chemical elements

The concurrence of the group of symmetry of the periodic system of elements with the group of dynamical symmetry of a hydrogenlike atom is employed in the theoretical investigation of atoms. The character of the degeneracy of the eigenvalues of a hydrogenlike atom Hamiltonian, without changing its eigenfunctions, was changed by introducing into this Hamiltonian a term which violates the symmetry in relation to transformations from the subgroup O(4) of the group SO(4, 2). In consequence, it was realized that such “reorganization” of the states of a hydrogenlike atom, which form a representation of the group SO(4, 2), effects the splitting of this representation into finite-dimensional multiplets, first of which are in full agreement with the experimentally observable composition of electron shells of atoms, and retains the physical meaning of quantum numbers that define electron states. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 499–508, 1999

Visible photoluminescence of ion irradiated polysiloxane films

We have studied the photoluminescence (PL) of inorganic polymers submitted to irradiations with increasing fluences of energetic He, C or Au ions and correlated the changes in luminescence spectra to structural transformations, evidenced by means of ion beam analyses, Raman, FTIR and spectroscopic ellipsometry. The films exhibit a strong yellow emission when the energy transferred by the ions to electron shells of target atoms is within a given range of 20 to 60 eV/atom. For this optimal amount of ionizations, the precipitation of quantum dots made of free carbon becomes noticeable. The vanishing of the luminescence for larger energy transfers is attributed to the percolation or growth of these dots, combined with a subcritical depletion in the H content of the surrounding SiO 1.5 C x : H y matrix.

Ceramic coatings by ion irradiation of polycarbosilanes and polysiloxanes: Part I Conversion mechanism

Changes of composition and structure of various types of polysiloxanes and polycarbosilanes when submitted to irradiation with ions of increasing mass, were analysed by means of several ion-beam analytical techniques, Raman and Fourier transform-infrared spectroscopies. Ion irradiations is as efficient as annealing at temperatures above 1000°C for releasing hydrogen from these organic-inorganic polymers, and the radiolytic evolution of hydrogen is selective, whereas methane, silanes and carbon monoxide are also evolved during heat treatments. The kinetics of the polymer conversion into amorphous ceramics depends strongly on the linear density of energy transferred by ions to electron shells of target atoms, according to the ion energy per nucleon and to the nature of the side groups. Some of the carbon atoms segregate in clusters exhibiting a diamond-like hybridization state, in contrast to the clusters of turbostratic graphite formed in pyrolysed films.

Fast sampling algorithm for the simulation of photon Compton scattering

A simple algorithm for the simulation of Compton interactions of unpolarized photons is described. The energy and direction of the scattered photon, as well as the active atomic electron shell, are sampled from the double-differential cross section obtained by Ribberfors from the relativistic impulse approximation. The algorithm consistently accounts for Doppler broadening and electron binding effects. Simplifications of Ribberfors' formula, required for efficient random sampling, are discussed. The algorithm involves a combination of inverse transform, composition and rejection methods. A parameterization of the Compton profile is proposed from which the simulation of Compton events can be performed analytically in terms of a few parameters that characterize the target atom, namely shell ionization energies, occupation numbers and maximum values of the one-electron Compton profiles.