Search results for " shell"
showing 10 items of 307 documents
Shell-model study on event rates of lightest supersymmetric particles scattering offKr83andTe125
2016
We investigate the elastic and inelastic scattering of lightest supersymmetric particle (LSP) dark matter off two possible target nuclei, $^{83}\mathrm{Kr}$ and $^{125}\mathrm{Te}$. For the nuclear-structure calculations, we employ the nuclear shell model using recently generated realistic interactions. We have condensed the nuclear-physics contribution to a set of nuclear-structure factors that are independent of the adopted supersymmetric (SUSY) model. Total event rates are then easily calculated by combining the nuclear-structure factors with SUSY parameters of choice. In particular, $^{125}\mathrm{Te}$ shows promise as a detector material with both the elastic and inelastic channels yie…
Positron Production In Heavy-Ion Collisions
1985
Atomic systems with a nuclear charge Z much greater than 100 exhibit a number of unique features not otherwise found in nature. Two characteristic properties are illustrated in Figs. 1 and 2. In Fig. 1 we have plotted the binding energy of a K-shell electron around hypothetical nuclei up to Z ≈ 200. For Z > 150 the binding energy exceeds the rest energy m e c 2 of the electron; i.e., adding the electron to the nucleus actually diminishes the total mass of the system. At the critical charge Z c ≈ 170–175 the binding energy reaches twice the electron rest mass, the threshold for spontaneous creation of an electron-positron pair. As has been discussed extensively in the literature (Pieper and …
Quantum-state-selective decay spectroscopy of Ra213
2017
An experimental scheme combining the mass resolving power of a Penning trap with contemporary decay spectroscopy has been established at GSI Darmstadt. The Universal Linear Accelerator (UNILAC) at GSI Darmstadt provided a $^{48}\mathrm{Ca}$ beam impinging on a thin $^{170}\mathrm{Er}$ target foil. Subsequent to velocity filtering of reaction products in the Separator for Heavy Ion reaction Products (SHIP), the nuclear ground state of the $5n$ evaporation channel $^{213}\mathrm{Ra}$ was mass-selected in SHIPTRAP, and the $^{213}\mathrm{Ra}$ ions were finally transferred into an array of silicon strip detectors surrounded by large composite germanium detectors. Based on comprehensive geant4 s…
Towards a spin-adapted coupled-cluster theory for high-spin open-shell states
2006
A spin-adapted coupled-cluster (SA-CC) scheme based on the additional consideration of spin constraints is proposed for the quantum chemical treatment of high-spin open-shell cases. Its computational feasibility is demonstrated via a pilot implementation within the singles and doubles approximation. Test calculations indicate that the suggested SA-CC scheme provides results of similar accuracy as the more traditional schemes without spin adaptation.
Determination of ion-induced K-shell ionization cross sections by comparison with nuclear Coulomb excitation
1979
Abstract A new method for the determination of cross sections for K-shell ionization of heavy atoms by charged particles is proposed. The method is based on a comparison of photon lines due to K X-rays and low-energy γ-rays, the latter ones being produced in nuclear Coulomb excitation with accurately known cross sections. This procedure applies within a limited energy range to the study of targets comprising deformed even nuclei, but can also be extended to other targets having Z≳30. A test of the new technique has been carried out for Gd, W, Th and U natural targets irradiated by 4.75 MeV protons. For Th, also energies of 6.80–10.10 MeV were used. The results are briefly discussed with ref…
Electrons on a spherical surface: Physical properties and hollow spherical clusters
2012
We discuss the physical properties of a noninteracting electron gas constrained to a spherical surface. In particular we consider its chemical potentials, its ionization potential, and its electric static polarizability. All these properties are discussed analytically as functions of the number $N$ of electrons. The trends obtained with increasing $N$ are compared with those of the corresponding properties experimentally measured or theoretically evaluated for quasispherical hollow atomic and molecular clusters. Most of the properties investigated display similar trends, characterized by a prominence of shell effects. This leads to the definition of a scale-invariant distribution of magic n…
Exchange and correlation energy functionals for two-dimensional open-shell systems
2009
We consider density functionals for exchange and correlation energies in two-dimensional systems. The functionals are constructed by making use of exact constraints for the angular averages of the corresponding exchange and correlation holes, respectively, and assuming proportionality between their characteristic sizes. The electron current and spin are explicitly taken into account, so that the resulting functionals are suitable to deal with systems exhibiting orbital currents and/or spin polarization. Our numerical results show that in finite systems the proposed functionals outperform the standard two-dimensional local spin-density approximation, still performing well also in the importa…
Thin plastic shell x-ray optics: an update
2003
We present new results from a program to develop large area X-ray telescopes that are made from thin plastic shells. We use multi-shell cylindrical lenses in a point-to-point configuration to form full aperture images of the small focal spot in a an X-ray tube on a microchannel plate detector. The image data are analyzed to yield radial profiles and encircled energy curves. The derived parameters can be extrapolated to the case of a telescope that is a conical approximation to Wolter 1 optics. The plastic shells can be coated with suitable mono- or multilayers that allow for a wideband coverage of X-ray energies. Our current program is focused on the development of a large area, hard X-ray …
Superheavy element flerovium (element 114) is a volatile metal.
2014
The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Expe…
Analysis of the Electronic Structure of Non-Spherical Ligand-Protected Metal Nanoclusters : The Case of a Box-Like Ag67
2017
In this work we introduce a new strategy to investigate the electronic shell structure of ligand-protected metal nanoclusters of polyhedral core shape. The central idea is to identify the symmetry of the Kohn–Sham molecular orbitals of an atomistic structure based on their projection onto the electronic states of a jellium system with a similar shape of the background charge density. Herein, we study the connection between a reduced atomistic model of the recently reported box-like [Ag67(SR)32(PR3)8]3+ nanocluster and a jellium box consisting of 32 free electrons. With this approach, we determine the symmetry of electronic states of the metal core and identify those that are involved in the…