Search results for "shell model"
showing 10 items of 146 documents
Method to compute the stress-energy tensor for a quantized scalar field when a black hole forms from the collapse of a null shell
2020
A method is given to compute the stress-energy tensor for a massless minimally coupled scalar field in a spacetime where a black hole forms from the collapse of a spherically symmetric null shell in four dimensions. Part of the method involves matching the modes for the in vacuum state to a complete set of modes in Schwarzschild spacetime. The other part involves subtracting from the unrenormalized expression for the stress-energy tensor when the field is in the in vacuum state, the corresponding expression when the field is in the Unruh state and adding to this the renormalized stress-energy tensor for the field in the Unruh state. The method is shown to work in the two-dimensional case wh…
Collective features of Cr and Fe isotopes
2014
The question of the sudden increase of collectivity in neutron-rich nuclei when approaching N = 40 has recently interested both experimentalists and theorists. In this paper we study the development of collectivity along the chromium and iron isotopic chains. The calculations are performed within two different perspectives, namely, the proton-neutron interacting boson model (IBM-2) and interacting shell model (ISM) and compared with the available experimental data. The onset of collectivity is studied through nuclear quantities and observables that suggest differences in the nuclear structure of Cr and Fe isotopical chains. Furthermore, a prediction for the shape transition from a spherical…
Étude théorique de la dynamique du réseau de PbTiO3 dans la phase quadratique
1999
Resume La dynamique du reseau du titanate de plomb PbTiO 3 est etudiee en phase quadratique a l'aide d'un modele a coquille tenant compte des polarisabilites electroniques des ions de la maille elementaire et des interactions a longue et a courte portee. Les resultats de nos calculs mettent en evidence le role important joue par l'anisotropie de la polarisabilite electronique de l'oxygene. Il est montre aussi que les courbes de dispersion des phonons calculees dans la premiere zone de Brillouin sont en bon accord avec l'experience.
Silica nanoparticle core structure examined by the E?Si? center 29Si strong hyperfine interaction
2015
Abstract β-Ray irradiation up to 1.2 GGy was employed to induce E′Si γ defects and to study the structure of silica nanoparticles with diameters from 7 up to 20 nm. Defect concentration and their 29 Si strong hyperfine doublet were investigated through electron paramagnetic resonance measurements. Our data indicate that stable defects are located in the nanoparticle core. Furthermore, the E′Si γ hyperfine interaction evidences that the core structure is denser than bulk silica and independent from the particle size. Finally, we put in evidence that the core structure is stable and unaffected by the irradiation in the investigated dose range maintaining the specific features of nanoparticles.
Nuclear shell model applied to metallic clusters
1993
We apply the nuclear shell model to jellium clusters of up to twenty-one Na atoms. Binding energies, ionization potentials, and photoabsorption cross sections are calculated and compared with mean-field results.
Defect Calculations for Yttrium Aluminum Perovskite and Garnet Crystals
2000
Native and impurity point defects in both Yttrium Aluminum Perovskite and Garnet crystals are studied in the framework of the pair-potential and the shell model approximations. The calculated formation energies for native defects suggest that the antisite disorder is preferred over the Frenkel and Schottky-like disorder in both YAP and YAG. In non-stoichiometric compounds, the calculated reaction energies indicate that excess of Y2O3 or Al2O3 is, most likely, to be accommodated by the formation of antisites rather than vacancies or interstitials in the lattice. Enthalpies of the reactions for impurity (Ca2+, Mg2+, Sr2+, Ba2+, Cr3+, Fe3+, Nd3+, Si4+) incorporation into both YAP and YAG latti…
Spectroscopy of low-spin states in $^{157}\mathrm{Dy}$: Search for evidence of enhanced octupole correlations
2019
Low-spin states of 157Dy have been studied using the JUROGAM II array, following the 155Gd ({\alpha}, 2n) reaction at a beam energy of 25 MeV. The level scheme of 157Dy has been expanded with four new bands. Rotational structures built on the [523]5/2- and [402]3/2+ neutron orbitals constitute new additions to the level scheme as do many of the inter- and intra-band transitions. This manuscript also reports the observation of cross I- to (I-1)- and I- to (I-1)+ E1 dipole transitions inter-linking structures built on the [523]5/2- (band 5) and [402]3/2+ (band 7) neutron orbitals. These interlacing band structures are interpreted as the bands of parity doublets with simplex quantum number s =…
The first large-scale shell-model calculation of the two-neutrino double beta decay of $^{76}$Ge to the excited states in $^{76}$Se
2022
Large-scale shell-model calculations were carried out for the half-lives and branching ratios of the $2\nu\beta\beta$ decay of $^{76}$Ge to the ground state and the lowest three excited states $2_1^+$, $0_2^+$ and $2_2^+$ in $^{76}$Se. In total, the wave functions of more than 10,000 intermediate $1^+$ states in $^{76}$As were calculated in a three-step procedure allowing an efficient use of the available computer resources. In the first step, 250 lowest states, below some 5 MeV of excitation energy, were calculated without truncations within a full major shell $0f_{5/2}-1p-0g_{9/2}$ for both protons and neutrons. The wave functions of the rest of the states, up to some 30 MeV, were compute…
Extended shell model calculation for even N = 82 isotones with a realistic effective interaction
1996
The shell model within the $2s1d0g_{7/2}0h_{11/2}$ shell is applied to calculate nuclear structure properties of the even Z=52 - 62, N=82 isotones. The results are compared with experimental data and with the results of a quasiparticle random-phase approximation (QRPA) calculation. The interaction used in these calculations is a realistic two-body G-matrix interaction derived from modern meson-exchange potential models for the nucleon-nucleon interaction. For the shell model all the two-body matrix elements are renormalized by the $\hat{Q}$-box method whereas for the QRPA the effective interaction is defined by the G-matrix.
Shell-Model Effective Operators for Muon Capture in ^{20}Ne
1999
It has been proposed that the discrepancy between the partially-conserved axial-current prediction and the nuclear shell-model calculations of the ratio $C_P/C_A$ in the muon-capture reactions can be solved in the case of ^{28}Si by introducing effective transition operators. Recently there has been experimental interest in measuring the needed angular correlations also in ^{20}Ne. Inspired by this, we have performed a shell-model analysis employing effective transition operators in the shell-model formalism for the transition $^{20}Ne(0^+_{g.s.})+\mu^- \to ^{20}F(1^+; 1.057 MeV) + \nu_\mu$. Comparison of the calculated capture rates with existing data supports the use of effective transiti…