摘要 :
Properties of the ~1S_0 superfluid phase are studied for symmetric nuclear matter at finite temperature. It is described within a covariant hadronic field model, of the σω type, with addition of density dependent correlations si...
展开
Properties of the ~1S_0 superfluid phase are studied for symmetric nuclear matter at finite temperature. It is described within a covariant hadronic field model, of the σω type, with addition of density dependent correlations simulating effects due to finite extension of nucleons. The model is solved in a self-consistent HartreeBogoliubov approach, assuming instantaneous interactions in the superfluid phase. A comparison with the results obtained from several hadronic field models is made. Main characteristics of our description of the superfluid gap are in qualitative agreement with some studies using microscopic potentials, although further refinements could improve its performance.
收起
摘要 :
S-wave pairing in neutron matter is studied within an extension of correlated basis function (CBF) theory to include the strong, short range spatial correlations due to realistic nuclear forces and the pairing correlations of the ...
展开
S-wave pairing in neutron matter is studied within an extension of correlated basis function (CBF) theory to include the strong, short range spatial correlations due to realistic nuclear forces and the pairing correlations of the Bardeen, Cooper and Schrieffer (BCS) approach. The correlation operator contains central as well as tensor components. The correlated BCS scheme of [S. Fantoni, Nucl. Phys. A 363 (1981) 381], developed for simple scalar correlations, is generalized to this more realistic case. The energy of the correlated pair condensed phase of neutron matter is evaluated at the two-body order of the cluster expansion, but considering the one-body density and the corresponding energy vertex corrections at the first order of the Power Series expansion. Based on these approximations, we have derived a system of Euler equations for the correlation factors and for the BCS amplitudes, resulting in correlated nonlinear gap equations, formally close to the standard BCS ones. These equations have been solved for the momentum independent part of several realistic potentials (Reid, Argonne upsilon(14) and Argonne upsilon(8')) to stress the role of the tensor correlations and of the many-body effects. Simple Jastrow correlations and/or the lack of the density corrections enhance the gap with respect to uncorrelated BCS, whereas it is reduced according to the strength of the tensor interaction and following the inclusion of many-body contributions. (c) 2008 Elsevier B.V. All rights reserved.
收起
摘要 :
The surface nature of nuclear pairing is confirmed microscopically. A two-step approach is used in which the full Hilbert space S is split into the model subspace So and the complementary one, S'. The gap equation is solved in the...
展开
The surface nature of nuclear pairing is confirmed microscopically. A two-step approach is used in which the full Hilbert space S is split into the model subspace So and the complementary one, S'. The gap equation is solved in the model space in terms of the effective interaction V-eff(P) which obeys the Bethe-Goldstone-type equation in the complementary subspace. The simplest nuclear systems with one-dimensional inhomogeneity are considered, i.e. semi-infinite nuclear matter and the nuclear slab. Numerical solution is carried out for the separable representation of the Paris NN-potential. The equation for the effective pairing interaction is solved directly, without use of any form of local approximation. A version of the local approximation, the local potential approximation, is suggested which works sufficiently well even in the surface region. The effective pairing interaction obtained in our calculations reveals a strong variation in the surface region changing from a strong attraction outside the nuclear matter to almost zero value inside. The effective interaction is found to be dependent on the chemical potential mu. At mu = -8 MeV, it reproduces qualitatively the phenomenological density-dependent effective pairing interaction, with the surface-dominance, which was found previously in the self-consistent finite Fermi systems theory and in the new version of the energy functional method by Fayans et al. As \mu\ decreases, the surface attraction becomes stronger. The gap equation was solved in semi-infinite matter and in the slab system with the help of the method by Khodel, Khodel and Clark which was suggested recently for nuclear matter. This method extended to non-homogeneous systems turned out to be very efficient in this case. The gap Delta found for both the systems exhibits a strong variation in the surface region with a pronounced maximum near the surface. The surface effect in J turned out to be it-dependent being enhanced at small I \mu\. (C) 2003 Elsevier B.V. All rights reserved. [References: 46]
收起
摘要 :
The pairing off of two-dimensional vortices with opposite orientation and constant strength has its analog in nuclear pairing forces, where the constant vortex strength corresponds to the projection of the angular momentum on the ...
展开
The pairing off of two-dimensional vortices with opposite orientation and constant strength has its analog in nuclear pairing forces, where the constant vortex strength corresponds to the projection of the angular momentum on the symmetry axis. This occurs as a second-order phase transition for a critical value of the interaction strength. Interactions leading to configurational mixing are analyzed in terms of Euler's equation of an asymmetrical top in the strong coupling limit. The dynamics of pairing forces, configurational mixing, and deformation alignment, due to quadrupole forces and the coupling of the total angular momentum to the intrinsic spin of the odd nucleon, are analyzed by imposing constraints on the coefficients of a quadratic rotational Hamiltonian. Processes leading to deformation alignment give rise to precessional motion of the total angular momentum about the nuclear symmetry axis.
收起
摘要 :
Quantum condensates in nuclear matter are treated beyond the mean-field approximation, with the inclusion of cluster formation. The occurrence of a separate binding pole in the four-particle propagator in nuclear matter is investi...
展开
Quantum condensates in nuclear matter are treated beyond the mean-field approximation, with the inclusion of cluster formation. The occurrence of a separate binding pole in the four-particle propagator in nuclear matter is investigated with respect to the formation of a condensate of a-like particles (quartetting), which is dependent on temperature and density. Due to Pauli blocking, the formation of an a-like condensate is limited to the low-density region. Consequences for finite nuclei are considered. In particular, excitations of self-conjugate 2n-Z-2n-N nuclei near the n-alpha-breakup threshold are candidates for quartetting. We review some results and discuss their consequences. Exploratory calculations are performed for the density dependence of the a condensate fraction at zero temperature to address the suppression of the four-particle condensate below nuclear-matter density.
收起
摘要 :
The level structure of W-185 has been studied using the prompt and delayed gamma-gamma coincidences from thermal neutron capture in W-184 accompanied with the one-nucleon transfer reactions (d, p) and (d, t) with polarized beams. ...
展开
The level structure of W-185 has been studied using the prompt and delayed gamma-gamma coincidences from thermal neutron capture in W-184 accompanied with the one-nucleon transfer reactions (d, p) and (d, t) with polarized beams. From these data and those of previous studies a total of 183 levels has been established for energies below 3 MeV. Many of these states have been grouped into rotational bands built on 28 intrinsic states of quasiparticle and quasi particle-plus-phonon character. Although the DWBA analysis permitted definite spin-parity assignments for most of states a large number of particle transitions have,anomalous' angular and asymmetry shapes with respect to the DWBA which indicate an influence of strong mixing between particle and hole states. The extra exchange of phonons and the significance of configurational Delta N = +/- 2 mixing across the Fermi surface lead to a fine structure in the fragmentation of most single-particle strengths and at the same time has the effect of breakdown of the individual properties of Nilsson states. The accumulated l = 1 (d, p) sum is about a factor two smaller than the equivalent (d, t) strength. Thus, the previously observed loss of the (d, p) strength in the W nuclei with A = 184, 185 is presumably because of their redistribution amongst particle- and hole-type states. The observed states below 2 MeV are compared with predictions of the quasi particle-phonon nuclear model. (c) 2005 Elsevier B.V. All rights reserved.
收起
原文获取