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1.
《Nuclear Physics A》1988,489(2):252-268
By use of semiclassical mean-field methods, we study the dependence of the curvature-energy coefficient and other surface properties of nuclear matter upon the energy-density functional. This is done both by solving the Euler-Lagrange equation with a simplified phenomenological functional and by obtaining a variational solution with a fourth-order extended Thomas-Fermi functional. The calculated curvature-energy coefficient ac decreases with increasing value of the bulk nuclear incompressibility coefficient K for physically relevant values of K, but always remains larger than 3 MeV in either approach when the volume-energy coefficient, saturation density, surface-energy coefficient and surface diffuseness are constrained to their experimental values. The calculated values of the curvature-energy coefficient ac are significantly larger than experimental values obtained from analyses of fission-barrier heights and ground-state masses of nuclei throughout the periodic table. Among possible resolutions of this anomaly, we suggest that relativistic effects or correlations may play a significant role in the nuclear surface, or that the leptodermous expansion may break down in regions of large curvature, such as occurs for highly deformed shapes and for light nuclei.  相似文献   

2.
On the basis of gross properties of nuclei, a simple semiempirical equation of state is developed for cold hadronic matter composed of light quarks of two flavors. The source of binding energy in the model is the decreasing asymmetry between the number of up and down quarks in extended regions of overlapping nucleons. The resulting incompressibility of symmetric nuclear matter at equilibrium density is K=324 MeV. The incompressibility decreases rapidly with decreasing density but increases only slowly with increasing density until homogenous quark matter is reached at a density just above three times ordinary nuclear matter density.  相似文献   

3.
《Nuclear Physics A》1997,615(2):135-161
In an attempt to extend the range of values of Kv, the incompressibility of symmetric nuclear matter, for which fits to the measured breathing-mode energies are possible, we investigate generalized Skyrme-type forces with a term that is both density- and momentum-dependent. Acceptable fits are found to be possible only for values of Kv in the range 215±15 MeV. For higher values fits are impossible, while for lower values fits are achieved only by introducing an unphysical collapse of nuclear matter. Thus our generalization of the Skyrme force does not permit a significantly wider range of values of Kv than that already given by force SkM1. However, with a view to having a more reliable estimate of the compressional properties of the highly neutron-rich nuclear matter that comprises the core of collapsed stars, we present a new version of this latter force giving a much better fit to the masses of neutron-rich nuclei. Comparison with force SkM1 also shows that the value of Kv extracted from the breathing-mode energies is essentially independent of the choice of effective mass. By providing a counter-example, we show that Kv cannot be extracted from masses and charge distributions alone. As for the third-order coefficient K′, we cannot be more precise than to say that it lies in the interval 700 ± 500 MeV.  相似文献   

4.
The extraction of nuclear matter properties from measured nuclear masses is investigated in the energy density functional formalism of nuclei.It is shown that the volume energy a1 and the nuclear incompressibility Ko depend essentially on μnN + μpZ - 2EN,whereas the symmetry energy J and the density symmetry coefficient L as well as symmetry incompressibility Ks depend essentially on μn - μp,where μp =μp - ∂Ec/∂Z,μn and μp are the neutron and proton chemical potentials respectively,EN the nuclear energy,and Ec the Coulomb energy.The obtained symmetry energy is J = 28.5 MeV,while other coefficients are uncertain within ranges depending on the model of nuclear equation of state.  相似文献   

5.
On the basis of a bosonized Nambu- Jona-Lasinio (NJL) model with derivative expansions, quark condensates in nuclear matter are studied at one-quark loop level and the dependence of meson masses and couplings on the constituent quark mass is investigated. The condensate ratio obtained here < q?q > ρB / < q?q > vac is roughly 0.66 with constituent quark mass of 313 MeV, which yields a corresponding σ N value to be roughly 42.2 MeV at the mean field level and σ N =31.4 MeV with the vacuum dependence, where the model parameters describing a Lorentz scalar and a vector field are self-determined.  相似文献   

6.
The thermostatic properties of symmetric nuclear matter are calculated by extension of a recent Thomas-Fermi approach to ground-state nuclei by Myers and Swiatecki [1]. We have computed the free energy per nucleon f(T, n) in Landau's quasiparticle approximation and have derived from it the relevant thermostatic properties. In view of its application to finite excited nuclei, the degenerate limit of nuclear matter is discussed in particular. As an interesting result we find at higher temperatures van-der-Waals-like isotherms in the p-n plane. Below the critical temperature Tc = 17.3 MeV two phases of nuclear matter, liquid and vapour, are defined by these. Comparing these results with the reduced phase transition data of 3He, 4He, and “inert gases,” we find that nuclear matter is similar to the He-isotopes, but differs considerably from the inert gases.  相似文献   

7.
We discuss the relation between the compressibility of nuclear matter and the frequencies of the collective monopole vibrations of nuclei. We analyse some of the problems which arise when one extrapolates from properties of finite nuclei to those of infinite nuclear matter. The best way to perform this extrapolation is to use a theory capable of describing both systems on the same footing. Self-consistent calculations using phenomenological effective interactions realize such a program. The general properties of these effective interactions are discussed. The theory we used is described; we emphasize that it accounts for both the properties of the ground states of nuclei and the small amplitude collective vibrations. Simple models of compression modes in infinite nuclear matter and in nuclei are presented; they illustrate various features of the collective modes in both systems. In particular we discuss the role of the shell structure and the effects of the nuclear surface. Results of extensive self-consistent calculations of the breathing mode of nuclei are presented and many features of the mode are analyzed. The role of the single particle spectrum on the frequencies of the collective modes is studied. Finally we briefly review the experimental situation on the monopole excitations of nuclei.We show that experimental data are compatible with a well defined value of the compression modulus of nuclear matter: K = 210±30 MeV.  相似文献   

8.
A phenomenological momentum-independent(MID) model is constructed to describe the equation of state(EOS) for isospin asymmetric nuclear matter,especially the density dependence of the nuclear symmetry energy Esym(ρ).This model can reasonably describe the general properties of the EOS for symmetric nuclear matter and the symmetry energy predicted by both the sophisticated isospin and momentum dependent MDI model and the Skyrme-Hartree-Fock approach.We find that there exists a nicely linear correlation betwee...  相似文献   

9.
We use a Yukawa-plus-exponential macroscopic model and a folded-Yukawa single-particle potential to systematically calculate the ground-state masses of 4023 nuclei ranging from 16O to {279}112. The method is also used to calculate the fission-barrier heights of 28 nuclei ranging from 109Cd to 252Cf. We introduce several previously neglected physical effects, including a smaller nuclear radius constant, a proton form factor, an exact diffuseness correction, an A0 term, a chargeasymmetry term, and microscopic zero-point energies. The nuclear radius constant is determined from elastic electron scattering and microscopic calculations of nuclear density distributions, the range of the Yukawa-plus-exponential folding function is determined from heavy-ion elastic scattering, the surface-energy constant and surface-asymmetry constant are determined from the fission-barrier heights of the 28 nuclei that are considered, and the remaining constants are determined from the ground-state masses of 1323 nuclei ranging from 16O to 259No for which experimental values are known with experimental errors less than 1 MeV. For the final formula, the root-mean-square error in the ground-state masses is 0.835 MeV and the root-mean-square error in the fission-barrier heights is 1.331 MeV. Some of the remaining discrepancies in the groundstate masses can be understood in terms of instabilities with respect to ε3 and ε6 deformations.  相似文献   

10.
《Nuclear Physics A》1987,464(4):740-768
An equation of state for cold nuclear matter for the region of densities ρnm−4ρnm, where ρnm is empirical nuclear-matter density, is constructed. We begin from the detailed calculation of Day and Wiringa for the two-body interactions; these give a saturation density of ∼2ρnm. This density is brought down to ρnm by the addition of relativistic corrections. Additional binding is obtained from three-body forces. A reasonable picture is obtained with the Day-Wiringa compression modulus for the two-body calculation, but the picture can be further improved by choosing this to be smaller.Our equation of state is similar to that of Friedman and Pandharipande in the region of nuclear matter denstiy ρnm, but, due to higher-order terms in the loop correction, is substantially softer at high density. Basically what happens is that the many-body effects saturate with increasing density, leaving only the two-body interactions.With this equation of state, prompt supernova explosions are very powerful when the compression modulus of neutron-rich matter (twice as many neutrons as protons) is ∼150 MeV, which corresponds to Knm ∼ 190 MeV for symmetric nuclear matter.Analysis shows that hot nuclear matter formed in heavy ion collisions demands a very stiff equation of state. We understand this as arising from the strong velocity dependence in the real part of the optical model potential which follows chiefly from the Lorentz character of the interactions, the vector mean field growing with increasing density and the scalar one decreasing. This gives a substantial repulsive contribution to the energy per particle and produces a stiff effective equation of state for several hundred MeV heavy-ion collisions. With increasing degree of equilibration the magnitude of the repulsive energy decreases since equilibration decreases the effective momentum. Given the strong velocity dependence in the interaction, the hot equation of state can be reconciled with the cool one.  相似文献   

11.
A non-local, separable potential which matches the phase shifts up to 320 MeV and gives saturation for nuclear matter in the first order at a Fermi-momentum ofk F =1.6 f?1 with an energy per particle of ?8 MeV has been constructed byTabakin. We have employed this potential for calculations of finite nuclei using the Fermi-gas-model. The binding energy has been minimalized with respect to two parametersb andc (the surface-thickness and the radius of the nucleus). However the calculations show that an arbitrarily sharp surface is possible.  相似文献   

12.
The properties of nuclear matter are studied in the frame of the Brueckner theory. The Brueckner-Hartree-Fock approximation plus two-body density-dependent Skyrme potential which is equivalent to three-body interaction are used. Various modern nucleon-nucleon potentials are used in the framework of the Brueckner-Hartree-Fock approximation, e.g.: CD-Bonn potential, Nijm1 potential, and Reid 93 potential. These modern nucleon-nucleon potentials fit the deuteron properties and are phase shifts equivalent. The equation of state at T = 0, pressure at T = 0, 8, and 12 MeV, free energy at T = 8 and 12 MeV, nuclear matter incompressibility, and the symmetry energy calculation are presented. The hot properties of nuclear matter are calculated using T 2-approximation method at low temperatures. Good agreement is obtained in comparison with previous theoretical estimates and experimental data, especially at low densities.  相似文献   

13.
The nuclear matter (N = Z and no Coulomb interaction) incompressibility coefficient, K nm , which is directly related to the curvature of the nuclear matter equation of state, is a very important physical quantity in the study of properties of nuclei, supernova collapse, neutron stars and heavy-ion collisions. We review the current status of K nm and the experimental and theoretical methods used to determine the value of K nm from the excitation crosssections σ(E) and the transition strength distributions S(E) of compression modes in nuclei. In particular, we will consider the isoscalar giant monopole resonance (ISGMR) and the isoscalar giant dipole resonance (ISGDR) and provide a simple explanation to the long standing problem of the conflicting results obtained for K nm , deduced from experimental data on excitation cross sections for the ISGMR and data for the ISGDR.  相似文献   

14.
Accurate assessment of the value of the incompressibility coefficient, K , of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei by employing the microscopic theory based on the Random Phase Approximation (RPA). The importance of full self-consistent calculations is emphasized. In recent years, a comparision between RPA calculations based on either non-relativistic effective interactions or relativistic Lagrangians has been pursued in great detail. It has been pointed out that these two types of models embed different ansatz for the density dependence of the symmetry energy. This fact has consequences on the extraction of the nuclear incompressibility, as it is discussed. The comparison with other ways of extracting K from experimental data is highlighted. The text was submitted by the author in English.  相似文献   

15.
16.
The relationship between the centroid energies of the isovector giant dipole resonance of finite nuclei and the symmetry energy has been studied.It is found the excitation energies of the dipole resonance in finite nuclei are correlated linearly with the symmetry energy at and below the saturation density.This linear correlation leads to the symmetry energy at the saturation density at the interval 33.0 MeV ≤ S(ρ_0) ≤ 37.0 MeV,and the symmetry energy at ρ=0.1 fm~(-3) at the interval 21.2-22.5 MeV.It is proposed that a precise measurement of the dipole mode in nuclei could set up an important constraint on the equation of state for nuclear matter.  相似文献   

17.
Accurate assessment of the value of the incompressibility coefficient, K, of symmetric nuclear matter, which is directly related to the curvature of the equation of state (EOS), is needed to extend our knowledge of the EOS in the vicinity of the saturation point. We review the current status of K as determined from experimental data on isoscalar giant monopole and dipole resonances (compression modes) in nuclei, by employing the microscopic theory based on the random-phase approximation (RPA).  相似文献   

18.
The σ-ω coupling is introduced phenomenologically in the linear σ-ω model to study the nuclear matter properties. It is shown that not only the effective nucleon mass M* but also the effective σ meson mass m σ * and the effective ω meson mass m ω * are nucleon-density-dependent. When the model parameters are fitted to the nuclear saturation point, with the nuclear radius constant r 0 = 1.14 fm and volume energy a 1 = 16.0 MeV, as well as to the effective nucleon mass M * = 0.85M, the model yields m σ * = 1.09m σ and m ω * = 0.90m ω at the saturation point, and the nuclear incompressibility K 0 = 501 MeV. The lowest value of K0 given by this model by adjusting the model parameters is around 227 MeV. Received: 23 March 2001 / Accepted: 8 June 2001  相似文献   

19.
《Nuclear Physics A》1988,481(2):294-312
Phase diagrams of superconducting nuclear matter are calculated by solving a set of finite temperature gap equations, using several Skyrme effective interactions. Our results indicate that nuclear matter may have a superconducting phase in a small region with density near one half of the normal nuclear matter density and temperature kBT ≲ 1.4 MeV. Our calculation is based on a finite temperature Green's function method with an abnormal pair cutoff approximation. The same approximation is employed in deriving the internal energy, entropy and chemical potential of superconducting nuclear matter. In this way, its equation of state is obtained, and compared with that of normal nuclear matter. The energy gap of superconducting nuclear matter is found to depend rather sensitively on both density and temperature. This dependence is analysed in terms of the Skyrme interaction parameters. The correlation effect on chemical potential is found to be important at high density, and its inclusion is essential in determining the equation of state of superconducting nuclear matter.  相似文献   

20.
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