Incompressibility and single-particle potential for asymmetric nuclear matter with Skyrme potential

The incompressibility and the single-particle potential of asymmetric nuclear matter have been investigated in the framework of the Skyrme interaction. These parameters have been studied as functions of the nuclear density, the neutron excess parameter, and the temperature. The ratio of the isothermal incompressibility of hot nuclear matter to the incompressibility of cold nuclear matter for different values of neutron excess as a function of temperature is calculated. It is observed that this ratio decreases with temperature increasing apart from pure neutron matter when the growth of temperature leads to the growth of incompressibility. The symmetry incompressibility has been calculated as a function of density for different values of temperature. The text was submitted by the authors in English.     

Comparison between microscopic and phenomenological nuclear pairing calculations

The isospin and density dependent effective pairing interaction is revisited by fitting the neutron gaps from the microscopic calculations for the neutron matter and the symmetric nuclear matter.The neutron pairing gaps for 1S0 channel for asymmetric nuclear matter are obtained from the BCS gap equation with a realistic bare nucleon-nucleon interaction in the Skyrme mean field.It is shown that the neutron gaps obtained from the new effective pairing interaction for the asymmetric nuclear matter are much imp...     

利用非对称核物质状态方程对中子星的质量和半径的研究

在温度、密度及同位旋相关的核物质状态方程的基础上,通过求解Tol-man-Oppenheimer?Volkoff方程得到了中子星的质量与中心密度的关系,发现随着中心密度的变化,中子星存在一个最大质量.同时计算结果表明,中子星的最大质量与核物质状态方程的不可压缩系数、有效质量及对称能强度系数等密切相关.对中子星半径的研究表明,较硬的核物质状态方程给出的中子星半径较大,而且较大的对称能强度系数和较大的核子有效质量也会给出较大的中子星半径.     

Equation of state of asymmetric nuclear matter: a VMC study

A Variational Monte Carlo (VMC) method is employed to investigate the properties of symmetric and asymmetric nuclear matter. The realistic Urbana V ₁₄ twonucleon interaction potential of Lagaris and Pandharipande was used to describe the microscopic interactions. Also, many body interactions are included as a density dependent term in the potential. Total kinetic and potential energies per particle are calculated for asymmetric nuclear matter by VMC method at various densities and isospin asymmetry parameters. The results are compared with data found in literature, and it was observed that the results obtained in this study reasonably agree with the results found in the literature. Also, the symmetry energy and incompressibility factor of the nuclear matter were obtained. The results obtained are in good agreement with those obtained by various authors with different methods and techniques.     

Isovector Scalar Field Effects in Asymmetric Nuclear Matter

Density-dependent parametrization models of the nucleon-meson coupfing constants, including the isovector scalar δ-field, are applied to asymmetric nuclear matter. The nuclear equation of state （EOS） and the neutron star properties are studied in a relativistic Lagrangian density, using the relativistic mean field （RMF） hadron theory. It is known that the δ-field in the constant coupling scheme leads to a larger repulsion in dense neutron-rich matter and to a definite splitting of proton and neutron effective masses, finally influences the stability of the neutron stars. We use density-dependent models of the nucleon-meson couplings to study the properties of neutron star matter and to reexamine the （~-field effects in asymmetric nuclear matter. Our calculation shows that the stability conditions of the neutron star matter can be improved in presence of the δ-meson in the density-dependent models of the coupling constants. The EOS of nuclear matter strongly depends on the density dependence of the interactions.     

Nucleon Finite Volume Effect and Nuclear Matter Properties in a Relativistic Mean-Field Theory

Effects of excluded volume of nucleons on nuclear matter are studied, and the nuclear properties that follow from different relativistic mean-field model parametrizations are compared. We show that, for all tested parametrizations, the resulting volume energy al and the symmetry energy J are around the acceptable values of 16 MeV and 30 MeV, and the density symmetry L is around 100 MeV. On the other hand, models that consider only linear terms lead to incompressibility Ko much higher than expected. For most parameter sets there exists a critical point （pc, δc）, where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero. This critical point depends on the excluded volume parameter r. If this parameter is larger than 0.5 fm, there is no critical point and the pure neutron matter is predicted to be bound. The maximum value for neutron star mass is 1.85M⊙, which is in agreement with the mass of the heaviest observed neutron star 4U0900-40 and corresponds to r = 0.72 fm. We also show that the light neutron star mass （1.2M⊙） is obtained for r ≌ 0.9 fro.     

Proton radioactivity with a Yukawa effective interaction

The half-lives of proton radioactivity of proton emitters are investigated theoretically. Proton-nucleus interaction potentials are obtained by folding the densities of the daughter nuclei with a finite-range effective nucleon-nucleon interaction having Yukawa form. The Wood-Saxon density distributions for the nuclei used in calculating the nuclear as well as the Coulomb interaction potentials are predictions of the interaction. The quantum mechanical tunneling probability is calculated within the WKB framework. These calculations provide reasonable estimates for the observed proton radioactivity lifetimes. The effects of neutron-proton effective mass splitting in neutron-rich asymmetric matter as well as the nuclear matter incompressibility on the decay probability are investigated.     

Isoscalar and isovector nuclear matter properties and neutron skin thickness

Isoscalar and isovector nuclear matter properties are investigated in the Skyrme Hartree-Fock (SHF) and the relativistic mean field (RMF) models. The Skyrme parameters are related analytically to the isoscalar and the isovector nuclear matter properties of the Hamiltonian density. Linear correlations are found among the isovector nuclear matter properties of the Hamiltonian density in both the SHF and the RMF models. We also discovered that the correlations between the isovector properties and the incompressibility K show a singularity at the critical incompressibility K_c=306 MeV. It is shown that the neutron skin thickness gives crucial information about not only for the neutron EOS but also about the isovector nuclear matter properties and about the parameterization of Skyrme interaction. Charge exchange spin-dipole (SD) excitations are proposed to determine the neutron skin thickness model independently.     

The Properties of Pure Neutron Star

For a given equation of state of neutron matter in the relativistic σ-ω model, ๏๏๏๏๏ including the vacuum fluctuation of neutron and σ meson, the properties of pure neutron star are studied. We find that the maximum mass of pure neutron star is ～ 2.0 M_{\odot}. At the same time, the influence of incompressibility of the nuclear matter to the properties of neutron star is also studied. We also find that the maximum mass of neutron stars decreases as equation of state of neutron matter becomes softer.     

非对称核物质不可压缩系数的微观计算(英文)

在带微观三体力的Brueckner-Hartree-Fock方法下研究了非对称核物质的不可压缩系数,得到了不可压缩系数的同位旋以及密度依赖, 并做了进一步的讨论。在一定密度下,不可压缩系数作为同位旋非对称度的函数随同位旋单调递增。 预测了非对称核物质在平衡态的同位旋依赖性质并与其他理论方法做了比较。 We have investigated the incompressibility of asymmetric nuclear matter within the Brueckner Hartree Fock approach extended to include a microscopic three body force. The isospin dependence and density dependence of the nuclear incompressibility have been obtained and discussed. It is shown that the incompressibility at a fixed density increases monotonically as a function of isospin asymmetry. The isospin asymmetry dependence of the equilibrium properties of asymmetric nuclear matter is also predicted and compared with the results of other theoretical approaches.     

Folding-model analysis of elastic and inelastic α-particle scattering using a density-dependent force

A folding model with a density-dependent form of the semi-realistic M3Y effective interaction is applied to α-particle scattering. A previous analysis of elastic scattering at 140 and 172 MeV is now applied to data at other energies from 25 to 120 MeV. The model is also extended to inelastic scattering, using both the collective model and a valence-plus-core-polarization model for the transition densities. The proton transition densities were normalized to measured B(EL) values. When necessary, the neutron transition densities were rescaled to fit the (α, α′) data, providing a source of information on the neutron contributions. The neutron transition multipole moments thus obtained are compared to those derived from (p, p′) data at 800 MeV, as well as from other sources.     

A simple semiempirical equation of state for cold nuclear matter

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.     

Spin polarised nuclear matter and its application to neutron stars

An equation of state (EOS) of nuclear matter with explicit inclusion of a spin-isospin dependent force is constructed from a finite range, momentum and density dependent effective interaction. This EOS is found to be in good agreement with those obtained from more sophisticated models for unpolarised nuclear matter. Introducing spin degrees of freedom, it is found that it is possible for neutron matter to undergo a ferromagnetic transition at densities realisable in the core of neutron stars. The maximum mass and the surface magnetic field of the neutron star can be fairly explained in this model. Since finding quark matter rather than hadronic matter at the core of neutron stars is a possibility, the proposed EOS is also applied to the study of hybrid stars. It is found using the bag model picture that one can in principle describe both the mass as well as the surface magnetic field of hybrid stars satisfactorily.     

Probing the density content of the nuclear symmetry energy

The nature of equation of state for the neutron star matter is crucially governed by the density dependence of the nuclear symmetry energy. We attempt to probe the behaviour of the nuclear symmetry energy around the saturation density by exploiting the empirical values for volume and surface symmetry energy coefficients extracted from the precise data on the nuclear masses.     

Finite nuclei to nuclear matter: a leptodermous approach

The liquid drop model (LDM) expansions of energy and incompressibility of finite nuclei are studied in an analytical model using Skyrme-like effective interactions to examine, whether such expansions provide an unambiguous way to go from finite nuclei to nuclear matter, and thereby can yield the saturation properties of the latter, from nuclear masses. We show that the energy expansion is not unique in the sense that, its coefficients do not necessarily correspond to the ground state of nuclear matter and hence, the mass formulas based on it are not equipped to yield saturation properties. The defect is attributed to its use of liquid drop without any reference to particles as its basis, which is classical in nature. It does not possess an essential property of an interacting many-fermion system namely, the single particle property, in particular the Fermi state. It is shown that, the defect is repaired in the infinite nuclear matter model by the use of generalized Hugenholtz–Van Hove theorem of many-body theory. So this model uses infinite nuclear matter with well defined quantum mechanical attributes for its basis. The resulting expansion has the coefficients which are at the ground state of nuclear matter. Thus a well defined path from finite nuclei to nuclear matter is found out. Then using this model, the saturation density 0.1620 fm⁻³ and binding energy per nucleon of nuclear matter 16.108 MeV are determined from the masses of all known nuclei. The corresponding radius constant r₀ equal to 1.138 fm thus determined, agrees quite well with that obtained from electron scattering data, leading to the resolution of the so-called ‘r₀-paradox’. Finally a well defined and stable value of 288±20 MeV for the incompressibility of nuclear matter K_∞ is extracted from the same set of masses and a nuclear equation of state is thus obtained.     

Interactions of neutrons with239Pu in the energy range between 1.5 and 5.5 MeV

Neutron scattering angular distributions of²³⁹Pu were measured at seven primary neutron energies between 1.5 and 5.5 MeV. Absolute differential scattering cross-section results are plotted and tabulated. Cross section calculations using a central optical model were made and the results were compared with the experimental values. Moreover, nuclear temperatures of the fission and the inelastic neutron evaporation processes were extracted from the measured spectra.     

Quadrupole moments and nucleon excitation strengths in even-A Sm isotopes

We present a coherent coupled-channel analysis of 7 MeV neutron and 16 MeV proton elastic and inelastic scattering from ^{148, 152, 154}Sm. The optical potential and nuclear deformation parameters are determined so as to fit not only these elastic and inelastic scattering data but also the low-energy neutron scattering properties and the total cross sections over a wide energy range. This analysis provides evidence of the same excitation strengths for both projectiles in the case of ^{152, 154}Sm, and of a smaller excitation strength for the proton than for the neutron in case of ¹⁴⁸Sm. Moreover the quadrupole moments of these deformed optical potentials are in good agreement with those extracted from Coulomb excitation measurements and from nuclear matter distribution calculations.     

Medium polarization and pairing in asymmetric nuclear matter

The many-body theory of asymmetric nuclear matter is developed beyond the Brueckner–Hartree–Fock approximation to incorporate the medium polarization effects. The extension is performed within the Babu–Brown induced interaction theory. After deriving the particle–hole interaction in the form of Landau–Migdal parameters, the effects of the induced component on the symmetry energy are investigated along with the screening of ¹ S ₀ proton–proton and ³ PF ₂ neutron–neutron pairing, which are relevant for the neutron-star cooling. The crossover from repulsive (screening) to attractive (anti-screening) interaction going from pure neutron matter to symmetric nuclear matter is discussed.     

Nuclear symmetry energy in terms of single-nucleon potential and its effect on the proton fraction of <Emphasis Type="Italic">β</Emphasis>-stable <Emphasis Type="Italic">npeμ</Emphasis> matter

Momentum and density dependence of single-nucleon potential u_τ (k, ρ, β) is analyzed using a density dependent finite range effective interaction of the Yukawa form. Depending on the choice of the strength parameters of exchange interaction, two different trends of the momentum dependence of nuclear symmetry potential are noticed which lead to two opposite types of neutron and proton effective mass splitting. The 2nd-order and 4th-order symmetry energy of isospin asymmetric nuclear matter are expressed analytically in terms of the single-nucleon potential. Two distinct behavior of the density dependence of 2nd-order and 4th-order symmetry energy are observed depending on neutron and proton effective mass splitting. It is also found that the 4th-order symmetry energy has a significant contribution towards the proton fraction of β-stable npeμ matter at high densities.     

中子星物质中的K介子凝聚与三体核力效应

利用Brueckner-Hartree-Fock方法，计算了β稳定中子星物质的状态方程以及三体核力的影响，特别是研究了三体核力对中子星物质中K介子凝聚的影响. 结果表明三体核力对β稳定中子星物质中出现K介子凝聚的临界密度以及中子星物质中各种粒子所占的比例均有重要影响. 三体核力的主要作用是降低了中子星物质中出现K介子凝聚的临界密度并使K凝聚相中的核物质更加接近于对称核物质.