Spin-Polarized States of Nuclear Matter

The equations of state of spin-polarized nuclear matter and pure neutron matter are studied in theframework of the Brueckner-Hartree-Fock theory including a three-body force. The energy per nucleon E A (δ) calculatedin the full range of spin polarization δ = (ρ↑ - ρ↓)/ρ for symmetric nuclear matter and pure neutron matter fulfills aparabolic law. In both the cases the spin-symmetry energy is calculated as a function of the baryonic density alongwith the related quantities such as the magnetic susceptibility and the Landau parameter Go. The main effect of thethree-body force is to strongly reduce the degenerate Fermi gas magnetic susceptibility even more than the value withonly two-body force. The equation of state is monotonically increasing with the density for all spin-aligned configurationsstudied here so that no any signature is found for a spontaneous transition to a ferromagnetic state.     

Antiferromagnetism of nuclear matter in the model with effective Gogny interaction

The possibility of ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions in symmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with effective Gogny interaction. It is shown that, at some critical density, nuclear matter with the D1S effective force undergoes a phase transition to the AFM spin state (opposite directions of neutron and proton spins). The self-consistent equations of spin-polarized nuclear matter with the D1S force have no solutions corresponding to FM spin ordering (the same direction of neutron and proton spins) and, hence, the FM transition does not appear. The AFM spin polarization parameter is found for zero and finite temperature. It is shown that the AFM spin polarization parameter of partially polarized nuclear matter at low enough temperatures increases with temperature. The entropy of the AFM spin state for some temperature range is larger than the entropy of the normal state. Nevertheless, the free energy of the AFM spin state is always less than the free energy of the normal state, and the AFM spin-polarized state is preferable for all temperatures below the critical temperature. The text was submitted by the authors in English.     

Microscopic three-body force for asymmetric nuclear matter

Brueckner calculations including a microscopic three-body force have been extended to isospin-asymmetric nuclear matter. The effects of the three-body force on the equation of state and on the single-particle properties of nuclear matter are discussed with a view to possible applications in nuclear physics and astrophysics. It is shown that, even in the presence of the three-body force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry β = (N - Z)/A is fulfilled in the whole asymmetry range 0≤β≤1 up to high densities. The three-body force provides a strong enhancement of the symmetry energy which increases with density in good agreement with the predictions of relativistic approaches. The Lane's assumption that proton and neutron mean fields linearly vary vs. the isospin parameter is violated at high density due to the three-body force, while the momentum dependence of the mean fields turns out to be only weakly affected. Consequently, a linear isospin split of the neutron and proton effective masses is found for both cases with and without the three-body force. The isospin effects on multifragmentation events and collective flows in heavy-ion collisions are briefly discussed along with the conditions for direct URCA processes to occur in the neutron star cooling. Received: 18 February 2002 / Accepted: 16 May 2002     

Effect of f0(975) and φ(1020) Mesons on Neutron Star Mater

In the RMF approach, considering the contributions of the σ^* and φ mesons and the hyperons in the baryon octet {N,P,Λ,∑^－,∑⁰,∑⁺,Ξ^－,Ξ⁰}, the properties of neutron star matter have been investigated. It is found that with the contributions of the σ^* and φ mesons, the critical baryon density of hyperon appearance decreases, the number of hyperons increases, the transition density ρ_0H of hyperon stars decreases, the equation of state turns soft, the maximum mass of neutron star decreases and the corresponding radius increases, the central density, the central energy density and the central pressure are all reduced.     

High Spin States and Shape Coexistence in 134Ce

high spin states in ¹³⁴Ce nucleus have been studied by using the heavy–ion induced reaction ¹²²Sn(¹⁶O,4n) carried out at china institute of atomic energy. the early level scheme has been extended with spin up to 22. however,our result is different from that in a recent publication,and the magnetic rotation bands reported there have not been confirmed. our observed level structures may be interpreted as shape coexistence. the 10+ state at the backbending with h_11/2 quasineutron configuration has an oblate deformation with an asymmetry parameter γ≈–60°(lund convention),and the 10+ isomer is a yrast trap of prolate deformation with γ≈–120°,whereas the other signature partner bands with h_11/2 and g_7/2 proton configuration probably have a prolate deformation with γ≈0°.     

Measurement of Reaction Cross Section for 17C and Finite-Range Glauber Model Analysis

We have measured the reaction cross section σ_R of ¹⁷C on the carbon target at the intermediate energy of 97A MeV by using transmission method.finite-range Glauber model has been employed to investigate the density distribution of ¹⁷C by fitting the present result and the previous result of interaction cross section σ_I.By contrast with the result from the analysis of σ_I,a tail in the neutron density distribution of ¹⁷C is found necessary to interpret the present result.Considering the configuration of the valence neutron,a dominant 1d_5/2(77±21%)occupancy is found,which is in agreement with results of momentum distribution measurements.     

Ultrahigh Spin Structures in 157,158,159Er

Rotational structures at ultrahigh spin in ^157,158,159 Er have been investigated with the configuration-dependent cranked Nilsson-Strutinsky approach. Configurations of observed bands are assigned and the corresponding deformations are given theoretically. The calculations suggest that one of ultrahigh spin bands in ^158 Er is triaxial highly deformed and the other is normal-deformed, while both ultrahigh spin bands in ^157Er are suggested to be triaxial highly deformed. The possible ultrahigh spin bands in ^159Er are predicted to be triaxial highly deformed and have shape coexistence in the same configuration. The configurations with two neutron holes in the Nose = 4 orbitals and two neutron holes in the h11/2 orbitals in ^159Er are favoured for ultrahigh spin states but unfavoured for band termination, which is similar to ultrahigh spin bands in ^157,15SEr.     

Skyrme-Hartree-Fock Description of the Nuclear Structure in Ca Isotopes (Ⅰ)Binding Energy and Shell Effects,Radii and Density Distributions

The ground state properties of Ca isotopes far from stability line were systematically studied using the Skyrme Hartree Fock model.The shell effects on the binding energy and two neutron separation energy are discussed.The isospin dependency of the unclear radii and nucleon density distributions and the shell effects on these properties are also studied.It is shown that the neutron magic number affests the width of nuclear surface and the nucleon density distributions beyond the nuclear surface.The change of proton rms radii R_rms with neutron number excess I=(N-Z)/A follows R_rms=3/5(1+αI+βI²)r_pZ^1/3.The effect of the centrifugal potential on the nuclear density in the outer trach of nuclear surface is clearly shown.     

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.     

Three-Body Force Effects on EOS of Asymmetric Nuclear Matter and Proton Fraction in Neutron Star Matter

The three-body force effects on the equation of state and its iso-spin dependence of asymmetric nuclearmatter and on the proton fraction in neutron star matter have been investigated within Brueckner-Hartree-Fock approachby using a microscopic three-body force. It is shown that, even in the presence of the three-body force, the empiricalparabolic law of the energy per nucleon vs. isospin asymmetry β＝ ( N - Z) /A is fulfilled in the whole asymmetry range0≤β≤1 and also up to high density. The three-body force provides a strong enhancement of symmetry energy at highdensity in agreement with relativistic approaches. It also shows that the three-body force leads to a much more rapidincreasing of symmetry energy with density in relatively high density region and to a much lower threshold density forthe direct URCA process to occur in a neutron star as compared to the predictions adopting only pure two-body force.     

Two-body and three-body effective interactions in nuclei

Finite-range two-body and zero-range three-body effective forces for use in spin unsaturated systems are determined so as to reproduce the total binding energies, rms radii, and single-particle energies of ¹⁶O, ⁴⁰Ca, ⁴⁸Ca and ⁹⁰Zr; the saturation of nuclear matter; and experimental two-body matrix elements extracted by Schiffer and True. In addition to the Skyrme three-body force which acts only in spatially even states, a spatially odd force is introduced to obtain sufficient generality. The Landau parameters and the effective mass specified by this force are also discussed.     

Investigation of Self-Consistent Relativistic Microscopic Optical Potential

In Dirac-Brueckner calculations for nuclear matter,the average binding energy per nucleon versus density curve is not uniquely defined if coupling to anti-particle is neglected.According to the Hugenholtz-Van Hove theorem,a constraint requires that the nucleon separation energy equals to the fermi energy at saturation density.Choosing saturation energy as empirical value E_B/A=－15.8MeV,the self-consistent calculation leads to the saturation density k_f=1.41fm^－1 and effective mass m*=0.52m,in compressive coefficient k=208MeV.Applying the first law of thermodynamics,self-consistent effective mass (real scalar potential) and the binding energy per nucleon as function of the nuclear density can be obtained.With the realistic nucleon-nucleon interaction (Bonn potential),the vector potential can be obtained from solving the RBBG equation,which weakly depends on the momentum.The cross section and spin observables of the nucleon-nucleus scattering are studied with this new self-consistent relativistic microscopic optical potential.     

Spin-polarized electron–electron quantum bilayers: Finite width effect

We study the effect of finite width on the ground-state of a spin-polarized electron–electron quantum bilayers (EEBL) system at temperature T=0. Correlations among carriers are treated beyond the static mean-field theories by using the quantum or dynamical version of Singwi, Tosi, Land and Sjölander (qSTLS) theory. Numerical results are presented for the pair-correlation function, the ground-state energy, the static density susceptibility, and the static local-field correction factor as a function of density parameter r_sl and interlayer spacing d. Interestingly, we find that the inclusion of finite width lowered the critical density, for the onset of Wigner crystal (WC) ground-state, as compared to the similar recent study of spin-polarized EEBL system without finite width effect. Further, spin-polarization effect is seen to introduce a marked change in the ground-state energy of the EEBL system as compared to the results of unpolarized EEBL system with finite width. Results of ground-state energies are also compared with the recent diffusion Monte Carlo (DMC) and variational Monte Carlo (VMC) simulation studies of spin-polarized EEBL system with zero width.     

A Simulation of Emitted Nucleons:An Extended BUU Model

On the basis of the old BUU method,the neutrons and protons of the projectile and target nucleus was distinguished,meanwhile,the droplet model which included the surface diffusion parameter,neutron skin and deformation parameter etc.was considered during simulating original nucleon's distribution.Condersing the fact σ_np≈3σ_nn≈3σ_pp in intermediate energy domain,it was incorapated into the collision term of BUU.Before studying 44MeV/A ⁸⁶Kr+¹⁹⁷Au reaction by the improved BUU model,the stability of the model has been checked,then the condition of nucleons emission was defined,finally the impact parameter dependence of the abraded neutrons and protons from the projectile was obtained,so was the correlation of TLF and PLF.     

MEASUREMENT OF ISOMERIC CROSS-SECTION RATIO IN 133Cs(n,γ) 134Cs REACTION

The isomeric absolute cross-section have been measured for the reaction ¹³³Cs (n,c) ¹³⁴ Cs at 14.8 MeV neutron energy.The results are:σ_n,γ^134mCs=1.76±0.14mb;σ_n,γ^134gCs=5.17±0.41mb;σ_n,γ^134+gCs=6.93±0.55mb.The isomeric cross-section ratio is σ^134m_Cs/σ^134gCs=0.34±0.03 The experimental results are in agreement with the values given by S.M. Qaim andcompared with the theoretical results calculated by Huizenga-Vandenbosch theory.From this, the spin cut-off paramenter σ and the number of γ-Cascades have been de-termined.     

Spin-dependent quantum transport through an Aharonov--Bohm structure spin splitter

Using the tight-binding model approximation, this paper investigates theoretically spin-dependent quantum transport through an Aharonov-Bohm （AB） interferometer. An external magnetic field is applied to produce the spinpolarization and spin current. The AB interferometer, acting as a spin splitter, separates the opposite spin polarization current. By adjusting the energy and the direction of the magnetic field, large spin-polarized current can be obtained.     

Electrical detection of spin-polarized current in topological insulator Bi1.5Sb0.5Te1.7Se1.3

Spin-momentum locked (SML) topological surface state (TSS) provides exotic properties for spintronics applications. The spin-polarized current, which emerges owing to the SML, can be directly detected by performing spin potentiometric measurement. We observed spin-polarized current using a bulk insulating topological insulator (TI), Bi_1.5Sb_0.5Te_1.7Se_1.3, and Co as the ferromagnetic spin probe. The spin voltage was probed with varying the bias current, temperature, and gate voltage. Moreover, we observed non-local spin-polarized current, which is regarded as a distinguishing property of TIs. The spin-polarization ratio of the non-local current was larger than that of the local current. These findings could reveal a more accurate approach to determine spin-polarization ratio at the TSS.     

3PF2 neutron superfluidity in neutron stars and three-body force effect

We investigate the ^3PF2 neutron superfluidity in H-stable neutron star matter and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the threebody force effect on the ^3PF2 neutron pairing gap. It is found that the three-body force effect is to enhance remarkably the ^3PF2 neutron superfluidity in neutron star matter and neutron stars.     

Cosmological Models with Time Dependent G and Λ Coupling Scalars

A cosmological model in which the universe has its critical density and gravitational constants generalized as coupling scalars in Einstein's theory is considered. A general method of solving the field equations is given. An exact solution for matter distribution in cosmological models satisfying G=G₀(R/R₀)ⁿ is presented. Corresponding physical interpretations of the cosmological solutions are also discussed.     

The spin-isospin decomposition of the nuclear symmetry energy from low to high density

The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter.