THERMOSTATIC PROPERTIES OF ASYMMETRIC NUCLEAR MATTER AT LOW TEMPERATURE

The Küpper, Wegmnn, and Hilf's theory on the thermostatic properties of symmetric nuclear matter is extended to the asymmetric nuclear matter at low temperature less than 10 MeV. The numerical result shows that the entropy per nucleon s depends on the asymmetry δ weakly while the compressibility coefficient K depends on δ very strongly. At the neutron drip point the nucleon density n decreases while the asym-, metry ^δND increases linearly with T² at low temperature. The thermodynamic stability of the asymmetric nuclear matter is studied by means of the Gibbs-Duhem inequality.     

The Effective Mass of Nucleon in Asymmetric Nuclear Matter

The effective mass of nucleon in asymmetric nuclear matter is studied by the RHF approach.It is found that there exist critical densities ρ_c(δ). When ρ > ρ_c a phase transition from Fermi sphere to Fermi shell.pattern for ground state will occur.     

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.     

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.     

Surface and curvature properties of neutron-rich nuclei

We use the extended Thomas-Fermi approximation and Skyrme-type interactions to describe the energy density of a semi-infinite slab of neutron-rich nuclear matter at zero temperature. We allow for the existence of a drip phase at low proton fractions in addition to the more dense nuclear phase. We determine various bulk properties of both phases when the system is in equilibrium. We extend the usual definition of the surface energy to apply to the case where drip is present. Assuming the density profile has the form of a Fermi function to a power, we perform a constrained variational calculation to determine the parameters of the density profile. The surface and curvature energies are calculated for proton fractions ranging from 0.5 (symmetric nuclear matter) to 0 (pure neutron matter) for typical Skyrme-type interactions. We find significantly different asymmetry dependences for different interactions. For proton fractions close to 0.5, our results are in close agreement with the predictions of the droplet model. We also present results of calculations for fission barrier properties and phase transitions between nuclei and bubbles to highlight the role of surface and curvature energies in the neutron-rich regime.     

Nucleon Tensor Charge from the Quark Model

The ndcleon tensor charge is studied in the quark model. It is found that the contributions from valence constituent quarks are δu_q = 1.17 and δu_g = -0.29, while the contributions from valence current quarks are δu_v = 0.89 and δu_v = -0.22 at scale about 1 Ge V.     

Vacuum renormalization of the chiral-sigma model and the structure of neutron stars

Vacuum renormalization corrections are calculated for normal nuclear matter and neutron star matter in the chiral-sigma model. The theory is generalized to include hyperons in equilibrium with nucleons and leptons. The equations of state corresponding to two compression moduli, a “stiff” and “soft” one for nuclear matter, are studied. It is shown that fully one half the mass of a neutron star at the limiting mass is composed of matter at less than twice nuclear density. Neutron star masses are therefore moderately sensitive to the properties of matter near saturation and to the domain of the hyperons, but dominated by neither. The predictions for the two equations of state are compared with observed neutron star masses, and only the stiffer is compatible.     

Neutron stars in relativistic hadron-quark models

Neutron star properties are computed in relativistic models that contain both hadron and quark degrees of freedom. Neutron matter is assumed to have a low-density phase described by quantum hadrodynamics (QHD) and a high-density phase described by quantum chromodynamics (QCD). Several different QHD models and approximations are employed; all use parameters that reproduce the binding energy and density of equilibrium nuclear matter. Calculated neutron star properties depend primarily on the high-density equation of state and cannot be inferred from the symmetry energy or compressibility of equilibrium nuclear matter. If interactions are neglected in the QCD phase, the density of the hadron-quark phase transition is determined by one free parameters, which is the energy/volume needed to create a “bubble” that confines the quarks and gluons. Observed neutron star masses do not constrain this parameter, but stable neutron stars with quark cores can exist only for a limited range of parameter values. When second-order gluon-exchange corrections are included in the QCD phase, these conclusions are unchanged, and the parameter values that lead to stable hadronquark stars are restricted even further.     

Properties of nuclear pastas

In this review we study the nuclear pastas as they are expected to be formed in neutron star crusts. We start with a study of the pastas formed in nuclear matter (composed of protons and neutrons), we follow with the role of the electron gas on the formation of pastas, and we then investigate the pastas in neutron star matter (nuclear matter embedded in an electron gas).Nuclear matter (NM) at intermediate temperatures (1 MeV ≲ T ≲ 15 MeV), at saturation and sub-saturation densities, and with proton content ranging from 30% to 50% was found to have liquid, gaseous and liquid–gas mixed phases. The isospin-dependent phase diagram was obtained along with the critical points, and the symmetry energy was calculated and compared to experimental data and other theories. At low temperatures (T ≲ 1 MeV) NM produces crystal-like structures around saturation densities, and pasta-like structures at sub-saturation densities. Properties of the pasta structures were studied with cluster-recognition algorithms, caloric curve, the radial distribution function, the Lindemann coefficient, Kolmogorov statistics, Minkowski functionals; the symmetry energy of the pasta showed a connection with its morphology.Neutron star matter (NSM) is nuclear matter embedded in an electron gas. The electron gas is included in the calculation by the inclusion of an screened Coulomb potential. To connect the NM pastas with those in neutron star matter (NSM), the role the strength and screening length of the Coulomb interaction have on the formation of the pastas in NM was investigated. Pasta was found to exist even without the presence of the electron gas, but the effect of the Coulomb interaction is to form more defined pasta structures, among other effects. Likewise, it was determined that there is a minimal screening length for the developed structures to be independent of the cell size.Neutron star matter was found to have similar phases as NM, phase transitions, symmetry energy, structure function and thermal conductivity. Like in NM, pasta forms at around T ≈ 1.5 MeV, and liquid-to-solid phase changes were detected at T ≈ 0.5 MeV. The structure function and the symmetry energy were also found to depend on the pasta structures.     

Parameterization of Nuclear Hulthén Potential for Nucleus-Nucleus Elastic Scattering

In contrast to Gaussian or Woods-Saxon potential a two-term four parameter nuclear Hulth′en type interaction is considered to describe the α-α, α-~3He and α-~3H systems. By exploiting the phase function method, scattering phase shifts are computed up to ELab = 100 MeV for the α-α system and ELab = 15 Me V for α-~3He and α-~3H systems.The S-wave phase shift δ_0 for the α-α system tends to 2π and δ_(3/2)-for the α-~3He system tends to π, in the limit of zero energy. Reasonable agreements in phase shifts with the standard data are obtained with this simple potential model except for the 5/2~- states of α-~3He and α-~3H systems. With an additional energy-dependent correction factor to our potential, a good agreement with experimental data is obtained for 5/2~- states. We have also compared our results with the convenient Born approximations.     

Exploring proton rich systems and Coulomb induced instabilities

The thermodynamic properties of proton rich systems are explored in a mean field approach which is generated from a Skyrme interaction. The addition of Coulomb interactions result in asymmetries which modify the chemical and mechanical instability of the system and its equilibrium properties. These properties are studied for systems with proton fraction y on the proton richer side of the valley of β-stability as well as the neutron rich side. Coulomb induced instabilities lead to proton diffusion processes on the proton richer side and also large asymmetries in chemical and mechanical instabilities and coexistence curves. Considering the whole range of 0y1, we can study how the symmetry about y=1/2 is broken by asymmetric interaction and we can also explicitly show that the role between proton and neutron is exchanged around y_E which is the point where the liquid and gas have the same proton fraction. It is shown that there are two asymmetric coexistence surfaces in (y,P,T) space, one for y<y_E and another for y>y_E and touching each other at y_E. These asymmetries in instabilities show up as new branches, one for y<y_E and one for y>y_E, and thus form a closed loop in pressure versus ρ for both chemical instability and coexistence regions. The branch of y>1/2>y_E was not previously investigated since only the y<1/2 region is usually considered. In our simplified model, mechanical instability is still symmetric around a point y_E≠1/2 even with Coulomb forces present.     

Quark matter formation in dense stellar objects

It is expected that at very large densities and/or temperatures a quark-hadron phase transition takes place. Lattice QCD calculations at zero baryon density indicate that the transition occurs at T _c ∼ 150–170 MeV. The transition is likely to be second order or a cross over phenomenon. Although not much is known about the density at which the phase transition takes place at small temperatures, it is expected to occur around the nuclear densities of few times nuclear matter density. Also, there is a strong reason to believe that the quark matter formed after the phase transition is in colour superconducting phase. The matter densities in the interior of neutron stars being larger than the nuclear matter density, the neutron star cores may possibly consist of quark matter which may be formed during the collapse of supernova. Starting with the assumption that the quark matter, when formed consists of predominantly u and d quarks, we consider the evolution of s quarks by weak interactions in the present work. The reaction rates and time required to reach the chemical equilibrium are computed here. Our calculations show that the chemical equilibrium is reached in about 10⁻⁷ seconds. Further more during the equilibration process enormous amont of energy is released and copious numbers of neutrinos are produced. Implications of these on the evolution of supernovae will be discussed.     

Deconfinement Phase Transition Including Perturbative QCD Corrections in （Proto）neutron Star Matter

Deconlinement phase transition and neutrino trapping in （proto）neutron star matter are investigated in a chiral hadronic model （also referred to as the FST model） for the hadronic phase （HP） and in the color-flavor-locked （CFL） quark model for the deconlined quark phase. We include a perturbative QCD correction parameter αs in the CFL quark matter equation of states. It is shown that the CFL quark core with K^0 condensation forms in neutron star matter with the large value of αs. If the small value of αs is taken, hyperons suppress the CFL quark phase and the liP is dominant in the high-density region of （proto）neutron star matter. Neutrino trapping makes the fraction of the CFL quark matter decrease compared with those without neutrino trapping. Moreover, increasing the QCD correction parameter as or decreasing the bag constant B and the strange quark mass ms can make the fraction of the CFL quark matter increase, simultaneously, the fraction of neutrino in protoneutron star matter increases, too. The maximum masses and the corresponding radii of （proto）neutron stars are not sensitive to the QCD correction parameter αs.     

核物质液-气相变和热核稳定性

简述了研究核物质液－气相变的理论计算及研究热核稳定性的二相平衡模型．讨论了相变的临界温度及其对核物质大小、不对称度及库仑相互作用的依赖性．比较了用各种核力或模型算得的热核极限温度及实验结果． A brief introduction of the theoretical studies of liquid gas phase transition in nuclear matter and a two phase equilibrium model for studying stability of hot nuclei is presented. The critical temperature of the phase transition and its dependence on size and asymmetry of nuclear matter and Coulomb interaction are discussed. The limiting temperatures of hot nuclei calculated with various nuclear forces or models and experimental results are compared.     

CO2及其碳同位素比值高精度检测研究

改进了一种基于傅里叶变换红外光谱法测量CO₂气体的装置, 改进后的装置能够提高CO₂检测精度, 并能同时测量CO₂碳同位素比值. 研究了温度和压力对CO₂浓度值和CO₂碳同位素比值测量的影响规律. 利用该装置连续测量了标准CO₂气体和环境大气, 对标准CO₂气体测量得到的CO₂浓度值及其碳同位素比值进行温度和压力影响修正, 获得了较好的精度和准确度. 关键词： 光谱学 同位素比值 傅里叶变换红外光谱 二氧化碳     

Study of Survival Probability of Super Heavy Nuclei

The survival probability of super heavy nuclei produced in cold fusion reactions is studied by using the standard Fermi gas level density formula and analyzed with fission and neutron evaporation characteristics predicted in different theoretical models. The level density formula used in this letter suppresses the ratio of neutron emission width to fission width, Гn/Гf. The dependence of Гn/Гf on the saddle point level density parameter and excitation energy is also investigated.     

129Xe NMR研究MCM-22分子筛中的Xe-Xe作用

¹²⁹Xe NMR 测量得到Xe-Xe碰撞产生的δ_Xe-Xe，该值要比自由 的Xe和在NaY、CaA分 子筛中的值小很多. 通过一定的理论分析，证明在MCM-22分子筛超笼中的Xe-Xe碰撞作用类似于一维气体碰撞，同时表明δ_Xe-Xe也和δ_S（由Xe与孔壁碰撞产生 的化学位移）一样与分子筛的孔道结构密切相关.      

Hot and cold,nuclear and neutron matter

We report variational calculations of the equation of state of hot and cold, nuclear and neutron matter. The calculations cover a wide density range of interest in heavy-ion collisions and astrophysics. The “hot” calculations are limited to temperatures less than 20 MeV. A realistic nuclear hamiltonian that contains two- and three-nucleon interactions and fits the nucléon-nucléon scattering, as well as nuclear matter data, is used. Neutron star structure calculations are reported and their sensitivity to the three-neutron interactipn is examined. The liquid-vapor phase equilibrium, as well as the behavior of the effective mass in nuclear matter is discussed.     

Thermodynamics of the Apparent Horizon in FRW Universe with Massive Gravity

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive gravity model in cosmology proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified Misner-Sharp internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation δQ=T dS, where the heat flow δQ is the energy-supply of pure matter projecting on the vector ζ tangent to the apparent horizon and should be looked on as the amount of energy crossing the apparent horizon during the time interval dt and the temperature of the apparent horizon for energy crossing during the same interval is 1/2πrA, the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit H_c→0, which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if α₃+4α₄<0. Without this condition, even for the simplest model of dRGT massive cosmology with α₃=α₄=0, the generalized second law of thermodynamics could be violated.