Symmetry Energy Of Nuclear Matter,Neutron Star Structure And Propenies Of Superheavy Nuclei

The symmetry energy which characterizes the isospin-dependent part of the equation of state (EOS) of asymmetric nuclear matter, plays a crucial role in many issues of nuclear physics as well as astrophysics, such as in neutron stars. Neutron stars are related to many branches of contemporary physics and astrophysics, and are important for fundamental physics. The synthesis and identification of superheavy nuclei (SHN) have been receiving a worldwide at-tention since the prediction of the existence of superheavy island in1960s. Up to now superheavy nuclei (SHN) with Z=104-118have been synthesized in experiment. In this work, these three issues have been investigated.We investigated the α-decay energies and half-lives for the new synthe-sized superheavy nuclei. A formula is proposed to compute the Qα values for the superheavy nuclei with a good accuracy, according to which the long-lived SHN should be neutron rich. The Qα formula is found to work well for these nuclei, confirming its predictive power. A simple formula for the correlation be-tween the α-decay Q values of the SHN has been proposed, which works very well for an estimation of the α-decay energies of the recently synthesized SHN. They thus allow us to reliably predict the Q values of the still unknown SHN with a good accuracy, and is going to be very useful for the future experiment design. Also, the agreements between the calculated and experimental values indicate the reliability of the experimental observations and measurements on these synthesized SHN to a great extent. Z=114and N=172turn out to be not shell closures for the presently observed superheavy region experimentally. The observed increase of α-decay half-lives with increasing neutron number, i.e., the increased stability of these SHN not around shell closures with larger neutron number, is primarily attributed to the effect of the symmetry energy. The α decay half-lives of newly synthesized SHN have been investigated in terms of the correlation between the half-lives of a decay, and correspondingly an ana-lytic formula is given which is turned out to be quite accurate. In addition, we test the application of the Wentzel-Kramers-Brillouin (WKB) approximation. It is found that the WKB approximation works well for a, proton and cluster radioactivity.We extracted a universal relation in widely different mean field interac-tions. With this relation and other constraint conditions, the density dependence of the nuclear symmetry energy S(p) has been investigated and the result is in good agreement with that from the analysis of anti-protonic atoms data. With the obtained density dependence of the symmetry energy, the neutron skin thick-ness of208Pb and some properties of neutron stars were analyzed. The neutron skin thickness of208Pb displays a linear correlation with curvature parameter Ksym. Thus, once the neutron skin thickness is measured accurately, not only slope parameter L but also curvature parameter Ksym of the symmetry energy around the saturation can be determined. Thus, a richer information about the density dependent behavior of the symmetry energy can be achieved.In part II, the properties of dense matter in strong magnetic field, such as the density dependent symmetry energy, fractions and polarizations of particles have been studied by employing the relativistic mean field models. The symme-try energy can be obtained by the difference between the energies per nucleon in pure neutron matter and symmetric matter since the energy per nucleon in asymmetric nuclear matter still presents a parabola law in the magnetic field under consideration in this work. The strong magnetic field leads to an en-hancement of the symmetry energy with respect to field free case, in particular at low densities. The fraction of each composition was calculated with some modified FSU-Gold interaction that can provide both stiff and soft symmetry energy. The density dependent symmetry energy affects the proton polariza-tion obviously but almost takes no effect on neutron polarization. Finally, the structure of anisotropic neutron star induced by strong magnetic field has been studied within a modified TOV equation based on general relativity. It is found that both the mass and radius can be reduced obviously by the magnetic field, which may be a good news since nowadays the stellar radii predicted by the theoretical models tend to be larger than the observed. If the magnetic field is large enough, the mass becomes not sensitive to the radius and thus the masses of neutron stars lie in a narrow region, which to a large extent agrees with the observations.