Exotic nuclei and relativistic mean-field theory.

摘要

A relativistic mean-field model is used to study the ground-state properties of neutron-rich nuclei. Nonlinear isoscalar-isovector terms, unconstrained by present day phenomenology, are added to the model Lagrangian in order to modify the poorly known density dependence of the symmetry energy. These new terms soften the symmetry energy and reshape the theoretical neutron drip line without compromising the agreement with existing ground-state information. A strong correlation between the neutron radius of 208Pb and the binding energy of valence orbitals is found: the smaller the neutron radius of 208Pb, the weaker the binding energy of the last occupied neutron orbital. Thus, models with the softest symmetry energy are the first ones to drip neutrons. Further, in anticipation of the upcoming one-percent measurement of the neutron radius of 208Pb at the Thomas Jefferson Laboratory, a close relationship between the neutron radius of 208 Pb and neutron radii of elements of relevance to atomic parity-violating experiments is established.; On the basis of relativistic mean field calculations, we demonstrate that the spin-orbit splitting of p3/2 and p1/2 neutron orbits depends sensitively on the magnitude of the proton density near the center of the nucleus, and in particular on the occupation of s1/2 proton orbits. We focus on two exotic nuclei, 46Ar and 206Hg, in which the presence of a pair of s1/2 proton holes would cause the spin-orbit splitting between the p3/2 and p1/2 neutron orbits near the Fermi surface to be much smaller than in the nearby doubly-magic nuclei 48Ca and 208Pb. We also explore how partial occupancy of the s1/2 proton orbits affects this quenching. We note that these two exotic nuclei depart from the long-standing paradigm of a central potential proportional to the ground state baryon density and a spin-orbit potential proportional to the derivative of the central potential.