稳定和不稳定核巨共振性质的相对论研究

GIANT RESONANCE PROPERTIES IN β STABLE AND UNSTABLE NUCLEI

在相对论平均场的基态上自洽的相对论无规位相近似 (RRPA)理论框架下 ,研究稳定核和不稳定核的巨共振性质 .研究了稳定核2 0 8Pb ,14 4Sm ,116Sn ,90 Zr ,4 0 Ca,16O和不稳定核Ca同位素链同位旋标量和同位旋矢量集体巨共振激发 ,并讨论了Dirac海负能核子态和矢量介子空间分量对核的巨共振性质的影响 .研究的结果表明 ,Dirac海负能核子态和矢量介子空间分量对同位旋标量激发有贡献 ,特别是对重核 ,而对轻核它的贡献减弱 ,对于同位旋矢量激发的贡献可忽略 .几组常用的相对论平均场非线性模型参量 ,不仅能成功的描述有限核的基态性质 ,也能很好地描述核的巨共振激发 .对于 N/Z 极端情况下 ,同位旋矢量巨偶极激发模式存在低能集体激发 。

We study the giant resonances of stable and unstable nuclei in the framework of the consistent relativistic random phase approximation built on the nonlinear relativistic mean field (RMF) ground states. The isoscalar and isovector modes of giant resonances for stable nuclei, such as 208 Pb, 144 Sm, 116 Sn, 90 Zr, 40 Ca, 16 O and Ca isotope chains are investigated. The contribution to the giant resonances from the Dirac sea states and the currents of vector mesons are examined. The results show that the effects of the Dirac sea states on the isoscalar giant modes are pronounced, but become weaker for light nuclei, while the contributions of the isovector modes are negligible. The few sets of parameterizations of nonlinear RMF model, which are commonly used to give a good description of ground\|state properties of finite nuclei, could also well describe the nuclear dynamic properties\_giant resonances. For nuclei with the extreme value of N/Z , low\|lying collective excitations are found in isovector dipole modes, which are mainly due to the ph excitation of the weakly bound states near Fermi surface and the isospin mixture effect.