Fe和Ni丰质子同位素中同位旋矢量巨偶极共振

Isovector giant dipole resonance in proton-rich Fe and Ni isotopes

以完全自洽的方法系统地研究了Fe和Ni的丰质子同位素中同位旋矢量巨偶极共振(IVGDR),并且使用Skyrme Hartree-Fock加上Bardeen-Cooper-Schrieffer(BCS)近似的方法来计算基态的性质。采用准粒子无规则相位近似法(QRPA)研究丰质子核中偶极激发态的性质,同时在计算中考虑了SLy5 Skyrme相互作用和密度依赖配对作用。除了巨偶极共振(GDR)之外,还在能量低于10 MeV的区域中发现了矮偶极共振(PDR),接近质子滴线的核子的能量加权求和规则约占经典的TRK求和规则的3%左右,并且随着各同位素链上质量数的增加,其值呈递减趋势。通过偶极激发强度和质子、中子的跃迁密度可以看出这一低能状态是典型的具有等同位旋标量性质的矮偶极共振状态。分析给定低能状态下质子和中子2qp构型的准粒子无规位相变化(QRPA)振幅,发现只有一两个质子构型做出主要贡献,它们对总QRPA振幅贡献约为99%,这种情况也表现出矮偶极共振(PDR)的集体性并不强。

The isovector giant dipole resonances in proton-rich Fe and Ni isotopes are investigated with a fully self-consistent approach.The ground states properties are calculated in the Skyrme Hartree-Fock and the Bardeen-Cooper-Schrieffer approach.The quasiparticle random phase approximation(QRPA)method is used to explore the properties of excited dipole states.In the calculations the SLy5 Skyrme interaction and density-dependent pairing interaction is employed.In addition to the giant dipole resonances,pygmy dipole resonances(PDR)are found to be located in the energy region below 10 MeV in proton-rich Fe and Ni isotopes.Energy-weighted moments of the PDR in nuclei close to proton drip-line exhaust about 3%of the Thomas-ReicheKuhn(TRK)sum rule,the values are decrease with the mass number increasing in each isotope chain.The strength and transition density show that the low-lying states are typical PDR states.However,analyzing the QRPA amplitudes of proton and neutron 2 quasiparticle(2qp)configurations for a given low-lying state in proton-rich Fe and Ni isotopes,we find that only one or two proton 2qp configurations give the main contribution,they contribute about 99%to the total QRPA amplitudes,which means the PDR states are less collective,more like a single 2qp excitation.