Low-lying dipole response: Isospin character and collectivity in 68 Ni, 132 Sn, and 208 Pb
Low-lying dipole response: Isospin character and collectivity in 68 Ni, 132 Sn, and 208 Pb
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DOI：
10.1103/physrevc.85.024601
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发表时间：
2011-12
影响因子：
3.1
通讯作者：
X. Roca-Maza;G. Pozzi;M. Brenna;K. Mizuyama;G. Colò
中科院分区：
文献类型：
--
作者：
X. Roca-Maza;G. Pozzi;M. Brenna;K. Mizuyama;G. Colò
同位旋特征、集体或单粒子性质以及对低能等向量偶极子响应（称为侏儒偶极子共振）的核对称能斜率的敏感性目前正在争论中。在目前的工作中，我们研究在基于 Skyrme Hartree-Fock 加上随机相位近似 (RPA) 的完全自洽非相对论平均场 (MF) 方法中，测量的偶偶核 ${}^{68}$Ni、${}^{132}$Sn 和 ${}^{208}$Pb。为了分析侏儒偶极子强度预测中的模型依赖性，我们采用了三种不同的 Skyrme 参数集。我们发现所有三个原子核的等标量和等矢量偶极子响应都显示出一个低能峰，其幅度增加，并且随着饱和时对称能斜率值的增加而转移到更大的激发能。我们强调这样一个事实，即与贡献该峰值的 RPA 状态相关的集体在等标量和等矢量情况下是不同的，或者换句话说，它取决于外部探针。虽然这些 RPA 态对等向量算子的响应没有表现出明显的集体性质，但对等标量算子的响应明显是集体的，因为{\it all}分析了原子核并{\it all}研究了相互作用。
The isospin character, the collective or single-particle nature, and the sensitivity to the slope of the nuclear symmetry energy of the low-energy isovector dipole response (known as pygmy dipole resonance) are nowadays under debate. In the present work we study, within the fully self-consistent non-relativistic mean field (MF) approach based on Skyrme Hartree-Fock plus Random Phase Approximation (RPA), the measured even-even nuclei ${}^{68}$Ni, ${}^{132}$Sn and ${}^{208}$Pb. To analyze the model dependence in the predictions of the pygmy dipole strength, we employ three different Skyrme parameter sets. We find that both the isoscalar and the isovector dipole responses of all three nuclei show a low-energy peak that increases in magnitude, and is shifted to larger excitation energies, with increasing values of the slope of the symmetry energy at saturation. We highlight the fact that the collectivity associated with the RPA state(s) contributing to this peak is different in the isoscalar and isovector case, or in other words it depends on the external probe. While the response of these RPA states to an isovector operator does not show a clear collective nature, the response to an isoscalar operator is recognizably collective, for {\it all} analyzed nuclei and {\it all} studied interactions.