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引用次数: 0
摘要
根据电偶极子和四极矩阵元素,推断出了原子核中低洼激发态的电偶极子极化率 αE1 的新方程,以及相关的总光吸收截面 (-2) 矩 σ-2。这些方程对初始态/基态和最终态/激发态的任意角矩都是有效的,并在考虑构型混合的选定 p 壳核和 sd 壳核的完全收敛 1ℏω 壳模型(SM)计算中得到了利用;推进了从 17O 到 36Ar 的先前知识,其中数千个电偶极子矩阵元素是通过包括巨偶极子共振(GDR)区域在内的等矢量激发计算得出的。我们的结果与之前的 SM 计算结果相当吻合,而且除了 6,7Li 和 17,18O 外,都遵循了米格达尔流体力学模型与二阶非退化扰动理论相结合所提供的全球趋势。6,7Li 和 17O 中的差异是由于奇数质量原子核中存在 α 簇构型,而 18O 中的差异则是由于入侵态的混合,这在 SM 相互作用中是缺乏的。对低洼激发态的偶极极化率进行的更先进的 Ab initio 计算涵盖了 GDR 区域内的所有等矢量态,但这种计算目前还很欠缺,因此对本文介绍的结果可能非常有价值,并能进一步揭示原子核如何偏离基态极化。
Electric dipole polarizability of low-lying excited states in atomic nuclei
New equations for the electric dipole polarizability αE1 of low-lying excited states in atomic nuclei—and the related (−2) moment of the total photo-absorption cross section, σ−2—are inferred in terms of electric dipole and quadrupole matrix elements. These equations are valid for arbitrary angular momenta of the initial/ground and final/excited states and have been exploited in fully converged 1ℏω shell-model (SM) calculations of selected p- and sd-shell nuclei that consider configuration mixing; advancing previous knowledge from 17O to 36Ar, where thousands of electric dipole matrix elements are computed from isovector excitations which include the giant dipole resonance (GDR) region. Our results are in reasonable agreement with previous SM calculations and follow—except for 6,7Li and 17,18O—Migdal’s global trend provided by the combination of the hydrodynamic model and second-order non-degenerate perturbation theory. Discrepancies in 6,7Li and 17O arise as a result of the presence of α-cluster configurations in odd-mass nuclei, whereas the disagreement in 18O comes from the mixing of intruder states, which is lacking in the SM interactions. More advanced ab initio calculations of the dipole polarizability for low-lying excited states covering all the isovector states within the GDR region are missing and could be very valuable to benchmark the results presented here and shed further light on how atomic nuclei polarize away from the ground state
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