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arXiv 1009.5697nucl-th
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瞬时形状取样--过渡核$γ$吸收截面模型

Instantaneous Shape Sampling - a model for the $γ$-absorption cross section of transitional nuclei

I. Bentley, S. Brant, F. Doenau, S. Frauendorf, B. Kampfer, R. Schwengner, S. Zhang

摘要:

在瞬时形状取样模型的框架下,研究了四极形状涨落对过渡核偶极振动的影响.该模型结合了慢集体四极运动的相互作用玻色子模型和快偶极振动的随机相位近似.耦合到复杂的背景配置考虑到折叠的结果与能量依赖的宽度的洛伦兹。$γ$吸收截面的低能能量部分,这是重要的光-核过程,研究的同位素系列的Kr,Ba,Sm。实验截面重现良好。低能截面由偶极强度的朗道碎裂和形状起伏引起的重分布决定。碰撞阻尼只是消除了吸收截面的波动,产生了实验中观察到的平滑的能量依赖性。在半魔核的情况下,发现与实验一致的浅侏儒共振。

英文摘要:

The influence of the quadrupole shape fluctuations on the dipole vibrations in transitional nuclei is investigated in the framework of the Instantaneous Shape Sampling Model, which combines the Interacting Boson Model for the slow collective quadrupole motion with the Random Phase Approximation for the rapid dipole vibrations. Coupling to the complex background configurations is taken into account by folding the results with a Lorentzian with an energy dependent width. The low-energy energy portion of the $γ$- absorption cross section, which is important for photo-nuclear processes, is studied for the isotopic series of Kr, Xe, Ba, and Sm. The experimental cross sections are well reproduced. The low-energy cross section is determined by the Landau fragmentation of the dipole strength and its redistribution caused by the shape fluctuations. Collisional damping only wipes out fluctuations of the absorption cross section, generating the smooth energy dependence observed in experiment. In the case of semi-magic nuclei, shallow pygmy resonances are found in agreement with experiment.

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