Multidimensionally constrained relativistic mean-field study of triple-humped barriers in actinides
Multidimensionally constrained relativistic mean-field study of triple-humped barriers in actinides
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锕系元素三峰势垒的多维约束相对论平均场研究
DOI：
10.1103/physrevc.91.014321
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发表时间：
2014-04
影响因子：
3.1
通讯作者：
Zhou, Shan-Gui
中科院分区：
文献类型：
--
作者：
Lu, Bing-Nan;Vretenar, Dario;Zhao, En-Guang;Zhou, Shan-Gui
背景：锕系元素核的势能面具有双峰势垒结构。在超过第二个障碍的大变形时，20世纪70年代通过宏观-微观模型计算预测了第三个障碍的发生，但后来许多使用不同方法的研究报告了相互矛盾的结果。目的：在协变密度泛函理论（CDFT）框架下研究锕系核中的三峰势垒。研究方法：计算采用多维约束相对论平均场（MDC-RMF）模型，在粒子-空穴通道中采用非线性点耦合泛函PC-PK 1和密度依赖的介子交换泛函DD-ME 2.在BCS近似中，用有限范围的可分离对力处理配对关联。结果：绘制了Th 226，228，230，232和U 232，234，236，238的二维PES，并定位了这些表面上的第三个极小值。然后详细分析了裂变过程沿着一维势能曲线，确定了第二势垒、第三极小值和第三势垒的能量。功能DD-ME 2预测的发生在所有的Th核和238 U的第三个障碍。230、232 Th的第三个极小值非常浅，而226、228 Th和238 U的第三个极小值非常突出。对于功能性PC-PK 1，第三个势垒仅在226，228，230 Th中发现。在Th 226中对费米面附近的单核子能级进行了分析，发现第三个极小值的形成主要是由于β20 <$1.5和β30 <$0.7处Z=90的质子能隙。结论：在锕系核的PES上可能发生的第三势垒取决于多维CDFT计算中使用的有效相互作用。与功能性PC-PK 1相比，DD-ME 2功能性预测更明显的最小值。Th同位素的第三阱深度随中子数的增加而减小。第三个最小值的起源是由于质子Z=90壳层间隙在相关的变形。
Background: Potential energy surfaces (PES's) of actinide nuclei are characterized by a two-humped barrier structure. At large deformations beyond the second barrier, the occurrence of a third barrier was predicted by macroscopic-microscopic model calculations in the 1970s, but contradictory results were later reported by a number of studies that used different methods. Purpose: Triple-humped barriers in actinide nuclei are investigated in the framework of covariant density functional theory (CDFT). Methods: Calculations are performed using the multidimensionally constrained relativistic mean field (MDC-RMF) model, with the nonlinear point-coupling functional PC-PK1 and the density-dependent meson exchange functional DD-ME2 in the particle-hole channel. Pairing correlations are treated in the BCS approximation with a separable pairing force of finite range. Results: Two-dimensional PES's of Th226, 228, 230, 232 and U232, 234, 236, 238 are mapped and the third minima on these surfaces are located. Then one-dimensional potential energy curves along the fission path are analyzed in detail and the energies of the second barrier, the third minimum, and the third barrier are determined. The functional DD-ME2 predicts the occurrence of a third barrier in all Th nuclei and 238U. The third minima in 230, 232Th are very shallow, whereas those in 226, 228Th and 238U are quite prominent. With the functional PC-PK1 a third barrier is found only in 226, 228, 230Th. Single-nucleon levels around the Fermi surface are analyzed in Th226, and it is found that the formation of the third minimum is mainly due to the Z=90 proton energy gap at β20≈1.5 and β30≈0.7. Conclusions: The possible occurrence of a third barrier on the PES's of actinide nuclei depends on the effective interaction used in multidimensional CDFT calculations. More pronounced minima are predicted by the DD-ME2 functional, as compared to the functional PC-PK1. The depth of the third well in Th isotopes decreases with increasing neutron number. The origin of the third minimum is due to the proton Z=90 shell gap at relevant deformations.