自洽理论中钍和铀同位素的第三极小值
Third minima in thorium and uranium isotopes in a self-consistent theory
摘要：
背景：在一些非自洽模型中，深三分之一极小区已经被预测会影响钍和铀同位素的裂变途径。这些预测指导了对实验中看到的共振的解释。另一方面，自洽计算一致预测非常浅的势能面在第三个最小区域。目的：研究用双分子态解释第三最小构型。本文研究了几种激发能下钍和铀的偶偶同位素的等熵势能面。为了理解第三极小值存在背后的驱动效应，我们研究了配对和壳效应之间的相互作用。方法：采用有限温度超流体核密度泛函理论。我们认为一个传统的功能，SkM*，和最近的功能，UNEDF 1，优化裂变研究。结果：我们预测在232 Th和232 U的势能面中存在非常浅或没有第三个极小值。在N=136和138的Th和U同位素中，第三个极小值更深。我们发现，反射不对称配置周围的第三个最小值可以与双分子态涉及的球形双魔132 Sn和更轻的变形Zr或Mo片段。给出了几种激发能下~（228）、~（232）Th和~（232）U的势能面。结论：我们表明，中子壳效应，支配周围的第三个最小值的双分子状态的存在是一致的球形变形的形状转变的Zr和Mo同位素周围N=58。我们证明，在小的激发能的配对和增强壳效应的热减少有助于发展更深的第三个极小。在大的激发能下，壳层效应消失，第三极小值完全消失。
英文摘要：
Background: Deep third minima have been predicted in some non-self-consistent models to impact fission pathways of thorium and uranium isotopes. These predictions have guided the interpretation of resonances seen experimentally. On the other hand, self-consistent calculations consistently predict very shallow potential-energy surfaces in the third minimum region. Purpose: We investigate the interpretation of third-minimum configurations in terms of dimolecular states. We study the isentropic potential-energy surfaces of selected even-even thorium and uranium isotopes at several excitation energies. In order to understand the driving effects behind the presence of third minima, we study the interplay between pairing and shell effects. Methods: We use the finite-temperature superfluid nuclear density functional theory. We consider a traditional functional, SkM*, and a recent functional, UNEDF1, optimized for fission studies. Results: We predict very shallow or no third minima in the potential-energy surfaces of 232Th and 232U. In Th and U isotopes with N=136 and 138, the third minima are deeper. We show that the reflection-asymmetric configurations around the third minimum can be associated with dimolecular states involving the spherical doubly magic 132Sn and a lighter deformed Zr or Mo fragment. The potential-energy surfaces for 228,232Th and 232U at several excitation energies are presented. Conclusions: We show that the neutron shell effect that governs the existence of the dimolecular states around the third minimum is consistent with the spherical-to-deformed shape transition in the Zr and Mo isotopes around N=58. We demonstrate that the thermal reduction of pairing and enhancement of shell effects at small excitation energies help to develop deeper third minima. At large excitation energies, shell effects are washed out and third minima disappear altogether.
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