Ferro-deformation and shape phase transitions over the nuclear chart: 50 < protons (Z) < 82 and 50 < neutrons (N) < 126

TL;DR

This paper analyzes systematic patterns in nuclear structure data, identifying a reinforced deformation called 'ferro-deformation' in nuclei with specific proton and neutron numbers, linked to spin-orbit interactions and shape phase transitions.

Contribution

It introduces the concept of ferro-deformation based on experimental data, explaining shape transitions and semi-double shell closures in nuclei within Z=50-82 and N=50-126.

Findings

Identification of ferro-deformation at Z=64/66 and N=90

Reinforced deformation spans Z=58-72 and N=100-106

Correlation with spin-orbit interactions at critical points

Abstract

We study a global nuclear structure in the framework of experimental observables. With the aid of large nuclear structure data at the national nuclear data center, NNDC, we present the distinctive systematic patterns emerged in the first 2+ excited energies, E(2+) and their energy ratios to the first 4+ levels, R = E(4+)/E(2+), in the even-even nuclei, over 50 < Z < 82 for protons, and 50 < N < 126 for neutrons. We introduce the so-called pseudo-shell configurations from the subshells mixture in order to explain a semi-double shell closure, a shape phase transition, and a reinforced deformation. It is found that the reinforced deformation arises when Z = 64 or 66 correlates with N = 90 and reaches its maximum, indicating R = 3.3. Such a saturated reinforced deformation spans over Z = 58 to 72 and N = 100 to 106 as showing its center at Z = 64 or 66 and at N = 102 or 104. We define this reinforced deformation 'a ferro-deformation' like a ferro-magnetism in condensed matter physics. The shape coexistence would be expected to occur, such as a ferro-deformation, with a strong rotational mode, and a near spherical shape, with a vibrational mode, at the critical points of Z = 64 or 66, with N = 88 and 90; 150Sm and 152Sm, 152Gd and 154Gd, and 154Dy and 156Dy. We suggest that a super-deformation, which can be formed at high-lying excited states in a moderate deformed nucleus, would correspond to the ferro-deformation at N = 88 for the nuclei; Sm, Gd, and Dy. We argue that the ferro-deformation can be closely associated with a strong spin-orbital interaction between neutrons and protons in the spin-orbit doublet, h9/2-h11/2, leading to the critical points at Z, N = 64, 104.