A unified description of the shape phase transition, shape coexistence and mixing phenomena in nuclei

¹ "Horia Hulubei" - National Institute for R&D in Physics and Nuclear Engineering, St. Reactorului no. 30, RO-077125, POB-MG6, Bucharest-Magurele, Romania
² Academy of Romanian Scientists. St. Splaiul Independentei no. 54, RO-050044, Bucharest, Romania

^* e-mail: buganu@theory.nipne.ro

Published online: 11 April 2025

Abstract

The shape phase transition, shape coexistence and mixing phenomena can be described in a unified way within the framework of the phenomenological Bohr-Mottelson model involving a sixth order anharmonic oscillator potential in the intrinsic deformation variable. This potential can have alternatively, depending on its parameters, a single spherical minimum, a single deformed minimum, a flat shape and simultaneously spherical and deformed minima, respectively. Thus, an entire phase transition from a spherical shape to a deformed one can be covered, crossing the critical point where the potential is flat (second order phase transition) or it has a small barrier (first order phase transition), while the shape coexistence and mixing phenomena emerge by simply increasing the barrier in the critical point. The type of axial deformations (prolate, triaxial, γ-unstable) are given here by the additional degree of freedom γ in relation to the γ potential shape.