Analytical comparison between X(3) and X(5) models of the Bohr Hamiltonian

TL;DR

This paper presents an analytical comparison of the X(3) and X(5) models of the Bohr Hamiltonian, deriving exact solutions and exploring their relationships and dynamical symmetries, with applications to nuclear isotopes.

Contribution

It introduces an exact analytical solution for the X(3) model with an inverse square potential and compares it with X(5), revealing their dynamical symmetry relationships and improving modeling of nuclear spectra.

Findings

Solutions interpolate between U(5), X(5), and SU(3) symmetries.

Good agreement with existing X(3) models and experimental data.

Enhanced modeling of first excited states in certain isotopes.

Abstract

The 3-D Bohr-Mottelson Hamiltonian for $\gamma$-rigid prolate isotopes, known as $X(3)$, is solved via inverse square potential having only one free parameter, $\beta_{0}$. The exact form of the wave functions and the energy spectra are obtained as a function of the free parameter of the potential that determines the changes in the spectra ratios and the $B(E2)$. Since $X(3)$ is an exactly separable $\gamma$-rigid version of $X(5)$, the solutions are compared with the $X(5)$ model and some new set of equations that show the relationships between the two models are stated. In other to show the dynamical symmetry nature of the solutions, the entire solutions from $\beta_{0}=0$ to $\beta_{0}=\infty$ are compared with $U(5)$, $X(5)$ and $SU(3)$. The solutions spread from the region around $U(5)$ over $X(5)$ and approach $SU(3)$ at $\beta_{0}=\infty$. The exact solutions obtained via variational procedure are compared favourably with some existing $X(3)$ models found in the literature. The strong agreement between the present model and $X(3)$ via infinite square well potential is discussed. Twelve best critical point isotopes, $^{102}$Mo, $^{104-108}$Ru, $^{120-126}$Xe, $^{148}$Nd, $^{184-188}$Pt are chosen for experimental realization of the model and moderate agreements are recorded. An excellent agreement which appears in the first $\beta$-excited state in the comparison of the present model with three $N=90$ isotones: $^{150}$Nd, $^{154}$Gd, and $^{156}$Dy, known to be $X(5)$ candidates, suggests that the present model compensates the $X(5)$ models whose predictions are excellent in the ground states but moderately bad in the first $\beta$-excited states.