Experimental signals for broken axial symmetry in excited heavy nuclei from the valley of stability

TL;DR

This paper reviews experimental evidence of broken axial symmetry in heavy nuclei within the valley of stability, highlighting the role of quantum effects and theoretical models like HFB calculations in understanding nuclear deformation.

Contribution

It demonstrates that experimental data consistently support axial symmetry breaking in heavy nuclei, aligning with Hartree-Fock-Bogoliubov predictions and emphasizing the importance of quantum considerations.

Findings

Experimental data indicate widespread axial symmetry breaking in heavy nuclei.

HFB calculations accurately predict deformation parameters without free adjustments.

Quantum zero point oscillations are crucial for interpreting symmetry breaking phenomena.

Abstract

An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability: Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree-Fock-Bogoliubov (HFB) calculations [1] ; this indicates a nuclear Jahn-Teller effect. We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.