A New Evidence of Interplay Between Tetrahedral and Octahedral Symmetries and Symmetry Breaking: Exotic Rotational Bands in $^{152}$Sm

TL;DR

This paper presents experimental evidence for a new tetrahedral symmetry band in $^{152}$Sm, supporting theories of nuclear tetrahedral symmetry and symmetry breaking in heavy nuclei through observed unique transition patterns.

Contribution

It reports the discovery of a second tetrahedral band in $^{152}$Sm with unique transition characteristics, expanding understanding of nuclear tetrahedral symmetry.

Findings

Identification of a new tetrahedral band with mixed parity

Absence of E2 and strong E3 transition indications

Supports theoretical predictions of tetrahedral symmetry in nuclei

Abstract

We report on an experimental evidence for a new, second tetrahedral band in $^{152}_{\;\;62}$Sm$^{}_{90}$. It was populated via fusion evaporation reaction, $^{150}{\rm Nd}(\alpha, 2n)^{152}$Sm, employing 26 MeV beam of $\alpha$ particles from K-130 cyclotron at Variable Energy Cyclotron Centre, Kolkata, India. The newly observed possible mixed parity sequence with absence of E2 and strong indication of E3 transitions is consistent with the spectroscopic criteria for a tetrahedral-symmetry rotational band that could be constructed from the allowed spin-parity assignments. This structure differs from the structure of the band previously found in the same nucleus, the new one manifesting tetrahedral symmetry not accompanied by the octahedral one. Our new experimental results are interpreted in terms of group representation theory and collective nuclear-motion theory of Bohr. We propose to generalize the notion of the tetrahedral vibrational bands and believe that our new experimental results support a number of theory predictions related to nuclear tetrahedral symmetry published earlier and bring a new light into the issue of spontaneous symmetry breaking in heavy nuclei.