Rotational constants of multi-phonon bands in an effective theory for deformed nuclei

TL;DR

This paper develops an effective theory for deformed nuclei that predicts how rotational constants change with multi-phonon excitations and spin, successfully explaining experimental data for specific isotopes.

Contribution

It introduces a novel effective theory framework that accounts for small variations in rotational constants due to multi-phonon excitations in deformed nuclei.

Findings

Explains variations in rotational constants of 166Er and 168Er.

Describes decreasing rotational constants with increasing spin in 232Th.

Incorporates time-odd terms for odd nuclei, explaining high level densities.

Abstract

We consider deformed nuclei within an effective theory that exploits the small ratio between rotational and vibrational excitations. For even-even nuclei, the effective theory predicts small changes in the rotational constants of bands built on multi-phonon excitations that are linear in the number of excited phonons. In 166Er and 168Er, this explains the main variations of the rotational constants of the two-phonon gamma vibrational bands. In 232Th, the effective theory correctly explains the trend that the rotational constants decrease with increasing spin of the band head. We also study the effective theory for deformed odd nuclei. Here, time-odd terms enter the Lagrangian and generate effective magnetic forces that yield the high level densities observed in such nuclei.