Observation of Positive-Parity Bands in $^{109}$Pd and $^{111}$Pd: Enhanced $\gamma$-Softness

TL;DR

This study reports the first observation of positive-parity bands in neutron-rich $^{109}$Pd and $^{111}$Pd, revealing their extreme $ ext{γ}$-softness and transitional nuclear structure through experimental and theoretical analysis.

Contribution

It provides the first identification of positive-parity bands in $^{109}$Pd and $^{111}$Pd, highlighting their $ ext{γ}$-softness and transitional nature in Pd isotopes.

Findings

Positive-parity bands observed in $^{109}$Pd and $^{111}$Pd.

Both nuclei exhibit $ ext{γ}$-softness with shallow triaxial minima.

First band crossing attributed to $h^2_{11/2}$ neutron alignment.

Abstract

The neutron-rich nuclei $^{109}$Pd and $^{111}$Pd were produced as fission fragments following the $^{30}$Si + $^{168}$Er reaction at 142 MeV. Using the identification based on the coincidences with the complementary fission fragments, the only positive-parity bands observed so far in $^{109}$Pd and $^{111}$Pd emerged from this work. A band, built on top of the 5/2$^+$ ground state exhibiting $\Delta I$ = 1 energy-level staggering, was observed in each of these nuclei. Both nuclei of interest, $^{109}$Pd and $^{111}$Pd, are suggested to lie in the transitional region of Pd isotopes of maximum $\gamma$-softness. The ground states of both nuclei are predicted by TRS calculations to be extremely $\gamma$-soft with shallow triaxial minima. The first crossing in the new bands is proposed to be due to an alignment of $h^2_{11/2}$ neutrons.