New insights into the nuclear structure in neutron-rich112,114,115,116,117,118Pd

摘要

New level schemes of ~(112,114,115,116,117,118)Pd are established by means of γ-γ-γ, γ-γ-γ-γ and γ-γ(θ) measurements of prompt fission γ rays from ~(252)Cf using the Gammasphere multi-detector array. Spins/parities were assigned to levels based on γ-γ angular correlation measurements, level systematics and decay patterns. In the even-N isotopes ~(112,114,116)Pd, two sets of odd-parity bands were identified and extended with spins measured in each band. The odd-parity bands with large level staggerings were interpreted as disturbed chirality with less pronounced triaxial deformations in the Pd isotopes than observed in the chiral symmetry breaking ~(110,112)Ru with maximum triaxiality. Onset of wobbling motion was identified from the sign of the signature splitting in the γ band of even-even ~(114)Pd, and probably also in ~(116)Pd, as first seen in the N=68 isotone ~(112)Ru. Maximal triaxiality in Ru and Pd isotopes is found to be reached for N=68, ~(112)Ru and ~(114)Pd, 4 neutrons more than predicted in the theoretical calculations. The new data and TRS calculations allowed a systematic study of the band crossings in the even-N ~(112,114,116)Pd and odd-N ~(115,117)Pd isotopes. Now we find a new overall, more complex shape evolution than previously proposed from triaxial prolate in ~(110)Pd via triaxial oblate in ~(112)Pd to nearly oblate in ~(114,116)Pd with a large change of the triaxial deformation parameter γ toward nearly oblate in the (πg9/2)2 alignment in ~(114,115,116,117,118)Pd, and triaxial-prolate-triaxial-oblate shape coexisting bands in 115Pd.