Experimental studies of proton-neutron mixed symmetry states in the mass A ∼ 130 region

Considerable progress has been achieved recently in the experimental investigation of quadrupole-collective isovector excitations in the valence shell, the so called mixed-symmetry states (MSSs), in the mass A ≈ 130 region. This is due to a new experimental technique for study MSSs which is based on the observation of low-multiplicity γ-ray events from inverse kinematics Coulomb excitation with the large 4π spectrometer, such as Gammasphere. The obtained experimental information for the MSSs of stable N 80 isotones indicates that for low-collective vibrational nuclei the underlying single-particle structure can be the most important factor for preserving or fragmenting the MSSs through the mechanism of shell stabilization. The evolution of the MSSs from 134Xe to 138Ce is also used to determine the local strength of the proton-neutron interaction derived for first time from states with symmetric and antisymmetric nature

Experimental studies of proton-neutron mixed symmetry states in the mass A ≈ 130 region

Considerable progress has been achieved recently in the experimental investigation of quadrupole-collective isovector excitations in the valence shell, the so called mixed-symmetry states (MSSs), in the mass A ≈ 130 region. This is due to a new experimental technique for study MSSs which is based on the observation of low-multiplicity γ-ray events from inverse kinematics Coulomb excitation with the large 4π spectrometer, such as Gammasphere. The obtained experimental information for the MSSs of stable N = 80 isotones indicates that for low-collective vibrational nuclei the underlying single-particle structure can be the most important factor for preserving or fragmenting the MSSs through the mechanism of shell stabilization. The evolution of the MSSs from ¹³⁴Xe to ¹³⁸Ce is also used to determine the local strength of the proton-neutron interaction derived for first time from states with symmetric and antisymmetric nature

Search for one-phonon mixed-symmetry states in the radioactive nucleus Nd-140

Low-spin excited states of Nd-140 have been studied via the Ce-140(He-3,3n)Nd-140 reaction. The data show that one of the candidates for the one-phonon mixed-symmetry state (MSS) of Nd-140, namely, the 2(3)(+) state at 2140 keV with an effective lifetime of 220(90) fs, exhibits a fast M1 decay to the 2(1)(+) state. Thus, this state can be considered, at least, as a fragment of the one-phonon MSS of Nd-140. This is the first example where mixed symmetry character is tentatively assigned to a state of an unstable nucleus from the mass A approximate to 140 region based on the data on absolute M1 transition rates. However, the data are not conclusive on whether this decay exhausts the total M1 strength or whether the one-phonon MSS of Nd-140 is fragmented