Abstract
The low-lying collective states of the ground, β and γ bands in154Sm and238U are investigated within the framework of the microscopic proton-neutron symplectic model (PNSM). For this purpose, the model Hamiltonian is diagonalized in a U(6)-coupled basis, restricted to the symplectic state space spanned by the fully symmetric U(6) vectors. A good description of the energy levels of the three bands under consideration, as well as the intraband B(E2) transition strengths between the states of the ground band is obtained for the two nuclei without the use of an effective charge. The calculations show that when the collective quadrupole dynamics is covered already by the symplectic bandhead structure, as in the case of154Sm, the results show the presence of a very good U(6) dynamical symmetry. In the case of238U, when we have an observed enhancement of the intraband B(E2) transition strengths, then the results show small admixtures from the higher major shells and a highly coherent mixing of different irreps which is manifested by the presence of a good U(6) quasi-dynamical symmetry in the microscopic structure of the collective states under consideration.
Highlights
Experimental spectra in heavy nuclei show the emergence of simple collective patterns represented primarily by the nuclear collective rotation
It has been shown that the Sp(6, R) symplectic model is a microscopic generalization of the Bohr-Mottelson [4] collective model, augmented by the intrinsic vortex spin degrees of freedom, which is compatible with the microscopic nucleon structure of nucleus [5]
The model Hamiltonian is diagonalized in a U(6)-coupled basis, restricted to the symplectic state space spanned by the fully symmetric U(6) vectors
Summary
Experimental spectra in heavy nuclei show the emergence of simple collective patterns represented primarily by the nuclear collective rotation. PNSM (or its macroscopic hydrodynamic limit), the full range of low-lying states could be described by microscopically based U(6) structure along the lines of the IBM, albeit in contrast to the latter, renormalized by their coupling to the giant resonance vibrations This result could not be overestimated recalling that in order to obtain the low-lying excited collective bands (e.g., beta bands) within the framework of the one-component symplectic model [2] one needs to involve a representation mixing caused by, e.g., pairing, spin-orbit and other symplectic-breaking components of the nuclear interaction This result could not be overestimated recalling that in order to obtain the low-lying excited collective bands (e.g., beta bands) within the framework of the one-component symplectic model [2] one needs to involve a representation mixing caused by, e.g., pairing, spin-orbit and other symplectic-breaking components of the nuclear interaction (cf. Ref. [9])
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