$${\Delta}{I=1}$$ Staggering Effect in the Energy Spectrum of the $${\gamma}$$ Band of Heavy Even–Even Nuclei

Quadrupole-type collective excitations of even–even nuclei are studied in the free-triaxiality approximation. The zigzagging behavior of the $$\Delta I=1$$ staggering effects in the energy spectrum of collective excitations of the $$\gamma$$ bands of heavy even–even $${}^{152}$$ Sm, $${}^{156}$$ Dy, $${}^{164,166}$$ Er, and $${}^{230}$$ Th nuclei is considered in this approximation. The first- and second-order terms in the expansion of the rotational-energy operator in the variable $$\gamma$$ are taken into account in describing the energies of levels of these nuclei. It is shown that the $$\Delta I=1$$ staggering effect occurs in the case of a strong coupling between the ground-state and $$\gamma$$ bands in the limit of $$SU$$ (3) dynamical symmetry.

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