There exists a relation in asymmetric, inertial and variable of moment of inertia parameters that describes rotational band energies. The present study indicates the splitting of the so-called γ-band into two separate rotational energy branches of odd spin (3+, 5+, 7+…) and even spin (2+, 4+, 6+, 8+…).

The present study deals with a topic of current interest, getting clear evidence for triaxiality in the 120−130 Xe nuclei near A = 130. The odd-even staggering in a so-called gamma-vibrational band may be treated using the asymmetric rotor model (ARM) on employing the Lipas parameter. The Hilbert space is too limited to describe the full variation of the moment of inertia and, therefore, the Lipas Ansatz is made to correct the ARM energies, which conserve the good result for B(E2) values.Résumé : Cette étude se concentre sur un sujet d'intérêt actuel en cherchant une preuve manifeste du caractère triaxial des noyaux 120−130 Xe près de A = 130. L'étalement pairimpair dans la bande dite gamma-vibrationnelle peut être étudié dans le modèle du rotateur asymétrique (ARM) en utilisant le paramètre de Lipas. L'espace de Hilbert est trop limité pour décrire la variation complète du moment d'inertie et l'ansatz de Lipas a pour but de corriger les énergies ARM , tout en préservant les bonnes valeurs des B(E2).[Traduit par la Rédaction]

The mechanisms by which atomic nuclei generate angular momentum of the γ -band are surface oscillations in the γ -soft structure or nuclear rotation in the γ -rigid structure. We propose that if the experimental γ -band energies are found to obey the formula E = (I (I + 1)/J 0 (1 + α I )), the nucleus may be said to belong to the γ -rigid triaxial region at low spin and low energy.

The staggering indices S(I, I−1, I−2) versus spin (I ) graphs have been plotted using known experimental data along with empirical calculations of Varshney et al (2007 Phys. Scr. 75 451) in some nuclei of mass region A ∼ 100-110. Most of the transional nuclei of Mo, Ru and Pd isotopes have been found to be triaxial. The known B(E2) values of these nuclei are also close to the triaxial rotor model predictions (Davydov A S and Filippov G F 1958 Nucl. Phys. 8 237).

The signatures of rigid triaxiality in low-energy, low-spin nuclear spectra are discussed. Eight nuclei in the range of structural parameter 2.9 < R 4/2 < 3.3 are explored to find out whether they are γ -static. Interestingly, this region is a transition path between X (5) critical point and the rigid rotor limit which is described by the confined β-soft (CBS) rotor model of Pietralla and Gorbachenko (2004 Phys. Rev. 70 011304).