The New Particle-rotor Model For Transitional Odd-A Nuclei

Based on the triaxial rotor model,the new particle-rotor model is established by introducing the quadrupole-quadrupole interaction of the even-even core with a single particle suitable to describe low-lying spectra of odd-nuclei within the vibrational to triaxial transi-tion region.Matrix elements of the operators in the model calculation are derived,for which a computation code is complied accordingly.As an initial application,the new particle-rotor model is applied to describe low-lying level energies,reduced E2 transition probabilities,and some electric quadrupole moments of¹³⁵Ba and¹³¹Xe in the transitional region.The results are compared to the experimental data and those of the original particle plus rotor model,the critical point symmetry E(5/4)model,and the interacting boson-fermion model.It is shown that the new model fitting results of the low-lying level energies,reduced E2transition probabilities,and the ground-state electric quadrupole moment of¹³⁵Ba and¹³¹Xe are the best,of which the model parameters of the even-even core are determined by the triaxial rotor model in fitting the low-lying spectra of¹³⁴Ba and¹³⁰Xe.In comparison with the E(5/4)model results of¹³⁵Ba,it is also shown that the quadrupole-quadrupole interaction of the even-even core with the single particle adopted can indeed reproduce the critical behavior of the vibrational to triaxial transition.The fitting quality of the reduced E2 transition probabilities among low-lying states by the new model is also noticeably improved.Thus,it can be concluded that the new particle-rotor model is suitable to describe low-lying properties of odd-nuclei within the transitional region.