Examination of different strengths of octupole correlations in neutron-rich Pr and Pm isotopes

摘要

Recent prompt γ -ray spectroscopy studies of 149,151Pr have revealed weak octupole correlations. These arenmanifested by the absence of strong intraband E1 transitions between bands of opposite parities. On the othernhand, in their isotones 151,153Pm, which have only two additional protons, the E1 transition rates are several ordersnof magnitude stronger, indicating enhanced octupole correlations. The quasiparticle phonon model combinednwith the particle-rotor model, which allows octupole correlations and Coriolis mixing to be taken into account,nhas been applied to calculate the E1 transition rates between low-lying states of the nuclei 149,151Pr and 151,153Pm.nThe dependence of the E1 rates on the magnitude of the quadrupole deformation, the magnitude and signnof the hexadecapole deformation parameter, the Coriolis and recoil attenuation parameters, the energies ofnthe vibrational bandheads, and the parameters of the Nilsson Hamiltonian have been thoroughly investigated.nFrom this investigation an overall conclusion can be drawn that, even if the intrinsic quasiparticle structurenof the bandheads and the octupole correlations vary as the parameters of the model are changed, the octupolencorrelations in the odd Pr isotopes are much weaker than those in the odd Pm isotopes. Moreover, the experimentalnE1 transition rates can be satisfactorily describedwith the values of the quadrupole and hexadecapole deformationnparameters expected in this region. In the case of 151Pr, two possible dominant configurations have been assignednto the 35.1-keV isomeric state, namely, the 3/2[422] and 1/2[420] orbitals. Our calculations show that the firstnassignment provides an E1 value closer to the experimental observations.