Octupole correlations at medium spin in odd-proton153Eu nucleus

Abstract

Abstract. Medium-spin experimental data on alternating parity bands in 153Eu are analysed and compared with results of cranking calculations assuming no octupole deformation, dynamic octupole deformation and static octupole deformation. It is concluded that the existence of static octupole deformation is plausible in this nucleus at medium spin.PACS: 27.70.+q; 21.60.Cs Alternating-parity rotational bands linked by the enhanced El-transitions have been observed in the A ~ 150 (N 88, Z ~ 60) mass region. These bands are interesting because they can be considered as parity doublets (PD's) associated with the breaking of the intrinsic reflection symmetry [1,2] On the other hand, the tendency towards octupole deformation can be magnified with increasing spin [8,9]. The deformed shell model indicates that proton number Z = 62 is octupole driving not only at low spin but also at rotational frequency ha; -=-0.3 MeV [9]. While the N = 88 octupole deformed gap, which is clearly seen at ha; = 0, disappears with increasing rotational frequency, the neutron numbers N = 90, 91 become octupole-driving towards moderate octupole deformation/33 ~ 0.05 at rotational frequency hw ~ 0.3 (see Fig. 2 in ref.[9]). Therefore, the neighbouring even-even nuclei 152Sm and 154Gd are calculated octupolesoft at high rotational frequencies [9]. The odd nuclei with an octupole soft core can get octupole deformed in the case when unpaired nucleons in specific orbitals polarize the * Permanent address: Nuclear Research Center, Latvian Academy of Sciences, LV-2169, Salaspils, Miera str. 31, Latvia shape towards static octupole deformation. That can be examplified by the fact that the octupole barriers for low-lying band-heads of the odd-mass nuclei in the A ~ 145 region are calculated significantly larger compared to the ones in the even-even neighbours [10].Recently, the experimental data on the alternating-parity bands with f2 = 5/2 in 153Eu has been expanded to higher spins [11]. Levels of the same spin but opposite parity lie close in energy and strong electric dipole transitions connect appropriate band members. Intrinsic dipole moments Do deduced from B(E1)/B(E2) values do not reveal any pronounced spin dependence. This aspect of the data is consistent with static octupole deformation. At the same time, the difference of magnetic moments of opposite parity bands, obtained from (9K --gR)/Qo values, was considered as evidence in favour of reflection-symmetric description of the intrinsic states of these bands.In this article, we will try to clarify the nature of strong octupole correlations observed at medium spin in this nucleus. Firstly, the analysis of rotational properties of the alternating-parity bands with f2 = 5/2 will be expanded to higher spins compared with ref. [4]. Then, the results obtained within the cranking model with and without inclusion of static and dynamic octupole deformation will be compared with experiment.Both the static and dynamic octupole deformation can be responsible for the existence of the alternating-parity ban...