Several new high-spin states are observed in the prompt ␥-rays emitted from the neutron-rich, odd-Z 145,147 La fragments produced in the spontaneous fission of 252 Cf. Alternating parity bands are extended up to spins 41/2 and 43/2 in 145,147 La, respectively. A new band completes the evidence for two sets of parity doublets expected for octupole correlations. Eight B(E1)/B(E2) ratios ͑four new͒ between two bands in 145 La are all essentially constant and somewhat larger than similar ratios in 143,144 Ba, where stable octupole deformation and/or correlations are reported. The new ratios out of the 31/2 Ϫ levels in both nuclei show a sharp spike compared to other states, presumably from a strong reduction in E2 strengths in this backbending region. In 145 La, collective bands show competition and coexistence between symmetric and asymmetric shapes. Band crossings occur in both nuclei around បϷ0.26-0.30 MeV. Their backbends are associated with the alignment of two i 13/2 neutrons according to cranked shell model calculations. ͓S0556-2813͑99͒08402-2͔ PACS number͑s͒: 21.10. Re, 23.20.Lv, 27.60.ϩj, 25.85.Ca

No abstract

No abstract

No abstract

No abstract

From an experiment with Gammasphere and a 252 Cf spontaneous fission source, a new negative-parity band in 154 Nd and new negative-parity levels in 152 Nd were identified and the yrast bands were extended to 18 ϩ in 154 Nd and 20 ϩ in 152 Nd in a triple gamma coincidence study. These new negative-parity bands are consistent with octupole vibrational mode. There is a constant difference as a function of spin between the J 1 values for the negative-parity band in 152 Nd and J 1 for the similar negative-parity band in 154 Nd, however, their J 2 values are essentially identical. These bands indicate a new kind of identical band. ͓S0556-2813͑98͒01004-8͔PACS number͑s͒: 23.20. Lv, 21.10.Re, 25.85.Ca, 27.70.ϩq The neutron-rich neodymium (Zϭ60) nuclei with Aу142 are situated at the important intersection of two transitional regions: the transition from spherical to prolate quadrupole deformation and the transition from octupole vibrational excitations to the static octupole deformation ͓1-6͔. So far little is known about octupole excitation states in the neutron-rich nuclei in contrast to the considerable data on quadrupole collectivity ͓5,7͔. Studies on octupole vibrational excitations in neodymium nuclei can provide tests of relevant nuclear models.Our previous studies ͓5,8͔ in neutron-rich nuclei in the Aϳ155 region revealed both identical moments of inertia ͑kinetic and dynamic͒ and identical gamma-ray energies in some cases. Therefore it is very interesting to identify possible sidebands in neodymium nuclei, looking for phenomena connected to identical bands as well as octupole deformation. In 144,146 Ba identical octupole bands associated with stable octupole deformation were observed ͓5,9͔.The new levels in 152,154 Nd were obtained from the analysis of ␥-ray spectra produced in the spontaneous fission of 252 Cf. A detailed description of the experimental procedures and analysis methods can be found in Ref. ͓5͔ and Ref. ͓10͔.The new transitions assigned to 154 Nd were identified by setting double gates on the known yrast transitions in 154 Nd from Ref. ͓5͔ and making sure that whenever a double gate was set on the new transitions, one not only observes the transitions corresponding to the partners ( 94,95,96 Sr) of 154 Nd with 4, 3, and 2 neutrons emitted, respectively, but also obtains the same yield ratios for their partners as obtained from double gating on the well known yrast transitions in 154 Nd. Figure 1 shows two partial coincidence spectra obtained by FIG. 1. ͑a͒ Coincidence spectrum obtained by double gating on the 162.8 and 895.0 keV transitions in 154 Nd. ͑b͒ Coincidence spectrum obtained by double gating on the 268.5 and 338.3 keV transitions in 154 Nd.

No abstract