[en] Neutron-rich ^147,149,151Pr nuclei, produced in the spontaneous fission of ²⁵²Cf, were studied using the Gammasphere array. Possible parity doublets in ¹⁴⁷Pr with N=88 and πh_11/2 bands in ^149,151Pr are proposed. These new data on the level structures of odd Pr isotopes suggest that octupole correlations may also be present in the neutron-rich ₅₉¹⁴⁷Pr₈₈ nucleus such as those observed in ₅₈¹⁴⁶Ce₈₈, and also that the h_11/2 bands in the ^149,151Pr track in energy the yrast bands in ^148,150Ce. The backbending related to the breaking of the neutron i_13/2 pair is observed at ℎω∼0.27 (MeV) for the proton h_11/2 band of ¹⁴⁹Pr

[en] The yrast band was significantly extended to 14⁺ and the γ band to 5⁺ in neutron-rich ¹¹⁸Pd by measuring the γ-γ-γ coincidences emitted from the spontaneous fission of ²⁵²Cf with Gammasphere. The first band crossing was observed in the yrast band in ¹¹⁸Pd at a frequency of ℎω∼0.36 MeV at the starting point of the backbending, which is similar to that found in ^112-116Pd. The first bandbending in the yrast cascade in ¹¹⁸Pd is interpreted to be built on a two h_11/2 neutron configuration based on its similarity to the yrast bands in even-even ^112-116Pd. Our result indicates ¹¹⁸Pd still maintains a prolate shape. The quasineutron Routhian calculations indicate a lower crossing frequency for the h_11/2 level

[en] From prompt γ-γ-γ coincidence studies with a ²⁵²Cf source, the yrast levels were identified from 2⁺ to 16⁺ and 14⁺ in neutron-rich ^162,164Gd, respectively. Transition energies between the same spin states are higher and moments of inertia lower at every level in N = 100 ¹⁶⁴Gd than in N = 98 ¹⁶²Gd. These observations are in contrast to the continuous decrease in the 2⁺ energy to a minimum at neutron midshell (N = 104) in Er, Yb and Hf nuclei. Mean-field calculations of the deformations do not follow the data, but give a smooth increase in β₂ deformation to N = 102 for Gd nuclei. (letter to the editor)

[en] Evidence for stable octupole deformation in neutron-rich nuclei bounded by Z=54-58 and N=85-92 is described. More vibrational type octupole modes are observed to either side of this region in ¹⁴⁰Ba and ^152,154Nd. The largest stable octupole deformation (β₃∼0.1) is reported in ¹⁴⁴Ba_gg. The theoretically predicted quenching (β₃→0) of stable octupole deformation with increased rotation is observed in ¹⁴⁶Ba. There is good agreement between theory and experiment for the strongly varying electric dipole moments as a function of mass for ^142-148Ba. In odd-A ¹⁴³Ba and odd-Z, ¹⁴⁵La, two pairs of positive and negative parity bands with opposite spins, parity doublets are observed. In ¹⁴⁵La the ground band with symmetric shape coexists with the asymmetric octupole shape which stabilizes above about spin 19/2⁺. The isotope ¹⁰⁹Mo was identified and a new region of stable octupole deformation is identified in ^107,109Mo centered around N=64-66 as earlier predicted. This is the first case of stable octupole deformation involving only one pair of orbitals

[en] Evidence for stable octupole deformation in neutron-rich nuclei bounded by Z=54-58 and N=85-92 is described. More vibrational type octupole modes are observed to either side of this region in ¹⁴⁰Ba and ^152,154Nd. The largest stable octupole deformation (β₃∼0.1) is reported in ¹⁴⁴Ba_gg. The theoretically predicted quenching (β₃→0) of stable octupole deformation with increased rotation is observed in ¹⁴⁶Ba. There is good agreement between theory and experiment for the strongly varying electric dipole moments as a function of mass for ^142-148Ba. In odd-A ¹⁴³Ba and odd-Z, ¹⁴⁵La, two pairs of positive and negative parity bands with opposite spins, parity doublets are observed. In ¹⁴⁵La the ground band with symmetric shape coexists with the asymmetric octupole shape which stabilizes above about spin 19/2⁺. The isotope ¹⁰⁹Mo was identified and a new region of stable octupole deformation is identified in ^107,109Mo centered around N=64-66 as earlier predicted. This is the first case of stable octupole deformation involving only one pair of orbitals. (c) 1999 American Institute of Physics

[en] We have used our analysis of γ-γ-γ data (5.7 x 10¹¹ triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of ²⁵²Cf to study the collective bands in ^104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich ^104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in ^104,106Mo, along with the first β-type vibrational band in ¹⁰⁶Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in ¹⁰⁶Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus

[en] New band structures in the neutron-rich ^113,115,117Pd nuclei have been constructed by measuring the γ-γ-γ coincidences emitted from the spontaneous fission of ²⁵²Cf with GAMMASPHERE. The triple γ-ray coincidence data revealed new negative-parity bands built on 11/2^- isomeric states in ^113,115,117Pd. These bands built on the νh_11/2 orbital suggest a band crossing at a frequency of (ℎ/2π)ω≅0.45 MeV. The rotational behavior and energy level spacings of these bands suggest a prolate shape. Two previously unreported bands are also observed in ^113,115Pd and tentatively assigned positive parity. These have band crossings at 0.25 and 0.32 MeV. (c) 1999 The American Physical Society

[en] From γ-γ-γ coincidence measurements in spontaneous fission of ²⁵²Cf, level energies were established to spins 14⁺ to 20⁺ in many neutron-rich nuclei. New isotope ¹⁶²Gd was identified. Yrast bands of ^152,154,156Nd, ^156,158,160Sm, and ^160,162Gd exhibit near-identical transition energies and moments of inertia (MOI) shifted by the same constant amounts for every spin state from 2⁺ to 12⁺ or 14⁺ for nuclei differing by 2n, 4n, 2p, 4p, α, α+2p, and α+2n. These shifted identical bands (SIB) are a new phenomenon. Analysis of all known even-even proton- to neutron-rich nuclei from Ba(Z=56) to Os(Z=76) reveal no SIB for proton-rich nuclei and few cases of SIB for the most neutron-rich pairs around N=98-102 separated by 2n and 2p

[en] The high-spin nuclear structure of Tc isotopes is extended to more neutron-rich regions based on the measurements of prompt γ rays from the spontaneous fission of ²⁵²Cf at the Gammasphere. The high-spin level scheme of N=67 neutron-rich ¹¹⁰Tc (Z=43) is established for the first time, and that of ¹¹¹Tc is extended and expanded. The ground band of ¹¹¹Tc reaches the band-crossing region, and the new observation of the weakly populated α=-1/2 member of the band provides important information on signature splitting. The systematics of band crossings in the isotopic and isotonic chains and a CSM calculation suggest that the band crossing of the ground band of ¹¹¹Tc is due to alignment of a pair of h_11/2 neutrons. The best fit to signature splitting, branching ratios, and excitations of the ground band of ¹¹¹Tc by the rigid triaxial rotor plus particle model calculations result in a shape of ε₂=0.32 and γ=-26 deg. for this nucleus. Its triaxiality is larger than that of ^107,109Tc, which indicates increasing triaxiality in Tc isotopes with increasing neutron number. The identification of the weakly populated K+2 satellite band provides strong evidence for the large triaxiality of ¹¹¹Tc. In ¹¹⁰Tc, the four lowest-lying levels observed are very similar to those in ¹⁰⁸Tc. At an excitation of 478.9 keV above the lowest state observed, ten states of a ΔI=1 band are observed. This band of ¹¹⁰Tc is very analogous to the ΔI=1 bands in ^106,108Tc, but it has greater and reversal signature splitting at higher spins

[en] Rare cold (zero neutron emission and low excitation energy) binary fission, cold α and ¹⁰ Be-accompanied ternary fission and cold fission with two neutrons emitted at scission and new nuclear structure effects have been observed in the spontaneous fission of ²⁵² Cf. Evidence for stable octupole deformation in ^143,144,146 Ba and ^145,147 La are presented. The roles of rotation in both enhancing and quenching stable octupole deformation are observed. In ¹⁴⁵ La one has a new class of shape coexistence with symmetric and asymmetric rotational bands (Authors)