Lifetimes of triaxial superdeformed states in 163Lu and 164Lu

Lifetimes of states in the yrast superdeformed bands of ¹⁶³Lu and ¹⁶⁴Lu were determined in a Doppler-shift attenuation-method experiment. From fractional Doppler shifts and line shapes, average transition quadrupole moments, Q _t = 8.2_-0.6 ^+1.0 b and 7.1_-0.6 ^+0.5 b, were deduced for one of the bands in ¹⁶³Lu and ¹⁶⁴Lu, respectively. These values are much larger than the quadrupole moment of the normal-deformed yrast band in ¹⁶³Yb, Q _t = 4.9_-0.4 ^+1.3 b, that was also determined in this experiment. Comparison to cranking calculations indicates that both superdeformed bands correspond to a local potential energy minimum with a pronounced triaxiality, γ∼ 20^°. Received: 8 November 2001 / Accepted: 9 January 2002     

Comparative quadrupole moments of triaxial superdeformed states in 163, 164, 165Lu

Average transition quadrupole moments in the yrast triaxial superdeformed bands of ¹⁶³Lu, ¹⁶⁴Lu and ¹⁶⁵Lu were determined in a Doppler-shift attenuation-method experiment. Fractional Doppler shifts were determined in γ-ray coincidence spectra measured with the Gammasphere array. The transition quadrupole moments derived from these data show a decrease from ¹⁶³Lu to ¹⁶⁵Lu which is not predicted by total-energy surface calculations. Received: 12 August 2002 / Accepted: 23 October 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: schoenwa@iskp.uni-bonn.de Communicated by D. Schwalm     

Quantitative Assessment of B−B−B,B−Hb−B,and B−Ht Bonds: From BH3 to B12H122−

We report the thermodynamic stabilities and the intrinsic strengths of three-center-two-electron B−B−B and B−H_b−B bonds ( : bridging hydrogen), and two-center-two-electron B−H_t bonds ( : terminal hydrogen) which can be served as a new, effective tool to determine the decisive role of the intermediates of hydrogenation/dehydrogenation reactions of borohydride. The calculated heats of formation were obtained with the G4 composite method and the intrinsic strengths of B−B−B, B−H_b−B, and B−H_t bonds were derived from local stretching force constants obtained at the B3LYP-D2/cc-pVTZ level of theory for 21 boron-hydrogen compounds, including 19 intermediates. The Quantum Theory of Atoms in Molecules (QTAIM) was used to deepen the inside into the nature of B−B−B, B−H_b−B, and B−H_t bonds. We found that all of the experimentally identified intermediates hindering the reversibility of the decomposition reactions are thermodynamically stable and possess strong B−B−B, B−H_b−B, and B−H_t bonds. This proves that thermodynamic data and intrinsic B−B−B, B−H_b−B, and B−H_t bond strengths form a new, effective tool to characterize new (potential) intermediates and to predict their role for the reversibility of the hydrogenation/dehydrogenation reactions.     

(68)(28)Ni(40): Magicity versus superfluidity

The neutron-rich (66,68)Ni have been produced at GANIL via interactions of a 65.9A MeV 70Zn beam with a 58Ni target. Their reduced transition probability B(E2;0(+)(1)-->2+) has been measured for the first time by Coulomb excitation in a (208)Pb target at intermediate energy. The B(E2) value for (68)Ni(40) is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the B(E2) values and indicates the erosion of the N = 40 harmonic-oscillator subshell by neutron-pair scattering.     

Study of 170,171,173Ta isotopes at high spinṡ

High-spin data are presented for ¹⁷⁰Ta and ¹⁷¹Ta for the first time, and the known level scheme of ¹⁷³Ta is extended to higher spins. Anomalies found in the crossing frequencies for the alignment of a pair of neutrons are considered. At high spin a large and constant value of J⁽²⁾, with J⁽²⁾ > J⁽¹⁾, is found for two ¹⁷¹Ta bands and the implications of this are discussed. The πi_13/2 [660]1/2⁺, α = + 1/2 orbital is identified as it crosses the rotational band built on the [402]5/2⁺, α = + 1/2 orbital in ¹⁷¹Ta. Magnetic transition probabilities obtained from measured branching ratios show the effects of the aligning pair of neutrons and the spectator orbital. The data are interpreted using cranked shell-model calculations and a semiclassical vector-coupling scheme developed by Donau and Frauendorf.     

Coexisting wobbling and quasiparticle excitations in the triaxial potential well of 163 Lu

High-spin states of the nucleus ¹⁶³Lu have been populated through the fusion-evaporation reaction ¹³⁹La(²⁹Si, 5n) with a beam energy of 157 MeV. In addition to the two lowest excited triaxial strongly deformed (TSD) bands, recently interpreted as one- and two-phonon wobbling excitations, a third excited TSD band has been firmly established decaying to the yrast TSD band. The assignment of this band as a three-quasiparticle band shows together with the normal deformed (ND) level scheme the presence not only of shape coexistence between ND and TSD structures, but also an interplay of wobbling and quasiparticle excitations in the triaxial strongly deformed potential well of ¹⁶³Lu.Received: 18 July 2003, Revised: 28 August 2003, Published online: 23 December 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 23.20.Lv transitions and level energies - 25.70.-z Low and intermediate energy heavy-ion reactions - 27.70. + q H. Amro: Present address: Wright Nuclear Structure Laboratory, Yale University, New Haven, CT 06520-8124, USA.     

High spin states in 74Se

Gamma-ray transitions from the bombardment of ⁶⁴Ni by ¹⁶O up to 81 Me V were studied in a variety of experiments. Four transitions in coincidence with four previously known transitions in ⁷⁴Se were discovered. Information on energies, angular distributions, intensities multiplicities and lifetimes is given for these transitions. Excitation functions for this and several other channels are presented. Statistical calculations are in satisfactory agreement with experiment.     

Heavy ion induced transfer reactions on 148Nd

Transfer reactions induced by ¹⁶O and ¹⁸O beams on ¹⁴⁸Nd were measured with a time-of-flight setup at 72 MeV incident energy. The angular distributions are bell shapes having their maxima at angles somewhat below the grazing angle. The excitation in the final nuclei takes place (if possible) near the optimum Q-value and is spread over 5 MeV for the one-particle transfer reactions and up to 10 MeV for the multiparticle transfers. The cross sections for the individual channels are explained mostly by Q-window considerations. In spite of the differences in the individual channels the total transfer cross section integrated over excitation energy, angle, and all channels turns out to be the same same for both ¹⁶O and ¹⁸O beams. This cross section amounts to 20 % of the total reaction cross section and nicely fills the gap between the measured fusion cross section and the total reaction cross section obtained from optical model calculations based on elastic scattering data.