Triaxial superdeformation in Lu

High-spin states in ¹⁶³Lu have been investigated using the Euroball spectrometer array. The previously known superdeformed band has been extended at low and high energies, and its connection to the normal-deformed states has been established. From its decay the mixing amplitude and interaction strength between superdeformed and normal states are derived. In addition, a new band with a similar dynamic moment of inertia has been found. The experimental results are compared to cranking calculations which suggest that the superdeformed bands in this mass region correspond to shapes with a pronounced triaxiality (γ≈±20°).     

Shape Coexistence and Band Termination in Doubly Magic Nucleus 40Ca

Shape coexistence and band structure near yrast line of the Z=N doubly magic nucleus ⁴⁰Ca have been investigated by the configuration-dependent cranked Nilsson-Strutinsky approach. The observed normal deformed and superdeformed bands are explained and the terminating states are confirmed by the calculations. The transition quadrupole moment Q_t of the calculated superdeformed band is in good agreement with the observed one at high spin. There is shape coexistence within the same configuration. Possible normal deformed and superdeformed bands with rotation around the intermediate axis in several interesting configurations of ⁴⁰Ca are discussed. Possible favored superdeformed band terminations in ³⁸Ca and ³⁸Ar are predicted. The experimental results in ³⁸Ar are discussed simply.     

High spin investigation in 193Pb with EUROGAM 2: coexistence of superdeformed and dipole bands

The nucleus ¹⁹³Pb was populated via the ¹⁶⁸Er(³⁰Si, 5n) reaction at a beam energy of 159 MeV and studied with the EUROGAM II spectrometer. Five new dipole ΔI = 1 cascades have been found. The ¹⁹³Pb dipole bands are discussed in terms of microscopic HF+BCS calculations. The proposed configurations are based on a high-K two-quasiproton excitation coupled to rotation aligned quasineutrons. Parallel to the dipole bands the six superdeformed bands have been discussed in the framework of microscopic mean-field calculations. The bands are interpreted as three pairs of signature partners based on quasineutron excitations. Cross-talk transitions linking two signature partner superdeformed bands have been observed and, for the first time in lead isotopes, a mean B(M1)/B(E2) ratio value of 0.15±0.04 μ _N ² /e^2b2 has been extracted.     

New results on the superdeformed 196Pb nucleus: decay of the excited bands to the yrast band

The study of the superdeformed ¹⁹⁶Pb nucleus has been revisited using the EUROGAMphase 2 array. In addition to the known yrast and two excited SD bands, a third excited SD band has been found. All of the three excited bands were found to decay to the yrast SD band through presumably E1 transitions. Comparisons with calculations using RPAapproximation indicate that the excited bands can be interpreted as octupole-vibrational structures.     

Isospin and Symmetry Structure in 36Ar

The interacting boson model-3(IBM-3) has been used to study the isospin excitation states and electromagnetic transitions for ³⁶Ar nucleus. The mixed symmetry states and superdeformed band at low spin are also analyzed. The theoretical calculations are in agreement with experimental data, and the ³⁶Ar is superdeformed rotational nucleus close to the SU(3) limit. The present calculations indicate that the 2₄⁺ state is the lowest mixed symmetry state and the lowest isospin T=1 excitation state and at about 6.2 MeV, and the bandhead of superdeformed band is 0₂⁺ state.     

Evidence for wobbling excitation in 161Lu

High-spin states in ¹⁶¹Lu were investigated using the EUROBALL spectrometer. A previously known triaxial superdeformed band has been extended to higher spins and a new band with similar characteristics has been discovered. Comparison to systematically occurring wobbling bands in Lu isotopes strongly suggests that these two bands represent the n_w = 0 and 1 wobbling excitations in ¹⁶¹Lu.     

Triaxial superdeformation in 163Lu

High-spin states in ¹⁶³Lu have been investigated using the Euroball spectrometer array. The previously known superdeformed band has been extended at low and high energies, and its connection to the normal-deformed states has been established. From its decay the mixing amplitude and interaction strength between superdeformed and normal states are derived. In addition, a new band with a similar dynamic moment of inertia has been found. The experimental results are compared to cranking calculations which suggest that the superdeformed bands in this mass region correspond to shapes with a pronounced triaxiality (γ≈±20°).     

Criteria of the Spin Assignment of Rotational Band

Based on the very general properties of the rotational band of axially symmetric nucleus, some rules of the I variation of the kinematic and dynamic moments of inertia are obtained, which may serve as the effective criteria of the spin assignment of rotational band. Extensive analysis of large amount of ro tational bands (below bandcrossing) of normally deformed eveneven nuclei whose spins were established shows that these rules do hold without exception. The spins of the yrast superdeformed bands of even-even nuclei in the actinide region (fission isomeric bands), and in the A～190, 150 regions are analyzed also. The spin of the lowest observed level of the yrast superdeformed band in ¹⁵²Dy is determined to be I₀ = 26, rather than I₀ = 22 or 24.     

In-beam γ-ray spectroscopy with GASP

The performance of the multi-detector array GASP is described in detail with emphasis on the improvement due to utilization of ancillary detectors. GASP has been running for three years producing interesting new data on different nuclear structure topics. The study of the decay-out of superdeformed bands in the A=130 mass region is presented. The sudden disappearance of the superdeformed bands in the odd^{133, 135, 137}Nd isotopes is explained by the Total Routhian Surface calculations through a change of the nuclear shape which is microscopically related to the transfer of the valence neutron from a N=6 to a N=4 Nilsson orbital. A transient fieldg-factor measurement in the superdeformed band of¹³³Nd will also be presented. A meang-factor of $\bar g = 0.31(8)$ has been determined at the I*=41/2⁺ superdeformed state. The experimental value is compared with theoretical predictions and supports the assignment of the superdeformed band to thev[660]1/2⁺ Nilsson intruder orbital.     

Superdeformed bands in195Tl

Two superdeformed (SD) bands have been found and assigned to¹⁹⁵Tl on the basis of excitation function and cross bombardment results. The two bands are almost identical in transition energies to those observed in¹⁹³Tl. They are signature partners with a splitting, presumably due to the proton i_13/2 (=5/2) orbital, characteristic of all known SD bands in the thallium isotopes. Their alignments relative to the¹⁹³Tl bands were found to be zero.On leave from Comision National de Energia Atomica 1429 Buenos Aires, Argentina.     

Identification of Collective Bands in Neutron-Rich 113Ru Nucleus

Through measuring high-fold prompt γ- ray coincidence events following the spontaneous fission of 252 Cf with the Gammasphere detector array, new level scheme in the very neutron-rich odd-A 113Ru nucleus has been established. An intruder collective band based on 11/2^－ level has been identified with spin up to 31/2 k and excitation energy 3.6 MeV. This band most probably originates from vh_11/2. intruder orbital. Another collective band probably built on 9/2^－ level is also observed. Some important characteristics of the collective bands have been systematically discussed.     

Excited superdeformed band in146Gd

A non-yrast superdeformed band has been found in¹⁴⁶Gd using the¹¹⁰Pd(⁴⁰Ar, 4n)¹⁴⁶Gd reaction. The nuclear assignment was made from the analysis of an experiment using a backed target. This band and the previously identified yrast SD band are probably not signature partners.     

190区超形变核中转动带的组态结构

通过系统研究A～190区超形变核中转动带的转动惯量、角动量顺排、旋称分裂随转动频率的变化规律, 结合我们用处理对力的粒子数守恒方法的计算结果, 对A～190区所有转动带的组态结构给出了一个整体的描述. 绝大多数超形变带都建立在强耦合轨道上, 例如中子[512]5/2, [624]9/2. 少数超形变带则建立在高j闯入轨道上, 即中子[761]3/2, [752]5/2. 根据我们提出的组态结构所进行的理论计算结果表明, A～190区所有转动带的一般行为、反常变化和带交叉都得到了满意的解释.     

Observation of superdeformed states in 88Mo

High-spin states in ⁸⁸Mo were studied using the Gammasphere germanium detector array in conjunction with the Microball CsI(Tl) charged-particle detector system. Three γ-ray cascades with dynamic moments of inertia showing similar characteristics to superdeformed rotational bands observed in the neighbouring A= 80 region have been identified and assigned to the nucleus ⁸⁸Mo. The quadrupole moment of the strongest band, deduced by the Residual Doppler Shift Method, corresponds to a quadrupole deformation of β₂≈ 0.6. This confirms the superdeformed nature of this band. The experimental data are interpreted in the framework of total routhian surface calculations. All three bands are assigned to two-quasi-particle proton configurations at superdeformed shape. Received: 20 May 1999 / Revised version: 25 August 1999     

Observation of superdeformed bands in194Hg

Two rotational bands, with energy spacings characteristic of superdeformed shapes, have been observed following bombardment of¹⁵⁰Nd with⁴⁸Ca. The more intensively populated band consists of 18 transitions and is assigned to¹⁹⁴Hg. The depopulation of this band occurs around spin 10. The second band, consisting of at least 16 transitions, was populated less strongly and is tentatively assigned to¹⁹⁴Hg also. The lowest level in this band is assigned spin 8. The energy differences between transitions for both bands decrease from ～40 keV at low rotational frequencies to ～30 keV at the highest observed frequencies. The moments of inertia of the bands are similar to those of the two previously observed superdeformed bands in^191,192Hg. The similarities and differences of the four known bands in the mercury region are discussed.     

Description of the Superdeformed Bands of the Lutetium Isotopes

In the cases with and without a perturbation possessing the S0_sdg(5) (or SU_sdg(5)) symmetry in the supersymmetry scheme with many-body interactions, superdeformed bands in the odd-A Lu isotopes ^163,165,167Lu are investigated. Quantitatively good results of γ-ray energies and dynamical moments of inertia are obtained in both of the two cases. It shows that the supersymmetry scheme with many-body interactions has almost the same power to describe the triaxial superdeformed bands as to the other superdeformed bands.     

Identification of Hg and shape coexistence in odd-A Hg isotopes

In-beam γ-ray transitions in ¹⁸¹Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2⁻[521] ground state was observed up to 29/2⁻. A 5/2⁻[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i_13/2 orbitals and are proposed to decay to an i_13/2 isomeric state associated with an oblate state.     

First triaxial superdeformed band in 170Hf

First evidence is presented for triaxial superdeformation in ¹⁷⁰Hf. High-spin states in this nucleus have been investigated in a γ-ray coincidence measurement using the EUROBALL spectrometer array. A new band was discovered which has moments of inertia that are very similar to the ones of triaxial superdeformed bands in neighbouring Hf and Lu nuclei. The intensities with which these bands are populated are different from what may be expected from calculated potential-energy minima. Received: 11 September 2002 / Accepted: 15 October 2002 / Published online: 10 December 2002 RID="a" ID="a"e-mail: neusser@iskp.uni-bonn.de Communicated by D. Schwalm     

Effect of E1 decay in the population of superdeformed structures

Spectra of the yrast and excited superdeformed bands, forming the E2 quasi-continuum, are measured with the EUROBALL array for the nucleus ¹⁴³Eu, in coincidence with high-energy γ-rays (E_γ>3 MeV). It is found that the intensity population of the superdeformed states is enhanced by a factor of ≈1.6 when a coincidence with a γ-ray with energy >6 MeV is required, in reasonable agreement with the increase of the line shape of the Giant Dipole Resonance built on a superdeformed configuration. This result shows that when an high energy E1 γ-ray is involved in the decay it is more likely connected with a SD rather than a ND nucleus. In addition, the analysis of the rotational quasi-continuum suggests the presence of a superdeformed component. The data are also compared and found consistent with simulation calculations of the relative intensities of the SD states, including the E1 decay of superdeformed nature.     

Total Routhian Surface Calculations on Hf Isotopes

The two-dimensional total routhian surface calculations have been carried out to study the triaxial superdeformed structure of a neutron-rich nucleus ¹⁷³Hf firstly. In particular the effects of the rotational frequency ω and pairing-energy gap parameter Δ are discussed in detail in the course of shaping its triaxial superdeformation; additionally the neutron-shell correction energy is analyzed with emphasis in the confirmed triaxial superdeformed nucleus ¹⁷³Hf. Finally, more systematical results have been investigated for some confirmed superdeformed nuclei experimentally and a few predicted triaxial superdeformed nuclei theoretically with quadropole deformation ε₂≈0.4 and triaxial deformation γ≈20^º or 30^º in the Z=72 region.