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     

First observation of a superdeformed nucleus produced in an α xn reaction channel

Excited states in the neutron deficient ¹⁴⁵ Dy nucleus have been identified by means of the reaction ¹¹²Sn(³⁵ Cl,pn) at 159 MeV. The level scheme above the 11/2 ^? state and up to spin I～37/2 was obtained using γ-ray spectroscopy methods. The level structure is discussed in terms of the coupling of a h _11/2 neutron hole with the N=80 core excitations.     

Observation of a superdeformed band in192Pb

A new superdeformed band, identified in data from the²⁴Mg+¹⁷³Yb reaction, is assigned to¹⁹²Pb on the basis of excitation function and coincidence results. Properties of this band are discussed briefly, and compared to the superdeformed bands known in other Pb nuclei.     

Superdeformed band in Gd. First observation of band crossing

A discrete superdeformed band is found in ¹⁴⁶Gd. Lifetime measurements yield an average quadrupole moment of 12±2 e b. A band crossing corresponding to an alignment of ≈2 is observed at a rotational frequency of 0.65 MeV. A theoretical analysis suggests that the band has a π6²v7¹ configuration with odd spins and odd parity. Arguments are given that the [651 1/2] and [642 5/2] single-particle states are involved in the band crossing.     

Confirmation of the superdeformed band in192Pb

High-spin states in¹⁹²Pb were populated via the reaction¹⁷³Yb(²⁴Mg,5n) at a beam energy of 140 MeV, and the resulting-rays were deteced using GAMMASPHERE. A previously observed superdeformed band in¹⁹²Pb has been confirmed.     

Characterization of the superdeformed band in189Hg

New measurements of the pionic double charge exchange on⁵⁶Fe exhibit a pronounced energy dependence of this reaction at low energies in accordance with similar observations on other nuclei. We show that this peculiar energy dependence finds its natural explanation by a resonance in theNN subsystem withJ ^p =0^–,T=0 and a mass of 2.065 GeV.This work has been funded by the German Federal Minister for Research and Technology (BMFT) under the contract numbers 06 TÜ 656 and 06 KA 266 and by the DFG (Mu 704/3, Graduiertenkolleg)     

A superdeformed band in131Ce

A rotational band of 16γ-rays has been found in¹³¹Ce with a high moment of inertia indicating a deformation ε₂～0.38 and extending to spin ～40?. Its intensity is ～～5% of the total in¹³¹Ce, confirming a difference in the intensity systematics for superdeformed states in Ce nuclei compared with Nd.     

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.     

Single-step link of the superdeformed band in 143Eu

A discrete γ-ray transition with an energy of 3360.6 keV deexciting the second lowest SD state in ¹⁴³ Eu has been discovered. It carries 3.2 % of the full intensity of the band and feeds into a nearly spherical state which is above the I = 35/2⁽⁺⁾, E_x=4947 keV level. The exact placement of the single-step link is, however, not established due to the specially complicated level scheme in the region of interest. The energy of the single-step link agrees well with the previously determined two-step links.     

Single-step link of the superdeformed band in143Eu

²⁰⁹Fr has been produced by irradiation of¹⁹⁷Au with¹⁶O,and studied using a He-jet recoil tape transport system.A decay scheme is proposed for the first time,based on X-γ and γ-γ coincidence measurements,which takes account of 20 observed γ-rays. The branching ratio for (EC+β ⁺) decay of²⁰⁹Fr has been estimated to be 3.0±1.5%. Five members of low-lying states in²⁰⁹Rn can be explained with the configuration [(²¹⁰Rn 2⁺)(νf5/2)^?1].     

The observation of a superdeformed structure in82Y

The⁵⁸Ni(³⁰Si,αpn)⁸²Y reaction at a beam energy of 134 MeV was used to populate the odd-odd nucleus⁸²Y and coincidentγ rays depopulating high spin states in the evaporation residues were detected with the EUROGAM Phase 2 array. A superdeformed structure has been observed with an intensity of 1.5±0.5%. The cascade of 9 coincidentγ rays has consecutive energy spacing of ～160 keV. This corresponds to a dynamic moment of inertia which is almost constant at approx mately 25h ² MeV^?1. The band is interpreted as a signature=0, negative parity SD band with aπ5¹ V5² intrinsic intruder configuration.     

On the decay of the superdeformed band in194Pb

We report on new results for the decay of the superdeformed (SD) band in¹⁹⁴Pb. No transitions linking the SD structure with the known level scheme of¹⁹⁴Pb could be found, but the feeding intensities into the normal-deformed states are determined and limits on the one-step decay of the SD band are given.     

First observation of yrast band in odd-odd162Lu

High spin states of the odd-odd¹⁶²Lu nucleus have been studied via¹⁴⁷Sm(¹⁹F,4nγ)¹⁶²Lu reaction at 95 MeV beam energy. Level scheme for yrast band based onπ[h_11/2 v[i_13/2] quasiparticle configuration was established up to I ^π = (23^?) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in¹⁶²Lu is larger than that in the¹⁶⁰Tm nucleus.     

First observation of yrast band in odd-odd 162Lu

High spin states of the odd-odd ¹⁶²Lu nucleus have been studied via ¹⁴⁷Sm(¹⁹F,4nγ)¹⁶²Lu reaction at 95 MeV beam energy. Level scheme for yrast band based on π[h_11/2]υ[i_13/2] quasiparticle configuration was established up to I^π=(23^?) for the first time. This band shows the signature inversion in energy before backbending generally appeared in this mass region. It is stressed that the signature splitting in ¹⁶²Lu is larger than that in the ¹⁶⁰Tm nucleus.     

New results on the superdeformed band in192Hg

New results on the¹⁹²Hg superdeformed band have been obtained with EUROGAM. The experiment has been performed with the¹⁶⁰Gd(³⁶S,4n) reaction at 159 MeV. Above 800 keV the γ-ray energies differ from the previously published ones. Thus the rise of the dynamical moment of inertia $\mathfrak{F}^{(2)} $ above ?ω=0.4 MeV is no longer observed. This is in better agreement with recent cranked Hartree-Fock-Bogoliubov calculations.     

γ-Rays draining the superdeformed band in152Dy

Further analysis of earlier¹⁵²Gd(α,4n) in-beam data revealed several previously unplaced¹⁵²Dy γ-rays feeding the oblate yrast states, among them γ-transitions emitted in decay of the superdeformed band. We can also weakly detect the lowest two members of the superdeformed cascade, but our data were not quite good enough to make a firm connection to them.