H. Schnare

Development of segmented Ge detectors for future γ-ray arrays

The EUROBALL Cluster detector is composed of seven encapsulated Ge detectors in a common cryostat with a total volume of 2000 ccm of HP Gemanium. The development and the performance of the Cluster detector is summarized. Up to six Cluster detectors were used in pre-EUROBALL experiments at the S-DALINAC Darmstadt, at the tandem-postaccelerator facility of the MPI-K Heidelberg and at the UNILAC at GSI. Examples of these experiments - the excitation of dipole modes with (γ, γ′)-reactions and the first coincidence spectroscopy of the N=Z-nucleus 68Se with a CLUSTER Cube - are discussed. The development of segmented encapsulated Ge detectors for a MINIBALL at the radioactive beam facility REX-ISOLDE has been launched. The status of the project is presented.

Superdeformed band in 146Gd. First observation of band crossing

Abstract A discrete superdeformed band is found in 146 Gd. Lifetime measurements yield an average quadrupole moment of 12±2 e b. A band crossing corresponding to an alignment of ≈2ħ is observed at a rotational frequency of 0.65 MeV. A theoretical analysis suggests that the band has a π6 2 v7 1 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.

Two-phonon J = 1 states in even-mass Te isotopes with A = 122–130☆

Abstract Excited states of the nuclei 122,126,130 Te were populated via the (γ, γ′) reaction at endpoint energies of the bremsstrahlung between 4.5 and 5.5 MeV. Gamma rays were detected with a EUROBALL CLUSTER detector and a single HPGe detector. In all investigated nuclei two or three prominent dipole transitions were identified at E γ ≈ 3 MeV. The corresponding low-lying J = 1 states are interpreted as two-phonon excitations. Quasiparticle-phonon-model calculations predict at about 3 MeV one 1 − state arising from the coupling of the first quadrupole and the first octupole phonon, and one 1 + state arising from the coupling of the first and the second quadrupole phonon, where the latter has isovector character. Such an excitation mode can be considered as an analogue of the scissors mode in vibrational nuclei. The calculated transition strengths are compatible with experimental ones within a factor of about 1.5.

Study of band structures and crossings in 179Os

Abstract High-spin states in 180 Os have been populated in the 166 Er( 18 O, 4n) reaction and studied with in-beam spectroscopy techniques. A γ-coincidence measurement with 5 anti-Compton spectrometers allowed to establish eleven bands, the ground band up to spin-32, the highest spin identified in this work. The extraction of g K factors, based on the analysis of branching ratios and M1/E2 mixing ratios, permitted configuration assignments for some of the bands. Calculations in the framework of the pairing self-consistent rotating BCS model, taking into account shape evolution have been carried out to interpret the observed band crossing features. The two crossings found in most of the bands are considered to result from the rotation alignment of ν( i 13 2 ) 2 and π( h 9 2 ) 2 or π( i 13 2 ) 2 configurations, respectively. The signature splitting observed in certain negative-parity bands indicates that the nucleus may have a triaxial shape. The staggering effect in the low-lying γ-band suggests that the nucleus is γ-soft.

Structure and evolution of electric dipole strength in 204,206,208Pb below the neutron emission threshold

Abstract The electric dipole strength distributions below threshold in stable even-mass Pb isotopes have been extracted from photon scattering experiments at the superconducting Darmstadt electron linear accelerator S-DALINAC. Between 4 and 6.5 MeV excitation energy a resonance-like clustering of strength is observed. A strong evolution of a fragmentation of the dipole strength with opening the neutron shell is found. The fine structure of the strength is compared to microscopic quasiparticle-phonon model calculations that quantitatively reproduce the data quite well and explain the fragmentation of the dipole strength. Models suggesting the oscillation of excess neutrons with respect to an N ≃ Z core as a possible origin of low-lying E1 strength are critically examined.

Identification of excited states in the N = Z nucleus 68 Se with cluster detectors

A first level scheme of

Resonant photon scattering on the semi-magic nucleus 89Y up to 7 MeV

{}^{68}\mathrm{Se}

Excited superdeformed band in146Gd

with five states up to 4.2 MeV excitation energy and tentative spins

Spectroscopy of 160Hf

{6}^{+}

Note on a search for the two-octupole phonon 2+ state in 208 Pb with resonant photon scattering

and