The figure shown above illustrates the main themes addressed recently by the NBI group in close collaboration with groups from France, Germany, Italy, Norway, Poland, Sweden, UK and US.

 

The experimental nuclear structure programme has the last years been concentrated on the following main themes.

The research is carried out exclusively as travel physics. Our main instrumental investment is in the Euroball IV Ge-detector array, which at present is sub-divided into installations at GSI-Darmstadt (RISING), LNL-Legnaro, and University of Jyvaskyla. The group has also sought projects promoted at alternative accelerator installations, and several experiments have been carried out with Gammasphere, the US counterpart to Euroball IV, presently installed at Argonne National Laboratory, US. The group also has vital interests in the detector array Exogam dedicated to nuclear structure studies with radioactive beams created by ISOL techniques at GANIL, and in MINIBALL built at University of Cologne, mainly to be used at REX-ISOLDE and GSI. An advanced target chamber with remote control has been constructed and manufactured at the NBI for these studies. The group is also involved in complementary experiments with exotic fragmentation beams at relativistic energies.

The nuclear manybody system may under the influence of rotational induced forces develop various exotic shapes. Most appealing is the strongly elongated, axially symmetric hyperdeformed (HD) shape with axis frequency ratio 3:1, which is predicted in different regions though still not experimentally identified by the sought discrete rotational bands. Encouraging hints are seen as rotational patterns, the so-called ridge structures, with appropriate dynamic moments of inertia in 126Xe and 126Ba nuclei. Much emphasis has been devoted to studies of the interplay between reaction dynamics, binding energies and fission barriers to optimize the population of HD structures at the border of reachable angular momentum. Regions with ongoing experiments are Cd, Sn, Ba, Xe, and Nd nuclei. These nuclei are, with increasing angular momentum, expected to pass through a region of Jacoby instability, for which the experimental signatures are being investigated. More details: Recent Preprint.

Nuclei may also develop shapes in which the axial symmetry is broken. The group has played a central role in the latest accomplishment concerning triaxial superdeformed (TSD) shapes in the Lu-Hf region. Most recently we have provided the first experimental evidence for the wobbling excitation mode in nuclei, predicted more than 20 years ago. This analysis is based on a Euroball experiment for 163Lu from late 1999. Most recently, in the summer 2001 a search for the second phonon wobbling mode built on TSD bands in 163Lu is made at Euroball IV in Strasbourg. See more details under 1. Phonon Wobbler, 2. Phonon Wobbler.)

The complex region in the nuclear excitation spectrum where the average distance between rotational bands become comparable to the 2-body residual interaction is characterized by a damping mechanism and the E2 rotational strength function becomes spread out on many bands in each decay step. New methods in multidimensional analysis of spectra are under development to separate the rotational damping mechanism into its basic components, of which one is predicted to be proportional to , the decay-rate of excited mean field states into compound states.(See more details under Recent Pre-prints.)

Features related to multi-quasiparticle structures with large angular momentum projection on the nuclear symmetry axis have been investigated in 2 experiments at Gammasphere in year 2000. New insight into the abnormal decay of high-K isomeric states are expected. The possibility of high-K band-structures also in the SD well has been addressed in yet another Gammasphere experiment, and the data are examined with the aim of identifying K-isomerism in the SD potential well.

Experiments with radioactive beams at GANIL focus on nuclei with large neutron excess. An example is 24O at the neutron dripline. A central question is whether the magic numbers expected in shell models prevail with a massive excess of one type of nucleons.

 

Information Related to the Group


Last modified: 25. Sept. 2004.
Questions or comments to: herskind@nbi.dk