New insights into extremely deformed nuclei

An overview is given of the new physics that it has been possible to address with the very large γ-ray spectrometer array EUROGAM. Evidence is presented for the establishment of very stable oblate mean fields at very high spins produced by 10 to 12 aligned valence nucleons in Er nuclei. Examples are given of the spectroscopic information obtained by studying fission fragments. Unique data on the structure of very neutron rich nuclei has been obtained by studying the spectroscopy of fission fragments. the high resolving power of EUROGAM allows many new excited superdeformed bands to be studied. Some of these bands cross and/or interact giving a wealth of information on the nucleon orbitals at the superdeformed Fermi surface. Lifetime measurement have also been made for some excited superdeformed bands in 149Gd which show how the core quadrupole moment and shape alters with the outer valence nucleon configuration. The very small ΔJ = 4 staggering of γ-ray energies in some superdeformed bands is found to persist with improved measurements. The first evidence for collective vibrations of the superdeformed shape has been found in 190Hg. RPA calculations with pairing give a good description, not only of the very abnormal behaviour of the excited superdeformed bands in 190Hg, but also of the lowest excited bands in 192Hg and 194Hg. The magnetic properties of a single nucleon at the superdeformed Fermi surface have been measured by observing M1 dipole transitions between signature partner superdeformed bands in 193Hg and 193Tl to give a measure of neutron and proton single particle g-factors respectively. Within experimental errors, the effective spin g-factor is found to be the same for superdeformed and normally deformed nuclei. (author)