The High-Spin Domain of 158Er Up to and Above Band Termination and 157,158,159Dy in the I=30-50ħ Spin Regime

by Akis PIPIDIS (Florida State University, USA)

Tuesday 23 Mar 2010, 11:00 → 12:30 Europe/Rome

LNL Meeting Room (INFN LNL)

The response of atomic nuclei to increasing angular-momentum values, or rotational stress, continues to be a fundamental and fascinating field of scientific study. Indeed, the quest to observe ever increasing high-spin states in nuclei has driven the field of γ-ray nuclear spectroscopy for many decades. In the rare-earth region of the nuclear landscape, nuclei can accommodate the highest values of angular momentum and have provided a wealth of new nuclear-structure phenomena. State of the art γ-ray detector systems have been used to investigate a series of rare-earth nuclei with mass A~158. This presentation will focus on 158Er which, over the last thirty years, has been featured highly in the excitement and development of high-spin nuclear physics. In the past, the angular-momentum induced transition from a deformed state of collective rotation to a non-collective configuration has been studied thoroughly, for 158Er. This transition manifests itself as favored, fully-aligned, band termination near I~45ħ in three rotational structures. The feeding of these band terminating states has been investigated for the first time, using the GAMMASPHERE spectrometer. A large number of weakly populated states, lying at high excitation energy, that decay into these special states have been discovered. Additionally, a new frontier of discrete-line γ-ray spectroscopy at ultra-high spin has been opened in the rare-earth nucleus 158Er. Two rotational structures, displaying high moments of inertia, have been identified, which extend up to spin ~65ħ and bypass the band-terminating states near I~45ħ. Finally, I will present the significant extensions to the high-spin excitation spectrum of the N = 91, 92, 93 isotopes 157,158,159Dy, that have been achieved using the high-efficiency γ-ray spectrometers EUROBALL and GAMMASPHERE. The latest generation of very high-efficiency γ-ray detector arrays, such as the above, provides the opportunity to study nuclear structure phenomena at high spin in rare-earth nuclei, populated even at a very small fraction of the total reaction cross section (in our case 157,158,159Dy). The significantly extended data on 157,158,159Dy show regular rotational structures up to spin I~50ħ.