Search for the Exotic Wobbling Mode in Rhenium-171
Abstract
It is often assumed that the nucleus of an atom is spherical; however, this is not always the case. At excited or high-spin states, where the nucleus is rotating very rapidly, it can either stretch or compress along a body-fixed, principal axis, giving it the shape of an American football or a doorknob. Very rarely, a nucleus can assume an asymmetric shape where it does not rotate around a principal axis but instead wobbles. This wobbling motion is analogous to the spinning motion of an asymmetric top. The wobbling mode has been found in several isotopes of lutetium (Lu). Surprisingly, this mode was not observed in the neighboring hafnium (Hf) and thulim (Tm) isotopes and was only recently found in an isotope of tantalum (Ta). The observation of a wobbling band, associated with the i13/2 band is a strong indication that a nucleus possesses asymmetric deformation. In order to determine the role of the atomic number on the observation of asymmetric deformation, an experiment was conducted to search for the wobbling mode in 171Re. High-spin states in 171Re were produced in a reaction at Argonne National Laboratory. The off-center collisions between the 55Mn beam and the 120Sn target nuclei resulted in large amounts of angular momentum (spin) in the new compound nucleus. To dispel this angular momentum, rays were emitted by the nucleus; these rays were detected using germanium detectors in the Gammasphere spectrometer at Argonne National Laboratory. These gamma ray data were subsequently analyzed at the Naval Academy. Gamma rays that were emitted in coincidence, or nearly simultaneously, came from one unpaired nucleon in its decay to the ground state. Seven decay sequences in 171Re were established, but the focus of this project was based on sequences feeding into the previously determined i13/2 band. Two bands were found to feed into the i13/2 structure, and their characteristics have been assessed to determine if these sequences are associated with wobbling.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 13, 2011
- Accession Number
- ADA554673
Entities
People
- Eowyn E. Pedicini
Organizations
- United States Naval Academy