Evolution of nuclear structure in erbium-158

Article By:

Wang, Xiaofeng Department of Physics, Florida State University, Tallahassee, Florida.

Riley, Mark A. Department of Physics, Florida State University, Tallahassee, Florida.

Simpson, John Science and Technology Facilities Council, Daresbury Laboratory, Daresbury, Warrington, United Kingdom.

Paul, Edward S. Department of Physics, University of Liverpool, Liverpool, United Kingdom.

Last reviewed:2013

DOI:https://doi.org/10.1036/1097-8542.YB130211

The response of atomic nuclei to increasing angular momentum (or spin) and excitation energy is one of the most fundamental topics of nuclear structure research and is often studied through high-resolution gamma-ray spectroscopy. Erbium-158 (¹⁵⁸Er) is widely considered as a classic nucleus in this field since it exhibits a number of beautiful structural changes as it evolves with increasing excitation energy and angular momentum. At low spin it behaves like a weakly deformed prolate quantum rotor, similar to many other rare-earth nuclei. With increasing angular momentum, it undergoes Coriolis-induced alignments of high-j neutron or proton pairs until a dramatic prolate collective to oblate noncollective transition eventually takes place via the mechanism of band termination. At the highest spins, a spectacular return to collective rotation is observed, and it has been suggested that this is in the form of triaxial strongly deformed structures. This latter suggestion is based on a comparison of energies, spins, and transition quadrupole moments between experiment and theory. This observation confirms the longstanding prediction that such heavy nuclei will possess nonaxial shapes on their path toward fission.

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