The Fascinating $$\gamma $$-Ray World of the Atomic Nucleus: The Evolution of Nuclear Structure in $$^{158}\mathrm{{Er}}$$158Er and the Future of $$\gamma $$-Ray Spectroscopy

The rare-earth nucleus \(^{158}\mathrm{{Er}}\) exhibits a number of beautiful structural changes as it evolves with increasing excitation energy and angular momentum. After undergoing Coriolis induced alignments of high-\(j\) neutron and proton pairs, a dramatic prolate collective to oblate non-collective transition takes place via the mechanism of band termination. At the highest spins, a spectacular return to collective rotation is observed in the form of triaxial strongly deformed bands. This latter suggestion is based on a comparison of transition quadrupole moments (\(Q_\mathrm{{t}}\)) between experiment and theory, and long standing predictions that such heavy nuclei will possess nonaxial shapes on their path towards fission. These exciting discoveries in \(^{158}\mathrm{{Er}}\) have benefited greatly from the progression of \(\gamma \)-ray detector developments through recent decades. The new \(\gamma \)-ray energy tracking technique and the next generation detector arrays utilizing this technique, e.g., GRETINA (\(1\pi \)) and GRETA (\(4\pi \)), are briefly discussed.