Gammaband

A gamma band, or gamma-band, is a sequence of excited states observed in many well-deformed atomic nuclei that originates from gamma-vibrational motion of the nuclear shape about its symmetry axis. It is one of several collective rotational bands in deformed nuclei, alongside the ground-state (K = 0) band and the beta band (axial–vibrational mode).

In even-even nuclei with strong axial deformation, the gamma band is built on an intrinsic gamma-vibrational state and typically has a projection quantum number K = 2. The bandhead is usually a 2+ level, and the band contains higher-spin members with spins I = 2, 3, 4, and so on. Energies in the gamma band are generally above those of the ground-state band and follow a rotational-like pattern, though with characteristics influenced by the gamma degree of freedom. Transitions within the band are predominantly electric quadrupole (E2) transitions, and interband transitions to the ground-state or beta bands provide important information about shape and coupling.

Observationally, gamma bands are identified in gamma-ray spectroscopy through level schemes, transition rates, and characteristic energy patterns that reflect gamma-vibrational motion. Their properties help probe nuclear deformation, triaxiality, and the coupling between collective motion and single-particle degrees of freedom. The gamma band is a key concept in models of nuclear structure, including rotor models, the interplay of beta and gamma vibrations, and approaches such as the Interacting Boson Model. In nuclei with weak deformation or significant shape mixing, gamma-band features may be reduced or modified.