Decay of superdeformed bands

The excitation energy of a superdeformed (SD) band above the normal yrast line increases as it deexcites by emitting sharp E3 γ rays. This results in mixing with the underlying continuum of normal states, which is mainly responsible for the eventual sudden termination of the bands and its decay to the normal states. The spectrum of γ rays in the decay has been measured for 192Hg with EUROGAM by an Orsay-Lyon-Bonn-Liverpool-York-Argonne collaboration and with the Argonne-Notre Dame γ Array by an Argonne-INEL-Notre Dame-Purdue collaboration. The spectrum consists of: sharp lines (primarily from the last stages of the decay), broad structure (identified up to Eγ∼3.8 MeV) and a continuum extending up to ∼4 MeV. The observed spectrum suggests that: (i) the excitation energy of the SD band above the normal yrast line is 3.8 MeV at the point of decay, (ii) the multiplicity of transition linking SD and normal states is 4.3+1-2 MeV, and (iii) the decay is dominated by a statistical process, indicating a transition from ordered to chaotic-like motion, but mixing with collective normal states may also play a role