Probing the Order-to-Chaos Region in Superdeformed $^{151}$Tb and $^{196}$Pb Nuclei with Continuum $\gamma$ Transitions

The $\gamma$ decay associated with the warm rotation of the superdeformed nuclei 151Tb and 196Pb has been measured with the EUROBALL IV array. Several independent quantities provide a stringent test of the population and decay dynamics in the superdeformed well. A Monte Carlo simulation of the $\gamma$ decay based on microscopic calculations gives remarkable agreement with the data only assuming a large enhancement of the B(E1) strength for 1–2 MeV $\gamma$ rays, which may be related to the evidence for octupole vibrations in both mass regions.