Analysis of collective excitations of fast rotating nuclei in the oscillator potential

Spectrum of positive parity collective excitations is analysed over a wide range of the angular momenta within the random phase approximation. The model Hamiltonian is taken as the spherical harmonic oscillator potential combined with isoscalar quadrupole forces. Such a model enables one to describe the available data on the position of the giant quadrupole resonance at low spins and to trace the variations of the resonance characteristics when spin is increasing. It is shown that with an increase of the rotation velocity the energy of one of the resonance branches falls down to zero, while the state remains essentially collective. The model reconstructs also the low-lying vibration mode which is relate to the procession mode. The excitation energy and the B(E2) factor corresponding to this mode deviate essentially from the estimates based on the rigid rotator model