Damping mechanisms of high-lying single-particle states in Nb-91

Decay by proton emission from high-lying states in Nb-91, populated in the Zr-90(alpha,t) reaction at E-alpha=180 MeV, has been investigated. Decay to the ground state and semidirect decay to the low-lying (2(+),5(-), and 3(-)) phonon states in Zr-90 were observed. It was found that these phonon states play an important role in the damping process of the single-particle states. An optical-model coupled-channel approach was used successfully to describe the direct and semidirect parts of the decay.