Collective and single-particle states at high excitation energy

Damping of high-lying single-particle states was investigated by the study of decay by proton emission from high-lying states in 91 Nb, populated by the 90 Zr(α, t) reaction at E α =180 MeV. In addition to decay to the ground state of 90 Zr, semi-direct decay was observed to the low-lying (2 + /5 − and 3 − ) phonon states, confirming the conclusion from other experiments that phonon states play an important role in the damping process of the single-particle states. Furthermore, the population and decay of isobaric analogue states of 91 Zr, which are located at an excitation energy of about 10–12 MeV in 91 Nb, has been studied in the same reaction.