Energy sharing in the deexcitation of the Ru-90 compound nucleus via the p alpha channel

Using the 4 pi light charged-particle detector DIAMANT in combination with the gamma-ray spectrometer EUROGAM II, the decay of the Ru-90 compound nucleus via the p alpha channel was studied. These nuclei were produced at an excitation energy of 54.9 MeV and with a maximum angular momentum of 37 (h) over bar by the 120 MeV S-32 + Ni-58 reaction. The measurement of the energy of the two particles allowed the determination of the energy distribution of the entry states. A particular behavior of the sharing of the available energy between the two particles was found: For increasing values of the entry-state energy, the mean energy for protons remains almost constant while for alpha panicles it decreases. This behavior is well reproduced by the evaporation code LILITA_N95. The physics underlying the decay is discussed in the framework of the statistical model which predicts a strong correlation between the excitation energy and the angular momentum of the evaporation residue. This result encourages the use of the p alpha channel to select the excitation energy and the angular momentum of the evaporation residue for superdeformed band studies