The ridge structure with Δ${\mathit{E}}_{\gamma }$=±30 keV, recently observed in the reaction 187 MeV ${}_{}{}^{37}{}_{}{}^{}\mathrm{Cl}$${+}^{120}$Sn and attributed to a hyperdeformed nuclear shape, has been confirmed in a new proton-γ coincidence experiment and assigned to the ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$ nucleus. Estimates of the cross section for the population of the 30 keV ridge and for the associated entry states have been obtained. The proton spectra in coincidence with γ rays of different Dy isotopes show effects related to the exit channel and to the angular momentum but they are scarcely sensitive to the selection of different shapes (oblate, normal deformed prolate, superdeformed) in the same residual nucleus ${}_{}{}^{152}{}_{}{}^{}\mathrm{Dy}$. The energy of the protons in coincidence with the Δ${\mathit{E}}_{\gamma }$=±30 keV ridge is however larger than expected. This effect is discussed in the framework of the fission-evaporation competition.

• Received 22 November 1994

DOI:https://doi.org/10.1103/PhysRevC.51.2385