NUCLEAR PHYSICS A H +%:v~l~ Nuclear Physics A583 (1995) 215-220 Proton spectra in coincidence with super- and hyper-deformed structures in 152Dy. M. Lunardon", G. Viesti ~, D. Bazzacco~, R. Burch", D. Fabris a, S. Lunardi ~, N. Medina ~, G. Nebbia ~, C. Rossi-Alvarez~, G. de Angelis 6, M. De Poli 6, E. Fioretto b, G. Preter', J. Rico ~, P. Spolaore r', G. Vedovatob, A. Brondi c, G. La Rana c, R. Moro c and E. Vardaci% I.N.F.N. and Dipartimento di Fisica dell'Universit£ di Padova, 1-35131 Padova, Italy b I.N.F.N. Laboratori Nazionali di Legnaro, 1-35020 Legnaro ( Padova ), Italy c I.N.F.N. and Dipartimento di Scienze Fisiche dell'Universit~ di Napoli, 1-80125 Napoli, Italy The hyperdeformed ridge structure recently observed in the reaction of 187 MeV 3TC1on 12°Sn has been confirmed in a new proton-*/coincidence experiment at the GASP spectrometer and assigned to the nucleus 152Dy. Proton spectra have been measured in coincidence with 7-rays belongings to the different structures in l~2Dy (oblate, prolate, super- and hyper-deformed). The deformation of the final evaporation residue affects only weakly the proton evaporation from the compound nucleus. Evidence has been found that the energy of the protons in coincidence with the hyperdeformed structure is larger than expected. This effect is discussed in the framework of the fission-evaporation competition. 1. INTRODUCTION Rotational bands in nuclei built upon hyperdeformed (HD) shapes (axis ratios 3:1) are predicted at very high angular momenta ( I> 70 h) by theories which successfully explained the occurrence of superdeformed (SD) nuclear states and their properties [1,2]. The chances to experimentally observe these shapes are very low since fission is the dominant channel at those angular momenta. The first experimental signature for hyperdeformation was the observation of a ridge structure in a 7-7 coincidence matrix in the reaction 187 MeV 3?C1 + 12°Sn [3]. In that experiment the separation of the ridges from the diagonal was measured to be AE~= E-¢1 - E72 = -4- 30 :t: 3 keV which corresponds to a dynamical moment of inertia j2~ 130 h 2 MeV -1. The ridges at =1=30keV have been observed only when a coincidence with a proton was required. A cascade of 10 discrete lines with an average energy spacing of 30 keV was also proposed. This first experiment could not be conclusive for the assignment of the HD structure to a specific nucleus although the choice was limited to 152Dy or 15ZDy. We report here the results of a new proton-gamma coincidence experiment performed at the GASP spectrometer with the goal of confirming the earlier observation. Furthermore the average energy of the protons emitted in coincidence with the hyperdeformed structures has been measured and compared with that relative to other shapes in the residual nuclei. 0375-9474/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved. SSDI 0375-9474(94)00661-X