Volume 201, number 2 PHYSICS LETTERSB 4 February 1988 OBSERVATION OF ENHANCED LOW-ENERGY CHARGED-PARTICLE EMISSION IN THE COLD FUSION REACTION 9°Zr+SgY U. GOLLERTHAN 1, H.-G. CLERC, E. HANELT, W. MORAWEK, V. NINOV, W. SCHWAB lnstitut fur Kernphysik, TechnischeHochschule Darmstadt, D-6100 Darmstadt, Fed. Reg. Germany K.-H. SCHMIDT, F.-P. HEBBERGER, G. MUNZENBERG, R.S. SIMON Gesellschaftfur Schwerionenforschung, D-6100Darmstadt, Fed. Rep. Gemany J.-P. DUFOUR 2 Centre d'Etudes Nucleaires de Bordeaux Gradignan, F-33170 Gradignan, France and M. MONTOYA 2 Universidad Nacional de Ingenieria, Lima, Peru Received 23 September 1987 Protons and a-particles emitted from the compound nucleus 179Au excited to 26 MeV were detected in coincidence with the corresponding evaporation residues. The charged-particlespectra are shifted to lowerenergies than spectra from statistical-model calculations based on a spherical compound nucleus. The investigation of the evolution of a system con- sisting initially of two touching nuclei to a compound system which then continues to evolve towards an evaporation residue or towards fission, is of great im- portance for the understanding of the collective be- haviour of nuclear matter. Recently, T-rays as well as light particles emitted during the deexcitation of the compound nuclei have been used to obtain informa- tion about the dynamics of the emitting system. The high-energy tail of the 3'-ray spectrum can be interpreted as arising from the giant dipole resonance built on excited nuclear states [ 1 ]. As is well known from the giant dipole resonance of the nuclear ground state of axially-symmetric deformed nuclei, the giant dipole resonance splits into two components. Re- cently, the 3'-ray spectra from several highly-excited This work forms part ofthe PhD thesis of U. Gollerthan. 2 On leave. 206 compound nuclei have been interpreted in terms of nuclear deformation [ 2-5 ]. Another very sensitive tool for the investigation of the dynamical evolution of the compound nucleus is light-particle emission. For example, the protons and a-particles emitted from the highly-excited com- pound nuclei 156Er*, t94Hg* and 237Bk* were found to have a much lower mean energy than predicted by a calculation based on the assumption that the emit- ting nucleus is spherical [ 6 ]. The conclusion from this is that the compound nucleus has a reduced Cou- lomb barrier for the emission of charged particles due to deformation. However, reduced Coulomb barriers do not seem to be restricted to compound nuclei with a high fission probability. Alexander and coworkers [ 7 ] found that empirical barriers for fusion induced by a-particles are consistently larger than the barriers deduced from a-particles from inclusive energy spec- tra measured for the corresponding evaporation pro- cess in many hot compound nuclei. More recently, 0370-2693/88/$ 03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)