PRE-EQUILIBRIUM ALPHA-PARTICLE EMISSION AS A PROBE TO EXPLORE ALPHA CLUSTERING IN NUCLEI

Experimental data of the double-differential spectra of light particles emitted at pre- equilibrium stage of nuclear processes were obtained at Laboratori Nazionali di Legnaro for the heavy-ion reactions 130 and 250 MeV 16 O + 116 Sn. Light charged particles were measured in coincidence with evaporation residues in order to avoid unwanted competing mechanisms. The experimental data were collected in a wide angular range from 29 to 82 degrees in the laboratory system. Theoretical model was developed in order to describe simultaneously evaporative and pre-equilibrium emission of the light particles in heavy-ion reactions. Griffin exciton model was used for the description of the pre- equilibrium stage of the compound nucleus formation, while the equilibrium evaporation processes were analyzed in the framework of the statistical theory of heavy-ion reactions. Experimental data were compared with the results of the model calculations and new approach was suggested to take into account alpha cluster formation in the projectile nucleus by measuring and analyzing pre-equilibrium alpha-particle spectra.