Evaporation Residue Production in Complete and Incomplete Fusion Reactions of Ne-20 with Au-197 and Ho-165 at E = 14.9 x AMeV

Abstract

Velocity distributions of heavy residues (Ares > Atar), produced in irradiations of 197 Au and 165 Ho with 20 Ne at bombarding energies of E = 208 MeV, have been measured at the velocity filter SHIP. While for the products from 20 Ne + 165 Ho just a mean value of v/vCN = 0.91±0.01 was obtained, individual residues, attributed to isotopes of astatine and polonium with mass numbers ranging from A = 195 to A = 203 could be identified by means of α spectroscopy in the bombardments of 197 Au. A linear increase of the mean velocity from v/vCN ≈ 0.85 to v/vCN ≈ 0.93 with decreasing residue mass was observed. This effect was attributed to an increasing contribution of pre-equilibrium particle emission to the production of heavy residues. A quantititative estimation resulted in a 90% contribution of preequilibrium processes to the production of astatine isotopes, and a 50% contribution to the polonium isotopes.