Studying fusion reactions for effect of PCN on heavy nucleus formation and for nuclear structure effects

Abstract

The fusion reaction ²⁰⁸Pb (⁵⁰Ti, xn) ²⁵⁸⁻ x Rf (x = 1-3) was studied to determine PCN (probability that the mononucleus system evolves to form a compound nucleus inside the fission saddle point) and to establish the value of Wsur (survival probability) for the given reaction experimentally. The fission excitation function was measured at five beam energies. Angular distributions were fit using the Back et al. prescription to determine JCN and σCN. The total fission cross section (σfis) and compound nucleus cross section (σCN) at each of the energies were used for calculating PCN. These experimentally determined values of PCN and σfis and the values of σEVR determined in previous studies of this system were used in the equation σEVR = σc x PCN × Wsur to arrive at Wsur for each of the energies. The experimental value of Wsur for 1n channel agrees very well with the one based on theoretical predictions of Möller et al. The subsequent lowering in Wsur with beam energy is attributed to onset of 2n and 3n evaporation channels. The fusion reaction ⁹Li+ ⁷⁰Zn was studied to determine the effects of nuclear structure of the projectile (neutron skin) on fusion. The fusion excitation function was measured at seven near- and sub-barrier beam energies. Radioactivity in the irradiated target was measured by γ-spectroscopy and in radiochemically separated EVRs by β-spectroscopy. The ⁹Li fusion radius determined by fitting the excitation function with Wong formula was 12.1 ± 1.0fm, much larger than 2.5fm given by R₀xA¹/³. This extension of the radius is attributed to the presence of spatially extended neutron skin. The excitation function also showed a large sub-barrier fusion enhancement not explained by standard coupled channel model. An attempt was made at measuring the fusion excitation function with ¹¹Li projectile (neutron halo nucleus) which would enable us to do a comparative study as ⁹Li is the core of ¹¹Li halo nucleus but it failed due to low beam intensity.