A study on the effect of neutron excess on compound and non-compound nuclear reaction cross sections at above barrier energies

Abstract

The excitation functions for the evaporation residues populated in the \(^{18}\)O + \(^{154}\)Sm system has been measured at above-barrier energies (\(\approx \) 3–6 MeV/nucleon) using offline \(\gamma \)-ray spectrometry. A comparison of these measured excitation functions with the statistical model code PACE-4 reveals the involvement of non-compound nuclear reactions in the population of some residues, particularly for those populated via \(\alpha \) emission channels. To further explore fusion dynamics, a systematic analysis was carried out using the Universal Fusion Function framework. This analysis included compound nuclear fusion cross sections for 25 different systems induced by \(^{12,13}\)C and \(^{16,18}\)O projectiles. The experimental observations reveal a more substantial suppression of CNF cross sections in \(^{18}\)O induced reactions as compared to those involving \(^{16}\)O. Conversely, a lesser degree of fusion suppression was observed for \(^{13}\)C projectile induced reactions, relative to those with \(^{12}\)C. Furthermore, significant variations in the \(\alpha \)-separation energy (\(\textrm{Q}_{\alpha }\)) were found to correlate with changes in the projectile’s neutron-to-proton (N/Z) ratio. These observations suggest that the presence of additional neutrons not only modifies the interaction potential but also affects the internal nuclear structure of the projectile. Such structural modifications appear to enhance the probability of non-compound nuclear reactions in \(^{18}\)O induced reactions as compare to \(^{13}\)C.