A Systematic Study of Excitation Functions of Various Evaporation Residues in Heavy Ion Reactions at Moderate Excitation Energy: Incomplete Fusion vs. Complete Fusion

Abstract

Present work is an attempt to exclusively measure and study the excitation functions (EFs) of evaporation residues populated in ¹²C and ¹⁵⁹Tb system at energies ≈4.5–6.5 MeV/nucleon. The stacked foil activation technique followed by offline γ-ray spectroscopy with a high-resolution HPGe detector has been employed. The experimentally measured excitation functions are compared with the theoretical predictions obtained from statistical model code PACE-4. For $xn$ and/or $pxn$ channels, the experimentally measured excitation functions are found to be in good agreement with theoretical predictions. However, in case of α emitting-channels, the measured EFs had significantly more production cross-section values than PACE‑4 predicated values. This enhancement in the cross-section values for these reaction channels gives clear indication of incomplete fusion of the projectile with the target. To compare the relative contributions of complete and incomplete fusion and perceive the effect of entrance channel parameters on the onset and strength of incomplete fusion, an attempt was made to estimate the incomplete fusion fraction. The incomplete fusion fraction was found to be sensitive to the projectile energy and mass asymmetry of the entrance channel. The existence of incomplete-fusion below critical angular momentum (${{\ell }_{{{\text{crit}}}}}$), i.e., $\ell \leqslant {{\ell }_{{{\text{crit}}}}}$, has also been observed for this system.