Mass and mass resolved angular distribution of the fission products have been measured in the ${}^{20}\mathrm{Ne}+{}^{181}\mathrm{Ta}$ reaction at $E_{\mathrm{lab}}=150$ and 180 MeV using recoil catcher technique followed by off-line $\gamma$-ray spectrometry. Recoil range distribution (RRD) of the evaporation residues (ERs) have been measured at $E_{\mathrm{lab}}=180$ MeV. Due to high angular momentum of the fissioning nucleus, variances of the mass distribution in the present system have been found to be higher than those in similar systems involving comparatively less angular momentum. Significant contribution from noncompound nucleus processes such as deep inelastic collisions (DIC) and incomplete fusion reaction (ICF) is expected in the present system due to high angular momentum. The code HICOL predicts that the noncompound nucleus process would result in fission like events. In the present study, experimental fission cross sections are in reasonably good agreement with the calculation of statistical model code PACE2. Measurement of the ER cross section indicates significant contribution from the ICF reaction. The recoil range distributions of the ERs could resolve the complete fusion (CF) and ICF channels and were used to obtain ICF cross section. The experimentally measured ICF cross section accounts for almost entire cross section between $l_{\mathrm{crit}}$ and $l_{\max }$, indicating ICF reaction to be the dominant non-compound nucleus process at beam energies of the present study. DIC products could not be detected at both the beam energies. At these beam energies, the entrance channel pocket configuration for many collision trajectories is expected to be more elongated compared to the unconditional saddle point and, therefore, significant contribution form noncompound nucleus fission (i.e., fission without passing through the unconditional saddle point) is expected. However, the experimental anisotropies of fission products could be reproduced by the statistical theory calculation after considering the change in the saddle point shape with angular momentum of the fissioning nucleus. No correlation between the angular anisotropy and mass asymmetry of the fission products was observed in the present study.

• Received 28 March 2006

DOI:https://doi.org/10.1103/PhysRevC.74.014610