Entrance channel effects well above the Coulomb barrier energies

Quasi fission and fusion fission are two competing phenomena affecting the formation probability of Heavy Elements (HE) and Super Heavy Elements (SHE). In order to study these two competing phenomena in detail, both experimentally and theoretically, studies are being conducted worldwide. The factors governing the phenomena is the entrance channel of the reaction, namely the entrance channel mass asymmetry α, defined as (A_T-A_p)/(A_T+A_p) (A_p, A_T being the projectile and target mass, respectively), the charge product of the target and projectile combination (Z_pZ_t) and deformations of the target and projectile. In the conference, I will present the result of our recent experiment carried out at VECC cyclotron to study the fission fragment mass distribution of compound nucleus (CN) ²²⁵Pa populated by reactions ²⁰Ne + ²⁰⁵TI and ¹⁶O + ²⁰⁹Bi that have entrance channel mass asymmetry on either side of the Businaro Gallone mass asymmetry. As the beam energies were chosen well above the Coulomb barrier, the effect of target deformation on the fusion fission dynamics was minimal. Mass distribution of the fission fragments were calculated from the measured time of flight difference between the correlated fragments detected with two large area Multi-wire Proportional Counters. Comparison of the measured variances of the mass distribution at similar excitation energies allows to decipher the role of entrance channel mass asymmetry on the fusion fission dynamics of pre-actinides. (author)