Speaker
Description
A comprehensive understanding of the heavy-ion (HI)–induced fusion–fission process is important for fundamental nuclear physics, superheavy element synthesis, astrophysical applications, and the production of medically relevant isotopes. Therefore, a systematic study of the fusion–fission mechanism is essential to understand the complex dynamical evolution of the composite system formed in heavy-ion–induced reactions.
An experiment has been performed for the $^{12}$C+$^{208}$Pb system at E$_{\rm lab}$ = 81.99 and 75.8 MeV using the 15UD Pelletron accelerator facilities at the Inter-University Accelerator Center, New Delhi. The primary objective of this study is to investigate various aspects of heavy-ion-induced fission resulting from the evolution of a composite system through complete and/or incomplete fusion in the reaction $^{12}$C + $^{208}$Pb. The preliminary identification of reaction products was done using characteristic $\gamma$ lines, which were further confirmed by the decay curve analysis. In this work, 25 fission fragments in the mass range 76$\leq$A$\leq$141 have been identified. The production cross-sections of fission fragments were measured to draw charge and mass distribution and analyzed to obtain the dispersion parameters of fission fragments. The values of charge dispersion parameters for Sb and In isotopes show good agreement with those reported in the literature for similar systems. The mass distribution of fission fragments is a crucial post-fission observable that offers insights into the collective dynamics and underlying mechanism of the fission process, reflecting the potential energy landscape of the fissioning nucleus. The observed mass distribution is Gaussian-like and fitted with a Gaussian function, suggesting that these fission fragments are formed through the compound nuclear process. The full width at half maximum (FWHM) of the mass distributions is found to be comparable to those reported for the $^{20}$Ne + $^{209}$Bi [1], $^{20}$Ne + $^{208}$Pb [2]. An increasing trend in mass variance ($\sigma^2_{M}$) is observed with increasing excitation energy [3], suggesting a wider distribution of the masses of the fission fragments at higher energies. This trend in mass variance with excitation energy aligns with previous findings by Ghosh et al.[4], at energies above the Coulomb barrier.
In order to understand the role of the entrance channel on the mass distribution of fission fragments, the effect of mass asymmetry on the mass variance ($\sigma_m^{2}$) has been studied. The mass variance of fission fragments for the different projectile-target combinations is investigated as a function of mass asymmetry ($\alpha$ = (M$_{\rm T}$--M$_{\rm P}$)/(M$_{\rm T}$+M$_{\rm P}$)). The systems $^{12}$C + $^{181}$Ta [5], $^{12}$C + $^{208}$Pb (Present work) and $^{11}$B + $^{232}$Th [6] are compared at a constant normalized energy (E/V$_b$ $\approx$ 1.3). The results indicate that there is a linear increase in $\sigma_m^{2}$ with increasing mass $\alpha$ of the entrance channel. The rise in mass variance with increasing mass asymmetry highlights the significant influence of entrance-channel parameters on the spread of the mass distribution.
Detailed results and analysis will be presented during the conference.