Investigation of various decay mechanisms for Th*216 following the S32+W184 reaction in the range Ec.m.=118–196 MeV

Abstract

Various decay possibilities of the $^{216}\mathrm{Th}^{*}$ nuclear system formed via interaction of a $^{32}\mathrm{S}$ projectile on a $^{184}\mathrm{W}$ target are investigated within the collective clusterization approach of the dynamical cluster-decay model (DCM). The study is carried out at center-of-mass energies spread across the Coulomb barrier ($118.8\ensuremath{\le}{E}_{\mathrm{c}.\mathrm{m}.}\ensuremath{\le}195.9\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$) by including the quadrupole deformations (${\ensuremath{\beta}}_{2}$ static) and optimum orientations (${\ensuremath{\theta}}_{i}^{\mathrm{opt}.}$) of the decay fragments. According to experimental observation, the noncompound nucleus (nCN) component competes with the compound nucleus (CN) processes [evaporation residue (ER) and fusion-fission (ff)]. The anomalous behavior of calculated fission anisotropies ($A$) for the $^{216}\mathrm{Th}^{*}$ nucleus indicates the presence of nCN contributions, such as quasifission (QF) and fast fission (FF). With an aim to have comprehensive analysis of CN and nCN fission mechanisms (ff, QF, FF), the role of center-of-mass energy (${E}_{\mathrm{c}.\mathrm{m}.}$) and angular momentum ($\ensuremath{\ell}$) is explored in terms of various observables of DCM such as fragmentation potential, preformation probability, scattering potential, and penetrability. The fragmentation potential of the $^{216}\mathrm{Th}^{*}$ nucleus shows asymmetric fission mass distribution, independent of ${E}_{\mathrm{c}.\mathrm{m}.}$ and $\ensuremath{\ell}$ values. The capture excitation functions ${\ensuremath{\sigma}}_{\text{Cap.}}$ are obtained by adding the DCM-calculated CN (${\ensuremath{\sigma}}_{\mathrm{CN}}={\ensuremath{\sigma}}_{\mathrm{ER}}+{\ensuremath{\sigma}}_{\mathrm{ff}}$) and nCN (${\ensuremath{\sigma}}_{\mathrm{nCN}}={\ensuremath{\sigma}}_{\mathrm{QF}}+{\ensuremath{\sigma}}_{\mathrm{FF}}$) contributions. The calculated cross sections find nice agreement with the experimental data, and the evaporation residue contribution is predicted to be negligibly small. The compound nucleus fusion/formation probability ${P}_{\mathrm{CN}}$ is estimated as a function of ${E}_{\mathrm{c}.\mathrm{m}.}$, which in turn suggests that the maximum contribution from the CN channel is $\ensuremath{\approx}66%$. Finally, the effect of ${\ensuremath{\beta}}_{2}$-dynamic deformations on the various decay mechanisms of the $^{216}\mathrm{Th}^{*}$ nucleus is explored at highest center-of-mass energy (195.9 MeV), where nCN processes start competing with the CN decay mechanism.