Decay mechanism of the204Po*nucleus formed in16O and28Si induced reactions

Abstract

The basic aim of the present study is to investigate the role of deformations, orientations, angular momentum dependence along with possible presence of noncompound nucleus (nCN) component in the decay of preactinide nucleus ${}^{204}$Po${}^{*}$ formed in ${}^{16}$O and ${}^{28}$Si induced reactions over a wide range of projectile energies having comparable ${E}_{\mathrm{c}.\mathrm{m}.}/{V}_{c}$ values for two channels. Recently, an experiment was performed to extract fusion-fission and evaporation residue cross sections for ${}^{16}$O + ${}^{188}$O $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ and ${}^{28}$Si + ${}^{176}$Yb $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ reactions over a wide range of energies (${E}_{\mathrm{lab}}=84$--155 MeV). Within the dynamical cluster decay model (DCM), we have calculated the evaporation residue and the fission cross sections in reference to the available data at various incident energies by simultaneously fitting the only parameter, neck-length ($\ensuremath{\Delta}R$) for evaporation residue and fission. The choice of different neck-length parameter ($\ensuremath{\Delta}R$) values for ER and fission indicate that the two decay processes do not occur simultaneously, i.e., they occur in different time scales and evolve subject to the nature of dynamics of compound nucleus formed. The effects of nuclear deformations and orientations are duely incorporated in the framework of DCM and role of ${\ensuremath{\beta}}_{2}$ deformations is investigated in reference to decay path of ${}^{204}$Po${}^{*}$ nucleus. The calculated evaporation residue cross sections and fission cross sections show excellent agreement with the reported data at all incident center of mass energies, except at one highest energy for the channel ${}^{28}$Si + ${}^{176}$Yb $\ensuremath{\rightarrow}$ ${}^{204}$Po${}^{*}$ for fission. The disagreement between DCM calculations and reported data at highest incident center of mass energy for the ${}^{28}$Si + ${}^{176}$Yb entrance channel may be associated with the presence of small amount of nCN effects which is in line with the predictions of the preequilibrium model. Also the in-built property of barrier lowering effect of DCM seems to be operating in context of these reactions. The fission fragment anisotropies are also calculated using DCM-based parameters for the nonsticking moment of inertia, and they find reasonable comparison with experimental data. Finally, the isotopic effect is worked out by studying the decay of ${}^{202}$Po${}^{*}$ and ${}^{204}$Po${}^{*}$ nuclei formed in ${}^{16}$O induced reactions at comparable ${E}_{\mathrm{c}.\mathrm{m}.}/{V}_{c}$ value.