Fusion measurements for the ${}^{18}$O+${}^{194}\mathrm{Pt}$ reaction and search for neutron shell closure effects

Abstract

Evaporation residue (ER) and fission cross sections were measured for the reaction O+ forming the compound nucleus 212Rn. Fission fragment angular distributions and anisotropies are consistent with the saddle point model predictions. Measured ER cross sections were fitted with statistical model calculations assuming shell-corrected free energy fission barrier height. The non-zero dissipation strength required to fit the ER cross section supports the dissipative nature of fission dynamics in heavy ion fusion. In the present study shell closure effects are not observed in the dissipation strength.

Investigating the fission dynamics of the following neutron shell closed nuclei within a stochastic dynamical approach: 210Po, 212Rn, and 213Fr*

“…Moreover, the obtained mass distribution of the fragments in the fission of Po [65,66] reaffirms the absence of any shell corrections for the potential energy surface at the saddle point. Rn [21,23,24,67] formed through the reaction O+ Pt, Fr formed through reactions F+ Pt [15,22,26,68] and O+ Au [5,6], and their non-shell closed isotopes Rn generated via the reaction O+ Pt [21,23,24,67] and Fr ) as functions of the excitation energy for the following reactions: C Pt, O Os, and C Pt. The continuous line (red) denotes the obtained results with a universal frictional form factor, and the dashed line (black) represents the statistical model calculations.…”

“…It 19 194,196,198 16 197 is to be noted that an energy dependent dissipation was used in Refs. [21,22] to describe the data for these reactions. We also adopted a similar approach by employing temperature-dependent friction (TDF) in the stochastic calculations [69] (without changing any other parameters).…”

“…Another interesting aspect is the contradictory interpretation of the correlation between the neutron shell structure and the nuclear dissipation strength required to reproduce the measured ER and excitation functions of the N 126 shell closed nuclei, namely Rn and Fr. A theoretical analysis of the data for Rn [21] and Fr [22] reported a low dissipation strength at 50 MeV, which was attributed to the influence of neutron shell closure. On the contrary, no discernible shell influence was reported by ER cross-section studies of Rn and its isotope [23], although moderate nuclear dissipation was required to describe the data.…”

Detailed statistical model analysis of observables from fusion-fission reactions

“…One can estimate the pre-scission dissipation coefficient from the analysis of light particle spectra and giant dipole resonance (GDR) γ -ray multiplicities [20][21][22][23][24]. But, to acquire a precise and reliable information about the pre-saddle dissipation coefficient, one must employ those experimental signatures which are uniquely sensitive to the pre-saddle regime only, such as σ ER [25] and ER spin distribution [26]. Different combinations of pre-saddle and saddle-to-scission dissipation coefficients enabled success in interpreting particle multiplicity data [21,22,24,27].…”

Alleviating the inconsistencies in modelling decay of fissile compound nuclei

“…One can estimate the pre-scission dissipation coefficient from the analysis of light particle spectra and giant dipole resonance (GDR) γ-ray multiplicities [20][21][22][23][24]. But, to acquire a precise and reliable information about the presaddle dissipation coefficient, one must employ those experimental signatures which are uniquely sensitive to the pre-saddle regime only, such as, σ ER [25] and ER spin distribution [26]. Different combinations of pre-saddle and saddle-to-scission dissipation coefficients succeeded in interpreting particle multiplicity data [21,22,24,27].…”