Background: The synthesis of super heavy elements (SHE) is governed by two major competing processes: quasifission (QF) and fusion-fission (FF). Optimizing SHE production requires an extensive understanding of these processes. The dynamics of QF and FF are being studied experimentally worldwide, with special attention to the quantification of QF. The limited availability of robust theoretical models suggests that achieving higher predictive accuracy necessitates careful benchmarking of the developed models against experimental observations.

Purpose: The present study seeks to identify QF signatures in the fission of ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$ at excitation energies around the Coulomb barrier. Furthermore, this study intends to quantify the contribution of QF to total fission events and to compare it with the predictions by the DiNuclear System (DNS) model.

Methods: In the experiment, a pulsed heavy-ion beam around the Coulomb barrier energy was utilized, and the resulting binary fragments were detected using two position-sensitive multiwire proportional counters (MWPCs). By analyzing the time-of-flight (TOF) differences and position information of the binary fragments, mass and total kinetic energy (TKE) distributions were obtained for the reaction ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$.

Results: The experimental results showed no significant correlation between fragment mass and angle. The mass-TKE correlation, in contrast, exhibits a deviation from that prediction by the Liquid Drop Model (LDM). The contributions of QF were quantified as 22%, 12%, and 8% at excitation energies of 52.4, 59.1, and 62.4 MeV, respectively, as determined from mass and energy distribution analysis. These findings were found to be consistent with the DNS model's predictions.

Conclusion: Compelling evidence for slow quasifission is observed in the reaction ${}^{35}\mathrm{Cl}+{}^{181}\mathrm{Ta}$. The present analysis indicates that the average TKE and its variance offer the signature of slow quasifission.

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• Fission
• Low & intermediate energy heavy-ion reactions
• Nuclear reactions
• 190 ≤ A ≤ 219