Entrance channel effects on the evaporation residue yields in reactions leading to the $^{220}$Th compound nucleus

TL;DR

This paper investigates how entrance channel properties influence evaporation residue yields in reactions forming $^{220}$Th, using models to analyze the stages of compound nucleus formation and survival, highlighting the effects of angular momentum and reaction asymmetry.

Contribution

It introduces a detailed analysis of entrance channel effects on evaporation residue yields using combined DNS and statistical models, emphasizing the role of angular momentum and fusion hindrance.

Findings

Largest ER yield in $^{16}$O+$^{204}$Pb due to high fusion probability

ER yields decrease with higher excitation energy thresholds

Fusion hindrance explained by increased quasifission at higher angular momentum

Abstract

The evaporation residue yields from compound nuclei $^{220}$Th formed in the $^{16}$O+$^{204}$Pb, $^{40}$Ar+$^{180}$Hf, $^{82}$Se+$^{138}$Ba, $^{124}$Sn+$^{96}$Zr reactions are analyzed to study the entrance channel effects by comparison of the capture, fusion and evaporation residue cross sections calculated by the combined dinuclear system (DNS) and advanced statistical models. The difference between evaporation residue (ER) cross sections can be related to the stages of compound nucleus formation or/and at its surviving against fission. The sensitivity of the both stages in the evolution of DNS up to the evaporation residue formation to the angular momentum of DNS is studied. The difference between fusion excitation functions are explained by the hindrance to complete fusion due to the larger intrinsic fusion barrier $B^*_{\rm fus}$ for the transformation of the DNS into a compound nucleus and the increase of the quasifission contribution due to the decreasing of quasifission barrier $B_{\rm qf}$ as a function of the angular momentum. The largest value of the ER residue yields in the very mass asymmetric $^{16}$O+$^{204}$Pb reaction is related to the large fusion probability and to the relatively low threshold of the excitation energy of the compound nucleus. Due to the large threshold of the excitation energy (35 MeV) of the $^{40}$Ar+$^{180}$Hf reaction, it produces less the ER yields than the almost mass symmetric $^{82}$Se+$^{138}$Ba reaction having the lowest threshold value (12 MeV).