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The difference between observed cross sections of the evaporation residues for the reactions $^{34}{\rm S}+{}^{208}$Pb and $^{36}{\rm S}+{}^{206}$Pb [1] has been studied by the dynamical calculation of the capture probability and statistical calculation of the fusion probability in framework of the dinuclear system model [2].
The results of calculations show that the capture probability in the reaction with $^{36}$S is larger in comparison with the one on reaction with ${}^{34}$S since the nucleus-nucleus interaction of nuclei is more attractive in the $^{36}{\rm S}+{}^{206}$Pb reaction. The larger value of the N/Z -ratio in the projectile-like fragments of the DNS formed in the $^{36}{\rm S}+{}^{206}$Pb reaction decreases hindrance to complete fusion in this reaction in comparison with the $^{34}{\rm S}+{}^{208}$Pb reaction due to the decrease of the intrinsic fusion barrier in the first reaction. As a result the fusion probability PCN [2] calculated for the $^{36}{\rm S}+{}^{206}$Pb reaction is significantly larger than the one obtained for the $^{34}{\rm S}+{}^{208}$Pb reaction.
The similar dependence of the behavior of the fusion probabilities on the mass number of the projectile-nucleus obtained in our recent calculations for the $^{35}{\rm Cl}+{}^{181}$Ta and $^{37}{\rm Cl}+{}^{181}$Ta reactions. Conclusion is that the large difference between the experimental data of the evaporation residue cross sections of $^{34}{\rm S}+{}^{208}$Pb and $^{36}{\rm S}+{}^{206}$Pb reactions [1] is explained by the larger number events of capture leading to the formation DNS and by the larger fusion probability of DNS formed in the latter reaction in comparison with the ones calculated for the former reaction. Certainly, the deexcitation of a large number of intermediate excited evaporation nuclei leads to the increase the yield of the evaporation residues in the 36S+206Pb reaction.
[1] J. Khuyagbaatar et al, Phys. Rev. C 86, 064602 (2012).
[2] K.Kim, Y.Kim, A.K. Nasirov, G. Mandaglio, G. Giardina, Phys. Rev. C 91, 064608 (2015).
