Systematic Study On Survival Probability And Fusion Probability In New Nuclide Synthesis Mechanism

In recent years,the synthesis of new nuclides based on heavy ion fusion evaporation reaction has become an important research field of nuclear physics,and it can be theoretically decomposed into three processes according to the physical characteristics of the synthesis mechanism:capture process,fusion process,and survival process.the capture process described by the empirical coupled-channel model can basically reproduce the experimental values of capture cross sections well.The fusion process lacks relevant information in experiment,and is currently vaguest stage of theoretical understanding.The survival process is particularly sensitive to the nuclear structure information,which makes the survival probability estimated by statistical models has great uncertainty.That is to say,the fusion probability and survival probability are indispensable and important influencing factors to describe the fusion reaction process reasonably.The deexcitation process of compound nucleus is not only significantly affected by the nuclear structure effect(fission barrier height,neutron separation energy,shell effect),but also involves many approximations.Therefore,it is necessary to select reasonable input parameters to optimize the method of calculating the survival probability.In this paper,the influence of the survival probability of some superasymmetric(The fusion probabilities P_CN?1)reaction systems on the evaporation residual cross section has been systematically studied by considering two different approaches of shell effect washing out with excitation energy.Through systematic theoretical research,we find that the formation cross sections obtained by two possible methods do not significantly change with the input parameters in the heavy nuclei region,while it is sensitive to the relevant parameters in the superheavy nuclei region.However,due to the existence of a large number of adjustable parameters and assumptions,it is difficult to draw a conclusion that which approximate method is superior in estimating the survival probability.In addition,the dependence of the formation cross section on the isotope of the projectile and target nucleus was studied.The results show that if the structure effect and odd-even effect are not taken into account,then the formation cross section increases with the increase of the neutrons numbers of the projectile and target nuclei.The collision nuclei from contact to form the compound nucleus is a complex transport process,in which the coupling of multiple degrees of freedom and multiple reaction channels makes it more difficult to describe the dynamic evolution of the system states in the fusion process.Similarly,based on two approximate methods,the influence of fusion probability on the evaporation residual cross section has been systematically studied in the fusion reaction induced by⁴⁸Ca.One is numerically solving the master equation based on the dinuclear system modelto to estimate fusion probability,the other is proposing an analytical expression based on some empirical relations and related parameters(incident channel characteristics,quasi-fission,fusion fission,etc.).It is observed from the comparative results that the formation cross sections calculated by the analytical expression is significantly higher than that calculated by the dinuclear system model,but the theoretical results calculated by the latter are in better agreement with the experimental values of the formation cross sections of the superheavy nuclei.In addition,the formation cross of the 3n and 4n evaporation channels varies with the neutron numbers of the target nuclei is systematically analysed in the⁴⁸Ca induced target nucleus Yb,Hf,W,Os,Pt,Ra,Th,U,Pu,Cm and Cf isotope reaction system.The results show that the formation cross sections are significantly dependent on the target isotopes for most reaction system,and the more neutron-rich the target nuclei,the larger the formation cross section.