Theoretical Study On Probing Nuclear Shell Structure In The Superheavy Region Using Nuclear Dissipation

The nuclear shell model has always been a valuable theoretical tool for humans to investigate the microscopic world,since it is based on an explanation of the phenomenon of the magic number experiment.The center position of the superheavy element stability island,according to the macroscopic-microscopic model,lies around the double magic nucleus of Z=114 and N=184,while Z=108 and N=152 and 162 are plausible new magic numbers.Furthermore,other experimental data suggest that Z=108 and N=162 are deformed sub shells,and that there are a number of relatively stable deformed superheavy nuclei in the vicinity.Obviously,the nuclear shell effect is a significant factor to be taken into account when one studies the production of superheavy elements using the fusion-evaporation reaction.To date,the most potently nuclear reaction mechanism for the synthesis of new superheavy nucleus still is the fusion-evaporation reaction.The survival probability and evaporation residual cross section of compound nuclei in fusion-evaporation reactions are directly affected by the nuclear dissipation and the nuclear level density parameters,which are also essential inputs in the de-excitation stage of superheavy compound nuclei.Furthermore,it is worth to point out that the damping effect of nuclear dissipation during the whole deexcitation phase of the superheavy compound nuclei is consistent with the damping phenomenon due to the presence of nuclear shell effect.So,one can extract the nuclear structural information near the proton shell closure or the neutron subshell closure regions.In order to extract the structural information of the neutron subshell closure in the superheavy region,we respectively choose twenty-nine cold fusion channels and fourteen hot fusion channels of superheavy elements with Z=104?108 and Z=110.Furthermore,we choose five kinds of different strengths of nuclear dissipation and two kinds of level density parameters in the numerical calculations.The calculation results of cold fusion reactions show that the evaporation residual cross section of superheavy compound nuclei increases with the increasing of the strength of nuclear dissipation.In addition,the shell effect manifested primarily in the1n de-excitation channel.The strength of nuclear dissipation at the neutron subshells of N=152 and N=162 needs to be significantly get enlarged in order to properly reproduce the experimental data.The strength of nuclear dissipation in the higher energy regions is 7?8 times higher than that of its adjacent isotope reaction channels under the same conditions;however,the strength of nuclear dissipation in non-neutron subshells is weak,and the gap between different isotopic reaction channels is not obvious.The strength of nuclear dissipation for the4n deexcitation channel is much larger than that of its isotope around neutron N=162,which indicating a closed shell effect,according to the calculation results of hot fusion reactions.In order to get the structural information of the proton full shell closure in the superheavy region,we chose seven reaction channels for the synthesis of ₁₀₆Sg,₁₀₈Hs,₁₁₂Cn,₁₁₄Fl and ₁₁₆Lv to carry out numerical calculations.The numerical results about 3n and 4n evaporation channels show that the evaporation residual cross sections increase with the increasing of nuclear dissipation strength.The strength of nuclear dissipation at the proton shell falls from Z=114to both sides,and it is highest at Z=114.Fission is delayed with the increasing of strength of nuclear dissipation,the survival probabilities of compound nuclei raise,hence the evaporation residual cross-sections get rise,all of which is due to the effect of proton shell closure,which improves the stability of overweight composite nuclei.The aforementioned criteria propose a possible nuclear reaction probe to extract the structural information of superheavy nuclei.