Studies On Synthesis Mechanism Of Proton-rich Heavy Nuclei

Production of new nuclides is motivated by extending the nuclear chart,the synthesis of proton-rich heavy nuclei attracted much attention.There are three stages in understanding the heavy ion fusion-evaporation reactions,namely,the capture process of the colliding system to overcome Coulomb barrier;the formation of the compound nucleus to pass over the inner fusion barrier;the de-excitation of the excited compound nucleus against fission,this thesis focus on studying the survival stage.The main content of this thesis contains two parts.Firstly within the Weisskof evaporation theory and Fermi gas model,a statistical approach has been developed to describe the de-excitation process of highly excited heavy and superheavy nuclei,in particular for the excited protonrich nuclei including charged particles?p,d,??emission.Secondly within the framework of dinuclear system model and improved statistical approach,production mechanism of proton-rich nuclei with charged numbers Z=84-90 are investigated systematically.To describe the survival process of proton-rich heavy nuclei produced by heavy ion fusion-evaporation reactions,within the Weisskof evaporation theory and Fermi gas model,a statistical approach has been developed,charged particles?p,d,??emission included,comparing neutron emission,charged particles emission need considering coulomb barrier transition,also the structure effects?shell correction,fission barrier,particle separation energy?contribution to the de-excitation processes.The available data of fusion-evaporation excitation functions in the²⁸Si +¹⁹⁸Pt reaction can be reproduced nicely as a test of the model.The charged particle channels play significant contributions for residual nuclei.To study synthesis mechanism of proton-rich heavy nuclei,within the framework of the dinuclear system model,production cross sections of protonrich nuclei with charged numbers Z=84-90 are investigated systematically.Possible combinations with the²⁸Si,³²S,⁴⁰Ar bombarding the target nuclides ¹⁶⁵Ho,¹⁶⁹Tm,^170-174Yb,^175,176Lu,^174,176-180Hf and ¹⁸¹Ta are analyzed thoroughly.The optimal excitation energies and evaporation channels are proposed to produce the proton-rich nuclei.It is found that the neutron shell closure of N = 126 is of importance during the evaporation of neutrons;the experimental excitation functions in the⁴⁰Ar induced reactions can be nicely reproduced;the charged particle evaporation is comparable with neutrons in cooling the excited protonrich nuclei,in particular for the channels with ? and proton evaporation;the production cross section increases with the mass asymmetry of colliding systems because of the decrease of the inner fusion barrier;the channels with pure neutron evaporation depend on the isotopic targets,but it is different for the channels with charged particles and more sensitive to the odd-even effect.