Theoretical Studies Of Superheavy Nuclei Synthesis And Decay Properties

The superheavy nuclear production mechanism can be described by fusion reactions with the dinuclear system conception, and in the conception the deformations of the two nuclei are always assumed to stay at their ground state,and there are nucleons transferring between them. Actually the two nuclei have to deform due to very strong nuclear and Coulomb interactions between them.These deformations can be described by a Fokker-Planck equation analytically,and by combining them with a master equation, which describes the nucleon transfer between nuclei, the superheavy nuclear production cross sections are investigated systematically. The calculated results are in good agreement with available data, and the evaporation residue cross sections(ERCS)for synthesizing the superheavy nuclei(SHN) Z=119 and 120 are predicted. Actinide nuclei often have considerable hexadecapole deformation in addition to the quadrupole deformation, which is not considered in former theoretical study. With the dinuclear system concept, and by taking the hexadecupole deformation in to consideration in addition to the quadrupole deformation, the hot fusion probability leading to the synthesis of SHN is investigated systematically. Many theories are being carried out to understand the synthesizing mechanism of SHN. However, all of them have to use some basic nuclear data. Three data tables: FRDM1995(At. Data Nucl. Data Tables 59, 185(1995)), KTUY2005(Prog. Theor.Phys, 113,305(2005)) and WS2010(Phys. Rev. C 82, 044304(2010)) are used to investigate the SHN production.The dependence of the evaporation residue cross section(ERCS) to produce superheavy nuclei(SHN) on the isospin of colliding nuclei is analysed within the dinuclear system(DNS) concept. The ERCSs are discussed in detail and compared with existing experimental data. The fusion probabilities and surviving probabilities depend sensitively on the neutron numbers of the target and projectile nuclei. The prospects for the synthesis of superheavy nuclei(SHN)using radioactive beams are evaluated quantitatively within the framework of a dinuclear system(DNS) concept. In the most of cases the intensities of radioactive beams are significantly less than those of the stable beams, therefore using stable beam is predicted to be the most favorable method for producing SHN. In order to find a way which to produce superheavy nuclei(SHN), which appear in the gap between the SHN synthesized by cold fusion and those by hot fusion, or those so far have not yet been produced in the laboratory, we tried to make use of a set of projectile isotopic chain, to use radioactive beam projectile,and to test symmetric fusion reactions for gaining more neutrons to synthesize neutron richer SHN based on the DNS model via cold fusion reactions.The α-decay half-lives of recently synthesized superheavy nuclei(SHN)are investigated by employing a unified fission model(UFM), by a generalized liquid drop model(GLDM), the analytical formula of Royer [J. Phys. G: Nucl.Part. Phys. 26, 1149(2000)] and universal decay law(UDL). The good agreement with the experimental data indicates the UFM, GLDM and the analytical formula are useful tools to investigate these α-decays.We systematically calculate the spontaneous fission half-lives for heavy and spuerheavy nuclei between U and Z=114 isotopes. The results reproduce experimental data rather well. Relatively long half-lives are predicted for many unknown nuclei, sufficient to detect them if synthesized in a laboratory. A modified formula is proposed for determining the spontaneous fission half-lives based on Swiatecki’s formula, including the microscopic shell correction and isospin effect.The spontaneous fission half-lives for heavy and SHN in regions from Th and Fl are calculated systematically. Experimental data are well reproduced by the modified Swiatecki’s formula. The competition between α-decay and spontaneous fission is analyzed in detail and the decay modes are predicted for the unknown cases.We systematically investigate the branching ratios of the cluster radioactivity with respect to α-decay for even-even superheavy nuclei(SHN) with Z=104-120 using UDL formula. It is found that the cluster radioactivity can be compared to α-decay in neutron-rich SHN region.