Study Of Nuclear Yrast-state Collectivities In The Ytterbium Istopes

In recent years,due to the development of radioactive beam facilities and highly effective?-ray detector technology,not only can we obtain more information of nuclear spectrum,but also can more accurately describe the characteristics of high-spin states of nuclei.It also makes it possible for us to study the nucleus away from the?-stable line.On this basis,we have investigated the energy spectrum information of nucleus in the Yb isotope chain and found many interesting phenomena,such as backbending,band termination,shape transition,the neutron and proton alignments and so on.Based on the results of investigation,we investigate the collective properties along the yrast line of Yb isotopes based on the pairing-deformation self-consistent total-Routhian surface?TRS?method in three-dimensional deformation space??₂,?₄,??.The contents of this thesis are as follows:Firstly,The rotational bands of Yb nuclei are calculated systematically.Including the moment of inertia,angular momentum,deformation parameters,potential energy curves and so on.we reproduce the phenomenon of the backbending of the moment of inertia in the experiment,and by using the calculation of the aligned angular momentum,it is shown that the reason for the backbending is the effect of proton or neutron alignments.Then we calculated the?₂,?deformation parameters and potential energy curves of ground state and cranking state,summarized the nuclear deformation.Secondly,we study the rotational properties in well-deformed nuclei ^164-178Yb based on some phenomenological quantities,e.g.,the P factors and the R_4/2/2 ratios,E_S/E₂₊and so on.The evolution of collective motion modes along the yrast line are investigated using our developed Centipede-like E-GOS?E-gamma over spin?curve,indicating the possible effect of the vibration-rotational coupling.One can see that the signature of transition from rotation to?-soft or from vibration to rotation appears in^164-178Yb,and Considering the vibration-rotational coupling,to same extent,we can predict the evolution of the collective motion modes more accurate.In the end,the shape evolution of the ^164-178Yb nuclei is analyzed.The shape evolution of nuclei is studied by the calculation of directional potential energy surface and the calculation of wobbling parameters.It is found that these nuclei have prolate deformation at ground state,and the shape evolution from prolate to oblate exists in the ¹⁷⁸Yb nucleus with the change of the rotation frequency.