The Futher Study Of Nuclei's High Spin States And Superdeformation

The topic of superdeformation(SD) at high spin has been at the forefront of nuclear structure physics since the first superdeformed band in ¹⁵²Dy was observed by Twin et al in 1986.Recently,with the development in experiment and theory research in depth,nuclear physics has made a great progress in all aspects, and with the heavy-ion physics research being carried out,people have obtained a great many data in high-spin states,discovered deformed nuclei's band-back.Recentl years,SD has been discovered in different mass regions and extensively studied experimentally and theoretically.Up to now,some data for triaxial superdeformed nuclei are accumulated,and all of them are found in Lu, Hf,Ta,Er and Zr.Among the discovered nuclei,most of them are located in the A～190,160,150,130,80,60 regions.Many interesting phenomena are related to triaxiality,like signature inversion,signature splitting,chiral bands,the wobbling movement of nucear,etc.At present,nuclear triaxial superdeformation(TSD) has been one of the focus in nuclear physics.In this paper,firstly,we study the newly founded rotational band in ¹⁶⁰Yb nucleus.This band has both decay characteristics and high moment of inertia very similar to those observed as TSD candidate sequences in ^157,158Er.By using Total Routhian Surface(TRS) method the formation of the nucleus ¹⁶⁰Yb is studied.The result shows that the triaxial superdeformed state exists with deformation parametersε₂=0.38 andγ=21°,where proton shell correction energy plays a key role,and the sum of two quasi-proton particle energies gives an additional driving effect.The rotational energy also has an additional role to form triaxial superdeformed shape.The result is a good agreement with the TES calculation.Secondly,some new bands are found in ¹⁷⁴W nucleus,One of the new bands is studied.Samely,two-dimensional Total Routhian Surface calculation is carried out to determine the triaxial superdeformation of even-even nucleus ¹⁷⁴W,the result of which indicates that the TSD state exists with deformation parametersε₂=0.42 andγ=34.7°.In the same way,the authors also calculate the total routhian surface for nuclei ^172,176W,The calculation results indicate that the shell correction energy of neutron plays a key role in the formation of TSD even-even nuclei ^172,174,176W,the high j intruder orbital plays a crucial role to form TSD shape,the rotational energy also has an additional role to form TSD shape.Additionally,by another TRS method in the cranked Woods-Saxon potential, The nuclear shapes of ^187,189T1 are investigated theoretically in this work.The total routhian surface(TRS) calculations are performed for N=106 and 108 isotopes of thallium(Z=81),the calculated results show that oblate and prolate shapes coexist in ^187,189Tl nuclei in deferent rotational bands.The mechanism of coexistence is proposed.Finally,the Projected Shell Model is carried out to study the low energy scheme of the neutron-rich nomal-deformed isotopes of A～100 nuclei.The quasiparticle configuration is assigned.The calculation results are a good agreement with the experiment.It is shown that the Projected Shell Model is a valid method for studying the low energy scheme of heavy nuclei.