Microscopic study of triaxial deformation and non-principal-axis rotation in rapidly rotating nuclei

最近的实验数据表明，在Yrast态附近出现了一种有趣的三轴形变现象，即核平均场的三个主轴长度都不相同。本文以三轴变形为关键词，对三轴性引起的新的非主轴转动的产生机理进行了新的探讨，在近两年的研究中，我们取得了一些重要的成果，但仍有一些工作有待完成。特别地，关于倾斜角的集体自由度的量子力学方程的求解的主题尚未完成。1）利用斜轴推转方法研究了强耦合转动单准粒子带，该带是基于相对于对称轴具有高角动量分量的轨道.结果表明，考虑四极剩余相互作用，特别是它的K=1分量，很好地解决了低估起始倾斜点角频率的问题。2）用无规相位近似方法研究了Hf，Lu核三轴超形变带激发的摆动转动带。如果假定正伽玛三轴变形，由于三个转动惯量的无旋行为，人们不能期望摆动运动。然而，它是;阐明了准粒子排列，在微观随机相位近似计算中固有的，从它们的无旋行为改变了三个惯性矩的比率，然后摆动运动成为可能存在。

Recent experimental data suggest that an interesting phenomenon of the triaxial deformation, in which all three lengths of principal axes of the nuclear mean-field are different from each other, appears near the yrast states. In this resarch, with this triaxial deformation as a keyword, we shed new light on mechanism of the appearance of new non-principal-axis rotations, which is a consequence of triaxiality and leads to a tilting of rotation-axis with respect to the deformation axes.In these two year's of research, we have accomplished several important achievements, but still there are some parts which remains to be finished. Especially, the subject to solve the quantum mechanical equation with respect to the collective degrees of freedom for the tilting angles has not been accomplished. In the following, the physical results obtained are summarized.1)The strongly-coupled rotational one-quasiparticle bands, based on the orbits with the high-angular momentum component with respect to the symmetry axis, has been investigated in terms of the tilted axis cranking method. It is found that the problem of underestimating the angular frequency of starting tilting point is nicely sovled by including the quadrupole residual interaction, especially its K=1 component.2)The recently observed wobbling rotational band excited on the triaxial superdeformated band in Hf, Lu nuclei has been studied by using the random-phase-approximation. If assuming the positive-gamma triaxial deformation, one cannot expect the wobbling motion because of the irrotational behavior of three moments of inertia. It is, however; clarified that the quasiparticle alignment, inherent in the microscopic random-phase-approximation calculation, changes the ratio of three moments of inertia from their irrotational behavior, and then the wobbling motion became possible to exist.