A comprehensive view of nuclear shapes, rotations and vibrations from fully quantum mechanical perspectives

Abstract: The nuclear quadrupole collective states at low excitation energies are described in a novel, fully quantum mechanical and systematic manner as compared to traditional pictures initiated by Aage Bohr. The ellipsoidal shapes are shown to be triaxial in virtually all strongly deformed nuclei, in contrast to the Ansatz of axially symmetric shapes. The rotational bands of such triaxially deformed nuclei are described in a fully quantum mechanical way, i. e., without resorting to quantized free rotation of rigid body. The excitation energies within a rotational band, exhibiting the $J(J+1)$ dependence on angular momentum $J$, are shown to basically represent the change of binding energies due to nuclear forces. This differs from the interpretation \'a la Aage Bohr as rotational kinetic energies. The $K$ quantum numbers are shown to be practically conserved for triaxial ellipsoids, which turned out to be a real but positive surprise to many people in the field. The so-called $\gamma$ bands are shown to be $K$=2$^+$ rotations rather than $\gamma$-vibrations, leading to a nice description of the so-called $\gamma\gamma$ 4$^+$ state as a $K$=4$^+$ rotation. Vibrational modes are also shown to emerge in this study. Thus, the whole picture of low-energy quadrupole collective motion of heavy nuclei has been renewed in a fully quantum mechanical fashion, which differs from the traditional picture but appears to be simpler and more natural.