Other types of multipole deformations.

Aside from the ellipsoidal vibration of the nuclear surface for $\lambda$=2, the general expansion of the nuclear surface in equation allows the nucleus for different modes of vibration, a selection of which are shown in figure . Dipole deformations, $\lambda$=1, correspond to a shift of the centre of mass, i.e., a translation of the nucleus. Octupole deformations (pear-shaped vibrations), $\lambda$=3, are the principal asymmetric modes of the nucleus associated with negative-parity bands. In this case, the nucleus no longer has reflection symmetry. Hexadecapole deformations, $\lambda$=4, play an important role in admixture to quadrupole excitations for the ground-state shape of heavy nuclei [2].

Figure: Equal potential surfaces for different multipole distortions (taken from [5]).