Exotic rotation in weakly deformed and triaxial nuclei

Antimagnetic rotation in weakly deformed nuclei 100,101Pd, and chiral rotation in triaxial nuclei 135,136Nd have been investigated by means of gamma-ray spectroscopic measurements. These two modes of rotation are quite different from "standard" rotational motion observed in well deformed nuclei. In these new modes, the total angular momentum either originates purely from a few particles in high-j orbitals, or these orbitals couple to collective motion of a triaxial core. Two cascades of four "rotational-band-like" transitions were observed in 100Pd and 101Pd, respectively, and have been proposed as corresponding to antimagnetic rotation, based on the observed spectroscopic properties and a comparison with calculations in the configuration-dependent cranking Nilsson-Strutinsky formalism. Two DeltaI = 1 bands with close excitation energies and the same parity were observed in 135Nd. These bands are directly linked by DeltaI = 1 and DeltaI = 2 transitions. The chiral nature of these two bands is confirmed by comparison with three-dimensional tilted axis cranking calculations. This is the first observation of a three-quasiparticle chiral structure and establishes the primarily geometric nature of this phenomenon. Although there are no chiral partner bands observed in even-even nucleus 136Nd from our data, TAC calculations indeed give chiral solutions related to several DeltaI = 1 bands in the nucleus 136Nd.