First observation of excited states in 226U

The technique of recoil-decay tagging has been employed in order to observe excited yrast states in the neutron-deficient nucleus 226U, for the first time. Interleaved bands of positive- and negative-parity states suggest the octupole nature of this nucleus, and the behaviour of the difference in aligned angular momentum between the negative- and positive-parity states with rotational frequency is consistent with that expected of a rotating reflection-asymmetric shape. This represents an extension of the known octupole-deformed nuclei to Z = 92. The interleaved bands of alternating parity are connected by strong electric dipole transitions, and values of |D0/Q0|. extracted from E1/E2 γ-ray branching ratios, suggest that 226U possesses one of the largest E1 moments near to the ground state of the nuclei in this region.