Band structures in 123I

Excited states of 123I were populated via the 116Cd(14N, α3n) reaction at 65 MeV. The resultant γ-rays were detected using standard γ-ray spectroscopic techniques with the NORDBALL detector array. Two previously known positive-parity ΔI = 2 sequences have been extended up to 31/2+ and 41/2+. In addition, a number of ΔI = 1 transitions linking the two ΔI = 2 sequences have been observed. It is suggested that both ΔI = 2 sequences are based on a common configuration. This ΔI = 1 band is proposed to be built predominantly on the g7/2[404]7/2+ oblate configuration, based on the energy-level spectra, B(M1)/B(E2) ratios and the theoretical predictions from the particle-rotor model. The previously identified ΔI = 1 rotational band built on the prolate g9/2[404]9/2+ orbital has also been extended to higher spins. Another previously identified but weakly populated ΔI = 1 band is confirmed and is proposed to be built on the d5/2[413]5/2+ configuration with the ground state of 123I as the bandhead.