First observation of rotational bands in the nucleus ²³¹U

This work reports the first rotational bands observed in the neutron-deficient nucleus ²³¹ 231 U. Excited states were populated in the ²³² 232 Th( α α ,5n) reaction at a beam energy of 52 MeV. Coincident decay γ γ -rays were measured with the high-purity germanium detectors of the afrodite spectrometer array, in conjunction with a recoil detector to discriminate against the fission background. The bands are interpreted as the ground-state band ν [633]5/2⁺ ν [ 633 ] 5 / 2 + , yrast band ν [752]5/2⁻ ν [ 752 ] 5 / 2 - , and an excited band ν [631]3/2⁺ ν [ 631 ] 3 / 2 + . Configuration assignments are supported by Cranked Shell Model and B ( M 1)/ B ( E 2) calculations. The excitation energy of the ν [752]5/2⁻ ν [ 752 ] 5 / 2 - bandhead is suggested to be 113.0 keV.