Collective Rotation of 238U at High Spins

Abstract

An experimental study of the actinide nucleus 238U was performed by Coulomb excitation with 208Pb projectiles. The E2-transition matrix elements in the ground state band were measured up to spin 28 by comparing experimental Coulomb excitation yields to semiclassical calculations and by analysing Doppler broadened line shapes measured in coincidence with a gamma-ray sum spectrometer. The E2-metrix elements agree within their errors with the rigid rotor predictions. Neither an increase of the collective transition strength at high spin due to centrifugal stretching as predicted by the Rotation Vibration Model nor a cutoff in collectively as postulated by the Interacting Boson Model is observed. The excitation energies in the ground state band show the presence of an aligned angular momentum of 5ℏ at spin 30 which can be explained by a crossing of an aligned band at ℏω ≈ 250 keV. The octupole band shows a constant angular momentum alignment of 3ℏ (above spin 7) and no indication of a bandcrossing.