In-Beam Gamma-Ray Spectroscopy Of U-240 Using The (O-18,O-16) Reaction

In the two-neutron-transfer reaction of a 200-MeV O-18 beam with a U-238 target, deexcitation gamma rays in a neutron-rich nucleus of U-240 were measured. The gamma rays in U-240 were identified by taking coincidence with O-16, using Si Delta E-E detectors. The kinetic energies of O-16 particles allowed us to select the excitation energies of U-240 below the neutron separation energy. The ground-state band and the K-pi=0(-) octupole band of U-240 were established up to 12(+) and 9(-), respectively. The octupole-band head of U-240 is about a hundred keV higher than those of U-236,U-238, suggesting that a secondary maximum of octupole correlations exists at N=144-146 in U isotopes.