Dipole response of 238U to polarized photons below the neutron separation energy
Nuclear resonance fluorescence experiments were carried out at the High-Intensity γ-ray Source facility at Triangle Universities Nuclear Laboratory to characterize the low-energy dipole structure of 238U using 100% linearly polarized photon beams from 2.0 to 6.2 MeV. 113 transitions corresponding to de-excitations to the ground state in 238U were observed and the energy, spin, parity, integrated cross section, reduced width, and branching ratio were determined for each of these identified levels. The total E1 γ-ray interaction cross section was calculated and it was deduced that the observed concentration of low-lying E1 transitions were excited from the low-energy tail of the giant dipole resonance and were not a pygmy dipole resonance. Comparisons were made between quasiparticle random-phase approximation calculations and the experimentally observed strength. The observed and predicted M1 strength agreed well with each other. However, there was no similar agreement for the E1 strength. © 2012 American Physical Society.
Hammond, SL; Adekola, AS; Angell, CT; Karwowski, HJ; Kwan, E; Rusev, G; Tonchev, AP; Tornow, W; Howell, CR; Kelley, JH
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