Dipole response of ${}^{238}$U to polarized photons below the neutron separation energy

Dipole response of $^{238}$ U to polarized photons below the neutron separation energy

S. L. Hammond, A. S. Adekola, C. T. Angell, H. J. Karwowski, E. Kwan, G. Rusev, A. P. Tonchev, W. Tornow, C. R. Howell, and J. H. Kelley

Phys. Rev. C 85, 044302 – Published 2 April 2012

Abstract

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 $^{238}$ U using 100 $%$ linearly polarized photon beams from 2.0 to 6.2 MeV. 113 transitions corresponding to de-excitations to the ground state in $^{238}$ U 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 $E 1$ $γ$ -ray interaction cross section was calculated and it was deduced that the observed concentration of low-lying $E 1$ 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 $M 1$ strength agreed well with each other. However, there was no similar agreement for the $E 1$ strength.

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Received 15 August 2011

DOI:https://doi.org/10.1103/PhysRevC.85.044302

Authors & Affiliations

S. L. Hammond, A. S. Adekola^*, C. T. Angell^†, and H. J. Karwowski

Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA

E. Kwan^‡, G. Rusev^§, A. P. Tonchev^‡, W. Tornow, and C. R. Howell

Department of Physics, Duke University, Durham, North Carolina 27708, USA and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA

J. H. Kelley

Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, USA and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA

^*Present address: AREVA/Canberra Industries, Inc., Meriden, Connecticut 06450, USA.
^†Present address: Quantum Beam Science Directorate, Japan Atomic Energy Agency, Shirakara-Shirane 2-4, Tokai-mura, Ibaraki 319-1195, Japan.
^‡Present address: Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
^§Present address: Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.

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Vol. 85, Iss. 4 — April 2012

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