Speaker
Description
We investigate the dipole strength distributions in $^{56}$Fe using the nuclear resonance fluorescence (NRF) technique with 100% linearly polarized photons for incident beam energies below the neutron separation energy (~11 MeV) at the High Intensity Gamma-ray Source (HIgS) facility at the Triangle Universities Nuclear Laboratory. Preliminary NRF results of observed dipole states and their transition strengths will be compared with theoretical calculations based on the energy-density functional theory and quasi-particle phonon model [1]. We will determine the photon scattering cross sections from the measured elastic/ground state and inelastic transitions and then deduce the gamma-strength function (gSF) of $^{56}$Fe [2]. The measured NRF gSF will be compared with literature data obtained via the Oslo method [3,4] in which the low-energy enhancement, or upbend, has been observed. With the recent upgrade of the high-efficiency clover detector array and the increased g-ray flux at HIgS, we aim to study these low-energy primary g-ray transitions induced by incident photon beams using coincidence measurements to provide a multi-faceted understanding of the upbend phenomenon.
This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.
[1] N. Tsoneva and H. Lenske, Physics of Atomic Nuclei 79, 885 (2016).
[2] A.P. Tonchev et al., Phys. Rev. Lett. 104, 072501 (2010).
[3] A.V. Voinov et al., Phys. Rev. C 74, 014314 (2006).
[4] A.C. Larsen et al., Phys. Rev. Lett. 111, 242504 (2013).
