Dipole strength distribution in56Fe

Abstract

Electromagnetic dipole transitions in ${}^{56}$Fe were measured in photon-scattering experiments with a linearly polarized photon beam. The parity quantum numbers of the excited dipole states were determined by the intensity asymmetry of resonantly scattered $\ensuremath{\gamma}$ rays with respect to the polarization plane of the incident photon beam. While the summed magnetic dipole ($M1$) strength was determined as $\ensuremath{\Sigma}B(M1)\ensuremath{\uparrow}=3.52(17)$ ${\ensuremath{\mu}}_{N}^{2}$ at excitation energies between 7 and 10 MeV, the summed electric dipole ($E1$) strength below 10 MeV was obtained as $\ensuremath{\Sigma}B(E1)\ensuremath{\uparrow}=78.0(15)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ ${e}^{2}$ fm${}^{2}$. The observed $M1$ strength was compared with shell-model predictions in the $pf$ shell using the GXPF1J and KB3G effective interactions. In addition, the $E1$ strength was compared with random-phase approximation calculations with the Skyrme interaction.