Evidence for dipole nature of the low-energy $\gamma$ enhancement in ${}^{56}$Fe

Abstract

The $\gamma$-ray strength function of ${}^{56}$Fe has been measured from proton-$\gamma$ coincidences for excitation energies up to $\approx 11$ MeV. The low-energy enhancement in the $\gamma$-ray strength function, which was first discovered in the (${}^3$He,$\alpha \gamma$)${}^{56}$Fe reaction, is confirmed with the ($p,p^{\prime }\gamma$)${}^{56}$Fe experiment reported here. Angular distributions of the $\gamma$ rays give for the first time evidence that the enhancement is dominated by dipole transitions.

5 pages, 4 figures. Version accepted for publication in Phys. Rev. Letters

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