Evidence for dipole nature of the low-energy ${\hat{I}}^3$ enhancement in ${}^{56}$Fe

Abstract

The ${\hat{I}}^3$-ray strength function of ${}^{56}$Fe has been measured from proton-${\hat{I}}^3$ coincidences for excitation energies up to $\approx 11$ MeV. The low-energy enhancement in the ${\hat{I}}^3$-ray strength function, which was first discovered in the (${}^3$He,$\hat{I}\pm {\hat{I}}^3$)${}^{56}$Fe reaction, is confirmed with the ($p,p^{\prime }{\hat{I}}^3$)${}^{56}$Fe experiment reported here. Angular distributions of the ${\hat{I}}^3$ 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