Understanding the Nature of the Low-energy Enhancement in the Photon Strength Function of $^{56}$Fe.

A recent experiment designed to determine the multipolarity and electric or magnetic character of transitions in the region of the photon strength function (PSF) enhancement in $^{56}$Fe was performed at ANL using GRETINA in combination with the Phoswich wall\big[1\big]. A beam of 16 MeV protons impinged upon a 1 mg/cm$^{2}$ $^{56}$Fe target, inelastically exciting it to high energies. The scattered protons were then measured by the Phoswich wall, providing the entrance excitation energy, while the resulting $\gamma$-ray cascades were measured in GRETINA. The PSF can be extracted using two-step cascades from the quasicontiuum to specific low-lying levels by a model independent method first employed in $^{95}$Mo\big[2\big]. This method is being extended to take advantage of GRETINA as a polarimeter to obtain angular and polarization information in the region of the low-energy enhancement of the PSF. Preliminary results will be discussed. \\ \\ \big[1\big] D. G. Sarantites \emph{et al.} Nuclear Instruments and Methods A, 790, 42-55 (2015) \\ \big[2\big] M. Wiedeking \emph{et al.} Phys. Rev. Lett. 108, 162503 (2012)