Understanding the Low-Energy Enhancement of the $\gamma$-ray Strength Function of $^{56}$Fe

TL;DR

This study measures the gamma-ray strength function of $^{56}$Fe at low energies using a model-independent method, confirming the Brink hypothesis and revealing a slight magnetic bias in the enhancement region.

Contribution

First direct measurement of $^{56}$Fe gamma-ray strength function below 1 MeV using GRETINA and a model-independent approach, supporting the Brink hypothesis.

Findings

No energy dependence difference between $2^{+}$ and $4^{+}$ states.

Angular distributions consistent with dipole radiation.

Polarization indicates a small magnetic bias.

Abstract

A model-independent technique was used to determine the $\gamma$-ray Strength Function ($\gamma$SF) of $^{56}$Fe down to $\gamma$-ray energies less than 1 MeV for the first time with GRETINA using the $(p,p')$ reaction at 16 MeV. No difference was observed in the energy dependence of the $\gamma$SF built on $2^{+}$ and $4^{+}$ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.