Model parameterizations
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To describe the $\gamma$-ray strength function with the enhancement observed at low energy, we consider different ways to model its contribution to the total $E1$ strength. More specifically, we have applied the widely used Generalized Lorentzian (GLO) model [@ko87; @ko90] for the $E1$ strength, and modified it in order to describe the observed upbend structure.

The GLO model makes use of a temperature dependence that increases the $E1$ de-excitation strength at low energies and gives an $E_\gamma \rightarrow 0$ non-zero limit, but no upbend pattern. This non-zero limit was first introduced by Kadmenski[ĭ]{}, Markushev and Furman in 1983 on the basis of theoretical calculations within the Fermi liquid model [@ka83]. This was done in order to take into account quasi-particle fragmentation of the $E1$ strength, and to explain the observed low-energy data on the $\gamma$-ray strength function of several medium-mass and heavy nuclei studied with $(n,\gamma\alpha)$ and $(n,\gamma f)$ reactions (see [@ka83] and references therein). Later, Kopecky and Chrien [@ko87], and Kopecky and Uhl [@ko90] found it necessary to introduce a temperature dependence in order to describe the strength of primary $\gamma$-ray data from average resonance capture (ARC) reactions, and introduced the GLO model [@ko87; @ko90]. This 