{#sect_exp}
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Experimental results
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During the last decade, the Oslo group has developed an experimental method capable of extracting information on the nuclear level densities (NLD) and $\gamma$-ray strength functions by analyzing particle-$\gamma$ coincidence data from neutron pickup ($^3$He,$\alpha\gamma$) and inelastic scattering ($^3$He,$^3$He$^{\prime}$$\gamma$) reactions. Details about the method can be found in [@Schiller00].

One major result obtained through the Oslo method concerns an increase of the RSF at decreasing photon energy. This upbend structure has been observed in $^{44,45}$Sc, $^{50,51}$V, $^{56,57}$Fe, and $^{93-98}$Mo at energies typically smaller than 3 MeV. Heavier isotopes of Sn, Sm, Dy, Er and Yb for which similar experiments have been conducted do not show such a low-energy behavior. At the moment, only the Fe results have been confirmed by another experimental technique (the two-step cascade method, see [@Fe_Alex]), and theoretically there is no model that can provide possible explanations. Even the multipolarity of the strength remains unknown.

Guttormsen et al. [@Mo_RSF] showed that in the case of an $E1$ strength, the reduced strength in the $1-3$ MeV range would correspond to an average $B(E1)$ value of 0.02 $e^2$fm$^2$ (i.e. about 0.07% of the $E1$ sum rule), in case of an $M1$, $B(M1)\simeq 2~\mu_N^2$ which 