Level density of $^{56}$Fe and low-energy enhancement of $γ$-strength function

Abstract

The $^{55}$Mn$(d,n)^{56}$Fe differential cross section is measured at $E_d=7$ MeV\@. The $^{56}$Fe level density obtained from neutron evaporation spectra is compared to the level density extracted from the $^{57}$Fe$(^3$He,$αγ)^{56}$Fe reaction by the Oslo-type technique. Good agreement is found between the level densities determined by the two methods. With the level density function obtained from the neutron evaporation spectra, the $^{56}$Fe $γ$-strength function is also determined from the first-generation $γ$ matrix of the Oslo experiment. The good agreement between the past and present results for the $γ$-strength function supports the validity of both methods and is consistent with the low-energy enhancement of the $γ$ strength below $\sim 4$ MeV first discovered by the Oslo method in iron and molybdenum isotopes.