Width-Fluctuation Effects in (n, n′γ) Reactions

The effects of level-width fluctuations in ($n, n^{\prime }\gamma$) reactions have been studied for several nuclei. Moldauer has developed a formulation for describing width-fluctuation effects in neutron inelastic scattering. $\gamma$-ray angular distributions and cross sections in ($n, n^{\prime }\gamma$) reactions with ${\mathrm{Mg}}^{24}$, ${\mathrm{Al}}^{27}$, ${\mathrm{Si}}^{28}$, ${\mathrm{Ar}}^{40}$, ${\mathrm{Fe}}^{56}$, and ${\mathrm{Pb}}^{208}$ have been calculated on the basis of Satchler's theory, with the inclusion of width-fluctuation corrections based on Moldauer's formulation. It is found that in the region of threshold or in the cases where only a single level is excited, the inclusion of width-fluctuation effects reduces the cross sections by as much as 45%. The reduction in cross sections is smaller in the cases where several levels are excited. However, in all cases, the agreement between the experimental and calculated cross sections is significantly improved with the inclusion of width-fluctuation corrections. The shape and anisotropy of the $\gamma$ distributions are not significantly altered by the width-fluctuation corrections.