Measurements of Inelastic Scattering Cross Sections for Fast Neutrons

Abstract

Cross sections for inelastic neutron scattering by Fe, Mn, I, and F have been measured with a collimated neutron beam by observing the gamma radiations from the excited states. Excitation curves for the 850-kev level of ${\mathrm{Fe}}^{56}$, the 128-kev level of ${\mathrm{Mn}}^{55}$ and the levels at 62, 208, 435, and 632 kev in ${\mathrm{I}}^{127}$ were compared with the Hauser-Feshbach theory. The nuclear penetrabilities were obtained from the "cloudy crystal ball" model. In general, the best agreement with theory was obtained for the value of the nuclear absorption corresponding to a "black" nucleus. The angular distribution of the 850-kev radiation from ${\mathrm{Fe}}^{56}$ was given by: $W\left(\theta \right)=1+(0.54\mathrm{}\pm 0.05)P_2\left(cos\theta \right)-(0.28\mathrm{}\pm 0.05)P_4\left(cos\theta \right)$. Excitations of levels at 980 kev in ${\mathrm{Mn}}^{55}$; at 390, 725, and 950 kev in ${\mathrm{I}}^{127}$, and at 110, 197, and 1560 kev in ${\mathrm{F}}^{19}$ were also observed. No levels in ${\mathrm{S}}^{32}$ or Sr below 1 Mev were found. The excitation curves cannot be used to determine spins of excited states and even where spins and parities are known the agreement with theory is not good.