Scattering of 9.8-MeV Neutrons from Silicon and Sulfur

Elastic and inelastic differential cross sections for neutron scattering from Si and S have been measured at an incident neutron energy of 9.8 MeV, using the high-energy neutron group from the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(\alpha ,n){}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ source reaction. Due to the presence of the 4.439-MeV first-excited-state group from the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(\alpha ,n){}_{}{}^{12}{}_{}{}^{}\mathrm{C}_{}^{*}{}_{}{}^{}$ reaction only the scattering from the ground and first excited states in Si and S could be observed. Measurements were made on both elements by the time-of-flight technique in the angular region ${20}^{\circ }\le {\theta }_{\mathrm{lab}}\le {150}^{\circ }$ with an average neutron energy spread of 600 keV. The measured yields were corrected for flux attenuation, angular resolution, and multiple scattering. The cross sections were fitted by incoherently adding a compound-nuclear contribution to a direct-reaction contribution calculated by the optical-model-plus-distorted-wave-Born-approximation method and also by the coupled-channel method. Collective-model fits to S using oblate and prolate deformed rotational-model and vibrational-model form factors were all reasonably good. The fits to Si are not as good, possibly for reasons related to the large fluctuations in the neutron total and differential cross sections for Si in this energy region. The values of $\beta$ obtained from these fits are, for the most part, consistent with those obtained from other measurements.