Neutron scattering from nuclei near A = 20 at energies below 2.2 MeV

Abstract

The polarization and differential cross sections for neutrons scattered from F, Na, Al and P have been measured at five scattering angles, at energies from 0.2 to 2.2 MeV, with incident-energy spreads of 100 to 150 keV. Structure, characterized by peaks that are separated by energy intervals of 300 to 400 keV and have widths from 100 to 200 keV, is seen in the total and differential cross sections and in the polarization for these nuclei. Calculations based on a nuclear optical model are in reasonable agreement with an average through the measured total and differential cross sections, but give somewhat poorer fits to an average through the measured polarizations. The observed fluctuations cannot be reproduced by any calculations based on an optical-model potential with fixed or slowly varying parameter values. The possible interpretations of this structure are discussed.