Polarization and Angular Distribution Measurements on the Neutrons from theBe9(p,n)B9Reaction

Abstract

The polarization of the neutrons from the ${\mathrm{Be}}^9\mathrm{}(p,n)\mathrm{}{\mathrm{B}}^9$ reaction has been measured for laboratory emission angles of 30°, 50°, 70°, and 90°, for proton bombarding energies of 2.4, 2.75, 3.35, and 3.7 MeV. Angular distributions of the neutrons from this reaction have also been measured for nine proton bombarding energies between 2.5 and 4.1 MeV. For the polarization measurements, neutrons were scattered from analyzers of magnesium, oxygen, and carbon, and the asymmetries in the scattering were measured with the aid of an electromagnet which could rotate the polarization vector of the neutrons between the source and the scatterer. In detecting the neutrons, energy discrimination was employed to eliminate the effect of the three-body-breakup neutrons. The polarization is very small at 2.4 MeV, and at the higher energies is positive (Basel convention) at 30°, small at 50°, and negative at 70° and 90°. The largest value of the polarization found was 0.29±0.04 at an emission angle of 30° and a bombarding energy of 3.7 MeV. Above 3.0-MeV proton energy the angular distributions show a broad maximum in the backward direction. Calculations of the cross section and polarization were made assuming the reaction involves only three levels in the compound nucleus. Although partially successful in reproducing the polarization data, these calculations were unable to reproduce the measured cross sections.