Thorium Resonance Parameters for Neutron Energies from 20 to 222 eV

The neutron capture cross section for thorium has been measured over the neutron energy region from 20 to 222 eV. The pulsed neutron source for this investigation was obtained by stopping 30-MeV electrons in a water-moderated Fansteel target. The gamma rays resulting from neutron capture were detected by a 4000-liter liquid scintillator. Resonance parameters for the predominant $s$-wave levels were determined from the cross-section data. The resonance parameters were obtained by means of the multisample area-analysis technique. This analysis included multiple-scattering corrections. Of the 11 resonances studied the data indicate that, within the quoted experimental errors, the radiation width remained constant from level to level. The average value obtained for the radiation width was 24.5±1.5 meV.