Reanalysis of Neutron Multiplication Measurements in Thick Beryllium and Graphite Assemblies for 14-MeV Neutrons

Neutron multiplication measurements for 14-MeV neutrons were carried out in thick beryllium and graphite assemblies at the Institute for Reactor Development, Jülich, Federal Republic of Germany. Earlier Monte Carlo calculations using the ENDF/B-III library contained systematic errors that did not account for the predominant axial thermalization and non-1/v absorption in polyethylene. In addition, the calculational geometry differed considerably from the experimental geometry. These deficiencies have been eliminated in the present calculations, where the Los Alamos 30-group CLAW-IV library has been used. The anisotropy of the source in space and energy has also been taken into account. The results show that the calculated value of neutron multiplication is 20% higher (originally reported 30% higher) than the measured multiplication in beryllium. The results confirm the measurements made with BeO. For graphite and lead, excellent agreement is found between calculated and measured multiplication.