Experiment and Analysis of Neutron Spectra in a Concrete Assembly Bombarded by 14-MeV Neutrons

Abstract

The neutron spectra in a concrete assembly bombarded by 14-MeV neutrons are measured by a miniature NE-213 spectrometer and the multifoil activation method. The results obtained are within experimental error. The measured spectra are compared with calculated results obtained using the two-dimensional DOT3.5 transport code with 125-group structure cross-section libraries based on ENDF/B–IV, JENDL-2, and JENDL-3T (the test version of JENDL-3). In the deuterium-tritium neutron peak region, the measured and calculated neutron spectra are in agreement. However, all the calculations overestimate the measurements by 10 to 50% in the mega-electron-volt region. In a still lower neutron energy range, where the 197Au(n, γ)198Au reaction is dominant, discrepancies from −30 to +40% are observed. Possible reasons are considered, but none explain the discrepancies. Further investigation of the secondary neutrons in the mega-electron-volt region emitted by elastic and inelastic scattering from the main components of concrete, such as oxygen, silicon, and calcium, is necessary to improve the agreement between experimental and calculated results.