Determination of the neutron energy spectrum of a radial neutron beam at a TRIGA reactor

The neutron energy spectrum was measured as part of a neutron beam characterization effort performed on the Neutron Radiography Reactor (NRAD) at the Idaho National Laboratory. The spectrum was determined by using multi-foil activation measurements coupled with unfolding algorithms with the software package Unfolding with MAXED and GRAVEL (UMG) and the Monte-Carlo N-Particle (MCNP6) transport code. The resulting neutron energy spectrum which was implemented into an MCNP6 model of the neutron beam to contribute to future studies. The total neutron flux is 7.06 × 10⁷ n/cm²s with a 2σ error of 0.17%. The energy spectrum contains a large thermal neutron content, which is expected for the thermal reactor. The energy spectrum also includes a larger fast neutron content than typical neutron beams, which is attributed to the radial design of these beams where the beam has direct line of sight to the reactor core without much water to moderate the neutrons.