Development of a benchmark experimental method for large angle scattering cross section of 14 MeV neutrons using compound targets – Application to fluorine benchmarking using PTFE

In fusion reactors, large angle neutron scattering reactions significantly affect neutronics calculations, especially for the reactor blanket. Previous studies highlighted discrepancies in evaluated nuclear data, emphasizing the necessity for benchmarking large angle scattering cross sections. While the authors’ group previously developed a benchmark experimental system using the foil activation method, gaseous elements like fluorine could not be validated. This study introduces a new method that uses solid compounds containing the gaseous element to indirectly evaluate its large angle scattering cross section. Applying this method, benchmark experiments for fluorine were performed using graphite and polytetrafluoroethylene (PTFE) as the targets, and the fluorine contribution was extracted. The results were then compared with MCNP5 simulations using different nuclear data libraries and an excellent agreement was observed for ENDF/B-VIII.0 and JEFF-3.3. Future work will aim to reduce experimental uncertainties.