Validation fluorine total cross-section using broomstick experiment at VR-1 reactor

Abstract Paper presents a validation of the evaluated fluorine total cross section using a broomstick experiment conducted at the VR-1 reactor. Precise knowledge of fluorine cross-sections is crucial for nuclear applications. A collimated neutron beam was directed through PTFE (Polytetrafluoroethylene) cylinders of various thicknesses, and the transmitted fast neutron spectra were measured using a stilbene scintillation spectrometer. The setup's sensitivity to total cross-sections enables a robust comparison with evaluated nuclear data files. Last updates to the fluorine cross-section within the INDEN collaboration framework, to be adopted by ENDF/B-VIII.1 and JEFF-4.0, have shown improvements in criticality benchmarks and integral neutron spectrum measurements using PTFE. The measurements revealed that current standard libraries (ENDF/B-VIII.1, JEFF-3.3) underestimate the transmitted neutron flux by approximately 10%–20% in the 1.0–2.0 MeV energy range, indicating an overestimation of the total cross-section. The new INDEN f19f4t4_tot6 evaluation, which incorporates an reduction in the total cross-section below 2 MeV, corrects this discrepancy, bringing the calculated transmitted spectra within the 1s experimental uncertainty of the measured data.