Validation Fluorine Total Cross Section Using Broomstick Experiment at VR-1 Reactor

The 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 and 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 a reduction in the total cross section below 2 MeV, corrects this discrepancy, bringing the calculated transmitted spectra within the 1 sigma experimental uncertainty of the measured data.