Neutron capture cross-section measurement of 99 Tc from 5.9 to 735 keV

The neutron capture cross-section of the long-lived fission product 99Tc was measured in the energy range from 5.9 keV to 735 keV. The experiment was conducted using the time-of-flight technique at the Accurate Neutron-Nucleus Reaction measurement Instrument beamline of the Japan Proton Accelerator Research Complex. Prompt γ-rays from the 99Tc(n,γ) reaction were detected using a NaI(Tl) spectrometer, and the pulse-height weighting technique was applied to derive the capture yield. The absolute cross-section was normalized using the saturated resonance method at the 5.6 eV resonance of 99Tc. The results, obtained with a total uncertainty of approximately 7%, show a significant discrepancy with several prior measurements. Above 70 keV, the data shows good agreement with the evaluated libraries, though a 10–20% deviation from major evaluated libraries (ENDF/B-VIII.0, JENDL-5 and JEFF-3.3) is observed at lower energies. These findings suggest that current evaluations may underestimate the transmutation rate of 99Tc in fast-spectrum systems, providing critical data for the design of future nuclear waste management and accelerator-driven systems.