The neutron total cross section is fundamental nuclear data crucial for the design of nuclear energy systems and research in nuclear physics. For graphite, an important reactor moderator, significant discrepancies exist among the major evaluated nuclear data libraries concerning its high-energy neutron total cross section, particularly in the resonance structures and the regions above 20 MeV. These uncertainties constrain the precise design of advanced nuclear systems. To resolve these controversies and provide benchmark experimental data, this study performed a high-accuracy measurement of the neutron total cross section of natural carbon from 0.3 eV to 50 MeV using the transmission method combined with the time-of-flight (TOF) technique. The experiment was conducted at the back-streaming white neutrons (Back-n) at the China Spallation Neutron Source (CSNS), utilizing the NTOX spectrometer equipped with a multi-cell fission chamber. The neutron emission time (t0) was precisely calibrated using the prompt γ-flash from the spallation reaction. The 77-meter flight path was accurately calibrated using the known standard fission resonance peaks of 235U at 8.774 eV, 12.386 eV, and 19.288 eV. For the energy region above 100 keV, a Bayesian iterative algorithm was applied to unfold the double-bunch problem, effectively resolving the overlap of TOF spectra from neutrons produced in different beam bunches. The experimental results show excellent agreement with the ENDF/B-Ⅷ.1 evaluation and existing experimental data in the EXFOR database within the 0.3 eV-100 keV region. Owing to the high statistical accuracy, approximately 97.6% of the data points have statistical uncertainties of less than 1%, with the vast majority of total uncertainties better than 2%, significantly reducing the uncertainty level in this energy region. In the 100 keV– 50 MeV energy range, the data align with the overall trends observed in mainstream evaluation databases. No significant resonance effect was detected at 4.93 MeV, providing high-quality reference data for clarifying the resonance structure at this energy point. Systematically evaluated data above 20 MeV are currently only available in JENDL-5. The measurement results of this work provide indispensable high-quality experimental data to fill the high-energy data gap and to drive updates of the relevant evaluated libraries. This study not only provides critical benchmark data for the international nuclear data re-evaluation, especially for the CENDL-3.2 library which currently lacks complete data for natural carbon, but also systematically validates the methodological reliability of obtaining wide-energy-range, high-precision neutron total cross section data at the CSNS Back-n beamline.
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