Measurement of the neutron total cross section of carbon at the Back-n white neutron beam of CSNS

To verify the performance of the neutron total cross-sectional spectrometer, the neutron total cross section of carbon is initially measured in the energy range of 1eV to 20MeV using the time-of-flight method. The measurement is performed at the Back-n white neutron source with a 76-m time-of-flight path using the China Spallation Neutron Source. A multilayer fast fission chamber with U-235 and U-238 is employed as the neutron detector. The diameter and thickness of the natural graphite sample are 70mm and 40mm, respectively. Signal waveforms are collected using a data acquisition system. Off-line data processing was used to obtain the neutron time-of-flight spectra and transmissions. The uncertainty of the counting statistics is generally approximately 3% for each bin in the energy range of 1-20MeV. It is determined that the results for the neutron total cross section of carbon obtained using U-235 cells are in good agreement with the results obtained using U-238 cells within limits of statistical uncertainty. Moreover, the measured total cross sections show good agreement with the broadening evaluated data.