Measurement of the neutron total cross sections of aluminum at the back-n white neutron source of CSNS

Aluminum and its alloys are widely used in the nuclear industry. Therefore, it is essential to precisely measure and accurately know the neutron total cross section of aluminum in the wider energy region. The measurement is performed by using the transmission method at the Back-n White Neutron Source of CSNS. Two aluminum samples 70 mm in diameter and thicknesses of 40 and 60 mm, respectively, were positioned at 55 m from the neutron source. The transmission detector consisted of a multi-layer fast fission chamber loaded with 235 U and 238 U, and it was located at the 76-m measurement station. By applying the time-of-flight technique, it was possible to extract the n+ 27 Al total cross section in a wide energy region, from 1 eV to 20 MeV, after the correction for the double-bunch mode of the CSNS accelerator. The total cross sections obtained with the two Al samples are consistent and the results obtained with the 235 U fission cells are in good agreement with that with 238 U in the energy range of 1–20 MeV. The uncertainty of neutron total cross section measured with 235 U for 40 mm and 60 mm thick aluminum is 0.7–22.3% and 0.6–12.4% in the energy range of 10 keV–20 MeV. Results are in fair agreement with respect to previous data and evaluations.