Measurement of the neutron total cross section of 9Be at the Back-n white neutron source of CSNS

Abstract

Abstract The neutron total cross section data of 9Be play an important role in nuclear structure model research of light nuclei and nuclear power installations. A measurement of the neutron total cross section of 9Be in the 0.3 eV-120 MeV energy region has been carried out by using time-of-flight method and transmission method with the Neutron Total Cross Sectional Spectrometer (NTOX) based on the multi-cell fast fission chamber at the China Spallation Neutron Source (CSNS)- Back-n white neutron source (Back-n). The fission count-neutron energy distributions of 235U and 238U without sample and with Be samples in three thicknesses were measured in the double-bunch operation mode during beam power of 100 kW. The Bayesian method is used to eliminate the influence of the double-bunch problem on neutron measurement in the energy region above 10 keV. The neutron total cross section of 9Be results is well consistent with ENDF/B-VIII.0 evaluation library data in 0.3 eV-20 MeV energy region. In the energy range of 0.3 eV to 10 keV, the deviation between our results and the evaluation results of ENDF/B-VIII.0 is within 2.5%, which is within 15% from 0.01-20 MeV. In the resonance energy region, the measured resonance energies in our experiment are 0.63 MeV, 0.82 MeV and 2.8 MeV respectively. The results show that the total cross section uncertainties of three thicknesses Be samples are within 2.2% in the energy region below 1 MeV. The total cross section uncertainty of 30 mm Be from 235U is the smallest and less than 5% in the energy region 0.3 eV-120 MeV. The results of this experiment can provide technical support for further data analysis and related nuclear data evaluation.