Correlated uncertainties of measuring neutron total cross-sections with simulation

A system for measuring neutron total cross section, the Photo-Neutron Source (PNS, phase 1), has been developed for the acquisition of nuclear data from the Thorium Molten Salt Reactor(TMSR) at the Shanghai Institute of Applied Physics (SINAP). It is also used in the study of neutron detector and the irradiation material about reactor. The neutron total cross-sections of beryllium were measured in the neutron energy region from 0.007 to 0.100 eV. The present measurement result was compared with the existed experimental and the evaluated data of ENDF/VII.1. The correlated uncertainties were determined by using Geant4 Monte Carlo simulation method. In order to reduce the calculation time, the local weighted method was used in the simulation. The neutron time of flight spectrum and the neutron yield at the detector position in experiment and simulation were compared.