Geant4 simulation of multi-sphere spectrometer response function and the detection of 241 Am–Be neutron spectrum

This paper is aimed at detecting the neutron spectrum of 241 Am–Be, a widely used neutron source, with the SP9 3 He proportional counter, which is a multi-sphere spectrometer system of eight thermal neutron detectors embedded in eight polyethylene (PE) spheres of varying diameters. The transport processes of a neutron in the multi-sphere spectrometer are simulated using the Geant4 code. Two sets of response functions of the PE spheres are obtained for calculating the 241 Am–Be neutron spectrum. Response Function 1 utilizes the thermal neutron scattering model G4NeutronHPThermalScattering for neutron energies of ≤ 4 eV, and Response Function 2 has no thermal treatment. Neutron spectra of an 241 Am–Be neutron source are measured and compared to those calculated by using the response functions. The results show that response function with thermal treatment is more accurate and closer to the real spectrum.