Validation of Geant4 and MCNPX-PoliMi simulations of fast neutron detection with the EJ-309 liquid scintillator

Abstract

In organic liquid scintillators, the energy distribution of neutrons is indirectly measured by characterizing the pulse height distribution of light output produced through nuclear reactions within the detectors. However, the complexity of the light generation on these detectors makes simulating their response difficult with standard Monte Carlo techniques. This paper presents the response of 7.62-cm-long×7.62-cm-diameter and 12.7-cm-long×12.7-cm-diameter EJ-309 liquid scintillators, simulated using the Geant4 and MCNPX-PoliMi Monte Carlo codes. The simulations are restricted to the neutron transport and interaction models. Monoenergetic neutrons as well as fission neutrons emitted by a 252Cf spontaneous fission source are used in these simulations. The energy deposition of neutrons in organic liquid scintillators is dependent upon their collisions with hydrogen and carbon nuclei; therefore simulating neutron collisions on an event-by-event basis is important to generate neutron pulse height distributions. There are no default physics models in Geant4 hence proper selection of physics models is required for accurate simulation. In this paper, we compare Geant4 (ver. 4.9.5) and MCNPX-PoliMi (ver. 2.0) neutron pulse height distributions. The simulations are validated with time-of-flight (TOF) measurements obtained with 12.7-cm-long×12.7-cm-diameter EJ-309 detectors. Results show that both Geant4- and MCNPX-PoliMi-generated distributions are in good agreement with the measured data.