GEANT4 simulations of the n_TOF spallation source and their benchmarking

Abstract

Neutron production and transport in the spallation target of the n TOF facility at CERN has been simulated with GEANT4. The results obtained with different models of high-energy nucleon-nucleus interaction have been compared with the measured characteristics of the neutron beam, in particular the flux and its dependence on neutron energy, measured in the first experimental area. The best agreement at present, within 20% for the absolute value of the flux, and within few percent for the energy dependence in the whole energy range from thermal to 1 GeV, is obtained with the INCL++ model coupled with the GEANT4 native de-excitation model. All other available models overestimate by a larger factor, of up to 70%, the n TOF neutron flux. The simulations are also able to accurately reproduce the neutron beam energy resolution function, which is essentially determined by the moderation time inside the target/moderator assembly. The results here reported provide confidence on the use of GEANT4 for simulations of spallation neutron sources.

New measurement of the 242Pu(n,γ) cross section at n_TOF-EAR1 for MOX fuels: Preliminary results in the RRR

“…where L 0 (m) is the flight path from the target exit to the experimental, T oF is expressed in µs and λ(E n ) (m) is the time-of-flight resolution function, an energydependent equivalent moderation lenght in the targetmoderator assembly that takes into account for the nonunivocal relation between production time and neutron energy, obtained from the simulations of the n TOF spallation target [11]. Neutron capture measurements with C 6 D 6 detectors are analyzed following the Total Energy Detection Technique (TED) [12,13].…”

On the role of secondary pions in spallation targets

“…Its structure is described in detail in Refs. [2][3][4]. A 20-GeV/c proton beam impinges on the base of the lead cylinder at an angle of approximately 10…”

“…[3], Geant4 simulations of neutron production at the n TOF spallation target, performed with several PL, were compared between each other and to the energydifferential neutron fluence measured at n TOF in various experimental campaigns. It was shown that the lists based on the INCL++ model closely reproduce the energy dependence of the neutron spectrum and, within a 15-20% difference, the integrated yield.…”

“…In recent publications [3,4], the Geant4 toolkit for particle transport [5,6] was used to characterize the neutron and photon fluxes directed towards the n TOF experimental areas. Calculations of neutron and photon fluences performed with different Geant4 physics lists exhibited large relative differences.…”

Nuclear data activities at the n_TOF facility at CERN

“…The design was based on extensive Monte Carlo simulations with FLUKA [39] in order to optimize the beam line and collimation for a high neutron flux together with a minimized background. Additional simulations have been performed for data analysis purposes [112,113]. In order to remove charged particles from the beam, a permanent 0.25 T magnet had to be installed since, unlike in the beamline for EAR1, there was no room for an electromagnet.…”