Monte carlo simulations of the n_TOF lead spallation target with the Geant4 toolkit: A benchmark study

Monte Carlo (MC) simulations are an essential tool to determine fundamental features of a neutron beam, such as the neutron flux or the γ -ray background, that sometimes can not be measured or at least not in every position or energy range. Until recently, the most widely used MC codes in this field had been MCNPX and FLUKA. However, the Geant4 toolkit has also become a competitive code for the transport of neutrons after the development of the native Geant4 format for neutron data libraries, G4NDL. In this context, we present the Geant4 simulations of the neutron spallation target of the n TOF facility at CERN, done with version 10.1.1 of the toolkit. The first goal was the validation of the intra-nuclear cascade models implemented in the code using, as benchmark, the characteristics of the neutron beam measured at the first experimental area (EAR1), especially the neutron flux and energy distribution, and the time distribution of neutrons of equal kinetic energy, the so-called Resolution Function. The second goal was the development of aMonte Carlo tool aimed to provide useful calculations for both the analysis and planning of the upcoming measurements at the new experimental area (EAR2) of the facility.
The research that led to these results has received funding from the EC FP7 Programme under the projects NEUTANDALUS (Grant No. 334315) and CHANDA (Grant No. 605203), and the Spanish Ministry of Economy and Competitiveness projects FPA2011-28770- C3-02, FPA2013-45083-P and FPA2014- 53290-C2-2-P. The simulations have been performed at the computing cluster FISATOM, hosted at CICA (Seville, Spain), and of INFN-CNAF, University of Bologna; we thank the staff of both institutions for the operational maintenance of the machines.