Abstract
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 a Monte 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.
Highlights
Introduction and motivationThe neutron beam of the n TOF facility is generated through spallation reactions produced by 20 GeV/c protons provided by the CERN Proton Synchrotron (PS) on a 40 cm thick lead target
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 a Monte 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
Summary
The neutron beam of the n TOF facility is generated through spallation reactions produced by 20 GeV/c protons provided by the CERN Proton Synchrotron (PS) on a 40 cm thick lead target. Secondary particles produced in the target are followed and tracked up to the scoring volumes positioned at the entrance of the vacuum beam pipes where their position, time, angle, energy and particle type are registered. These scoring volumes shown, are the end point of our MC simulation. Geant v10.1.1 provides a wide variety of physics models that apply in different energy regimes To perform these simulations we worked with the officially released Physics Lists (PL) that include either the Fritiof (FTF) model or the Quark-Gluon-String (QGS) model above ∼10 GeV; the P after FTF or QGS denotes that the Geant native Precompound model is taken into account for nuclear de-excitation. ∼10 GeV three different intranuclear de-excitation cascade models are available: INCLXX [10, 11], Bertini (BERT) [12] or Binary Cascade
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