Time–energy relation of the n_TOF neutron beam: energy standards revisited

Abstract

The accurate determination of neutron cross-sections as a function of the neutron energy at a time-of-flight facility requires a precise knowledge of the time–energy relation for the neutron beam. For the n_TOF neutron beam at CERN, produced by spallation of high-energy protons on a Pb target, the time–energy relation is connected to the production mechanism and to the subsequent moderation process. A calibration of the neutron energy scale is proposed based on detailed Monte Carlo simulations of the facility. This time–energy relation has been experimentally validated by means of dedicated measurements of standard energy resonances, from 1 eV to approximately 1 MeV. On the basis of the present measurements, it is proposed to correct the energy of the 1.3 eV resonance of 193Ir, which is commonly considered as an energy standard.