On the resolution function of the n_TOF facility: a comprehensive study and user guide

The purpose of this report is to provide the necessary information and tools for the n_TOF Collaboration on how to correctly account for the neutron resolution function in the experimental areas (EAR1 and EAR2) for different n_TOF operation periods. The n_TOF target as well as the cooling/moderation system was designed to optimize the performances of the neutron beam for EAR1. Additionally, EAR1 is located underground 200 m away, in nearly the same direction as the incoming proton beam, from the spallation target. On the contrary, EAR2 was an extension of the existing facility. It is located above the ground at 20 m from the spallation target in the perpendicular direction with respect to the incoming proton beam. Even though the energy resolution is worse due to the shorter flightpath, the main issue with the resolution function comes from the geometry of the cooling/moderation system and the shape of the spallation target. Experimental data acquired in any of the experimental areas has embedded the effect of the resolution function. Therefore, when treating these data there are two options. Either deconvolute them from the resolution function or convolve the reference data, for instance evaluated cross sections, with the resolution function to be able to compare both sets of data in the same conditions. Usually, the second method is adopted for simplicity. In both cases the explicit distribution of the resolution function should be available. Even more, to perform the resonance analysis with SAMMY or REFIT this information must be known. The question here is: how to obtain the resolution function.