Monte Carlo simulations of the Neutron Wall detector system

A Monte Carlo simulation of the Neutron Wall detector system has been performed using GEANT4. Mechanisms for the detection of neutrons in an aggregate of liquid scintillator detectors have been investigated in details, with the main aim to define optimum conditions for the detection and identification of multiple neutrons. Special emphasis was put on studying the scattering of neutrons between different detectors, which is the main source of the apparent increase of the number of detected neutrons, and hinders the selection of events with more than one emitted neutron. The results of the simulations were compared to experimental data obtained at the EUROBALL spectrometer using fusion-evaporation reactions. The quality of γ-ray spectra gated by 2 neutrons was improved 40 times, in terms of the relative intensity of γ-ray lines from nuclei produced with the emission of 2 and 1 neutrons. A similar increase of the relative γ-ray intensity was achieved in case of lines associated with the emission of 3 neutrons, with respect to lines from both 2 and 1 neutron evaporation channels. The improvements were only possible with a significant reduction of the intensity of the true 3 neutron emission γ-ray lines. The influence of small amounts of γ-rays mis-interpreted as neutrons was studied. It was found that it dramatically reduces the quality of the reduction of the effects due to scattered neutrons