Scattered neutron background in thermal neutron detectors

TL;DR

This paper models and validates the scattered neutron background in thermal neutron detectors, crucial for low-background measurements in neutron scattering instruments, using detailed Geant4 simulations.

Contribution

First detailed Geant4 simulation of thermal neutron scattering background sources in a large-area detector for inelastic neutron spectrometers.

Findings

Scattering from detector components is less significant than from other sources.

Model validation shows good agreement with experimental data.

Understanding background sources aids in effective shielding design.

Abstract

Inelastic neutron scattering instruments require very low background; therefore the proper shielding for suppressing the scattered neutron background, both from elastic and inelastic scattering is essential. The detailed understanding of the background scattering sources is required for effective suppression. The Multi-Grid thermal neutron detector is an Ar/CO$_{2}$ gas filled detector with a $^{10}$B$_{4}$C neutron converter coated on aluminium substrates. It is a large-area detector design that will equip inelastic neutron spectrometers at the European Spallation Source (ESS). To this end a parameterised Geant4 model is built for the Multi-Grid detector. This is the first time thermal neutron scattering background sources have been modelled in a detailed simulation of detector response. The model is validated via comparison with measured data of prototypes installed on the IN6 instrument at ILL and on the CNCS instrument at SNS. The effect of scattering originating in detector components is smaller than effects originating elsewhere.