Description
Neutron scattering facilities rely on efficient moderators to optimise the performance of experiments for fundamental and applied physics. Cold and water moderators are crucial for tailoring neutron energy spectra and pulse profiles to meet diverse experimental requirements. Achieving optimal moderator design requires advanced computational tools to simulate neutron pulse evolution within the TRAM (Target Reflector and Moderator assembly) and integrate the resulting leakage from the moderators as a source into the instrument's optical model downstream to the sample location.
This study benchmarks the FLUKA-CERN simulation model of the ISIS Target Station 1 (TS1) against experimental neutron fluence rate measurements at instruments fed by either water or cold moderators. By coupling the TRAM FLUKA-CERN model with the McStas one of representative beamlines, a detailed analysis of neutron fluxes, energy spectra, and spatial distributions at sample positions was performed. The Monte Carlo predictions were compared with experimental data, providing critical validation and development insights for future advancements.
The integration of FLUKA-CERN and McStas required a specialised interface to optimise the coupling process. This interface ensured precise data transfer, enabling accurate and realistic simulations of neutron beams as they propagate through the instruments.
The findings confirm the robustness of FLUKA-CERN in simulating neutron transport and thermalisation processes for both cold and water moderators. This work is particularly significant for the development of next-generation pulsed neutron sources, such as ISIS-II, offering actionable recommendations for enhancing moderator performance and mitigating the background at the samples.
