Fig. 2: Optimization of the epithermal neutron flux from the moderator.
a Sketch of the moderator geometry. b–d Epithermal (1–10 eV) neutron flux from a PHITS simulation at the detector position as a function of moderator dimensions. A moderator with 17 × 20 × 10 cm3 was chosen for the experiment. Error bars are the result of statistical uncertainties in the simulation and represent one standard deviation. e Epithermal flux distribution in the horizontal plane simulated with the measured neutron flux from Fig. 1d (p on LiF). Most epithermal neutrons are emitted in the vicinity of the converter. f Simulated neutron flux at the detector with and without the moderating wings. The wings drastically improve moderation efficiency. g (red) Simulated ToF uncertainty caused by the moderation for this LDNS moderator design in comparison to simulations for the LANSCE31,32 spallation source. (blue) Resulting energy uncertainty at 1.8 m distance for both source types. Moderated LDNS have shorter pulse lengths than conventional neutron sources enabling shorter ToF distances for the same energy resolution.
