A liquid hydrogen-liquid water composite moderator may provide performance like liquid methane at high-power spallation sources where liquid methane is impractical. We have measured the neutronic properties of such a composite moderator, where a hydrogen layer 1.25cm thick was closely backed by water layers of 1.75cm and 3.75cm thickness. We also studied a moderator in which a 1.75cm water layer was closely backed by a 1.25cm hydrogen layer. We further performed simulations for each of these systems for comparison to the experimental results. We observed enhancement of the spectal intensity in the "thermal" energy range as compared to the spectrum from a conventional liquid hydrogen moderator. This enhancement grew more significant as the water thickness increased, although the pulse shapes became wider as well.
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