response functions for Cherenkov-based neutron detectors.

Neutron time-of-flight diagnostics at the NIF were recently outfitted with Cherenkov detectors. A fused silica radiator delivers sub-nanosecond response time and is optically coupled to a microchannel plate photomultiplier tube with gain from ∼1 to 10. Capitalizing on fast time response and gamma-ray sensitivity, these systems can provide better than 30 ps precision for measuring first moments of neutron distributions. Generation of instrument response functions (IRFs) is critical to meet the <1% uncertainty needed. A combination of Monte Carlo modeling, benchtop characterization, and comparison is employed. Close agreement is shown between the modeled IRFs and measurements using the NIF's short-pulse advanced radiographic capability beams. First and second moments of neutron spectra calculated using IRFs agree well with established scintillator measurements. Next-step designs offer increased sensitivity and time-response.