Evaluating Systematic Uncertainties in a High-Precision Neutron Time-of-Flight (nTOF) Detector Suite

The precision neutron time-of-flight (nTOF) system under development for the Z Machine is designed to measure fusion neutron velocities with precisions better than 12 km/s¹. The system will feature nTOF detectors along three horizontal lines of sight separated azimuthally by 120°. Each detector will be placed at a radial distance of ~18.6 meters from the neutron source and will feature a quartz Cherenkov detector and a bibenzyl or DPAC scintillator coupled to 4 PMTs (similar to the design of the Spec nTOF detectors being fielded at the NIF). The impact of systematic uncertainties – including uncertainties in distances from the neutron source to detectors, cross-timing multiple detectors, signal path and cable delays, effects of neutron attenuation and scattering, and determining a PMT-specific instrument response function – will be quantified by propagating synthetic neutron spectra through a full forward-fit model. Synthetic datasets of DT and DD fusion neutron spectra will be generated with varying velocity distributions. Intermediate detectors, located at each line of sight at radial distances of ~12.0 meters, are being considered to further constrain the inferred neutron velocity distribution². [1] GP Grim et al. Rev Sci Instrum 95 083519 (2024). [2] JM Mitrani et al. Rev Sci Instrum 95 083529 (2024). Prepared by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Sandia National Laboratory is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.