Calibration of a gated neutron time-of-flight spectrometer with low-afterglow.

Neutron Time-of-Flight (nTOF) detectors are key diagnostics to detect thermonuclear neutrons in laser-fusion experiments. This diagnostic, however, is often plagued by strong gamma-ray noise prior to neutron signals, especially in harsh fast-ignition (FI) environments. To address this issue, a combination of low-afterglow liquid scintillators with time-gated photomultiplier tubes as necessary nTOF components would be a natural solution. However, the calibration of such detectors is challenging due to low detection efficiency and low neutron yield in FI experiments. In this paper, we propose a novel method to cross-calibrate a gated low-afterglow nTOF spectrometer using a pre-calibrated traditional non-gated nTOF spectrometer. This approach was demonstrated using neutrons from counter-streaming deuterated-polystyrene plasmas driven by the ShenGuang-II (SG-II) laser facility, with neutron yields ranging from 4 × 105 to 1 × 107. By implementing this calibration method, we anticipate a significant improvement in the accuracy of neutron detection within a 10% uncertainty for double-cone ignition experiments.