Comparison of downscattered neutron measurements using gated images and time-of-flight detectors at the NIF

Data collected by the NIF neutron imaging system includes two energy gated neutron images and spatially averaged time-of-flight (nToF) data from the same neutron fluence used by the imaging system. Images are produced 28 m from the target, at time windows corresponding to neutron kinetic energies of 10 to 12 MeV and 13 to 17 MeV. Time-of-flight data are produced in a thin scintillating paddle detector located 27.26 m from the target. The preliminary corrected downscattered ratios produced by spatially averaging subregions of the image data from three cryogenic, equimolar DT implosions during June 2011 are: 2.5 $\pm $ 0.9{\%}, 2.5 $\pm $ 0.9 {\%}, and 2.9 $\pm $ 1.1 {\%}. The corresponding downscattered ratios produced by the nToF detector are 3.7 $\pm $ 0.9 {\%}, 3.8 $\pm $ 0.9 {\%}, and 5.6 $\pm $ 1.3 {\%}. We will present an overview of the measurement methodologies and analysis studies of the apparent systematic difference.