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High-order angular correlation of californium-252 fission neutrons and the effect of detector cross-talk

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E-pub ahead of print
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<mark>Journal publication date</mark>10/02/2019
<mark>Journal</mark>Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Publication statusE-pub ahead of print
Early online date10/02/19
Original languageEnglish

Abstract

High-order angular correlations of fast neutrons emitted by spontaneous fission in californium-252 (252^Cf) have been measured with a 2D array of 15 EJ-309 organic liquid scintillation detectors. These are compared with the results of Geant4 simulations using both an uncorrelated, average fission model and correlated fission models, which have also been used to quantify the impact of detector cross-talk on these distributions. In general, a bipolar trend is observed up to and including quadruple events, that is, 휃_12, 휃_13 and 휃_14. A bias as 휃→0 degrees in these data is observed that is consistent with the expectation of cross-talk being more prevalent for nearest- neighbour detectors. This is observed to be reduced for higher orders (휃_13 and 휃_14 relative to 휃_12) and for wider gate widths (25 ns rather than 10 ns), consistent with this phenomenon being cross-talk. For the case of 휃_13, each of the composite angular distributions for the 14 detector positions 24 degrees ≤ 휃 ≤ 336 degrees have also been derived: a variation from a bipolar trend to a more isotropic behaviour, accompanied by a reduction in the relative level of response, is observed in these data for detector angles orthogonal to the reference detector at 0◦ consistent with the majority of neutrons being emitted from accelerated fragments. This research constitutes an important step towards quantifying and managing cross-talk as arrays of organic scintillators attract interest for practical applications such as nuclear materials assay.