SANDD: A highly-segmented pulse-shape-sensitive plastic scintillator detector incorporating silicon photomultiplier arrays.

We have studied the key metrics of a prototype antineutrino detector module designed for directional sensitivity. SANDD (a Segmented AntiNeutrino Directional Detector) will eventually comprise a central module of 64 elongated segments of $^{6}$Li-doped pulse-shape-sensitive scintillator rods, each with a square cross section of 5.4 mm $\times$ 5.4 mm, surrounded by larger cross section bars of the same material. The most important metrics with the potential to impact the performance of the central module of SANDD are neutron and gamma-ray pulse-shape sensitivity using silicon photomultipliers (SiPMs), particle identification via scintillator rod multiplicity, and energy and position resolution. As a first step, we constructed a prototype detector to investigate the performance of a central SANDD-like module using two 64-channel SiPM arrays and rods of undoped pulse-shape-sensitive plastic scintillator. We report the first observation of neutron/gamma-ray pulse-shape sensitivity using a fully-instrumented 8 $\times$ 8 array of plastic scintillator segments coupled to two 5 cm $\times$ 5 cm 64-channel SiPM arrays.