Abstract
Abstract
The Single Volume Scatter Camera (SVSC) Collaboration aims to develop portable neutron
imaging systems for a variety of applications in nuclear non-proliferation. Conventional
double-scatter neutron imagers are composed of several separate detector volumes organized in at
least two planes. A neutron must scatter in two of these detector volumes for its initial
trajectory to be reconstructed. As such, these systems typically have a large footprint and poor
geometric efficiency. We report on the design and characterization of a prototype monolithic
neutron scatter camera that is intended to significantly improve upon the geometrical shortcomings
of conventional neutron cameras. The detector consists of a 50
mm×56 mm× 60 mm
monolithic block of EJ-204 plastic scintillator instrumented on two faces with arrays of 64
Hamamatsu S13360-6075PE silicon photomultipliers (SiPMs). The electronic crosstalk is limited to
< 5% between adjacent channels and < 0.1% between all other channel pairs. SiPMs introduce a significantly
elevated dark count rate over PMTs, as well as correlated noise from after-pulsing and optical
crosstalk. In this article, we characterize the dark count rate and optical crosstalk and present
a modified event reconstruction likelihood function that accounts for them. We find that the
average dark count rate per SiPM is 4.3 MHz with a standard
deviation of 1.5 MHz among devices. The analysis method we employ
to measure internal optical crosstalk also naturally yields the mean and width of the
single-electron pulse height. We calculate separate contributions to the width of the
single-electron pulse-height from electronic noise and avalanche fluctuations. We demonstrate a
timing resolution for a single-photon pulse to be (128 ± 4) ps. Finally, coincidence analysis is employed to measure
external (pixel-to-pixel) optical crosstalk. We present a map of the average external crosstalk
probability between 2×4 groups of SiPMs, as well as the in-situ timing characteristics
extracted from the coincidence analysis. Further work is needed to characterize the performance
of the camera at reconstructing single- and double-site interactions, as well as
image reconstruction.
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