Design and calibration of an optically segmented single volume scatter camera for neutron imaging

Abstract

The Optically Segmented Single Volume Scatter Camera (OS-SVSC) aims to image neutron sources for non-proliferation applications using the kinematic reconstruction of elastic double-scatter events. Our prototype system consists of 64 EJ-204 organic plastic scintillator bars, each measuring 5mm × 5mm × 200mm and individually wrapped in Teflon tape. The scintillator array is optically coupled to two silicon photomultiplier ArrayJ-60035 64P-PCB arrays, each comprised of 64 individual 6x6mm J-Series sensors arranged in an 8 × 8 array. We report on the design details, including component selections, mechanical design and assembly, and the electronics system. The described design leveraged existing off-the-shelf solutions to support the rapid development of a phase 1 prototype. Several valuable lessons were learned from component and system testing, including those related to the detector's mechanical structure and electrical crosstalk that we conclude originates in the commercial photodetector arrays and the associated custom breakout cards. We detail our calibration efforts, beginning with calibrations for the electronics, based on the IRS3D application-specific integrated circuits, and their associated timing resolutions, ranging from 3090ps. With electronics calibrations applied, energy and position calibrations were performed for a set of edge bars using 22Na and 90Sr, respectively, reporting an average resolution of 12.07±0.03mm for energy depositions between 900keVee and 1000keVee. We further demonstrate a position calibration method for the internal bars of the matrix using cosmic-ray muons as an alternative to emission sources that cannot easily access these bars, with an average measured resolution of 14.86+-0.29mm for depositions between 900keVee and 1000keVee. The coincident time resolution reported between pairs of bars measured up to 400ps from muon acquisitions. Energy and position calibration values measured with muons are consistent with those obtained using particle emission sources.

Evaluation of a Positron-Emission-Tomography-based SiPM readout for Compact Segmented Neutron Imagers

“…Worldwide, there are now multiple efforts to develop a "single-volume" directional neutron detectors [1][2][3][4][5][6][7][8][9], motivated primarily by a desire to reduce size and complexity of neutron imagers. An effective way to achieve the detection and characterization of multiple neutron scatters is to use an array of independent detector segments.…”

Design and Characterization of an Optically-Segmented Single Volume Scatter Camera Module

“…The bar calibration procedure involves a single 22 Na source. We use the simultaneous and back-to-back 0.511 MeV gammas using a procedure similar to methods in both [11] and [15]. The tag scintillator is a teflon-wrapped stilbene crystal that is 5.0 cm in height and has a 0.5 cm × 0.5 cm cross section.…”

“…Monolithic compact designs propose to reconstruct multiple interaction positions within a single block of scintillator [7,9]. In contrast, optically segmented (OS) approaches [10][11][12][13][14] employ an array of rectangular scintillator bars that are read out on both sides: for each interaction, the time and position along the bar are reconstructed, while the other two dimensions are determined by which bar the scintillation event occurred in. Current methods to reconstruct the position along the bar include the log of the ratio of amplitudes at the two readout ends and the difference in pulse time arrival at the two ends.…”

“…Based on our study of different scintillator materials and reflective wrappings, we previously constructed a prototype OS-SVSC system with 0.5 cm × 0.5 cm × 20 cm EJ-204 scintillator bars wrapped in Teflon tape, read out by two commercially available ArrayJ-60035-64P-PCB Silicon Photomultiplier (SiPM) arrays from SensL. The full description of that system and its performance are reported in [11].…”

“…The prior system was affected by electrical crosstalk at the 10 % level within the electronics chain and the SiPM array itself, which is expected to negatively affect interaction reconstructions, as crosstalk from one neutron interaction could bias the time and energy measurements of the other interaction. Further tests demonstrated that crosstalk in the commercial SiPM array occurs primarily in quadrants, suggesting that one large contributor to this crosstalk is the SAMTEC connector (QTE-040-03) [11].…”