Interaction position, time, and energy resolution in organic scintillator bars with dual-ended readout

Abstract

We report on the position, timing, and energy resolution of a range of plastic scintillator bars and reflector treatments using dual-ended silicon photomultiplier readout. These measurements are motivated by the upcoming construction of an optically segmented single-volume neutron scatter camera, in which neutron elastic scattering off of hydrogen is used to kinematically reconstruct the source direction and energy of an incoming neutron. For this application, interaction position resolutions of about 10 mm and timing resolutions of about 1 ns are necessary to achieve the desired efficiency for fission-energy neutrons. The results presented here indicate that this is achievable with an array of $5\times5\times190~\mathrm{mm}^3$ bars of EJ-204 scintillator wrapped in Teflon tape, read out with SensL's J-series $6\times6~\mathrm{mm}^2$ silicon photomultipliers. With two independent setups, we also explore the systematic variability of the position resolution, and show that, in general, using the difference in the pulse arrival time at the two ends is less susceptible to systematic variation than using the log ratio of the charge amplitude of the two ends. Finally, we measure a bias in the absolute time of interactions as a function of position along the bar: the measured interaction time for events at the center of the bar is $\sim$100 ps later than interactions near the SiPM.