Status and design of two-phase liquid-Xenon compton-imaging detector

PIXeY (Particle Identification in Xenon at Yale) is an R&D detector that uses xenon in gas-phase, liquid-phase, or two-phase mode. It features drift and proportional electric field regions set with 92%-transparent wire grids, highly reflective Teflon walls, and 14 high-quantum-efficiency PMTs (Hamamatsu R8778) to record both initial scintillation light (S1) and proportional scintillation light (S2) from the drifting of charge in the proportional region. It promises energy resolution and gamma/neutron discrimination that are competitive with previous systems. Recently, PIXeY has run stably for 12 weeks and the first data have been collected. Initial results are presented, along with planned design modifications that will transform PIXeY into a Compton imager. Crossed wires with 3-mm spacing will be used to record interaction locations. A preamp to read out each wire is also being designed to fulfill space and noise constraints. Finally, in order to precisely know the energy from each gamma-ray interaction, the scintillation light from each interaction must be distinguished from that due to others. Simulation is used to determine the optimal optical segmentation of the active volume using thin Teflon walls.