I will discuss the current status of my tests characterizing a detector to be used for R&D for the Enriched Xenon Observatory (EXO) to count an irradiated Cs-136 source from xenon cells. The source is produced at the TUNL lab by proton-irradiating gaseous xenon. The apparatus consists of a sodium iodide crystal coupled to a photomultiplier tube (PMT); the signal is fed to a high-speed digitizer card that is read and controlled by LabVIEW. I have performed extensive tests on the digitizer card with respect to the sampling rate, voltage offsets, resolution, and linearity, with the objective of understanding its properties. The Cs-136 source will be used at UMass as a tool to study the behavior of the barium ion in liquid xenon, with the ultimate goal of increasing the sensitivity of future beta-decay experiments.