Development of a tagged source of Pb-206 nuclei

There is a particular class of unavoidable backgrounds that plague low-background experiments and rare event searches, particularly those searching for nuclear recoil event signatures: decaying daughters of the ²³⁸U nuclear decay chain, which result from radon plate-out on detector materials. One such daughter isotope, ²¹⁰Po, undergoes α-decay and produces a recoiling 103 keV ²⁰⁶Pb nucleus. To characterize this important background in the context of noble element detectors, we have implemented a triggered source for these ²⁰⁶Pb recoils in a dual-phase xenon time projection chamber (Xe TPC) within the Davis Xenon R&D testbed system (DAX). By adhering ²¹⁰Po to the surface of a PIN diode and electrically floating the diode on the cathode of the TPC, we tag the α signals produced in the PIN diode and trigger on the correlated nuclear recoils in the liquid xenon (LXe). We discuss our methods for ²¹⁰Po deposition, electronic readout of the PIN diode signals at high voltage, and analysis methods for event selection.