Abstract
A $^{220}Rn$ source is deployed on the XENON100 dark matter detector in order to address the challenges in calibration of tonne-scale liquid noble element detectors. We show that the $^{212}Pb$ beta emission can be used for low-energy electronic recoil calibration in searches for dark matter. The isotope spreads throughout the entire active region of the detector, and its activity naturally decays below background level within a week after the source is closed. We find no increase in the activity of the troublesome $^{222}Rn$ background after calibration. Alpha emitters are also distributed throughout the detector and facilitate calibration of its response to $^{222}Rn$. Using the delayed coincidence of $^{220}Rn−^{216}Po$, we map for the first time the convective motion of particles in the XENON100 detector. Additionally, we make a competitive measurement of the half-life of $^{212}Po$, $t_{1/2}=(293.9 \pm(1.0)stat \pm(0.6)sys$) ns.
XENON Collaboration