Results from a Calibration of XENON100 Using a Source of Dissolved Radon-220

A ²²⁰Rn 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 ²¹²Pb 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 ²²²Rn background after calibration. Alpha emitters are also distributed throughout the detector and facilitate calibration of its response to ²²²Rn. Using the delayed coincidence of ²²⁰Rn−²¹⁶Po, 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 ²¹²Po, t_1/2=(293.9±(1.0)_stat±(0.6)_sys)  ns.