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, t1/2=(293.9±(1.0)ₛₜₐₜ±(0.6)sys) ns.