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

TL;DR

This paper demonstrates the use of a Rn-220 source for calibration in the XENON100 dark matter detector, enabling low-energy recoil calibration, mapping convective motion, and measuring Po-212 half-life with minimal background impact.

Contribution

It introduces a novel Rn-220 calibration method for large liquid noble detectors, improving calibration accuracy and understanding of internal particle dynamics.

Findings

Pb-212 beta emission enables low-energy calibration

Rn-220 source activity decays below background in a week

First mapping of convective particle motion in XENON100

Abstract

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