Measurement of the ion fraction and mobility of ${}^{218}$Po produced in ${}^{222}$Rn decays in liquid argon

Abstract

We report measurements of the charged daughter fraction of ${}^{218}$Po as a result of the ${}^{222}$Rn alpha decay, and the mobility of ${}^{218}$Po${}^{+}$ ions, using radon-polonium coincidences from the ${}^{238}$U chain identified in 532 live-days of DarkSide-50 WIMP-search data. The fraction of ${}^{218}$Po that is charged is found to be 0.37$\pm$0.03 and the mobility of ${}^{218}$Po${}^{+}$ is (8.6$\pm$0.1)$\times$10${}^{-4}$$\frac{{\text{cm}}^2}{\text{Vs}}$.