Abstract
Abstract
Radioactive radon atoms originating from the primordial
238U and 232Th decay chains are
constantly emanated from the surfaces of most materials. The radon
atoms and their radioactive daughter isotopes can significantly
contribute to the background of low-background experiments. The
222Rn progeny 214Pb, for example,
dominates the background of current liquid xenon-based direct dark
matter detectors. We report on a new detector system to quantify
the 222Rn surface emanation rate of materials. Using
cryogenic physisorption traps, emanated radon atoms are transferred
from an independent emanation vessel and concentrated within the
dedicated detection vessel. The charged radon daughter isotopes are
collected electrostatically on a silicon PIN photodiode to
spectrometrically measure the alpha decays of 214Po
and 218Po. The overall detection efficiency is
∼ 36 % for both polonium channels. The radon emanation
activity of the emanation vessel was measured to be
(0.16± 0.03) mBq, resulting in a detection sensitivity
of ∼ 0.06 mBq at 90 % C.L.