A High-Sensitivity Radon Emanation Detector System for Future Low-Background Experiments

TL;DR

This paper introduces a highly sensitive radon emanation detector system designed to measure surface radon release from materials, crucial for reducing background noise in low-background physics experiments like dark matter detection.

Contribution

The paper presents a novel detector system utilizing cryogenic traps and electrostatic collection to directly quantify radon emanation rates with high sensitivity.

Findings

Detection sensitivity of ~0.06 mBq at 90% C.L.

Emanation activity measured at (0.16 ± 0.03) mBq.

Overall detection efficiency of approximately 36%.

Abstract

Radioactive radon atoms originating from the long-lived primordial $^{238}\mathrm{U}$ and $^{232}\mathrm{Th}$ 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 $^{222}\mathrm{Rn}$ progeny $^{214}\mathrm{Pb}$, for example, dominates the background of current liquid xenon-based direct dark matter detectors. We report on a new detector system to directly quantify the $^{222}\mathrm{Rn}$ 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 daughter isotopes are collected electrostatically on a silicon PIN photodiode to spectrometrically measure the alpha decays of $^{218}\mathrm{Po}$ and $^{214}\mathrm{Po}$. The overall detection efficiency is $\sim 36\,\%$ for both polonium channels. The radon emanation activity of the emanation vessel was measured to be $(0.16\pm 0.03)\,\mathrm{mBq}$, resulting in a detection sensitivity of $\sim 0.06\,\mathrm{mBq}$ at $90\,\%\,\mathrm{C.L.}$.