Speaker
Description
A new hybrid system for trapping radon-222 emitted by an object is proposed. This text presents the calibration steps carried out at SNOLAB facility concerning low radon concentrations (~ µBq/m³). High-sensitivity background noise measurement is required in dark matter experiments to ensure that the system meets the projected noise limit (0.1 event/year for the PICO experiment). Indeed, radon is a known source of neutron-induced alpha background radiation (α, n). To quantify it, an ultra-pure charcoal with a low intrinsic radioactivity (0.2 mBq/kg) and suitable adsorption capacity (greater than that of bronze wool) is used. However, it is prone to clogging at low temperatures (<-60 °C), unlike bronze wool. By combining them, it is theoretically possible to exploit the advantages of both. Specifically, the length of the column, bonded to 15 g of carbon in a one-inch tube, is halved thanks to the bronze wool that separates and frames it. To assess the validity of this device, the trapping efficiency is determined at various cryogenic temperatures and assay time. It is possible to perform the measurement with a limited gas load (<0.1 mbar) in the emanating system with bronze wool as the sole trapping material. This method is not employed because it is ineffective for assessing huge emanating entities. This study involves allowing the system to emanate Rn under a certain amount of N₂. It provides a conservative measurement, as diffusion-induced emanation decreases with increasing vacuum pressure. The second approach does not require the introduction of N₂ into the system during emanations. N₂ is simply used to facilitate the transfer of Rn from the object to the trap. This strategy offers the greatest sensitivity. Note that a water trap is also used, as humidity can distort the measurement.
| Keyword-1 | Radon |
|---|---|
| Keyword-2 | Charcoal |
| Keyword-3 | Emanation |