Argon
DarkSide uses argon because it can be purified to extremely high levels and produces light that helps distinguish different types of particles. While ordinary atmospheric argon contains radioactive Argon-39, DarkSide-50 showed that underground argon is more than 1,000 times less radioactive, making it an excellent material for detecting dark matter.
Underground Argon
The distribution of argon between the collaboration facilities.
Deep underground sources of argon have been discovered and a method developed to extract and purify detector grade argon from these sources. An integrated supply chain has been developed for the production and validation of UAr, involving three key projects: Urania, Aria, and DArT.
This production chain is a crucial element for the success of the DarkSide-20k program and represents a significant technological effort with implications for both fundamental research and future commercial and industrial developments.
Urania
Urania, located in the United States at the Kinder Morgan site in Cortez, Colorado, is responsible for extracting UAr from deep underground wells and performing an initial chemical purification. The gas is then liquefied for transport to Italy, where Aria carries out further purification from chemical contaminants. The collaboration developed and built these large infrastructures to produce the globally-unique UAr target specifically for DarkSide-20k.
The ARIA Project
The Aria project is located within the Monte Sinni mining complex, a former coal mine in southwestern Sardinia (Carbosulcis S.p.A.), Italy. It consists of a 350-meter-tall cryogenic distillation column, housed in a disused mining shaft. While its primary purpose is to purify UAr for DarkSide, Aria is also designed for isotopic separation, with broader potential applications in fields such as medicine and nuclear technologies.
DArT in ArDM
The final step involves DArT, an argon-filled detector currently operating at the Laboratorio Subterráneo de Canfranc (LSC) in Spain, which validates the UAr by characterizing its radiopurity and performance in detector-like conditions. This vertically integrated production chain is a crucial element for the success of the DarkSide-20k program and represents a significant technological effort with implications for both fundamental research and future commercial and industrial developments.
The expected Argon-39 concentration in the DarkSide-20k target is approximately 10^-19 g/g, which is beyond the reach of conventional metrology (i.e. ICP-MS). DArTinArDM is designed to measure this tiny concentration, in the Canfranc Underground Laboratory. DArTinArDM exploits the infrastructure of the predecessor ArDM experiment, using it as a tonne-scale single-phase argon veto detector around the DArT apparatus designed to measure Argon-39 at the ultra-low levels needed for DarkSide-20k.
The DarkSide Collaboration aims to unveil the nature of dark matter through liquid argon detector technology and innovative underground experiments. It is located at the Laboratori Nazional del Gran Sasso in L’Aquila, Italy.