Development of an Experimental Setup to Measure the Radiopurity of Argon from Urania and Aria

Our current understanding of the universe establishes with scientific confidence that baryonic matter constitutes only \(\sim 5\%\) of the total mass-energy content. The remaining \(\sim 95\%\) is composed of Dark Energy and Dark Matter (DM). A major focus of 21st-century particle physics experiments is the pursuit of direct or indirect detection of DM particles. Among the most promising candidates under investigation are Weakly Interacting Massive Particles (WIMPs). In a \textit{large} and low-background target, WIMPs are expected to undergo \textit{nuclear recoil} with the target nucleus, producing a detectable signal above the background. DarkSide-20k (DS-20k) is a planned 20-tonne fiducial mass dual-phase Liquid Argon (LAr) Time Projection Chamber (TPC) for direct DM detection, currently under construction at Hall C of Laboratori Nazionali del Gran Sasso (LNGS), Italy. The experiment aims to achieve a background-free search for WIMPs within the mass range of 0.1 TeV to 10 TeV, focusing on spin-independent DM-nucleus interactions with a cross-section sensitivity of \(< 10^{-47}\) cm\(^2\). \hspace*{5mm} This thesis primarily addresses the challenges associated with preparing a low-radioactivity multi-tonne active volume for a DM detector, with a specific focus on the background contribution from \(^{39}\)Ar in the LAr active volume. To mitigate this, DS-20k plans to utilize underground argon (UAr), which, being shielded underground from cosmic spallation, exhibits significantly lower \(^{39}\)Ar activity compared to atmospheric argon (AAr). A global industrial-scale supply chain is being established to meet DS-20k's UAr requirements. The procurement process begins at the Urania plant, currently under construction in Cortez, Colorado, USA. After extraction, the UAr will be shipped to Sardinia, Italy, for purification at the ARIA distillation column located in the Carbosulcis mines. The ARIA column employs cryogenic distillation to remove lighter chemical impurities, such as O\(_2\) and N\(_2\), from UAr. The distillation process involves feeding the column at mid-height, with purified UAr being extracted from the bottom. The efficacy of this technology has been demonstrated by the prototype column, Seruci-0, for both N\(_2\) and Ar separation. Once purified, the UAr will be transported to LNGS for the final filling of the DS-20k detector. \hspace*{5mm} While ARIA is responsible for chemical purification, the radioactive assay of purified UAr represents a significant challenge. The radioisotope \(^{39}\)Ar is exceptionally difficult to characterize using conventional assay techniques. To address this, UAr samples collected at various points along the supply chain will be sent to the Laboratorio Subterráneo de Canfranc (LSC) in Spain for characterization by the DArTinArDM experiment. This experiment is specifically designed to measure the radiopurity of UAr by determining the specific activity of \(^{39}\)Ar. This thesis also encompasses the studies and efforts related to the development and construction of this experiment. The primary detector, DArT, which will be filled with UAr, has been operated in a test setup, successfully acquiring physics data to demonstrate proof of concept. Additionally, ArDM, serving as the active veto, has been refurbished with new photomultiplier tubes (PMTs) and equipped with an additional lead shield around the main vessel to minimize external background. \hspace*{5mm} Beyond the hardware activities associated with the assembly and operation of the experiment, the primary analysis presented in this thesis aims to achieve a competitive measurement of the \(^{39}\)Ar specific activity in AAr, using data collected from the test setup.