Abstract
Aria is a plant hosting a {350},hbox {m} cryogenic isotopic distillation column, the tallest ever built, which is being installed in a mine shaft at Carbosulcis S.p.A., Nuraxi-Figus (SU), Italy. Aria is one of the pillars of the argon dark-matter search experimental program, lead by the Global Argon Dark Matter Collaboration. It was designed to reduce the isotopic abundance of {^{39}hbox {Ar}} in argon extracted from underground sources, called Underground Argon (UAr), which is used for dark-matter searches. Indeed, {^{39}hbox {Ar}} is a beta -emitter of cosmogenic origin, whose activity poses background and pile-up concerns in the detectors. In this paper, we discuss the requirements, design, construction, tests, and projected performance of the plant for the isotopic cryogenic distillation of argon. We also present the successful results of the isotopic cryogenic distillation of nitrogen with a prototype plant.
Highlights
Large liquid argon detectors offer one of the best avenues for detecting galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei
Atmospheric Argon (AAr) has a naturally occurring radioactive isotope, 39Ar, of isotopic abundance of 8 × 10−16 in mass, which is a β-emitter of cosmogenic origin, and whose activity of about 1 Bq kg−1 raises background and pile-up concerns
Argon extracted from underground wells, called Underground Argon (UAr), has a greatly reduced 39Ar content and is pivotal to the physics potential of dark-matter search experiments
Summary
Large liquid argon detectors offer one of the best avenues for detecting galactic weakly interacting massive particles (WIMPs) via their scattering on atomic nuclei. The liquid argon target allows for powerful discrimination between nuclear and electron recoil scintillation signals via pulse-shape discrimination [1–3], provided the background rate is not too high This discrimination method cannot be applied in experiments that look at the ionization signal only [4,5]. In addition to cryogenic distillation, a few other techniques are currently available for the separation of argon isotopes These techniques are based on the difference in molecular mass, such as centrifugal separation and diffusion separation, the latter based on the different average speed, at thermal equilibrium, among isotopes of the same energy. The cryogenic isotopic distillation plant Aria appears as a very promising new avenue for the depletion from 39Ar of such large quantities of argon, at reasonable cost and time. The successful outcome of this run paved the way to the continuation of the project and the construction of the full plant
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