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Descripción
Liquid argon is used as active media in several neutrino and dark matter experiments (DUNE, SBND, Microboone, Icarus, Dark Side, DEAP, …). Ionization particles in liquid argon produce free charges and scintillation photons. Both signals are used to perform calorimetric measurements, particle identification, three dimensional reconstruction. Liquid argon scintillation light can be quenched and absorbed by the presence of nitrogen contaminations. In neutrino detectors electronegative contaminants, like oxygen and water, are continuously filtered, while nitrogen is not. This can lead to a reduction of scintillation signal in case of air leaks in the detector. Dark matter experiments are typically filtering nitrogen in gas phase at room temperature.
The innovative molecular sieve is the zeolites Li-FAU. Purification tests have been performed using the Liquid Argon (LAr) Purification Cryostat (PuLArC) at IFGW/Unicamp. Previous studies regarding N2 gas capturing at T = 89K revealed a strong interaction of nitrogen with the lithium cations present in zeolite LiX. The tests performed in PuLArC have unequivocally shown that the Li-FAU adsorbent is capable of capturing N2 from recirculating LAr. The Li-FAU was able to reduce a N2 contamination of 20-50 ppm to 0.1-1.0ppm in 1-2h of circulation time. The test was repeated several times. These results invoke further investigations in larger scale LAr cryostats at Fermilab and CERN in order to support the possible use of Li-FAU molecular sieve, in replacemente of Molecular Sieve 4A, in LBNF-DUNE and other LAr experiments.
