On concentration of 42Ar in liquid argon

Data from the DBA liquid argon ionization chamber experiment were used to obtain an estimate on the concentration of Ar-42 in the Earth's atmosphere, 9.2(-4.6)(+2.2) 10(-21) atoms of Ar-42/ atom of Ar-40. This corresponds to a specific activity of freshly produced liquid argon of 92(-46)(+22) mu Bq/kg.