Methods for using argon-39 to age-date groundwater using ultra-low-background proportional counting

• Published in: Applied radiation and isotopes Vol. 126; pp. 9 - 12
• Main Authors: Mace, Emily, Aalseth, Craig, Brandenberger, Jill, Day, Anthony, Hoppe, Eric, Humble, Paul, Keillor, Martin, Kulongoski, Justin, Overman, Cory, Panisko, Mark, Seifert, Allen, White, Signe, Wilcox Freeburg, Eric, Williams, Richard
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01-08-2017; Elsevier
• Subjects: Age-dating; Argon-39; ENVIRONMENTAL SCIENCES; GEOSCIENCES; Groundwater; Proportional counting; Ultra-low-background; Argon-39; Ultra-low-background; Groundwater; Proportional counting; Age-dating
• ISSN: 0969-8043; 1872-9800
• DOI: 10.1016/j.apradiso.2016.12.037

Argon-39 can be used as a tracer for age-dating glaciers, oceans, and more recently, groundwater. With a half-life of 269 years, 39Ar fills an intermediate age range gap (50–1,000 years) not currently covered by other common groundwater tracers. Therefore, adding this tracer to the data suite for groundwater studies provides an important tool for improving our understanding of groundwater systems. We present the methods employed for arriving at an age-date for a given sample of argon degassed from groundwater.
•Argon-39 age-dating of groundwater using proportional counters.•Degasification and purification of groundwater to extract 39Ar samples.•PNNL has demonstrated sensitivity for direct beta counting of 39Ar.•Data analysis techniques for determining an age-date for a degassed argon sample.•Measurement of 519 year old 39Ar groundwater sample from Fresno, CA.