39Ar/Ar measurements using ultra-low background proportional counters. (January 2016)

• Record Type: Journal Article
• Authors: Hall, Jeter; Aalseth, Craig E.; Bonicalzi, Ricco M.; Brandenberger, Jill M.; Day, Anthony R.; Humble, Paul H.; Mace, Emily K.; Panisko, Mark E.; Seifert, Allen
• Is Part Of: Applied radiation and isotopes. Volume 107(2016:Jan.)
• Page Start: 187
• Page End: 190
• Publication Date: 2016-01
• Subjects: Water age-dating -- 39Ar -- Low level couning; Radiology -- Periodicals; Radiation -- Industrial applications -- Periodicals; Nuclear chemistry -- Periodicals; Internet resource; Periodical; 660.298
• DOI: 10.1016/j.apradiso.2015.10.006
• Languages: English
• ISSNs: 0969-8043

Abstract

Abstract: Age-dating groundwater and seawater using the 39 Ar/Ar ratio is an important tool to understand water mass-flow rates and mean residence time. Low-background proportional counters developed at Pacific Northwest National Laboratory use mixtures of argon and methane as counting gas. We demonstrate sensitivity to 39 Ar by comparing geological (ancient) argon recovered from a carbon dioxide gas well and commercial argon. The demonstrated sensitivity to the 39 Ar/Ar ratio is sufficient to date water masses as old as 1000 years. Highlights: 39 Ar/Ar age dating is important for understanding environmental water migration. Ultra low background proportional counters have been developed. 39 Ar is detected in atmospheric argon at a rate of 70.3 counts per day. The demonstrated background is 166 counts per day. Age dating is possible for water with underground residence time of up to 1000 years.