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Title: 39Ar/Ar measurements using ultra-low background proportional counters

Age dating groundwater and seawater using 39Ar/Ar ratios is an important tool to understand water mass flow rates and mean residence time. For modern or contemporary argon, the 39Ar activity is 1.8 mBq per liter of argon. Radiation measurements at these activity levels require ultra low-background detectors. Low-background proportional counters have been developed at Pacific Northwest National Laboratory. These detectors use traditional mixtures of argon and methane as counting gas, and the residual 39Ar from commercial argon has become a predominant source of background activity in these detectors. We demonstrated sensitivity to 39Ar by using geological or ancient argon from gas wells in place of commercial argon. The low level counting performance of these proportional counters is then demonstrated for sensitivities to 39Ar/Ar ratios sufficient to date water masses as old as 1000 years.
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Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 0969-8043
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Radiation and Isotopes; Journal Volume: 107
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Org:
Country of Publication:
United States
39Ar/Ar measurements using ultra-low background proportional counters, Argon