California GAMA Special Study. Development of a Capability for the Analysis of Krypton-85 in Groundwater Samples

Technical Report · Mon Jun 01 00:00:00 EDT 2015

DOI:https://doi.org/10.2172/1252619· OSTI ID:1252619

Visser, Ate ^[1]; Bibby, Richard K. ^[1]; Moran, Jean E. ^[2]; Singleton, Michael J. ^[1]; Esser, Bradley K. ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. California State Univ. (CalState), Long Beach, CA (United States)

A capability for the analysis of krypton-85 (⁸⁵Kr) in groundwater samples was developed at LLNL. Samples are collected by extracting gas from 2000-4000 L of groundwater at the well, yielding approximately 0.2 cm³ STP krypton. Sample collection takes 1 to 4 hours. Krypton is purified in the laboratory using a combination of molecular sieve and activated charcoal traps, and transferred to a liquid scintillation vial. The ⁸⁵Kr activity is measured by liquid scintillation on a Quantulus 1220 liquid scintillation counter from PerkinElmer. The detection limit for a typical 0.2 cm³Kr sample size is 11% of the present day activity in air, corresponding to the decay corrected activity in air in 1987. The typical measurement uncertainty is below 10% for recently recharged samples. Six groundwater samples were collected, purified and counted. ⁸⁵Kr was not detected in any of the samples counted at LLNL. ⁸⁵Kr was detected by the low level counting laboratory of Bern University in all samples between 1.5 and 6.6 decays per minute per cm³ krypton, corresponding to decay corrected activities in air between 1971 and 1985. The new capability is an excellent complement to tritium-helium, expanding the existing suite of age dating tools available to the GAMA program (³⁵S, ³H/³He, ¹⁴C and radiogenic helium). ⁸⁵Kr can replace ³H/³He in settings where ³H/³He ages are impossible to determine (for example where terrigenic helium overwhelms tritiogenic helium) and provides additional insight into travel time distributions in complex mixed groundwater systems.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC52-07NA27344
• OSTI ID: 1252619
• Report Number(s): LLNL-TR-665865; TRN: US1601364
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
KRYPTON 85
GROUND WATER
LIQUID SCINTILLATION DETECTORS
LOW LEVEL COUNTING
AGE ESTIMATION
GROUNDWATER RECHARGE
SENSITIVITY
RADIOMETRIC ANALYSIS