ELFT HÍRADÓ

[Máté Zoltán <mate AT atomki.mta.hu>]

Az MTA Atommagkutató Intézet előadótermében
(Debrecen, Bem tér 18/c. 12. ép. III. em.)
2015. február 10-én, KEDDEN 11:00-kor

 
                       Karl B. HAASE     
      (US Geological Survey Groundwater Dating Laborator)                     

    Exploring Hydrofluorocarbons as Groundwater Age Tracers


címmel előadást tart.


Az előadás előtt 10:30-tól tea, vendégeket szívesen látunk.

                                                         Máté Zoltán


Kivonat:
Groundwater dating tracers are an essential tool for analyzing hydrologic 
conditions in groundwater systems. Commonly used tracers for dating 
post-1940s groundwater include sulfur hexafluoride (SF6), chlorofluorocarbons 
(CFCs), 3H-3He, and other isotopic tracers (85Kr, delta2H and delta18O 
isotopes, etc.). Each tracer carries a corresponding set of advantages and 
limitations imposed by field, analytical, and interpretive methods. 
Increasing the number available tracers is appealing, particularly if they 
possess inert chemical properties and unique temporal emission histories from 
other tracers.

Among the likely candidates identified are HCFC-22 and HFC-134a. Both 
compounds have unique atmospheric histories and chemical properties compared 
to other tracers, making them appealing for inclusion lumped parameter mixing 
models and in situations where SF6 or the CFCs are present in elevated 
concentrations from non-atmospheric sources such that they cannot be used for 
dating purposes. To measure these compounds we developed an analytical method 
that uses an atomic emission detector (GC-AED) in place of an ECD. In 
contrast to the ECD, the AED is a universally sensitive, highly linear, 
elementally specific detector, with sensitivities reaching into the low 
pico-gram range. The GC-AED system is capable of detecting concentrations 
cca. 200 fM (HCFC-22) and cca. 100 fM (HFC-134a), corresponding to piston 
flow ages of 54 and 18 yr, respectively, with a typical uncertainty of cca. 1 
yr. Comparisons between H(C)FCs, CFCS, and SF6 typically show broad 
disagreement between traditional dating methods and the H(C)FCs, indicating 
they are generally subject to loss processes, and may not be suitable for use 
as groundwater age tracers.
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