Dating of mineral samples through activation analysis of argon

  • M. Navarrete
  • L. Cabrera
  • F. Juarez
  • L. Rojas
Activation Analysis Techniques and Applications


Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the40Ar/40K ratio. This technique has been replaced since 1966 by measurement of40Ar/39Ar ratio, after artificial production of39Ar from the39K(n,p)39Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the40Ar/40K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (41Ar and42K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction41K(n,p)41Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric40Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.


Mass Spectrometry Argon Manganese Chlorine Activation Analysis 
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Copyright information

© Akadémiai Kiadó 1995

Authors and Affiliations

  • M. Navarrete
    • 1
  • L. Cabrera
    • 1
  • F. Juarez
    • 2
  • L. Rojas
    • 3
  1. 1.Faculty of ChemistryNational University of MexicoMexico City(Mexico)
  2. 2.Institute of GeophysicsNational University of MexicoMexico CityMexico)
  3. 3.National Institute of Nuclear ResearchMexico City(Mexico)

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