Advertisement

Dating of mineral samples through activation analysis of argon

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

Abstract

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.

Keywords

Mass Spectrometry Argon Manganese Chlorine Activation Analysis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. 1.
    J. KOLTHOFF, P. ELVING, Treatise on Analytical Chemistry, 2nd Ed., Wiley Interscience, New York (1986), 445.Google Scholar
  2. 2.
    M. LEDERER, J. HOLLANDER, I. PERLMAN, Table of Isotopes, 6th Ed., J. Wiley, New York (1967), 242.Google Scholar
  3. 3.
    Dictionary of Scientific and Technical Terms, 4th Ed., McGraw-Hill (1989), 650.Google Scholar
  4. 4.
    W. EHMANN, D. VANCE, Radiochemistry and Nuclear Methods of Analysis, Wiley Interscience New York (1991), 395–397.Google Scholar
  5. 5.
    L. CURRIE, Anal. Chem. 40 (1968), 586.Google Scholar

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)

Personalised recommendations