Cosmic ray exposure ages of iron meteorites using ³⁹K-⁴⁰K-⁴¹K dating

This research involves the determination of the cosmic ray exposure ages of iron meteorites using ³⁹K-⁴⁰K-⁴¹K dating. Potassium was separated from nickel using ~ 4 mL of Chelex-100 resin and 15 mL of ammonium acetate (a mixture of equal volumes of 2 M acetic acid and 3 M aqueous ammonia) as eluent. Nickel was retained as a complex and potassium elutes out. The method is effective because of a low value for the blanks (~ 50 ng of potassium) that could be achieved. The concentration of the separated K, measured using Graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled mass spectrometry (ICPMS) and isotope dilution mass spectrometry (IDMS) and will be used for the calculation of ³⁹K-⁴⁰K-⁴¹K exposure ages of iron meteorites. Potassium was successfully separated from multiple samples of 8 iron meteorites. The calculated CRE age (378 Ma) agrees for the meteorite Brownfield (355 Ma, Voshage and Feldmann, 1979) with the literature value. The literature value (645 Ma, Voshage and Feldmann, 1979) is ~3 times the value calculated (190 Ma, this work) for Picacho. Further studies are suggested and may be the awaited results from Harvard for some 8 samples will give us more information. A portion of the research is also focused on the measurement of activities of the cosmogenic nuclides ²⁶Al, ¹⁰Be, ³⁶Cl and ⁶⁰Fe. The ¹⁰Be(dpm/kg) and ³⁶Cl(dpm/kg) activities obtained were combined with available data from literature (Ammon et al., 2009) and the ⁴⁰K(dpm/kg) activities were predicted. The predicted K[subscript cos] (Total) concentrations were ~40 % higher for Brownfield and ~100 % higher for Picacho as compared with the experimentally determined values. To validate these results further work is suggested for the separation of potassium isotopes from irons and measuring the cosmogenic content. Newly measured ⁶⁰Fe activities of the meteorites Brownfield, Charlotte, Grant, NWA468, Picacho, Signal Mountain and Tlacotepec were reported and the ⁶⁰Fe(dpm/[kgNi] activities are in the range 0.3 – 1.5(dpm/[kgNi]). The ⁴⁰Ar-³⁹Ar apparent age, isochron, and cosmic ray exposure ages of 3 martian meteorites (ALHA 77005, Shergotty, Y000749) and a eucrite (Pasamonte) were also reported.Ph. D.Includes bibliographical referencesIncludes vitaby Nirmala Shanka