Noble gases anomalies in terrestrial ores and meteorites
"Analyses of the content and isotopic composition of xenon and krypton in terrestiral ores containing tellurium, selenium or iodine resulted in the following conclusions: 1. The double beta-decay half-life for ¹³⁰Te is 2.51 x 10²¹ years from analysis of tellurobismuthite from Boliden, Sweden and 2.83 x 10²¹ years from analysis of tellurides from Kalgoorlie, Australia. 2. The ratio of the double beta-decay half-life of ¹²⁸Te relative to that of ¹³⁰Te is ≥ 108 and ≥ 293 for Boliden tellurobismuthite and Kalgoorlie tellurides, respectively. 3. Selenium minerals and tellurium ores containing selenium exhibit ⁸²Kr excess attributed to the double beta-decay of ⁸²Se. Preliminary half -life value for this decay is (2-4)10²⁰ years. 4. The formation of excesses of ¹²⁹Xe and ¹³¹Xe in tellurium ores and excess ⁸³Kr in selenium ores result from nuclear reactions on tellurium and selenium, respectively. 5. The excess ¹²⁹Xe in iodyrite (silver iodide) is from the in situ decay of ¹²⁹I incorporated in the ore during its formation. From the observed isotopic composition of xenon, it is calculated that prior to the nuclear age, the equilibrium ratio of ¹²⁹I/¹²⁷ was between 2.2 x 10⁻¹⁵ and 3.3 x 10⁻¹⁵. 6. Measurements of the ¹³⁰Xe, formed from the decay of ¹³⁰Te, and the tellurium content allow the age determination of hydrothermal deposits of tellurium by the ¹³⁰Te-¹³⁰Xe dating method. The ages of three telluride samples obtained by this new dating technique agree with geologic age estimates. Application of the neutron irradiation method of ¹²⁹I-¹²⁹Xe dating to chondrules and matrix of Bjurböle meteorite reveal the following: 1. The ¹²⁹I/¹²⁷ ratios incorporated in the Bjurböle chondrules and matrix are identical thereby indicating that these fractions are contemporaneous within ± 1. 5 x 10⁶ years. 2. The method of ¹²⁹I-¹²⁹Xe age determination by the neutron irradiation method is dependent on the intensity of the neutron flux. The release pattern of iodine-correlated ¹²⁹Xe is altered for all extraction temperatures by the use of high neutron flux. The relative fission yields from the spontaneous fission of ²⁵²Cf for krypton and xenon isotopes are ⁸³Kr :⁸⁴Kr :⁸⁵Kr :⁸⁶Kr::¹³¹Xe:¹³²Xe:¹³⁴Xe:¹³⁶Xe = 0.010:0.017:0 0049:0.032:0.35:0.52:0.92:≡1.000. A comparison of these results with the spontaneous fission yields of other actinides suggests that the enrichment observed in the heavy xenon isotopes of primitive chondrites might arise from the spontaneous fission of a superheavy element. The alternate possibility of simple mass dependent fractionation causing this enrichment in the heavy xenon isotopes is examined through a review of the helium, neon and argon isotope data obtained for carbonaceous chondrites. This study reveals that mass fractionation effects are prominent in altering the is atopic ratios of individual noble gases and the total abundance pattern of these gases in carbonaceous chondrites"--Abstract,pages iii-v.
Missouri University of Science and Technology
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