XENON ISOTOPES IN COSMO- AND GEOCHRONOLOGY: CAPABILITIES AND APPLICATIONS (Invited Presentation)

Xenon has nine stable isotopes and is the least abundant terrestrial noble gas. Yet heavy Xe isotopes have high fission yields. Xe is also retained by minerals much better than other noble gases. These properties led to development of several dating schemes utilizing Xe isotopes. (i) U-Xe chronometer and its neutron activation version, Xes-Xen isochron chronometer, are used for dating of pitchblends [1], zircons [2] and other U-bearing minerals [3]. (ii) The decay of ¹²⁹I formed during neutron induced fission of ²³⁵U to ¹²⁹Xe provides the age of neutron exposure and, in conjunction with Xe_s-Xe_n isochron dating, can be used to estimate the time required to grow cm-size U-bearing veins. (iii) Double beta decay of ¹³⁰Te to ¹³⁰Xe allows dating gold deposits using associated Te minerals like calaverite [5]. This technique also has a neutron activation version where ¹³⁰Xe is converted to ¹³¹Xe, and then natural diffusional losses of radiogenic ¹³⁰Xe could be estimated by analyses of ¹³⁰Xe/¹³¹Xe in step-wise heating experiments. (iv) I-Xe dating is successfully used for study of early Solar system events. It is based on decay of primordial ¹²⁹I (T_1/2=15.7Ma) to ¹²⁹Xe. After neutron irradiation stable ¹²⁷I is converted to ¹²⁸Xe. An analysis of radiogenic ¹²⁹Xe/¹²⁸Xe ratio in the course of step-wise pyrolysis provides the mean to account for natural losses of ¹²⁹Xe and evaluate the thermal history of host meteorite. I-Xe is a relative chronometer and is anchored to an absolute time-scale through the standard of known Pb-Pb age. Finally light Xe isotopes can be used to estimate cosmic ray exposure ages.

Supported by NASA grant NNX14A124G. [1] Meshik et al. 2000. Mineralum Deposita 35, 190-205. [2] Shukolyukov et al. 2009. Petrology 17, 1-24. [3] Teitsma and Clarke. 1978. J. Geophys. Res. 83, 5443-5453. [4] Meshik et al. 1988. PhD Thesis. [5] Meshik et al. 2008. Nuclear Phys. A 809, 275-289. [6] Hohenberg and Pravdivtseva. 2008. Chemie der Erde 68, 339-351.