Xenon isotope anomalies and temperature of the sun during the deuterium-burning stage

Abstract

The xenon found in carbonaceous chondrites and in lunar fines is predominantly of solar origin and its isotopic composition represents that of primordial xenon, which was modified by exposure to a neutron flux during the deuterium-burning stage of the sun. The isotopic composition of atmospheric xenon, on the other hand, represents that of mass-fractionated primordial xenon, in which the heavier isotopes are systematically enriched relative to lighter isotopes. Solar xenon contains excesses of xenon isotopes, produced by neutron-capture reactions in the sun's core during the deuterium-burning stage. The enrichment of ¹³⁰Xe and ¹³²Xe in solar xenon is of special interest, because these isotopes can be enriched only through neutron-capture reactions on ¹²⁹Xe and ¹³¹Xe in the sun. The ratio of excess ¹³⁰Xe and ¹³²Xe may thus provide a direct measure of the temperature of the sun during the deuterium-burning stage. Although many capture cross-section measurements over a wide neutron energy range for the four xenon isotopes, ¹²⁹Xe, ¹³⁰Xe, ¹³¹Xe and ¹³²Xe, are needed before a reliable temperature scale can be established, it appears that an upper limit of roughly 10⁶⁰K can be set for the temperature of the sun on the basis of existing data and our current knowledge of the general pattern of neutron-capture excitation functions.