ABSTRACT

Five separate fractions of noble gases were extracted and analyzed as a 150g sample of the Canyon Diablo iron meteorite was heated to successively higher temperatures by direct coupling with an RF coil. Isotopic compositions of the light gases, He, Ne and Ar, demonstrate that essentially their entire inventory was produced by spallation reactions. Spallation products are also a prominent feature of the isotopes of Kr and Xe, but in each gas fraction the spallogenic heavy gases were mixed with a nonspallogenic component. The isotopic composition of Kr and Xe trapped in Canyon Diablo are shown to be type-Y, rather than the type-X Kr and Xe that is found with planetary He and Ne in mildly oxidized carbon fractions of chondrites. Large variations are observed in ratios of the light spallogenic noble gases. Spallation products in Kr and Xe tend to correlate with those in Ne, rather than in Ar, suggesting that diffusive fractionation is not responsible for variations in the ²¹Ne/³⁸Ar ratio. It is suggested that portions of the material in Canyon Diablo may have been preirradiated. Xenon contains a large component of excess ¹²⁹Xe and ¹³¹Xe from neutron capture on Te at energies above 0.4ev, but there is no indication that the decay of primordial ¹²⁹I or the incorporation of exotic interstellar dust produced the excess ¹²⁹Xe or ¹³¹Xe in our sample of Canyon Diablo. The maximum amount of excess ¹³⁶Xe in our sample from fission of the hypothetical superheavy elements is shown to be 600atoms/g if the trapped Xe is atmospheric in composition; however, if the trapped Xe is AVCC, it might be as high as 6, 000atoms/g.