PU-244 FISSION XENON AND PRIMORDIAL XENON IN LUNAR-SAMPLES AND METEORITES

Xenon found in lunar samples is a binary mixture of Pu-244 fission xen on and a trapped xenon, whose isotopic composition often shows a strik ing resemblance to that of TAKAOKA'S-1 primitive xenon. The decay prod uct of I-129 is conspicuously absent in lunar samples and this may be attributed to the facts that (a) the half-life of I-129 is much shorte r than that of Pu-244, and (b) the separation of xenon from plutonium may take place easily, since the former is a gaseous element, while th e latter is a refractory element. The separation of xenon from iodine may not take place easily, however,since the former is a gaseous eleme nt, while the latter is a volatile element. The isotopic compositions of the trapped xenon released from ordinary chondrites and achondrites resemble that of TAKAOKA's primitive xenon, which has been mass-fract ionated in such a manner that the heavier isotopes are systematically enriched relative to the lighter isotopes.