und gravimetrischen 24: Stimmung der Ergebnisse macht deutlich, daß früher für 25 °C veröffentlichte Werte von 10~9 oder gar Z)n = 1,0-10~6 cm2 s_1 10~20 cm2 s-1 auf den Einfluß von Grenzflächen- Messungen mit leichtem Wasserstoff. Sowohl die reaktionen zurückzuführen sind. Messungen mit Tritium als auch die röntgenogra- phischen und gravimetrischen Methoden sind von Herrn Prof. Dr. E. WICKE möchten wir an dieser Durchtrittshemmungen unabhängig. Die Überein- Stelle für wertvolle Hinweise und anregende Diskus- sionen herzlich danken. — Der Deutschen Forschungs- 24 E. WICKE U. A. OBERMANN, Z. Physik. Chem. N.F. (im gemeinschaft danken wir für die Unterstützung unserer Drude). — A. OBERMANN, Diplomarbeit, Münster 1970. Arbeit mit Personal- und Sachmitteln. Mass Fractionation and the Isotopic Anomalies of Xenon and Krypton in Ordinary Chondrites E. W. HENNECKE and 0. K. MANUEL Department of Chemistry, Universiy of Missouri, Rolla, Missouri (USA) (Z. Naturforsch. 26 a, 1980—1986 [1971] ; received 7 August 1971) The abundance and isotopic composition of all noble gases are reported in the Wellman chon- drite, and the abundance and isotopic composition of xenon and krypton are reported in the gases released by stepwise heating of the Tell and Scurry chondrites. Major changes in the isotopic com- position of Xe result from radiogenic Xe129 and from variations in the isotopic mass fractionation pattern in the different temperature fractions. The isotopic composition of trapped krypton in the different temperature fractions of the Tell and Scurry chondrites displays smaller fractional changes than xenon, but the isotopic composition of these two gases covary in the manner expected from mass dependent fractionation. Many clues of early geologic events have been noted that a comparison of the earth's inventory of recorded in the stable noble gases, He, Ne, Ar, Kr noble gases with the solar abundances of these ele- and Xe. The chemical inertness and volatile nature, ments shows preferential loss from terrestrial mate- even at relatively low temperatures, resulted in al- rial of the gases lighter than krypton. Subsequent most complete loss of these elements from more work on noble gases in terrestrial sediments 3 found condensable material when solid planetary matter high concentrations of xenon which, when added to formed in our solar system. Many isotopic anoma- the atmospheric inventory of noble gases, show that lies of these elements have been generated in solid the earth's fractionation of noble gases extends to planetary material subsequent to this separation, by the heaviest stable gas, xenon. The trapped noble induced nuclear reactions and by natural radio- gases in stone meteorites display a similar fractio- active decay of more abundant elements. nation pattern 4' 5 with the xenon preferentially re- Although the generation of isotopic anomalies of tained over neon by a factor 104 — 105. all the stable noble gases by nuclear processes is SIGNER and SUESS 6 discussed the role of mass well documented, there is also evidence for the pro- fractionation in generating isotopic anomalies of duction of isotopic anomalies of noble gases by neon and argon in planetary material. They noted simple isotopic masä fractionation at the time of a covariance of Ar36/Ar38, Ne20/Ne22 and Ne20/Ar36 the separation of these from more condensable ele- ratios in atmospheric and meteoritic gases. MA- ments. In 1949 SUESS 1 and BROWN 2 independently NUEL 7 reported variations in the trapped Ne20/Ne22 Reprint requests to Prof. Dr. O. K. MANUEL, Department 4 J. H. REYNOLDS, Phys. Rev. Letters 4, 351 [1960]. of Chemistry, University of Missouri-Rolla, Rolla/Missouri 5 O. K. MANUEL and M. W. ROWE, Geochim. Cosmochim. 65401, USA. Acta 28. 1999 [1964]. 1 H. E. SUESS, J. Geol. 57, 600 [1949], 6 P. SIGNER and H. E. SUESS. in: Earth Science and Meteo- 2 H. BROWN, The Atmosphere of the Earth and the Planets, rites, North-Holland Publ. Co., Amsterdam 1963. University of Chicago Press, Chicago 1949. 7 O. K. MANUEL, Geochim. Cosmochim. Acta 31, 2413 [1967]. 3 R. A. CANALAS, E. C. ALEXANDER, JR., and O. K. MANUEL, J. Geophys. Res. 73, 3331 [1968]. and Ne21/Ne22 ratios in the different temperature der to obtain additional data with which to examine fractions of the Fayetteville meteorite and suggested the current framework of ideas on the origin of that these variations result from isotopic mass frac- noble gas anomalies in meteorites. Samples of three tionation. However, PEPIN and coworkers8-10 re- ordinary chondrites were used for this investigation. ported that there is no sign that diffusive fractiona- tion is responsible for any of the isotopic variations Measurements of meteoritic neon. Recent results on the isotopic composition of trapped meteoritic He, Ne and Ar in Relatively large meteorite samples, weighing about the laboratories at Minnesota, Chicago and Rice 10 grams each, were used in this study. These were purchased from the American Meteorite Laboratory have been attributed to nuclear reactions 10 ~14, but (AML). The name and type of each meteorite, the 15-17 other authors have maintained that the ob- sample weight and the AML catalogue number of the served variations result from simple isotopic frac- specimen from which our samples were taken are as tionation. follows: The Wellman, Texas olivine bronzite chon- drite, 10.888 grams from specimen # H 12.56; the For the heavy noble gases, a similar divergence Tell, Texas olivinie hypersthene chondrite, 8.474 grams, of opinions has developed. SRINIVASAN et al.18 first from specimen #H 24.67; and the Scurry, Texas oli- suggested that spontaneous fission of superheavy vine bronzite chondrite, 7.909 grams, from specimen elements may be responsible for the enrichment of #H 65.25. heavy xenon isotopes in carbonaceous chondrites. The samples were mounted in side-arm chambers of a quartz extraction bottle. The samples were heated to ANDERS and HEYMANN 19 have arrived at a similar ~ 60 °C overnight to remove surface contamination, conclusion by comparing the excess heavy xenon the molybdenum crucible was degassed at 1800 °C and isotopes with the content of volatile elements in the pressure of the system reduced to 5 x 10-8 Torr. carbonaceous chondrites, and EBERHARDT et al. 20 The extraction bottle and preliminary "getters" were then isolated from the rest of the system by metal bel- have interpreted the isotopic composition of solar- lows valves, the sample to be analyzed was then drop- type xenon as evidence for large amounts of fissio- ped magnetically into the molybdenum crucible which genic xenon in carbonaceous chondrites. However, was heated by a radiofrequency induction heater. An KURODA and MANUEL 15 recently pointed out that optical pyrometer was used to estimate the extraction the enrichment of heavy xenon isotopes in carbon- temperatures. Each extraction temperature was main- tained for 30 minutes, and the evolved gases were aceous and gas-rich meteorites is paralleled by an cleaned in the extraction system by titanium at 850 °C enrichment of heavy neon isotopes. These authors and by copper-oxide at 550 °C. After these preliminary concluded that the enrichment of the heavier isoto- "getters" were cooled to room temperature, the gases pes of both gases result from isotopic mass fractio- were then pumped through the metal valve into a sec- ond clean-up system by adsorption on charcoal cooled nation. Additional evidence for the production of witl liquid N2 or solid C02 . After isolating the gases isotopic anomalies of meteoritic xenon and krypton in the second clean-up system, they were driven from by fractionation have been reported from noble gas the charcoal at 200 °C and exposed to a second surface analyses of the LEOVILLE 21 and POTTER22 chon- of titanium sponge at 850 °C. drites. In the case of Wellman, the noble gases were se- parated into four fractions for analysis by adsorption This study of the isotopic composition of noble on charcoal; the boiling temperature of N2 released gases in ordinary chondrites was undertaken in or- He and Ne, the sublimation temperature of C02 re- 8 R. 0. PEPIN, Earth Planet. Sei. Letters 2,13 [1967]. 17 B. SRINIVASAN and O. K. MANUEL, On the Isotopic Com- 9 R. 0. PEPIN, Origin and Distribution of the Elements, Per- position of Trapped Helium and Neon in Carbonaceous gamon Press, Oxford and New York 1968. Chondrites, Earth Planet. Sei. Letters, in press [1971]. 10 D. C. BLACK and R. 0. PEPIN, Earth Planet. Sei. Letters 6, 18 B. SRINIVASAN, E. C. ALEXANDER, JR., O. K. MANUEL, and 395 [1969]. D. E. TROUTNER, Phys. Rev. 179,1166 [1969]. 11 D. C. BLACK, Meteoritics 4, 260 [1969]. 19 E. ANDERS and D. HEYMANN, Science 164, 821 [1969]. 12 D. C. BLACK, Geochim. Cosmochim. Acta 34, 132 [1970]. 20 P. EBERHARDT, J. GEISS, H. GRAF, N. GRÖGLER, U. KRÄ- 13 E. ANDERS, D. HEYMANN, and E. MAZOR, Geochim. Cosmo- HENBÜHL, H. SCHWALLER, J. SCHWARZMÜLLER, and A. chim. Acta 34,127 [1970]. STETTLER, Geochim. Cosmochim. Acta Supp. 1, 2, 1037 14 E. MAZOR, D. HEYMANN, and E. ANDERS, Geochim. Cosmo- [1970]. chim. Acta 34, 781 [1970]. 21 O. K. MANUEL, R. J. WRIGHT, D. K. MILLER, and P. K. 15 P. K. KURODA and 0. K. MANUEL, Nature London 227, KURODA, J. Geophys. Res. 75, 5639 [1970]. 1113 [1970]. 22 O. K. MANUEL, D. K. MILLER, R. J. WRIGHT, and P. K. 16 0. K. MANUEL, Meteoritics 5, 207 [1970]. KURODA, Solar Type Krypton, submitted to J. Geophys. Res. [1971]. leased Ar, the freezing point of Hg released Kr, and analyses, where the identical procedures were followed finally the Xe was released from the charcoal at 150 °C. for gases evolved from a hot molybdenum crucible, For Tell and Scurry the noble gases were pumped into showed no significant contamination except at mass 78.