Geochemical Journal, Vol. 13, pp. 137 to 140, 1979 137

NOTE

Meteoritic barium and cerium versus the general isotopic anomalies in meteoritic xenon

P. K. KURODA

Department of Chemistry, University of Arkansas, Fayetteville, Arkansas 72702 U.S.A.

(Received March 10, 1979)

The difference in the isotopic compositions of barium from some meteorites and from the terrestrial barium is explained as due to the alteration of the isotopic ratios by a combined effect of mass-dependent fractionation, neutron-capture and cosmic-ray irradiation processes, which took place prior to and during the period of formation of the solar system. The abundances of 134Ba and ' 35 Ba in the meteorite Bruderheim seem to be slightly enhanced due to the decays of 2.06-year ' 34Cs and 2.3 X 106-year 13 5Ba A small difference in the isotopic compositions of cerium in the Bruderheim meteorite and the terrestiral sample can also be attributed to neutron-capture processes, which occurred during an early irradiation period. It is shown that the barium and xenon isotopic anomalies observed in meteorites are closely related to each other.

INTRODUCTION Sixteen years later, MCCULLOCHand WASSER BURG (1978) found isotopic anomalies for Soon after the discovery of the so-called barium and neodymium in two inclusions from special and general anomalies in meteoritic the Allende meteorite. They reported that xenon was made in 1960, KRUMENACHERet al. sample EKI-4-1 showed large positive excesses (1962) have reported that the barium from the in the unshielded isotopes 135Ba and 137Ba of Richardton chondrite was of normal isotopic 13.4 and 12.3 parts in 104, respectively, and con composition. At about the same time, UMEMOTO, cluded that both the barium and neodymium (1962) measured the relative abundances of anomalies could be explained by a model of r the isotopes of barium from terrestrial samples process addition. The barium isotope data ob and from the meteorites Bruderheim, Pasamonte tained by MCCULLOCH and WASSERBURG(1978) and Nuevo Laredo. He reported that the were such that the lighter isotopes were marked meteorites contained more of the low mass ly depleted relative to the heavier isotopes and isotopes relative to the highest mass isotope this trend happened to be opposite to that than do the terrestrial samples and the variation observed by UMEMOTO(1962). Thus it appeared was approximately linear with mass. He also as if the barium isotope data reported by reported that there was no significant difference UMEMOTO(1962) were unreliable. The purpose in the isotopic compositions of cerium from of this NOTE is to point out the fact that, on terrestrial samples and from Bruderheim. In the contrary, his data were of a very high an article dedicated to HAROLD D. UREY on his quality and can be explained quite well by the seventieth birthday, April 29, 1963, MURTHY recently proposed theory of KURODA (1979a, (1964) noted that the observation by UMEMOTO b,c). (1962), if real, was very important because it would be the first indication that the general RESULTS AND DISCUSSION anomalies exist in meteorites for the non-volatile heavy elements as well. MURTHY (1964) Tables 1 and 2 show that the isotopic com cautioned, however, that the possibility of iso positions of barium from the meteorites Pasa topic fractionation during the experiments monte and Nuevo Laredo are in essential agree existed and he stated that in view of this the ment with the isotopic composition of the ter general anomalies in barium needed confirma restrial standard, which has been mass-frac tion by other workers. tionated, except for the fact that 137Ba seems to 138 P. K. KURODA

Table 1. Isotopic composition of Ba from the Pasamonte meteorite

Sample €130 €132 €134 €135 €136 €137 €138

(1) Pasamonte(a) +173.4 +138.4 +83.4 +66.5 +43.8 +53.4 -0 ± 15.0 ± 13.6 ± 9.8 ± 8.7 ± 7.3 ± 7.1

(2) Mass-fractionation +177.4 +133.0 +88.7 +66.5 +44.3 +22.17 =0 effect (assumed) + 5.4 (3) Pasamonte corrected for 4.0 5.3 =0 0.5 +32.3 =0 mass-fractionation(b) ± 15.0 ± 13.6 ± 9.8 ± 7.3 ± 7.1

(a) UMEMOTO(1962).

Table 2. Isotopic composition of Ba from the Nuevo Laredo meteorite

Sample €130 €132 €134 €135 €136 €137 €138 (1) Nuevo Laredo(a) +167.3 +122.0 +85.5 +54.5 +39.3 +31.5 =0 ± 26.6 ± 25.0 ±14.2 ±20.9 ±11.0 ± 8.4

(2) Mass-fractionation +145.4 +109.0 +72.7 +54.5 +36.3 +18.18 =0 effect (assumed) + 21.9 + 13.0 +12.8 + 3.0 +13.3 (3) Nuevof Laredo corrected =0 =0 or mass-fractionation(b) ± 26.6 ± 25.0 ±14.2 ±11.0 ± 8.4

(a) UMEMOTO(1962).

Table 3. Isotopic composition of Ba from the Bruderheim meteorite compared with that of normal Ba exposed to a neutron flux and then subjected to a mass-dependent fractionation

Sample €130 €132 €134 €135 €136 €137 €138

(1) Bruderheim(a) +249.2 +179.0 +112.8 +73.0 +60.3 +12.2 =0 ± 13.7 ± 20.7 ± 10.1 ± 8.7 ± 6.4 ± 9.0 (2) Mass-fractionation +194.4 +145.8 + 97.2 +73.0 +48.7 +24.3 =0 effect (assumed) -12 (3) Bruderheim corrected for + 54.8 + 33.2 + 15.6 =0 +11.6 .1 =0 mass fractionation ± 13.7 ± 20.7 ± 10.1 ± 6.4 ± 9.0

(4) Normal Ba exposed to -17 -16 aneutron flux(b) 57.4 57.1 7.0 .9 + 8.6 .2 =0

(a) UMEMOTO(1962). (b) The 15KeV neutron-capture cross sections (BURBIDGEet al., 1957) were used in the calculation. All the results are expressed in parts per 104. be slightly enriched in the meteorites. Table 3 exposed to a neutron flux. In analogy to the shows that the isotopic composition of barium case of Xe isotopes, the abundances of the two from the Bruderheim chondrite can not be lightest isotopes 130Xe and '32Xe could be explained by the process of mass-fractionation enhanced by the addition of spallogenic com alone. The abundances of 130Ba, 132Ba, 134Ba, 135Ba and 136Ba are markedly enriched ponents. Moreover, the abundances of 134Ba , while and 135Bacould be enhanced in the meteorites, 137Ba appears to be slightly depleted in the by the decays of 2.06-year 134Cs and 2.3 X meteorite relative to the terrestrial standard. 106-year 135Cs, which existed in the early solar The relative abundances of the three heavy system together with other `extinct' radio isotopes 136Ba, 137Ba and 138Ba from the nuclides, such as 7.5 X 105-year 27A1, 6.5 X 106_ Bruderheim meteorite, however, show a striking year 117Pd and 1.59 X 107-year 12111,which may resemblance to those of the normal barium have been produced by similar processes: Meteoritic barium and cerium 139

133Cs(n from the Bruderh ' meteorite andd fromf m th e ,y)134Cs_ 2 .06y~ 134Ba~ terrestrial sample canelm be explained in a similar manner as due to the alteration of the isotopic ratios of the latter by neutron-capture processes. 134Xe(n ,y)135Xe ~135Cs 2 .3 Xa 106 y_ 13SBa, A contribution from the reaction

106Pd(n ,y )107pd 6.5 X 106 year_ 107Ag, 139La(n,y)140La 40.023 h .1 140Ce and is taken into account here, since cerium and its Te(n 129 129 Q _ 129 lanthanum are not likely to be chemically frac ,y) Te I 1.59 X 107y Xe' tionated in the meteorite. Although the experi mental uncertainties are rather large, the agree It is interesting to note here that the abun ment between the calculated and observed dance of 137Ba was apparently not much affected values seems to be satisfactory. by the reaction Table 5 compares the isotopic compositions of barium from the Bruderheim meteorite and 136 Xe(n 137 ~, 137 _x,.137 from Allende EK 1-4-1. It is at once obvious ,y) Xe Cs 30 .1 y Ba. that the Allende inclusion EK 1-4-1 represents a sample of barium, which had been subjected to a smaller neutron flux than the terrestrial This can be explained as due to the fact that barium. The abundance of 137Bain EK 1-4-1 th e neutron-capture cross-section of 136Xeis is enhanced relative to the terrestrial standard , abnormallysmall , because this nuclide con which means that the latter received a larger twins 82 neutrons, which is a magic number. neutron flux than the former. This explains A ccording to BURBIDGEet al. (1957), -capture cross sections of 13athe Xe the fact that magnesium in two Allende Ca-Alneutron 15KeV rich inclusions (EK 1-4-1 and Cl) showed and T '36Xe are 360mb and 4.9mb, respectively. negative S26Mg(WASSERBURG et al ., 1977) and able 4 shows that a small difference oxygen in these inclusions also showed negative between the isotopic composition of cerium 6170 and 61110(CLAYTON and MAYEDA, 1977).

Table4. Isotopiccomposition of Cefrom the Bruderheimmeteorite

Sample €136 €138 6140 €142 -390 -210 -130 (1) Bruderhiem(a) =0 ±150 ±140 ±140

(2) Normal Ce exposed to a neutron =0 flux together with La in the -291 -291 -291 cosmic abundance ratio(b)

(a) UMEMOTO(1962). (b) The following values of 15KeV neutron-capture cross-sections (a) and cosmic abundance values (N) were used: a = 72, 82, 140, 82 and 32 millibarns for 136Ce, 138Ce, 140Ce, 142Ceand 139La, respectively; N = 2.00 for both 140Ce and 139La (BURBIDGEet al., 1957). The results are expressed in parts per 104.

Table 5. A comparison of the isotopic compositions of Ba from the Bruderheim meteorite and from Allende EK 1-4-1

Sample €130 €132 €134 €135 €136 €137 €138

(1) Bruderheim(a) +249.2 +179.0 +112.8 +73.0 +60.3 +12.2 ;0 ± 13.7 ± 20.7 ± 10.1 ± 8.7 ± 6.4 ± 9.0 + 7.9 (2) Allende 30.0 28.0 17.8 =0 9.7 =0 EK 1-4-1 SCa(b) ± 7.0 ± 14.0 ± 1.2 ± 0.6 ± 0.4

(a) UMEMOTO(1962). (b) MCCULLOCHand WASSERBURG(1978). 140 P. K. KURODA

Table 6. A comparison of the isotopic compositions of Xe and Ba from the Bruderheim meteorite

Atomic Element Number €124 €126 €128 €139 €130 €131 €132 €134 €135 €136 €137 €138 (Z) (1) Xe(a) 54 +5556 +7030 +2755 +2412 +870 +574 +241 + 25.5 =0(c) +294.2 +179.0 +112.8 +73.0 +60.3 +12.2 (d) (2) Ba(b) ± 13.7 ± 20.7 ± 10.1 ± 8.7 ± 6.4 ± 9.0

(a) MANUELand RowE (1964). (b) UMEMOTO(1962). (c) The differencesin the `Xe/'36Xeratios in the meteorite and the earth's atmosphereare expressed in parts per 104. (d) The differences in the `Ba/'36Ba ratios in the meteorite and the terrestrialBa standard are expressedin parts per 104.

Table 6 compares the isotopic compositions and REYNOLDS,J. H. (1962) Meteoritic krypton of xenon and barium from the Bruderheim and barium versus the general isotopic anomalies in meteorite. The xenon data were taken from the meteoritic xenon. Geochim. Cosmochim. Acta 26, report of MANUEL and ROWE (1964). The 231-249. abundance of 129Xe is markedly enhanced in the KURODA,P. K. (1979a) Isotopic anomalies in the meteorite, because of the decay of 1.59 X early solar system. Geochem.J. 13, 83-90. 107-year 129I. The enhancement of the abun KURODA, P. K. (1979b) Isotopic compositions of dances of the light xenon isotopes is due to calcium, barium, neodymium and xenon in mete a combined effect of mass-fractionation, orites. Geochem. J. 13, 129-132. neutron-capture and cosmic-ray irradiation pro KURODA,P. K. (1979c) Palladium-107in the early cesses. These results show that the barium and solar system. Geochem. J. 13, 133-134. xenon itosopic anomalies observed in meteorites MANUEL, 0. K., and ROWE, M. W. (1964) Noble are closely related to each other. gases in the Bruderheim chondrite. Geochim. Cos mochim. Acta 28, 1999-2003. Acknowledgments-Thispaper is dedicated to the late MCCULLOCH,M. T., and WASSERBURG,G. J. (1978) Professor SHUNJI UMEMOTOof the University of Barium and neodymium isotopic anomalies in the Kyushu, Fukuoka, Japan. This investigationwas sup Allendemeteorite, Astrophys. J. 220, L15-L19. ported by the National ScienceFoundation under grant MURTHY,V. R. (1964) Stable isotope studies of some NSF EAR 76-00285. heavy elements in meteorites, in Isotopic and cosmic chemistry, edited by H. CRAIG, S. L. MILLER and REFERENCES G. J. WASSERBURG,North-Holland Publishing Com pany, Amsterdam, 488-515. BURBIDGE, E. M., BURBIDGE, G. R., FOWLER, W. UMEMOTO,S. (1962) Isotopic composition of barium A., and HOYLE,F. (1957) Synthesis of the ele and cerium in stone meteorites. J. Geophys. Res. 67, ments in stars. Rev. Mod. Phys. 29, 547-650. 375-379. CLAYTON, R. N., and MAYEDA, T. K. (1977) Cor WASSERBURG,G. J., LEE, T., and PAPANASTASSIOU related oxygen and magnesium isotope anomalies in (1977) Correlated 0 and Mg isotopic anomalies in Allende inclusions, I: oxygen Geophys. Research Allende inclusions: II. Magnesium. Geophys. Re Lett. 4, 295-298. search Lett. 4, 299-302. KRUMENACHER, D., MERRIHUE, C. M., PEPIN, R. 0.,