Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.230h&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 230
Astronomy and Astrophysics
Astrophysics
11
Scientific paper
The abundance of ^135Cs (T(sub)1/2 = 2.3 Ma) in the early solar system is a critical datum for modeling the astrophysical site of the solar system's origin. Thus far, however, no strong evidence of the decay signature of ^135Cs in meteorites has been found [1]. Mass spectrometry utilizing multicollector technology allows ^134Ba/^136Ba-normalized ^135Ba/^136Ba and ^137Ba/^136Ba ratios to be measured to a precision better than +-~8 ppm, 2 sigma, if >~500 ng Ba is available. Allende refractory inclusions (CAIs) are thought to have formed during the early stages of nebular accretion and are the oldest known well-dated non-presolar objects in meteorites. Many are highly depleted in volatiles and thus have CI-normalized Cs/Ba ratios <0.05, such that their ^135Ba abundances should represent initial compositions for their respective parental reservoirs. Hence, if ^135Cs was live in the early solar system, then CAIs should carry mass-135 deficits relative to material derived from isotopically identical reservoirs that did not fractionate Cs/Ba at such early times. Nonradiogenic anomalies, however, may be present in CAI Ba, and measurements of the FUN inclusion Cl [2] indicate that these may include ^135Ba deficits with an absence of similarly sized anomalies at other masses. We report high precision isotopic measurements of Ba separated from the Smithsonian bulk Allende reference powder and from 4 Allende CAIs for which Ti and Zr isotopes have been previously measured [3]. Results for 10 runs of the bulk sample ("ALL 2") indicate a well-resolved r- excess/s-deficit anomaly pattern in ^135Ba/^136Ba (+39+-7 ppm, 2 sigma) and ^137Ba/^136Ba (+23+-8 ppm, 2 sigma) relative to the (s-only) ^134Ba/^136Ba normalization. A similar pattern observed in bulk Orgueil ["ORG 2a", 1] is potentially attributable to non-dissolution of presolar SiC. However, if SiC has been metamorphically destroyed in Allende [4], then the anomaly pattern probably indicates a s/r source mixing "polarization" between the bulk Allende and bulk Earth reservoirs. Results for the CAIs are shown in the figure, plotted relative to the mean of 29 runs of terrestrial standard Ba made during the study. Well- resolved positive anomalies are present in all samples at both mass-135 and mass-137. However, no obvious interpretation concerning ^135Cs is apparent in the data. Interesting observations and inferences are the following: (i) Ba anomalies were observed in all CAIs investigated; (ii) Ba anomalies in bulk meteorites may provide a useful analog to ^17O as a reservoir identifier; and (iii) the presence of Ba anomalies in bulk chondrites relative to terrestrial Ba suggests that similar-scale anomalies in Nd may also be present. The latter possibility would affect estimates of CHUR ^142Nd/^144Nd and interpretations of ^142Nd/^144Nd heterogeneity in the Earth. References: [1] Halper C. L. et al. (1991) Meteoritics 26, 341; [2] McCulloch, M. T. and Wasserburg, G. J. (1978) Ap. J., 220, L15-L17; [3] Harper C. L. et al. (1990) Proc. Int. Symp. Nuclear Astrophysics "Nuclei in the Cosmos" (eds. H. Oberhummer and W. Hillebrandt) MPI fur Physik und Astrophysik, Garching. MPA/P4, 138-144; [4] Alexander C. M. O'D. et al. (1990) Lunar Planet. Sci. (abstract) 21: 9; Huss G. R. (1990) Nature, 347, 159-161.
Harper Charles L. Jr.
Nyquist Larry E.
Wiesmann Henry
No associations
LandOfFree
The Search for 135Cs in the Early Solar System: Very High Precision Measurements of Barium Isotopes in Bulk Allende and Refractory Inclusions does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Search for 135Cs in the Early Solar System: Very High Precision Measurements of Barium Isotopes in Bulk Allende and Refractory Inclusions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Search for 135Cs in the Early Solar System: Very High Precision Measurements of Barium Isotopes in Bulk Allende and Refractory Inclusions will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209498