Search for ^(26)Al effects in the Allende Fun Inclusion C1

The Mg isotopic composition in plagioclase from the Allende inclusion C1 has been measured to correlate excess ^(26)Mg^* with isotopic anomalies for elements of higher atomic number. No large ^(26)Mg^* excesses were observed in samples with ^(27)Al/^(24)Mg up to 165. The inferred initial ^(26)Al/^(27)Al is 5 × 10^(−6) which is a factor of ten less than previously observed in other Allende inclusions. The low ^(26)Al abundance may be the result of late formation of C1 (by 2.5 m.y.) or due to the non-uniform addition of ^(26)Al to the solar system. The major mineral phases in C1 which are Mg rich and the bulk alteration products all have a uniform Mg isotopic composition with 30‰ per mass unit fractionation and δ^(26)Mg≈ −1.6‰. The plagioclase data show variable Mg isotopic fractionation which ranges from 0 to 30‰ per mass unit. Isotopic homogeneity was demonstrated for the major mineral phases rich in Mg both in macroscopic samples and in microscopic individual crystals. The detailed correlation of ^(26)Al with the more general isotopic anomalies and its use as a chronometer marking the production and introduction of isotopically anomalous material into the solar system remains an open question

In Situ Ti Isotopic Measurements by Laser Ablation MC-ICP-MS

We have been developing Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS) technique to measure titanium isotopic composition in situ. A principal aim of this work is to search for isotopic heterogeneities larger than the few epsilons (e, in parts in 10^4) of the solar system. Our analytical precision of the ratios of 46Ti, 48Ti, and 50Ti to 49Ti after exponential-law mass discrimination correction normalizing 47Ti/49Ti to 1.33375 were about 2.5 £` (2£m). Mixture solutions were prepared by adding the expected level of Ca, Cr, Mg, and Alto the Ti solutions to demonstrate that our interference correction is effective. We then applied our technique with 213 nm Nd-YAG laser ablation to five Ti-rich terrestrial solids, and all of them also showed titanium isotopic composition that was consistent with one an other and agreed with that for the solution standard. It appears that the in situ laser technique did not significantly in crease the long-term reproducibility be yond the 2.5 established using the solution method. This is an order of magnitude better than the typical precision of a few permil for secondary ion mass spectrometry (SIMS). The combination of the ability to perform in situ analysis on 30 mm spots with e level precision is a niche for LA-MC-ICP-MS. We also ablated two lines on a fassaite grain from a large well studied CAI Egg-6 of the Allende meteorite. After the mass discrimination was corrected by normalizing 47Ti/49Ti, the 46Ti and 48Ti are nor mal within about 2 £ while 50Ti/49Ti shows a 9 £ excess. These data are in excellent agreement with thermalion ization mass spectrometry (TIMS) results. Comparing our ICP-MS results against the results from TIMS studies, we found that our normal titanium isotopic ratios were closest to the less precise data of Heydegger et al. (1979) who measured Ti+. We support the proposal to IUPAC to change the accepted Ti abundance to that measured by ICP-MS and TIMS without using Ti oxides

Isotopic Heterogeneities in the Solar System

The nature of isotopic anomalies in solar system material is discussed with emphasis on correlated anomalies in refractory elements. Evidence for the existence of short-lived radioactive nuclides in the early solar system is given and is used to estimate the time scale for the last injection of freshly synthesized nuclear material. It is shown that the early solar nebula was incompletely mixed and contained debris which was injected from a stellar source at most a few million years prior to the formation of the solar system. It appears that the average solar system material is made up of ambient interstellar material which was deficient in certain nuclear species to which was added a small fraction of freshly synthesized material. It is this mixture which now makes up the bulk solar system. At the present time there may still remain both substantial and subtle isotopic differences between the sun, the terrestrial planets, and volatile-rich planetary bodies including comets. The isotopic variations which are observed reflect slightly different proportions of nuclei from different stellar sources which were locally well mixed and homogenized prior to or during the formation of the early solar nebula condensates. The process of local homogenization apparently destroyed most pre-solar dust grains but preserved the distinctive average isotopic character of the local regions. Substantial isotopic differences existed between the cool gas and some condensed matter. This is manifest in major chemical and some associated isotopic alteration of the early condensates

Calcium Isotopic anomalies in the Allende meteorite

We report isotopic anomalies in Ca which were found in two Ca-Al-rich inclusions of the Allende meteorite. These inclusions previously had been shown to contain special anomalies for Mg and O which were attributed to fractionation and unknown nuclear effects. The Ca data, when corrected for mass fractionation by using ^(40)Ca/^(44)Ca as a standard show nonlinear isotopic effects in ^(48)Ca of + 13.5 per mil and in ^(42)Ca of +1.7 per mil for one sample. The second sample shows a ^(48)Ca depletion of - 2.9 per mil, but all other Isotopes are normal. Samples with large excesses in ^(26)Mg show no Ca anomalies. The effects demonstrate that isotopic anomalies exist for higher-atomic-number refractory elements in solar-system materials and do not appear to be readily explainable by a simple model. The correlation of O, Mg, and Ca results on the same inclusions requires the addition and preservation in the solar system of components from diverse nucleosynthetic sources. Observed anomalous Mg. and Ca compositions for coexisting mineral phases are uniform within each inclusion, and require initial isotopic homogeneity within an inclusion but the preservation of wide variations between inclusions. Assumming formation of these inclusions by condensation from a gaseous part of the solar nebula, this Implies Isotopic heterogeneity on a scale of 10-10^2 km within the nebula

Demonstration of ^(26)Mg excess in Allende and evidence for ^(26)Al

We report the discovery of a large anomaly in the isotopic composition of Mg in a Ca-Al rich chondrule from the Allende meteorite. This anomaly is manifest independently of instrumental fractionation and is due to an enrichment of about 1.3 percent in ^(26)Mg while the abundances of ^(25)Mg and ^(24)Mg are terrestrial in value. There is a strong correlation in this chondrule between the ^(26)Mg excess and the Al/Mg ratio so that the most plausible cause of the anomaly is the in situ decay of now extinct ^(26)Al (τ_½ = 0.72 × 10^6 yr). Mineral phases extracted from a Ca-Al-rich aggregate have distinct Al/Mg but show identical, small Mg anomalies which are apparent after correction for fractionation (δ^(26)Mg = 0.3%). These data indicate that this aggregate was isotopically homogenized in a high Al/Mg environment after the decay of ^(26)Al had occurred or that some of the Mg anomalies are due to effects other than in situ decay of ^(26)Al

Calcium isotopic anomalies and the lack of aluminum-26 in an unusual Allende inclusion

We have studied the Mg and Ca isotopic compositions of an unusual Allende inclusion dominated by hibonite, which is the most refractory and possibly the most primitive major oxide mineral. No ^(26)Mg excess was found in spite of the high ^(27)Al/^(24)Mg (1 ≳ 10^3) of some samples, indicating an initial (^(26)Al/^(27)Al)_0 < 2 X 10^(-7), a factor of 250 less than found in some other Allende inclusions. The upper limit for Mg isotopic fractionation is 20%o per amu. Anomalous but uniform Ca isotopic compositions were found for bulk samples of coexisting phases and microscopic grains. The Ca anomaly is a superposition of a large mass-dependent fractionation effect of 7.5‰ per amu favoring the heavy isotopes and small (1‰-2‰) "nonlinear" effects of presumably nuclear origin. If the lack of ^(26)Al is due to a time delay of 6 X 10^6 yr for the formation of the hibonite inclusion, then condensation models require modification. The Ca effects suggest the alternative that ^(26)Al was not uniformly distributed in the solar system. These results accentuate the curious and unexplained association between large mass fractionation and nuclear effects. They also reinforce the scenario which envisages an early solar system consisting of isotopically and chemically distinct reservoirs resulting from the incomplete mixing of several nucleosynthetic components. It is not evident whether these components originated within the solar system or from another star