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Significant fractionation of the isotopes of calcium has been observed during elution through short ion-exchange columns packed with Dowex 50W-X8 resin. A double isotopic tracer was used to provide correction for instrumental fractionation effects. The absolute 40Ca/44Ca ratio is determined by this method to 0.05 % and provides a measure of the fractionation of all Ca isotopes. It is found that the lighter isotopes are preferentially retained by the resin, with variations in 40Ca/44Ca between the first and last fractions of up to 1.1 %. An estimate of the separation factor between batch solute and resin gives e = 2.1 X 10~4. Details of the chemical or physical mechanisms causing isotope fractionation of Li, Na, Ca, and other elements during Ion-exchange chromatography are not yet clear.

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%o per amu favoring the heavy isotopes and small (1%0-2%o) "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.

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Secondary ion mass spectrometry (SIMS) analysis of patterned silicon wafers is complicated by the small areas available for study, the difficulty in finding the analysis location, the existence of thick insulating layers that cause charging, quantification of multilayer structures, and the presence of a high concentration of the element of interest adjacent to the area of study. Special SIMS test structures have been implemented to provide large, easily identifiable, analysis areas that have proved to be an asset in both process characterization and failure analysis of product wafers. Descriptions are provided for test structures ranging from a 400×600-μm pattern in a test chip design to a 100×125-μm pattern on a product wafer. Applications are shown for test sites generated by projection and step and repeat printing. The grid region between devices provides a practical location for SIMS test areas on current product wafers. The amount of grid space available may be insufficient to accommodate the full complement of structures needed to characterize a particular process technology, but space requirements can be reduced by the use of smaller patterns for certain applications. Analysis of patterned wafers using grid test patterns can still be affected by charging, and often requires the removal of insulating layers by etching and the use of primary beams that are well focused and do not impact on the sample outside of the test pattern.