Engineering topics
Publications and source records attributed to Nittler, L. R..
The NEAR X-ray spectrometer, based on calculations using an interactive meteorite database, should be able to identify potential meteorite class and subclass analogs on a scale of 2 to 3 kilometers on asteroid 433 Eros.
N, Al, and Si isotopic ratios differ between presolar SiC grains of type A ( C-12/C-13 < 3.5) and type B (3.5 < C-12/C-13 < 10). J and CH stars are promising sources but the lack of astronomical data and theoretical models limit the identification of these sources.
Carbon and Si isotopic ratios of SiC grains of type Y point to an origin in AGB stars of lower-than-solar metallicity. Comparison with model calculations indicate that stars with metallicity Z = 0.01 and 3-5 solar masses best account for the experimental data.
We report here the first use of a new ion-imaging system to locate a rare interstellar aluminum oxide grain in a Murchison acid residue. While several types of carbon-rich interstellar grains, including graphite, diamond, SiC, and TiC, have previously been found, isotopically anomalous interstellar oxide grains have proven more elusive. We have developed an ion imaging system which allows us to map the isotopic composition of large numbers of grains relatively quickly and is, thus, ideally suited to search for isotopically exotic subsets of grains. The system consists of a PHOTOMETRICS CCD camera coupled to the microchannel plate/fluorescent screen of the WU modified CAMECA IMS-3F ion microprobe. Isotopic images of the sample surface are focused on the CCD and digitized. Subsequent image processing identifies individual grains in the images and determines isotopic ratios for each. For the present work, we have imaged in O-16 and O-18; negligible contributions of (17)OH(-) and (16)OH2(-) signals to the O-18 signal allow the use of low mass resolution, simplifying the measurements. Repeated imaging runs on terrestrial corundum particles showed that the system measures isotopic ratios reproducibly to about +/- 40%. Each imaging run took about six minutes to complete, and for this study there were on average 5-15 grains in each image. We have conducted imaging searches in 2-4 micron size separates of both Orgueil and Murchison.