Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28q.405m&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 405
Other
1
Diamonds, Diffraction, Irradiation, Tem
Scientific paper
Ozima and Mochizuki [1] suggested that microdiamonds in primitive meteorites were formed by irradiation of carbonaceous matters such as graphite, amorphous carbon, or hydrocarbons with energetic particles emitted from supernova. To test this hypothesis, we carried out the following experiments. 1. We investigated a uranium-rich coal from Cluff Lake, Canada. Electron microprobe analysis of this sample showed that there are numerous uranium oxide grains of about 10-20 micrometers almost uniformly distributed in hydrocarbon matrix. A small amount of PbS was also identified by the EPMA analysis. If the U,Th-induced radiation were to produce diamonds, they must be found in radiation-damaged regions around the uranium oxide grains. Hence, we very carefully searched for microdiamonds in the radiation-damaged regions by TEM (transmission electron microscope). We observed many crystalline particles of about 20 nm, of which concentration in the radiation damaged region is about 500 ppm. Electron diffraction analysis with a TEM on the crystalline particles gave a powder ring pattern. Because of the limited resolution of the TEM, the electron diffraction was taken over an area (about 0.5 micrometers x 0.5 micrometers) that contained several grains. In Table 1, we show the spacing characteristics deduced from the diffraction analysis, where the observed d-spacings (denoted as D) are normalized to the table values corresponding to diamond, graphite, and PbS (denoted as d) respectively. If diamond is chosen for the normalization, the D/d ratios become almost constant for major diamond spacings, including the three most intense ones (shown by bold letters). One intense spacing at D = 1.887 angstroms, however, cannot be attributed to diamond, but may be due to PbS. We conclude that the observed electron diffraction pattern is primarily due to diamond, but other components such as PbS may also be present. Hence, the experiment seems to confirm Kaminsky's hypothesis [2] that high-energy particles derived from U,Th-decays interacted with hydrocarbon (i.e., natural coal ) to have formed microdiamonds in uranium-rich coals. 2. We irradiated 50-mesh graphite powder by a 50-MeV argon beam with a linear accelerator, and examined the irradiated sample with TEM. We observed a crystalline particle that showed a diffraction pattern similar to diamond. The diffraction pattern, however, may also be attributed to graphite. Since we could take the diffraction only from one direction, it is difficult to rule out the latter possibility. To resolve the ambiguity, it is essential to make the electron diffraction analyses of the crystalline particle at least from two directions, which is being carried out. Currently we are trying to see the irradiation effect on different target materials (amorphous carbon, graphite, and hydrocarbon) with different noble gas beams (Kr or Xe). References: [1] Ozima M. and Mochizuki M., this volume. [2] Kaminsky F. (1987) Dokl. Akad. Nauk SSSR, 294, 439-440. Table 1, which appears here in the hard copy, shows electron diffraction spacing characteristics of nanograins in natural coal.
Kitamura Masao
Mochizuki Kenji
Ozima Minoru
Shimobayashi Norimasa
Tuchiyama A.
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